Publications by year
In Press
Reynolds DJ, Scourse JD, Halloran PR, Nederbragt AJ, Wanamaker AD, Butler PG, Richardson CA, Heinemeier J, Eiríksson J, Knudsen KL, et al (In Press). Annually resolved North Atlantic marine climate over the last millennium.
Nat Commun,
7Abstract:
Annually resolved North Atlantic marine climate over the last millennium.
Owing to the lack of absolutely dated oceanographic information before the modern instrumental period, there is currently significant debate as to the role played by North Atlantic Ocean dynamics in previous climate transitions (for example, Medieval Climate Anomaly-Little Ice Age, MCA-LIA). Here we present analyses of a millennial-length, annually resolved and absolutely dated marine δ18O archive. We interpret our record of oxygen isotope ratios from the shells of the long-lived marine bivalve Arctica islandica (δ18O-shell), from the North Icelandic shelf, in relation to seawater density variability and demonstrate that solar and volcanic forcing coupled with ocean circulation dynamics are key drivers of climate variability over the last millennium. During the pre-industrial period (AD 1000-1800) variability in the sub-polar North Atlantic leads changes in Northern Hemisphere surface air temperatures at multi-decadal timescales, indicating that North Atlantic Ocean dynamics played an active role in modulating the response of the atmosphere to solar and volcanic forcing.
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2018
(2018). A stratigraphic investigation of the Celtic Sea megaridges based on seismic and core data from the Irish-UK sectors.
Quaternary Science Reviews,
198, 156-170.
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A stratigraphic investigation of the Celtic Sea megaridges based on seismic and core data from the Irish-UK sectors
© 2018 the Authors the Celtic Sea contains the world's largest continental shelf sediment ridges. These megaridges were initially interpreted as tidal features formed during post-glacial marine transgression, but glacigenic sediments have been recovered from their flanks. We examine the stratigraphy of the megaridges using new decimetric-resolution geophysical data correlated to sediment cores to test hypothetical tidal vs glacial modes of formation. The megaridges comprise three main units, 1) a superficial fining-upward drape that extends across the shelf above an unconformity. Underlying this drape is 2), the Melville Formation (MFm) which comprises the upper bulk of the megaridges, sometimes displaying dipping internal acoustic reflections and consisting of medium to coarse sand and shell fragments; characteristics consistent with either a tidal or glacifluvial origin. The MFm unconformably overlies 3), the Upper Little Sole Formation (ULSFm), previously interpreted to be of late Pliocene to early Pleistocene age, but here shown to correlate to Late Pleistocene glacigenic sediments forming a precursor topography. The superficial drape is interpreted as a product of prolonged wave energy as tidal currents diminished during the final stages of post-glacial marine transgression. We argue that the stratigraphy constrains the age of the MFm to between 24.3 and 14 ka BP, based on published dates, coeval with deglaciation and a modelled period of megatidal conditions during post-glacial marine transgression. Stratigraphically and sedimentologically, the megaridges could represent preserved glacifluvial features, but we suggest that they comprise post-glacial tidal deposits (MFm) mantling a partially-eroded glacial topography (ULSFm). The observed stratigraphy suggests that ice extended to the continental shelf-edge.
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Reynolds DJ, Hal IR, Slater SM, Mette MJ, Wanamaker AD, Scourse JD, Garry FK, Halloran PR (2018). Isolating and Reconstructing Key Components of North Atlantic ocean Variability from a Sclerochronological Spatial Network.
PALEOCEANOGRAPHY AND PALEOCLIMATOLOGY,
33(10), 1086-1098.
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Scourse JD, Ward S, Wainwright A, Uehara K, Bradley S (2018). The role of megatides and relative sea level in controlling the deglaciation of the British-Irish and Fennoscandian Ice Sheets.
Journal of Quaternary Science Full text.
Scourse JD, Small D, Smedley R, O Cofaigh C, Duller G, McCarron S, Burke M, Evans D, Fabel D, Gheorghiu DM, et al (2018). Trough geometry was a greater influence than climate-ocean forcing in regulating retreat of the marine-based Irish Sea Ice Stream.
Bulletin of the Geological Society of America, 1-19.
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2017
Butler PG (2017). A sclerochronological archive for Antarctic coastal waters based on the marine bivalve Yoldia eightsi (Jay, 1839) from the South Orkney Islands.
Holocene,
27(2), 271-281.
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A sclerochronological archive for Antarctic coastal waters based on the marine bivalve Yoldia eightsi (Jay, 1839) from the South Orkney Islands
© 2016, © the Author(s) 2016. The scarcity of long instrumental series from the Southern Ocean limits our understanding of key climate and environmental feedbacks within the Antarctic system. We present an assessment for the Antarctic mollusc bivalve Yoldia eightsi as an Antarctic coastal climatological archive, based on annually-resolved growth pattern of 20 live-collected specimens in 1988 from Factory Cove, Signy Island (South Orkney Islands). Two detrending methods were applied to the growth increment series: negative exponential detrending and regional curve standardization (RCS) detrending. The RCS-chronology showed consistent synchronous growth in the population for a 20 year period (1968-1988; expressed population signal ⩾ 0.85), a negative correlation between the RCS-chronology and the fast-ice duration record (r= -0.41, N= 24, P⩽ 0.05) and winter duration (r= -0.52, N=24, P⩽ 0.01) and positive correlations with mean winter sea surface temperature (SST; r= 0.57, N= 24, P⩽ 0.01), mean summer SST (r= 0.46, N= 24, P⩽ 0.05) and mean annual SST (r= 0.48, N= 24, P⩽ 0.05). The chronology appears to record the environmental conditions generated during the Weddell Polynya event (1973 -1976) as detectable abrupt changes in the annual growth patterns. Over eight years (1973-1980) a negative relationship between shell growth and suspended chlorophyll (i.e. a proxy for surface productivity) is apparent which is likely influenced by the seasonal deposition of organic phytodetritus on the seabed following surface water phytoplankton blooms. Our results form a basis for establishing Y. eightsi as an environmental archive for coastal Antarctic waters.
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Der Sarkissian C, Pichereau V, Dupont C, Ilsøe PC, Perrigault M, Butler P, Chauvaud L, Eiríksson J, Scourse J, Paillard C, et al (2017). Ancient DNA analysis identifies marine mollusc shells as new metagenomic archives of the past.
Molecular Ecology Resources,
17(5), 835-853.
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Ancient DNA analysis identifies marine mollusc shells as new metagenomic archives of the past
© 2017 John Wiley. &. Sons Ltd Marine mollusc shells enclose a wealth of information on coastal organisms and their environment. Their life history traits as well as (palaeo-) environmental conditions, including temperature, food availability, salinity and pollution, can be traced through the analysis of their shell (micro-) structure and biogeochemical composition. Adding to this list, the DNA entrapped in shell carbonate biominerals potentially offers a novel and complementary proxy both for reconstructing palaeoenvironments and tracking mollusc evolutionary trajectories. Here, we assess this potential by applying DNA extraction, high-throughput shotgun DNA sequencing and metagenomic analyses to marine mollusc shells spanning the last ~7,000 years. We report successful DNA extraction from shells, including a variety of ancient specimens, and find that DNA recovery is highly dependent on their biomineral structure, carbonate layer preservation and disease state. We demonstrate positive taxonomic identification of mollusc species using a combination of mitochondrial DNA genomes, barcodes, genome-scale data and metagenomic approaches. We also find shell biominerals to contain a diversity of microbial DNA from the marine environment. Finally, we reconstruct genomic sequences of organisms closely related to the Vibrio tapetis bacteria from Manila clam shells previously diagnosed with Brown Ring Disease. Our results reveal marine mollusc shells as novel genetic archives of the past, which opens new perspectives in ancient DNA research, with the potential to reconstruct the evolutionary history of molluscs, microbial communities and pathogens in the face of environmental changes. Other future applications include conservation of endangered mollusc species and aquaculture management.
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Reynolds DJ, Hall IR, Scourse JD, Richardson CA, Wanamaker AD, Butler PG (2017). Biological and Climate Controls on North Atlantic Marine Carbon Dynamics over the Last Millennium: Insights from an Absolutely Dated Shell-Based Record from the North Icelandic Shelf.
Global Biogeochemical Cycles,
31(12), 1718-1735.
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Biological and Climate Controls on North Atlantic Marine Carbon Dynamics over the Last Millennium: Insights from an Absolutely Dated Shell-Based Record from the North Icelandic Shelf
©2017. American Geophysical Union. All Rights Reserved. Given the rapid increase in atmospheric carbon dioxide concentrations (pCO 2 ) over the industrial era, there is a pressing need to construct long-term records of natural carbon cycling prior to this perturbation and to develop a more robust understanding of the role the oceans play in the sequestration of atmospheric carbon. Here we reconstruct the past biological and climate controls on the carbon isotopic (δ 13 C shell ) composition of the North Icelandic shelf waters over the last millennium, derived from the shells of the long-lived marine bivalve mollusk Arctica islandica. Variability in the annually resolved δ 13 C shell. record is dominated by multidecadal variability with a negative trend (−0.003 ± 0.002‰ yr −1 ) over the industrial era (1800–2000 Common Era). This trend is consistent with the marine Suess effect brought about by the sequestration of isotopically light carbon (δ 13 C of CO 2 ) derived from the burning of fossil fuels. Comparison of the δ 13 C shell. record with Contemporaneous proxy archives, over the last millennium, and instrumental data over the twentieth century, highlights that both biological (primary production) and physical environmental factors, such as relative shifts in the proportion of Subpolar Mode Waters and Arctic Intermediate Waters entrained onto the North Icelandic shelf, atmospheric circulation patterns associated with the winter North Atlantic Oscillation, and sea surface temperature and salinity of the subpolar gyre, are the likely mechanisms that contribute to natural variations in seawater δ 13 C variability on the North Icelandic shelf. Contrasting δ 13 C fractionation processes associated with these biological and physical mechanisms likely cause the attenuated marine Suess effect signal at this locality.
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Smedley RK, Chiverrell RC, Ballantyne CK, Burke MJ, Clark CD, Duller GAT, Fabel D, McCarroll D, Scourse JD, Small D, et al (2017). Internal dynamics condition centennial-scale oscillations in marinebased ice-stream retreat.
Geology,
45(9), 787-790.
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Internal dynamics condition centennial-scale oscillations in marinebased ice-stream retreat
© 2017 Geological Society of America. Rates of ice-stream retreat over decades can be determined from repeated satellite surveys and over millennia by paleoenvironmental reconstructions. Centennial time scales are an important temporal gap in geological observations of value in process understanding and evaluation of numerical models. We address this temporal gap by developing a 3 ka and 123 km retreat time series for the Irish Sea ice stream (ISIS), a major outlet draining the last British-Irish ice sheet. The Llŷn Peninsula (northwest Wales, UK) contains numerous ice-marginal indicators from which we reconstructed a robust chronological framework of margin oscillations. The landscape documents the retreat of a former marine-terminating ice stream through a topographic constriction, across a reverse bed slope, and across variations in calving margin width. New dating constraints for this sequence were integrated in a Bayesian sequence model to develop a high-resolution ice-retreat chronology. Our results show that retreat of the ISIS during the period 24-20 ka displayed centennial-scale oscillatory behavior of the margin despite relatively stable climatic, oceanic, and relative sea-level forcing mechanisms. Faster retreat rates coincided with greater axial trough depths as the ice passed over a reverse bed slope and the calving margin widened (from 65 to 139 km). The geological observations presented here over a 123-km-long ice-retreat sequence are consistent with theory that marine-based ice can be inherently unstable when passing over a reverse bed slope, but also that wider calving margins lead to much faster ice retreat.
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Smedley RK, Scourse JD, Small D, Hiemstra JF, Duller GAT, Bateman MD, Burke MJ, Chiverrell RC, Clark CD, Davies SM, et al (2017). New age constraints for the limit of the British–Irish Ice Sheet on the Isles of Scilly.
Journal of Quaternary Science,
32(1), 48-62.
Abstract:
New age constraints for the limit of the British–Irish Ice Sheet on the Isles of Scilly
Copyright © 2017 the Authors. Journal of Quaternary Science Published by John Wiley. &. Sons, Ltd. The southernmost terrestrial extent of the Irish Sea Ice Stream (ISIS), which drained a large proportion of the last British–Irish Ice Sheet, impinged on to the Isles of Scilly during Marine Isotope Stage 2. However, the age of this ice limit has been contested and the interpretation that this occurred during the Last Glacial Maximum (LGM) remains controversial. This study reports new ages using optically stimulated luminescence (OSL) dating of outwash sediments at Battery, Tresco (25.5 ± 1.5 ka), and terrestrial cosmogenic nuclide exposure dating of boulders overlying till on Scilly Rock (25.9 ± 1.6 ka), which confirm that the ISIS reached the Isles of Scilly during the LGM. The ages demonstrate this ice advance on to the northern Isles of Scilly occurred at ∼26 ka around the time of increased ice-rafted debris in the adjacent marine record from the continental margin, which coincided with Heinrich Event 2 at ∼24 ka. OSL dating (19.6 ± 1.5 ka) of the post-glacial Hell Bay Gravel at Battery suggests there was then an ∼5-ka delay between primary deposition and aeolian reworking of the glacigenic sediment, during a time when the ISIS ice front was oscillating on and around the Llŷn Peninsula, ∼390 km to the north. Copyright © 2017 the Authors. Journal of Quaternary Science Published by John Wiley. &. Sons, Ltd.
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Reynolds DJ, Hall IR, Slater SM, Scourse JD, Halloran PR, Sayer MDJ (2017). Reconstructing Past Seasonal to Multicentennial-Scale Variability in the NE Atlantic Ocean Using the Long-Lived Marine Bivalve Mollusk. Glycymeris glycymeris.
Paleoceanography,
32(11), 1153-1173.
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2016
Román-González A, Scourse JD, Butler PG, Reynolds DJ, Richardson CA, Peck LS, Brey T, Hall IR (2016). Analysis of ontogenetic growth trends in two marine Antarctic bivalves Yoldia eightsi and Laternula elliptica: Implications for sclerochronology.
Palaeogeography, Palaeoclimatology, Palaeoecology,
465, 300-306.
Abstract:
Analysis of ontogenetic growth trends in two marine Antarctic bivalves Yoldia eightsi and Laternula elliptica: Implications for sclerochronology
© 2016 the Authors There is an increasing use of marine species as palaeoclimate recorders for the marine realm. These archives provide novel baseline records of past oceanographic variability in regions devoid of instrumental observations. Here we report results of a study of the ontogenetic growth pattern of two Antarctic marine bivalve molluscs: Yoldia eightsi and Laternula elliptica from West Antarctic Peninsula populations using negative exponential detrending technique and multi-taper method spectral analysis. Our data show that the growth of both Y. eightsi and L. elliptica follows a general negative exponential trend over their longevity. However, our analyses also identified an innate 9.06 year periodic endogenous growth rhythm in the growth increment pattern of Y. eightsi and two innate periodic growth rhythms, 5 and 6.6 year period, were found in L. elliptica. We hypothesize that the Y. eightsi endogenous growth rhythm may be related to the reallocation of energetic resources between somatic growth and gametogenesis although more biological data are required to test this hypothesis. Further work into L. elliptica biology is required to understand the possible meaning of the innate growth rhythms found for this species. The identification of growth rhythms is important not only for their biological significance but also in sclerochronological analysis because of their importance in developing palaeoenvironmental reconstructions.
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Small D, Rinterknecht V, Austin WEN, Bates R, Benn DI, Scourse JD, Bourlès DL, Hibbert FD (2016). Implications of<sup>36</sup>Cl exposure ages from Skye, northwest Scotland for the timing of ice stream deglaciation and deglacial ice dynamics.
Quaternary Science Reviews,
150, 130-145.
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Implications of36Cl exposure ages from Skye, northwest Scotland for the timing of ice stream deglaciation and deglacial ice dynamics
© 2016 Elsevier Ltd Geochronological constraints on the deglaciation of former marine based ice streams provide information on the rates and modes by which marine based ice sheets have responded to external forcing factors such as climate change. This paper presents new 36 Cl cosmic ray exposure dating from boulders located on two moraines (Glen Brittle and Loch Scavaig) in southern Skye, northwest Scotland. Ages from the Glen Brittle moraines constrain deglaciation of a major marine terminating ice stream, the Barra-Donegal Ice Stream that drained the former British-Irish Ice Sheet, depending on choice of production method and scaling model this occurred 19.9 ± 1.5–17.6 ± 1.3 ka ago. We compare this timing of deglaciation to existing geochronological data and changes in a variety of potential forcing factors constrained through proxy records and numerical models to determine what deglaciation age is most consistent with existing evidence. Another small section of moraine, the Scavaig moraine, is traced offshore through multibeam swath-bathymetry and interpreted as delimiting a later stillstand/readvance stage following ice stream deglaciation. Additional cosmic ray exposure dating from the onshore portion of this moraine indicate that it was deposited 16.3 ± 1.3–15.2 ± 0.9 ka ago. When calculated using the most up-to-date scaling scheme this time of deposition is, within uncertainty, the same as the timing of a widely identified readvance, the Wester Ross Readvance, observed elsewhere in northwest Scotland. This extends the area over which this readvance has potentially occurred, reinforcing the view that it was climatically forced.
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Abbott PM, Bourne AJ, Purcell CS, Davies SM, Scourse JD, Pearce NJG (2016). Last glacial period cryptotephra deposits in an eastern North Atlantic marine sequence: Exploring linkages to the Greenland ice-cores.
Quaternary Geochronology,
31, 62-76.
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Last glacial period cryptotephra deposits in an eastern North Atlantic marine sequence: Exploring linkages to the Greenland ice-cores
© 2015 Elsevier B.V. The establishment of a tephra framework for the Greenland ice-cores spanning the last glacial period, particularly between 25 and 45 ka b2k, provides strong potential for precisely correlating other palaeoclimatic records to these key archives. Tephra-based synchronisation allows the relative timing of past climatic changes recorded within different depositional environments and potential causal mechanisms to be assessed. Recent studies of North Atlantic marine records have demonstrated the potential of tracing cryptotephra horizons in these sequences and the development of protocols now allows a careful assessment of the isochronous nature of such horizons. Here we report on tephrochronological investigations of a marine sequence retrieved from the Goban Spur, Eastern North Atlantic, covering ~25-60 ka b2k. Density and magnetic separation techniques and an assessment of potential transport and depositional mechanisms have identified three previously unknown isochronous tephra horizons along with deposits of the widespread North Atlantic Ash Zone II and Faroe Marine Ash Zone III. Correlations between the new horizons and the Greenland ice-core tephra framework are explored and despite no tie-lines being identified the key roles that high-resolution climatostratigraphy and shard-specific trace element analysis can play within the assessment of correlations is demonstrated. The previously unknown horizons are new additions to the overall North Atlantic tephra framework for the last glacial period and could be key horizons for future correlations.
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Reynolds DJ, Richardson CA, Scourse JD, Butler PG, Hollyman P, Román-González A, Hall IR (2016). Reconstructing North Atlantic marine climate variability using an absolutely-dated sclerochronological network.
Palaeogeography, Palaeoclimatology, Palaeoecology,
465, 333-346.
Abstract:
Reconstructing North Atlantic marine climate variability using an absolutely-dated sclerochronological network
© 2016 the Authors Reconstructing regional to hemispheric-scale climate variability requires the application of spatially representative and climatically sensitive proxy archives. Large spatial networks of dendrochronologies have facilitated the reconstruction of atmospheric variability and inferred variability in the Atlantic Ocean system. However, the marine environment has hitherto lacked the direct application of the spatial network approach because of the small number of individual absolutely-dated marine archives. In this study we present the first analyses of a network of absolutely-dated annually-resolved growth increment width chronologies from the marine bivalves Glycymeris glycymeris and Arctica islandica. The network contains eight chronologies spanning. >. 500 km along the western British continental shelf from the southern Irish Sea to North West Scotland. Correlation analysis of the individual chronologies and a suite of climate indices, including the Atlantic Multidecadal Oscillation (AMO), Central England surface air temperature (CET), northeast Atlantic sea surface temperatures (SST's) and the winter North Atlantic Oscillation (wNAO), demonstrates that, despite the large geographical distances been sites and the heterogeneous nature of the marine environment, the increment width variability in these series contains an element of coherence likely driven by a common response to changing environmental forcing. A nested Principal component analysis (PCA) was used to construct five composite series which explain between 31% and 74% of the variance across the individual chronologies. Linear regression analyses indicate that the composite series explain up to 41% of the variance in Northeast Atlantic SSTs over the calibration period (1975–2000). Calibration verification (reduction of error [RE] and coefficient of efficiency [CE] ) statistics indicate that the composite series contains significant skill at reconstructing multi-decadal northeast Atlantic SST variability over the past two centuries (1805–2010). These data suggest that composite series derived from sclerochronology networks can facilitate the robust reconstruction of marine climate over past centuries to millennia providing invaluable baseline records of natural oceanographic variability.
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Ward SL, Neill SP, Scourse JD, Bradley SL, Uehara K (2016). Sensitivity of palaeotidal models of the northwest European shelf seas to glacial isostatic adjustment since the Last Glacial Maximum.
Quaternary Science Reviews,
151, 198-211.
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Sensitivity of palaeotidal models of the northwest European shelf seas to glacial isostatic adjustment since the Last Glacial Maximum
© 2016 the Authors the spatial and temporal distribution of relative sea-level change over the northwest European shelf seas has varied considerably since the Last Glacial Maximum, due to eustatic sea-level rise and a complex isostatic response to deglaciation of both near- and far-field ice sheets. Because of the complex pattern of relative sea level changes, the region is an ideal focus for modelling the impact of significant sea-level change on shelf sea tidal dynamics. Changes in tidal dynamics influence tidal range, the location of tidal mixing fronts, dissipation of tidal energy, shelf sea biogeochemistry and sediment transport pathways. Significant advancements in glacial isostatic adjustment (GIA) modelling of the region have been made in recent years, and earlier palaeotidal models of the northwest European shelf seas were developed using output from less well-constrained GIA models as input to generate palaeobathymetric grids. We use the most up-to-date and well-constrained GIA model for the region as palaeotopographic input for a new high resolution, three-dimensional tidal model (ROMS) of the northwest European shelf seas. With focus on model output for 1 ka time slices from the Last Glacial Maximum (taken as being 21 ka BP) to present day, we demonstrate that spatial and temporal changes in simulated tidal dynamics are very sensitive to relative sea-level distribution. The new high resolution palaeotidal model is considered a significant improvement on previous depth-averaged palaeotidal models, in particular where the outputs are to be used in sediment transport studies, where consideration of the near-bed stress is critical, and for constraining sea level index points.
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2015
Ward SL, Neill SP, Van Landeghem KJJ, Scourse JD (2015). Classifying seabed sediment type using simulated tidal-induced bed shear stress.
Marine Geology,
367, 94-104.
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Classifying seabed sediment type using simulated tidal-induced bed shear stress
© 2015. An ability to estimate the large-scale spatial variability of seabed sediment type in the absence of extensive observational data is valuable for many applications. In some physical (e.g. morphodynamic) models, knowledge of seabed sediment type is important for inputting spatially-varying bed roughness, and in biological studies, an ability to estimate the distribution of seabed sediment benefits habitat mapping (e.g. scallop dredging). Although shelf sea sediment motion is complex, driven by a combination of tidal currents, waves, and wind-driven currents, in many tidally energetic seas, such as the Irish Sea, long-term seabed sediment transport is dominated by tidal currents. We compare observations of seabed sediment grain size from 242 Irish Sea seabed samples with simulated tidal-induced bed shear stress from a three-dimensional tidal model (ROMS) to quantitatively define the relationship between observed grain size and simulated bed shear stress. With focus on the median grain size of well-sorted seabed sediment samples, we present predictive maps of the distribution of seabed sediment classes in the Irish Sea, ranging from mud to gravel. When compared with the distribution of well-sorted sediment classifications (mud, sand and gravel) from the British Geological Survey digital seabed sediment map of Irish Sea sediments (DigSBS250), this 'grain size tidal current proxy' (GSTCP) correctly estimates the observed seabed sediment classification in over 73% of the area.
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(2015). Editorial: Quaternary revolutions.
Journal of Quaternary Science,
30(2), 101-103.
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2014
Furze MFA, Scourse JD, Pieńkowski AJ, Marret F, Hobbs WO, Carter RA, Long BT (2014). Deglacial to postglacial palaeoenvironments of the Celtic Sea: Lacustrine conditions versus a continuous marine sequence.
Boreas,
43(1), 149-174.
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Deglacial to postglacial palaeoenvironments of the Celtic Sea: Lacustrine conditions versus a continuous marine sequence
Recent work on the last glaciation of the British Isles has led to an improved understanding of the nature and timing of the retreat of the British-Irish Ice Sheet (BIIS) from its southern maximum (Isles of Scilly), northwards into the Celtic and Irish seas. However, the nature of the deglacial environments across the Celtic Sea shelf, the extent of subaerial exposure and the existence (or otherwise) of a contiguous terrestrial linkage between Britain and Ireland following ice retreat remains ambiguous. Multiproxy research, based on analysis of 12 BGS vibrocores from the Celtic Deep Basin (CDB), seeks to address these issues. CDB cores exhibit a shell-rich upward fining sequence of Holocene marine sand above an erosional contact cut in laminated muds with infrequent lonestones. Molluscs, in situ Foraminifera and marine diatoms are absent from the basal muds, but rare damaged freshwater diatoms and foraminiferal linings occur. Dinoflagellate cysts and other non-pollen palynomorphs evidence diverse, environmentally incompatible floras with temperate, boreal and Arctic glaciomarine taxa co-occurring. Such multiproxy records can be interpreted as representing a retreating ice margin, with reworking of marine sediments into a lacustrine basin. Equally, the same record may be interpreted as recording similar conditions within a semi-enclosed marine embayment dominated by meltwater export and deposition of reworked microfossils. As assemblages from these cores contrast markedly with proven glaciomarine sequences from outside the CDB, a glaciolacustrine interpretation is favoured for the laminated sequence, truncated by a Late Weichselian transgressive sequence fining upwards into fully marine conditions. Reworked rare intertidal molluscs from immediately above the regional unconformity provide a minimum date c.13.9cal. ka BP for commencement of widespread marine erosion. Although suggestive of glaciolacustrine conditions, the exact nature and timing of laminated sediment deposition within the CDB, and the implications this has on (pen)insularity of Ireland following deglaciation, remain elusive. © 2013 the Boreas Collegium.
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Rosier SHR, Green JAM, Scourse JD, Winkelmann R (2014). Modeling Antarctic tides in response to ice shelf thinning and retreat.
Journal of Geophysical Research: Oceans,
119(1), 87-97.
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Modeling Antarctic tides in response to ice shelf thinning and retreat
Tides play an important role in ice sheet dynamics by modulating ice stream velocity, fracturing, and moving ice shelves and mixing water beneath them. Any changes in ice shelf extent or thickness will alter the tidal dynamics through modification of water column thickness and coastal topography but these will in turn feed back onto the overall ice shelf stability. Here, we show that removal or reduction in extent and/or thickness of the Ross and Ronne-Filchner ice shelves would have a significant impact on the tides around Antarctica. The Ronne-Filchner appears particularly vulnerable, with an increase in M2 amplitude of over 0.5 m beneath much of the ice shelf potentially leading to tidally induced feedbacks on ice shelf/sheet dynamics. These results highlight the importance of understanding tidal feedbacks on ice shelves/streams due to their influence on ice sheet dynamics. © 2013. The Authors. Journal of Geophysical Research: Oceans published by Wiley on behalf of the American Geophysical Union.
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2013
(2013). A 30,000yr record of land-ocean interaction in the eastern Gulf of Guinea.
Quaternary Research (United States),
80(1), 1-8.
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A 30,000yr record of land-ocean interaction in the eastern Gulf of Guinea
A 30,000. yr dinocyst and pollen record from the eastern equatorial Atlantic (off Cameroon) has been investigated in order to identify land-ocean linkages during the last deglacial transition. A strong correlation between the abundance of Brigantedinium spp. and the Ca/Fe ratio during the last glacial period suggests enhanced marine productivity in association with cool seawater temperatures and nutrient input linked to coastal upwelling and/or a proximal river mouth. Dry conditions are recorded on the adjacent continent with a significant representation of open vegetation indicators and the Afromontane taxon Podocarpus. After 17. cal. ka. BP these indicators register a sharp decline as a result of a climatic transition from the dry/cooler conditions of the last glacial period to the wetter/warmer conditions of the deglaciation. Simultaneously, dinocysts show a significant shift from dominant heterotrophs to an increasing abundance of autotrophs, reflecting warmer conditions. Significant changes are observed during the Younger Dryas, with a return to drier conditions and higher salinities. The start of the Holocene is marked by very low-salinity conditions, reflecting optimal monsoonal conditions over west equatorial Africa. The end of the African Humid Period is observed between 6 and 5. cal. ka. BP, followed by significant fluctuations in both terrestrial and oceanic proxies. © 2013.
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Williams SM, Scourse JD, Richardson CA, Wanamaker AD, Austin WEN, Cage AG, Sayer MDJ (2013). A multiproxy reconstruction of Hebridean (NW Scotland) spring sea surface temperatures between AD 1805 and 2010.
Palaeogeography, Palaeoclimatology, Palaeoecology,
386, 275-285.
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A multiproxy reconstruction of Hebridean (NW Scotland) spring sea surface temperatures between AD 1805 and 2010
There is currently a deficiency of annually-resolved temperature series from the marine environment. We present a multiproxy reconstruction of Hebridean shelf sea (Tiree Passage; NW Scotland) spring sea surface temperatures (SSTs) for the period AD 1805-2010. The reconstruction is based on the growth increment series from the first absolutely dated annually-resolved multi-centennial Glycymeris glycymeris bivalve mollusc sclerochronology coupled with previously published stable oxygen isotope data (δ18O) from benthic foraminifera sampled from a dated sediment core from nearby Loch Sunart. The independent series contain significant correlations with SSTs across complementary frequency domains. The low frequency component of the sedimentary archive was combined with the mid and high frequency components of the G. glycymeris chronology indices to create a single multiproxy series. Split calibration-verification statistics (reduction of error, RE, coefficient of efficiency, CE, and R2) indicate that the multiproxy record, calibrated to local instrumental sea surface temperatures, contains significant precision and skill at reconstructing spring SSTs (RE=0.59, CE=0.26, R2=0.54). These data demonstrate that bivalve sclerochronologies, when combined with low frequency proxies such as sediment archives, can facilitate statistically robust reconstructions of palaeoceanographic variability during the late Holocene for hydrographically-significant regions of the temperate marine system previously void of annually-resolved archives. The reconstructed SSTs contain a general warming trend of 0.60±0.14°C per century. Only four years in the reconstructed period (1999, 2000, 2002 and 2003) exceed temperatures greater than two standard deviations higher than the reconstructed mean SST (9.03°C), whilst just three years in the first half of the 19th century (1835, 1838 and 1840) fall more than 2σ below the reconstructed mean (6.80°C). © 2013.
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McCarroll D, Clark CD, Cofaigh CO, Evans DJA, Ballantyne CK (2013). Bayesian modelling the retreat of the Irish Sea Ice Stream.
Journal of Quaternary Science,
28(2), 200-209.
Abstract:
Bayesian modelling the retreat of the Irish Sea Ice Stream
We present an 8000-year history spanning 650km of ice margin retreat for the largest marine-terminating ice stream draining the former British-Irish Ice Sheet. Bayesian modelling of the geochronological data shows the ISIS expanded 34.0-25.3ka, accelerating into the Celtic Sea to reach maximum limits 25.3-24.5ka before a collapse with rapid marginal retreat to the northern Irish Sea Basin (ISB). This retreat was rapid and driven by climatic warming, sea-level rise, mega-tidal amplitudes and reactivation of meridional circulation in the North Atlantic. The retreat, though rapid, is uneven, with the stepped retreat pattern possibly a function of the passage of the ice stream between normal and adverse ice bed gradients and changing ice stream geometry. Initially, wide calving margins and adverse slopes encouraged rapid retreat (∼550m a-1) that slowed (∼100m a-1) at the topographic constriction and bathymetric high between southern Ireland and Wales before rates increased (∼200m a-1) across adverse bed slopes and wider and deeper basin configuration in the northern ISB. These data point to the importance of the ice bed slope and lateral extent in predicting the longer-term (>1000 a) patterns and rates of ice-marginal retreat during phases of rapid collapse, which has implications for the modelling of projected rapid retreat of present-day ice streams. © 2013 John Wiley & Sons, Ltd.
Abstract.
(2013). Organic-walled microfossils from the north-west Weddell Sea, Antarctica: Records from surface sediments after the collapse of the Larsen-A and Prince Gustav Channel ice shelves.
Antarctic Science,
25(4), 565-574.
Abstract:
Organic-walled microfossils from the north-west Weddell Sea, Antarctica: Records from surface sediments after the collapse of the Larsen-A and Prince Gustav Channel ice shelves
Surface sediments from six box cores along the north-eastern Antarctic Peninsula document the dinoflagellate cyst (= dinocyst) and other non-pollen palynomorph (NPP) content soon after overlying ice shelves collapsed. Prince Gustav Channel (PGC) and Larsen-A (LA) areas exhibited markedly different dinocyst abundances, concentrations being low in LA (0-20 cysts g-1) and high in PGC (2600-9100 cysts g-1, average: c. 3800 cysts g -1). Since similar water masses impact both areas, differences may be due to low biological productivity, limited sediment accumulation, and/or restricted fine-grain deposition at Larsen-A. Islandinium minutum (Harland & Reid in Harland et al.) Head et al. dominated dinocyst assemblages, occurring as both excysted and encysted forms (lesser abundance). Other taxa (Echinidinium cf. transparantum Zonneveld, Impagidinium pallidum Bujak, Bitectatodinium tepikiense Wilson, Operculodinium centrocarpum Wall & Dale, Brigantedinium spp. Selenopemphix antarctica Marret & de Vernal, Polykrikos? sp. A, and Polykrikos schwartzii Bütschli) were rare. Such assemblage composition is unusual compared to previously published Southern Ocean data, but may be specific to ice shelf and/or recently ice-free environments. Alternatively, it may be attributable to excessive production facilitated by environmental factors and/or abundant food, or similar cyst morphologies produced by different dinoflagellates. Accompanying NPPs included zooplankton remains, acritarchs, and freshwater algae. Tintinnid loricae were most abundant (max. 800 g -1), followed by foraminiferal linings (max. 320 g-1), and the acritarch Palaeostomocystis fritilla (Bujak) Roncaglia (max. 150 g -1). Collectively, NPPs were more abundant in PGC compared to LA samples. © Antarctic Science Ltd 2013.
Abstract.
Scourse J, Smith IP (2013). QUATERNARY SEA-LEVEL AND PALAEOTIDAL CHANGES: a REVIEW OF IMPACTS ON, AND RESPONSES OF, THE MARINE BIOSPHERE. In (Ed)
, 1-69.
Author URL.
(2013). Reconstructions of surface ocean conditions from the northeast Atlantic and Nordic seas during the last millennium.
Holocene,
23(7), 921-935.
Abstract:
Reconstructions of surface ocean conditions from the northeast Atlantic and Nordic seas during the last millennium
We undertake the first comprehensive effort to integrate North Atlantic marine climate records for the last millennium, highlighting some key components common within this system at a range of temporal and spatial scales. In such an approach, careful consideration needs to be given to the complexities inherent to the marine system. Composites therefore need to be hydrographically constrained and sensitive to both surface water mass variability and three-dimensional ocean dynamics. This study focuses on the northeast (NE) North Atlantic Ocean, particularly sites influenced by the North Atlantic Current. A composite plus regression approach is used to create an inter-regional NE North Atlantic reconstruction of sea surface temperature (SST) for the last 1000 years. We highlight the loss of spatial information associated with large-scale composite reconstructions of the marine environment. Regional reconstructions of SSTs off the Norwegian and Icelandic margins are presented, along with a larger-scale reconstruction spanning the NE North Atlantic. The latter indicates that the 'Medieval Climate Anomaly' warming was most pronounced before ad 1200, with a long-term cooling trend apparent after ad 1250. This trend persisted until the early 20th century, while in recent decades temperatures have been similar to those inferred for the 'Medieval Climate Anomaly'. The reconstructions are consistent with other independent records of sea-surface and surface air temperatures from the region, indicating that they are adequately capturing the climate dynamics of the last millennium. Consequently, this method could potentially be used to develop large-scale reconstructions of SSTs for other hydrographically constrained regions. © the Author(s) 2013.
Abstract.
(2013). Simulated late-glacial and Holocene relative sea-level and palaeotidal changes on the isles of Scilly: a new approach for assessing changes in the areal extent of the inter-tidal zone.
Geoscience in South-West England,
13(2), 152-158.
Abstract:
Simulated late-glacial and Holocene relative sea-level and palaeotidal changes on the isles of Scilly: a new approach for assessing changes in the areal extent of the inter-tidal zone
Human palaeodietary analyses indicate that the Neolithic transition in NW Europe may have been characterised in coastal populations by a shift from a marine-based to a terrestrial diet. In order to test whether this shift was at least partly forced by a reduction in the size of the inter-tidal zone - from which human communities forage for marine resources - we reconstruct the areal extent of the inter-tidal zone on the Isles of Scilly over the last 13,000 years. This novel pilot analysis, which incorporates relative sea-level simulations based on glacial isostatic adjustment model output and palaeotidal simulations, demonstrates the significance of coastal topography/gradient in determining inter-tidal extent. The simulations for Scilly show only very modest changes in the extent of the inter-tidal zone across the Neolithic transition indicating minimal or no physical influence at this location for any palaeodietary change. Nevertheless, these model data contribute to an informed assessment of the changing palaeogeography of Scilly over the last 13,000 years that provides a basis for testing via field observations. Furthermore, the tidal amplitude data can be used to correct the indicative meaning of emerging sea-level index points from Scilly.
Abstract.
(2013). The dog cockle, Glycymeris glycymeris (L.), a new annually-resolved sclerochronological archive for the Irish Sea.
Palaeogeography, Palaeoclimatology, Palaeoecology,
373, 133-140.
Abstract:
The dog cockle, Glycymeris glycymeris (L.), a new annually-resolved sclerochronological archive for the Irish Sea
Cross-dated chronologies derived from internal growth increments in the shells of the long-lived bivalve, the dog cockle Glycymeris glycymeris (Linnaeus, 1758), live-collected from two different sites off the east (1997) and south (2009) coasts of the Isle of Man respectively, are described. The chronologies, developed from ten individuals from each site, were found to be statistically robust (Expressed Population Signal (EPS) = 0.87 and 0.94 respectively) with a significant common growth signal despite their location 27. km apart (R = 0.53; N = 49, P = < 0.0001). The period of common growth between the two chronologies is consistent with the 12-year difference in their dates of collection thus providing evidence of an annual periodicity of growth line formation. Significant positive correlations were identified between the chronology indices from both the southern (R = 0.55, N = 58, P = < 0.0001) and eastern sites (R = 0.64, N = 68, P = < 0.0001) and mean January to September sea surface temperatures. A significant positive correlation was also found between the southern site and the winter North Atlantic Oscillation index (R = 0.43; N = 49, P = 0.0009). These data indicate that annual growth increments in the shells of G. glycymeris have the potential to be used as a scleroclimatological archive. © 2012.
Abstract.
(2013). The potential of the marine bivalve mollusc Glossus humanus (L.) as a sclerochronological archive.
Holocene,
23(12), 1711-1720.
Abstract:
The potential of the marine bivalve mollusc Glossus humanus (L.) as a sclerochronological archive
In order to assess its potential as a sclerochronological archive, we present statistical and geochemical analyses of internal growth increment series in shells of the heart cockle Glossus humanus (L.), a large marine bivalve. The investigated samples were collected from Loch Sunart and the Sound of Mull, Scotland, United Kingdom. High-resolution stable isotope (δ18O) analyses and radiocarbon (14C) determinations indicated that G. humanus forms annual growth lines. Examination of the growth increment series revealed that the maximum longevity of G. humanus in this region was 78 years. Radiocarbon dating and crossmatching techniques, derived from dendrochronology, were used to provide an estimation of the temporal distribution of the fossil G. humanus. of the shells that contained >25 growth increments, seven were found to statistically crossmatch, including shells from two distinct sites 15 km apart. The calibrated 14C determinations independently confirmed the crossmatching of three G. humanus shells from the Sound of Mull with a separately constructed Glycymeris glycymeris chronology and a further three G. humanus shells from site 3, in the main basin of Loch Sunart, but indicate a significant difference (site 1) in the antiquity of the two G. humanus populations. Radiocarbon dating indicated that, despite their fragile nature, G. humanus shells remain preserved in near original condition for at least 700 years. Given the small amount of available shell material, it is unlikely that G. humanus will become a key species for the construction of long absolutely dated sclerochronologies. However, these data do indicate that the annually resolved G. humanus growth series could be used to supplement series from other long-lived bivalves and facilitate the construction of a robust multispecies sclerochronology spanning the last 1000 years. © the Author(s) 2013.
Abstract.
(2013). Variability of marine climate on the North Icelandic Shelf in a 1357-year proxy archive based on growth increments in the bivalve Arctica islandica.
Palaeogeography, Palaeoclimatology, Palaeoecology,
373, 141-151.
Abstract:
Variability of marine climate on the North Icelandic Shelf in a 1357-year proxy archive based on growth increments in the bivalve Arctica islandica
A multicentennial and absolutely-dated shell-based chronology for the marine environment of the North Icelandic Shelf has been constructed using annual growth increments in the shell of the long-lived bivalve clam Arctica islandica. The region from which the shells were collected is close to the North Atlantic Polar Front and is highly sensitive to the varying influences of Atlantic and Arctic water masses. A strong common environmental signal is apparent in the increment widths, and although the correlations between the growth increment indices and regional sea surface temperatures are significant at the 95% confidence level, they are low (r~. 0.2), indicating that a more complex combination of environmental forcings is driving growth. Remarkable longevities of individual animals are apparent in the increment-width series used in the chronology, with several animals having lifetimes in excess of 300. years and one, at 507. years, being the longest-lived non-colonial animal so far reported whose age at death can be accurately determined. The sample depth is at least three shells after AD 1175, and the time series has been extended back to AD 649 with a sample depth of one or two by the addition of two further series, thus providing a 1357-year archive of dated shell material. The statistical and spectral characteristics of the chronology are investigated by using two different methods of removing the age-related trend in shell growth. Comparison with other proxy archives from the same region reveals several similarities in variability on multidecadal timescales, particularly during the period surrounding the transition from the Medieval Climate Anomaly to the Little Ice Age. © 2012 Elsevier B.V.
Abstract.
2012
(2012). Characterizing the microstructure of Arctica islandica shells using NanoSIMS and EBSD.
Geochemistry, Geophysics, Geosystems,
13(4).
Abstract:
Characterizing the microstructure of Arctica islandica shells using NanoSIMS and EBSD
The bivalve mollusc Arctica islandica has received considerable attention in recent years because of its potential as an archive of marine palaeoclimate, based on its annually resolved incremental shell growth, longevity, and synchronous growth within populations. The robust interpretation of the archive depends on a detailed understanding of the shell formation process, and this in turn requires a reliable understanding of the shell microstructure. Research into this aspect, however, has so far been relatively limited. This study uses secondary ion mass spectrometry (NanoSIMS) to examine the compositions of the two annually formed growth increments, i.e. a narrow band of relatively slow growth referred to as growth increment I (GI I) and a usually wider accretion called growth increment II (GI II). High resolution composition maps are presented which clearly show lower concentrations of the organic ions 12C14N- and 32S- in GI I relative to GI II. This is consistent with the growth of larger crystallites in GI I, which is clearly demonstrated using a novel analysis method involving focused ion beam (FIB) milling. Electron backscatter diffraction (EBSD) analysis is also presented, and demonstrates that the orientation of the aragonite c-axis is the same in both GI I and GI II, and that the a- and b-axes assume preferred orientations consistent with the known angle of twinning in aragonite. By analyzing individual crystallites it is deduced that the (001) plane is likely to be the mineralizing face in GI I, and that the (011) and (102) planes are low energy interfaces in GI II. Copyright 2012 by the American Geophysical Union.
Abstract.
(2012). New constraints on European glacial freshwater releases to the North Atlantic Ocean.
Geophysical Research Letters,
39(15).
Abstract:
New constraints on European glacial freshwater releases to the North Atlantic Ocean
During the late Quaternary, both external and internal forcings have driven major climatic shifts from glacial to interglacial conditions. Nonlinear climatic steps characterized the transitions leading to these extrema, with intermediate excursions particularly well expressed in the dynamics of the Northern Hemisphere cryosphere. Here we document the impact of these dynamics on the north-eastern North Atlantic Ocean, focussing on the 35-10ka interval. Sea-surface salinities have been reconstructed quantitatively based on two independent methods from core MD95-2002, recovered from the northern Bay of Biscay adjacent to the axis of the Manche paleoriver outlet and thus in connection with proximal European ice sheets and glaciers. Quantitative reconstructions deriving from dinocyst and planktonic foraminiferal analyses have been combined within a robust chronology to assess the amplitude and timing of hydrological changes in this region. Our study evidences strong pulsed freshwater discharges which may have impacted the North Atlantic Meridional Overturning Circulation. © 2012. American Geophysical Union. All Rights Reserved.
Abstract.
(2012). North Atlantic storminess and Atlantic Meridional Overturning Circulation during the last Millennium: Reconciling contradictory proxy records of NAO variability.
Global and Planetary Change,
84-85, 48-55.
Abstract:
North Atlantic storminess and Atlantic Meridional Overturning Circulation during the last Millennium: Reconciling contradictory proxy records of NAO variability
Within the last Millennium, the transition between the Medieval Climate Anomaly (MCA; ca. 1000-1300. CE) and the Little Ice Age (LIA; ca. 1400-1800. CE) has been recorded in a global array of climatic and oceanographic proxies. In this study, we review proxy evidence for two alternative hypotheses for the effects of this shift in the North Atlantic region. One hypothesis postulates that the MCA/LIA transition included a weakening of the Atlantic Meridional Overturning Circulation (AMOC) and a transition to more negative North Atlantic Oscillation (NAO) conditions, resulting in a strong cooling of the North Atlantic region. The alternative hypothesis proposes a MCA/LIA shift to an increased number of storms over the North Atlantic linked to increased mid-latitude cyclogenesis and hence a pervasive positive NAO state. The two sets of proxy records and thus of the two competing hypotheses are then reconciled based on available results from climate model simulations of the last Millennium. While an increase in storm frequency implicates positive NAO, increased intensity would be consistent with negative NAO during the LIA. Such an increase in cyclone intensity could have resulted from the steepening of the meridional temperature gradient as the poles cooled more strongly than the Tropics from the MCA into the LIA. © 2011 Elsevier B.V.
Abstract.
(2012). Surface changes in the North Atlantic meridional overturning circulation during the last millennium.
Nature Communications,
3Abstract:
Surface changes in the North Atlantic meridional overturning circulation during the last millennium
Despite numerous investigations, the dynamical origins of the Medieval Climate Anomaly and the Little Ice Age remain uncertain. A major unresolved issue relating to internal climate dynamics is the mode and tempo of Atlantic meridional overturning circulation variability, and the significance of decadal-to-centennial scale changes in Atlantic meridional overturning circulation strength in regulating the climate of the last millennium. Here we use the time-constrained high-resolution local radiocarbon reservoir age offset derived from an absolutely dated annually resolved shell chronology spanning the past 1,350 years, to reconstruct changes in surface ocean circulation and climate. The water mass tracer data presented here from the North Icelandic shelf, combined with previously published data from the Arctic and subtropical Atlantic, show that surface Atlantic meridional overturning circulation dynamics likely amplified the relatively warm conditions during the Medieval Climate Anomaly and the relatively cool conditions during the Little Ice Age within the North Atlantic sector. © 2012 Macmillan Publishers Limited. All rights reserved.
Abstract.
(2012). The deglacial to postglacial marine environments of SE Barrow Strait, Canadian Arctic Archipelago.
Boreas,
41(2), 141-179.
Abstract:
The deglacial to postglacial marine environments of SE Barrow Strait, Canadian Arctic Archipelago
Core 86027-144 (74°15.56'N, 91°14.21'W) represents a rare, continuous record of Late Pleistocene to Holocene sediments from High Arctic Canada extending from the end of the Last Glaciation. Based on microfossils (dinocysts, non-pollen palynomorphs, benthic and planktonic foraminifera), foraminiferal δ 18O and δ 13C, and sedimentology, seven palaeoenvironmental zones were identified. Zone I (>10.8cal ka BP) records deglaciation, ice-sheet destabilization, float-off and subsequent break-up. Zone II (c.10.8-10.4cal ka BP) shows ice-proximal to ice-distal glaciomarine conditions, interrupted by pervasive land-fast sea-ice marked by a hiatus in coarse sediment deposition. Significant biological activity starts in Zone III (10.4-9.9cal ka BP), where planktonic foraminifera (Neogloboquadrina pachyderma) suggest early oceanic throughflow. Surface waters flowed NW-SE; however, the deep-water origin remains unclear (potentially NW Arctic Ocean or Baffin Bay). Postglacial amelioration (open-water season greater than present) in Zone IV (9.9-7.8cal ka BP) perhaps corresponds to the regional 'Holocene Thermal Maximum' previously proposed. A transitional period (Zone V; 7.8-6.7cal ka BP) of rapid environmental change fluctuating on a scale not observed today is marked by increasing sea-ice and reduced oceanic influence. This probably signals the exclusion of deeper Atlantic water owing to the glacio-isostatic shallowing of inter-island sills, coupled with generally cooling climate. Conditions analogous to those at present, with increased sea-ice and modern microfossil assemblages, commence at c. 6.7cal ka BP (zones VI-VII). Although climate ultimately forces long-term environmental trends, core 86027-144 data imply that regional dynamics, especially changes in sea-level, exert a significant control on marine conditions throughout the Canadian Arctic Archipelago. © 2011 the Boreas Collegium.
Abstract.
Butler PG, Witbaard R, Richardson CA (2012). The marine radiocarbon bomb pulse across the temperate North Atlantic: a compilation of Δ<sup>14</sup>C time histories from Arctica islandica growth increments.
Radiocarbon,
54(2), 165-186.
Abstract:
The marine radiocarbon bomb pulse across the temperate North Atlantic: a compilation of Δ14C time histories from Arctica islandica growth increments
Marine radiocarbon bomb-pulse time histories of annually resolved archives from temperate regions have been underexploited. We present here series of Δ14C excess from known-age annual increments of the long-lived bivalve mollusk Arctica islandica from 4 sites across the coastal North Atlantic (German Bight, North Sea; Tromsø, north Norway; Siglufjordur, north Icelandic shelf; Grimsey, north Icelandic shelf) combined with published series from Georges Bank and Sable Bank (NW Atlantic) and the Oyster Ground (North Sea). The atmospheric bomb pulse is shown to be a step-function whose response in the marine environment is immediate but of smaller amplitude and which has a longer decay time as a result of the much larger marine carbon reservoir. Attenuation is determined by the regional hydrographic setting of the sites, vertical mixing, processes controlling the isotopic exchange of14C at the air-sea boundary,14C content of the freshwater flux, primary productivity, and the residence time of organic matter in the sediment mixed layer. The inventories form a sequence from high magnitude-early peak (German Bight) to low magnitude-late peak (Grimsey). All series show a rapid response to the increase in atmospheric Δ14C excess but a slow response to the subsequent decline resulting from the succession of rapid isotopic airsea exchange followed by the more gradual isotopic equilibration in the mixed layer due to the variable marine carbon reservoir and incorporation of organic carbon from the sediment mixed layer. The data constitute calibration series for the use of the bomb pulse as a high-resolution dating tool in the marine environment and as a tracer of coastal ocean water masses. © 2012 by the Arizona Board of Regents on behalf of the University of Arizona.
Abstract.
(2012). The population structure and biology of the ocean quahog, Arctica islandica, in Belfast Lough, Northern Ireland.
Journal of the Marine Biological Association of the United Kingdom,
92(3), 539-546.
Abstract:
The population structure and biology of the ocean quahog, Arctica islandica, in Belfast Lough, Northern Ireland
The spatial distribution, density, growth rate, longevity, mortality and recruitment patterns of the long-lived clam Arctica islandica in Belfast Lough, Northern Ireland, UK are described. The A. islandica population at Belfast Lough appears to be restricted to a small area at the mouth of the Lough. Additional searches for specimens further into the Lough and into deeper waters found no evidence of a larger more widespread population and we report population densities of 4.5 individuals m -2. The ages of the clams were determined from the number of internal annual growth lines in acetate peel replicas of shell sections. The population growth curve was fitted using the Von Bertalanffy growth equation: Lt = 93.7 mm (1-e -0.03(t-1.25)). Based on catch curve analysis, the Belfast Lough population has an estimated longevity of 220 years and a natural mortality rate of 0.02. We compare growth characteristics and life history traits in this population with other analogous A. islandica populations. The overall growth performance and the phi-prime index were used to compare growth parameters with data from the literature and we observed no significant relationship between the growth performance indices and longevity or latitude. Analysis of the age-structure and reconstructed dates of settlement indicate that this population has experienced almost continual recruitment over the last century with a gap in successful recruitment into the population 90-100 years ago and another 140-150 years ago. The size-structure revealed a scarcity of small individuals which we believe may be an artefact of the dredge sampling process. © 2011 Marine Biological Association of the United Kingdom.
Abstract.
2011
(2011). Corrigendum: Late Devensian and Holocene relative sea-level change in North Wales, UK. Journal of Quaternary Science, 26(7).
(2011). Late Devensian and Holocene relative sea-level change in North Wales, UK.
Journal of Quaternary Science,
26(2), 141-155.
Abstract:
Late Devensian and Holocene relative sea-level change in North Wales, UK
Deglacial sea-level index points defining relative sea-level (RSL) change are critical for testing glacial isostatic adjustment (GIA) model output. Only a few observations are available from North Wales and until recently these provided a poor fit to GIA model output for the British-Irish Ice Sheet. We present results of an integrated offshore geophysical (seismic reflection), coring (drilling rig), sedimentological, micropalaeontological (foraminifera), biostratigraphical (palynology) and geochronological (AMS 14C) investigation into a sequence of multiple peat/organic sediment horizons interbedded within a thick estuarine-marine sequence of minerogenic clay-silts to silty sands from the NE Menai Strait, North Wales. Ten new sea-level index points and nine new limiting dates from the Devensian Late-glacial and early Holocene are integrated with twelve pre-existing Holocene sea-level index points and one limiting point from North Wales to generate a regional RSL record. This record is similar to the most recent GIA predictions for North Wales RSL change, supporting either greater ice load and later deglaciation than in the GIA predictions generated before 2004, or a modified eustatic function. There is no evidence for a mid-Holocene highstand. Tidally corrected RSL data indicate initial breaching of the Menai Strait between 8.8 and 8.4 ka BP to form a tidal causeway, with final submergence between 5.8 and 4.6 ka BP. Final breaching converted the NE Menai Strait from a flood-dominated estuary into a high energy ebb tidal delta with extensive tidal scouring of pre-existing Late-glacial and Holocene sequences. The study confirms the value of utilising offshore drilling/coring technology to recover sea-level records which relate to intervals when rates of both eustatic and isostatic change were at their greatest, and therefore of most value for constraining GIA models. © 2011 John Wiley & Sons, Ltd.
Abstract.
(2011). Long-term stability of δ13C with respect to biological age in the aragonite shell of mature specimens of the bivalve mollusk Arctica islandica.
Palaeogeography, Palaeoclimatology, Palaeoecology,
302(1), 21-30.
Abstract:
Long-term stability of δ13C with respect to biological age in the aragonite shell of mature specimens of the bivalve mollusk Arctica islandica
The stable carbon isotope ratio in bivalve shells (δ13CS) is an enigmatic geochemical archive whose interpretation is often frustrated by the intrusion of variable and unpredictable vital effects which can influence the mix of metabolic and dissolved inorganic carbon (DIC) in the shell material. The impacts of vital effects and rapid changes in calcification rates on the variability and value of δ13CShave been described in a number of studies and in many bivalve species with typical lifespans between a few years and a few decades, δ13CShas been observed to change (usually decreasing) with biological age. Very long-lived animals, by contrast, spend most of their lives in the mature, slow-growing phase, and it might be expected that in these instances the effect of changes in calcification rates on δ13CSwould be less marked, or even absent. Analysis of δ13CSin mature (>40years old) Arctica islandica, reported here, indicates that this is the case δ13CSin shell samples with biological ages between 42 and 391years from four distinct sites in the North Atlantic shelf seas (Gulf of Maine, north Icelandic shelf, Irish Sea and North Sea) shows no age-related trend. This suggests that metabolic vital effects in mature A. islandica may be reasonably stable at the population level. If the drivers of isotopic disequilibrium between shell and ambient environment can be identified and quantified, it may be feasible to adjust for them and use δ13CSin mature A. islandica to investigate long-term changes in nutrient sources and as a robust proxy for δ13C of environmental DIC. © 2010 Elsevier B.V.
Abstract.
2010
(2010). A 26,000-year integrated record of marine and terrestrial environmental change off Gabon, west equatorial Africa.
Palaeogeography, Palaeoclimatology, Palaeoecology,
297(2), 428-438.
Abstract:
A 26,000-year integrated record of marine and terrestrial environmental change off Gabon, west equatorial Africa
Dinoflagellate cysts, pollen and charred cuticle fragments from two sediment cores (giant piston Calypso core MD03-2708 and giant gravity Casq core MD03-2708CQ) collected off the Ogooué River mouth, Gabon (01°10.33́S-08°19.01́E, 920. m water depth) have been analysed to identify the direction and timing of marine-terrestrial environmental changes over western equatorial Africa during the last 26,000. yr. Changes in the proxy records indicate that both terrestrial and oceanic domains off Gabon were impacted synchronously by significant climate changes during the last glacial-interglacial transition and Holocene. Leading into, and during, the Last Glacial Maximum (LGM), heterotrophic dinoflagellate cysts and Ca X-ray fluorescence intensity suggest nutrient enrichment off the river mouth, while pollen records indicate expansions of open forest, savannah woodland, and the Afromontane forest in the catchment area. From the deglaciation to mid-Holocene, however, a marked decrease in Brigantedinium spp. as well as in Poaceae, Cyperaceae and Podocarpus pollen reflects a reduction in nutrient supply to the coastal ocean in parallel with a reduction in grassland, herbaceous communities and Afromontane forest within the catchment. A sharp decline or even disappearance of heterotrophic species during this period is almost contemporaneous with an appearance of Operculodinium aguinawense, reflecting enhanced river influence in the study area. A marked increase of Rhizophora (mangrove) pollen during this transition also indicates eustatic sea-level rise after the LGM which forced a major expansion of the mangrove ecosystem across the gradually submerging shelf. The combination during the late Holocene of a reoccurrence of heterotrophic dinoflagellate cysts with increased Poaceae, Cyperaceae and Podocarpus pollen indicates enhanced nutrient supply to the ocean concordant with a shift to cooler/drier conditions over the Gabon basin. This appears to be linked to a deterioration of the monsoon system induced by the low sea-surface temperatures in the tropical Atlantic Ocean in association with decreased summer insolation. © 2010 Elsevier B.V.
Abstract.
(2010). Comment: a Last Glacial Maximum pollen record from Bodmin Moor showing a possible cryptic northern refugium in southwest England. (Kelly et al. 2010). Journal of Quaternary Science, 25(5), 826-827.
(2010). Evolution of bed shear stress distribution over the northwest European shelf seas during the last 12,000 years.
Ocean Dynamics,
60(5), 1139-1156.
Abstract:
Evolution of bed shear stress distribution over the northwest European shelf seas during the last 12,000 years
Due to changes in relative sea level of order 100 m, the contribution of tides and waves to net bed shear stress in shelf sea regions has varied considerably over the Late Glacial and Holocene. Understanding the spatial and temporal distribution of this ratio leads to a deeper understanding of the erosion and deposition of sediments over the shelf seas throughout this time period. Tidal and wave models are here applied to palaeo time slices of the northwest European shelf seas over the last 12,000 years. The model simulations include a series of sensitivity tests to account for the influence of interannual variability in wind conditions on the resulting bed shear stress. The results show that there has been a significant decrease over the last 12,000 years in shelf-scale mobilisation of coarse sediment. Since there was a lower magnitude of wave orbital velocity penetrating to the sea bed as a result of increasing relative sea level, this reduction in sediment mobilisation was primarily controlled by a shelf-scale decrease in wave-induced bed shear stress over the last 12,000 years. The predictions of mean and residual bed shear stress for the modelled palaeo time slices are a useful tool with which to inform site-selection and subsequent interpretation of sediment cores. In addition, the modelled reconstructions of palaeo tidal range over the shelf seas demonstrates the potential errors associated with assuming a present-day tidal range when correcting palaeo sea-level proxies from their deposited datum (e.g. palaeo mean high water spring tide) to palaeo mean sea level. © 2010 Springer-Verlag.
Abstract.
(2010). Exposure-age constraints on the extent, timing and rate of retreat of the last Irish Sea ice stream.
Quaternary Science Reviews,
29(15-16), 1844-1852.
Abstract:
Exposure-age constraints on the extent, timing and rate of retreat of the last Irish Sea ice stream
We report 23 cosmogenic isotope exposure ages (10Be and36Cl) relating to the maximum extent and deglaciation chronology of the Irish Sea Ice Stream (ISIS), which drained the SW sector of the last British-Irish Ice Sheet. These show that the ISIS failed to reach the Preseli Hills of North Pembrokeshire yet extended southwards to impinge on northern Isles of Scilly (50°N) during the last glacial maximum. Four samples from western Anglesey demonstrate deglaciation of the southern Irish Sea Basin by c. 20-18 ka, and two from the Llŷn Peninsula in northwest Wales, if valid, suggest deglaciation by c. 23-22 ka followed by gradual oscillatory northwards retreat of the ice margin for over 3000 years. An alternative interpretation of our data suggests that ice reached Scilly as late as 22-21 ka then retreated 450 km northwards within the following three millennia, possibly in response to sea level rise and/or intrinsic reorganisation within the last British-Irish Ice Sheet. Samples from upland source areas of the ISIS in NW England and SW Scotland produced exposure ages ≤14.3 ka, suggesting possible persistence of ice in such areas into the Lateglacial Interstade of 14.7-12.9 ka. © 2010 Elsevier Ltd.
Abstract.
(2010). Identification of growth increments in the shell of the bivalve mollusc Arctica islandica using backscattered electron imaging.
Journal of Microscopy,
241(1), 29-36.
Abstract:
Identification of growth increments in the shell of the bivalve mollusc Arctica islandica using backscattered electron imaging
Summary: Annually resolved growth increments in the shell of the bivalve mollusc Arctica islandica have previously been used in combination with geochemical measurements to successfully construct high-resolution proxy records of past marine environmental conditions. However, to ensure the accuracy of these paleoenvironmental reconstructions it is essential that the annual growth series of increments within the examined shells are reliably identified, and can be distinguished from spurious lines caused by nonannual perturbations such as those resulting from storm disturbance. The current methods used for identifying the growth increment series are sometimes compromised because of ambiguity that results from the employed preparation methods. Here it is shown that backscattered electron imaging of polished shell cross sections may be used to clearly discriminate between the two compositionally and structurally distinct increments that comprise 1 year of outer shell growth. This method, involving minimal specimen preparation, is likely to be primarily useful as a validation technique of particular value in cases where increment identification using existing methods is difficult or ambiguous. © 2010 the Authors Journal of Microscopy © 2010 the Royal Microscopical Society.
Abstract.
(2010). Marine climate in the Irish Sea: analysis of a 489-year marine master chronology derived from growth increments in the shell of the clam Arctica islandica.
Quaternary Science Reviews,
29(13-14), 1614-1632.
Abstract:
Marine climate in the Irish Sea: analysis of a 489-year marine master chronology derived from growth increments in the shell of the clam Arctica islandica
We demonstrate here that the growth increment variability in the shell of the long-lived bivalve mollusc Arctica islandica can be interpreted as an indicator of marine environmental change in the climatically important North Atlantic shelf seas. Multi-centennial (up to 489-year) chronologies were constructed using five detrending techniques and their characteristics compared. The strength of the common environmental signal expressed in the chronologies was found to be fully comparable with equivalent statistics for tree-ring chronologies. The negative exponential function using truncated increment-width series from which the first thirty years have been removed was chosen as the optimal detrending technique. Chronology indices were compared with the Central England Temperature record and with seawater temperature records from stations close to the study site in the Irish Sea. Statistically significant correlations were found between the chronology indices and (a) mean air temperature for the 14-month period beginning in the January preceding the year of growth, (b) mean seawater temperatures for February-October in the year preceding the year of growth (c) late summer and autumn air temperatures and sea surface temperatures for the year of growth and (d) the timing of the autumn decline in SST. Changes through time in the correlations with air and seawater temperatures and changes towards a deeper water origin for the shells in the chronology were interpreted as an indication that shell growth may respond to stratification dynamics. © 2009 Elsevier Ltd.
Abstract.
(2010). Source, timing, frequency and flux of ice-rafted detritus to the Northeast Atlantic margin, 30-12 ka: Testing the Heinrich precursor hypothesis.
Boreas,
39(3), 576-591.
Abstract:
Source, timing, frequency and flux of ice-rafted detritus to the Northeast Atlantic margin, 30-12 ka: Testing the Heinrich precursor hypothesis
Increased fluxes of ice-rafted detritus (IRD) from European ice sheets have been documented some 1000-1500 years before the arrival of Laurentide Ice Sheet (LIS)-sourced IRD during Heinrich (H) events. These early fluxes have become known as 'precursor events', and it has been suggested that they have mechanistic significance in the propagation of H events. Here we present a re-analysis of one of the main cores used to generate the precursor concept, OMEX-2K from the Goban Spur covering the last 30 ka, in order to identify whether the British-Irish Ice Sheet (BIIS) IRD fluxes occur only as precursors before H layers. IRD characterization and planktonic foraminiferal δ 18 O measurements constrained by a new age model have enabled the generation of a continuous record of IRD sources, timing, frequency and flux, and of local contemporary hydrographic conditions. The evidence indicates that BIIS IRD precursors are not uniquely, or mechanistically, linked to H events, but are part of the pervasive millennial-scale cyclicity. Our results support an LIS source for the IRD comprising H layers, but the ambient glacial sections are dominated by assemblages typical of the Irish Sea Ice Stream. Light isotope excursions associated with H events are interpreted as resulting from the melting of the BIIS, with ice-sheet destabilization attributed to eustatic jumps generated by LIS discharge during H events. This positive-feedback mechanism probably caused similar responses in all circum-Atlantic ice-sheet margins, and the resulting gross freshwater flux contributed to the perturbation of the Atlantic Meridional Overturning Circulation during H events. © 2010 the Authors, Journal compilation © 2010 the Boreas Collegium.
Abstract.
2009
(2009). A novel method for imaging internal growth patterns in marine mollusks: a fluorescence case study on the aragonitic shell of the marine bivalve Arctica islandica (Linnaeus).
Limnology and Oceanography: Methods,
7(SEPT), 673-681.
Abstract:
A novel method for imaging internal growth patterns in marine mollusks: a fluorescence case study on the aragonitic shell of the marine bivalve Arctica islandica (Linnaeus)
In this article, we explore the use of fluorescence spectroscopy to image growth patterns in the marine bivalve Arctica islandica (L.). The method presented here does not require any chemical treatment of the polished shell section and yields results comparable to acetate peels of acid-etched shell sections and Mutveitreated shell sections. Further, our results indicate that the annual growth lines in A. islandica fluoresce in the blue light spectrum (450-490 nm), thus an ultraviolet source (mercury lamp) is not required. The reflected light entering the digital camera was filtered (510-540 nm) and later enhanced to emphasize the annual growth patterns. The fluorescence of annual growth lines was consistent among the four animals used in this study. Additionally, we measured growth increments in the umbo section of one A. islandica shell using both the traditional acetate method and fluorescence imaging. The two sets of measurements were highly correlated (r = 0.97; P < 0.0001). We suggest that the fluorescence imaging method presented here is a viable option for increment identification and measurement in this key marine archive. It is likely that the methods demonstrated here for A. islandica can easily be used/modified for other bivalve (mollusk) taxa. Fluorescence microscopy permits rapid analysis of shell growth patterns with minimal pretreatment and offers an objective method of determination of annual growth increments and lines. © 2009, by the American Society of Limnology and Oceanography, Inc.
Abstract.
Bryant CL, Harris I, Robertson I (2009). Accurate increment identification and the spatial extent of the common signal in five Arctica islándica chronologies from the Fladen Ground, northern North Sea.
Paleoceanography,
24(2).
Abstract:
Accurate increment identification and the spatial extent of the common signal in five Arctica islándica chronologies from the Fladen Ground, northern North Sea
The creation of networks of shell-based chronologies which can provide regionally extensive highresolution proxies for the marine environment depends on the spatial extent of the common environmental signal preserved in the shell banding and on the reliability of the dating model. Here Arctica islandica chronologies from five neighboring sites in the North Sea are compared, and the strength of the common environmental signal across distances up to 80 km is analyzed using statistical techniques derived from dendrochronology. The signal is found to be coherent across these distances. In a linked study, chronologies based on one of the same sites but constructed by two different research teams are compared. Methodological differences in increment interpretation are found to lead to slippage in the dating models. Systematic inclusion or exclusion of intermittently occurring increments results in the two chronologies becoming misaligned by 4 years over a 70-year period. Comparisons with neighboring chronologies indicate that such increments can generally be regarded as genuine annual increments even if they are not visible in all shells. Copyright 2009 by the American Geophysical Union.
Abstract.
(2009). Celtic Sea linear tidal sand ridges, the Irish Sea Ice Stream and the Fleuve Manche: Palaeotidal modelling of a transitional passive margin depositional system.
Marine Geology,
259(1-4), 102-111.
Abstract:
Celtic Sea linear tidal sand ridges, the Irish Sea Ice Stream and the Fleuve Manche: Palaeotidal modelling of a transitional passive margin depositional system
The linear tidal sand ridges (LTSR) of the Celtic Sea constitute the largest examples of their bedform type on Earth. Previous sedimentological and seismic stratigraphic interpretation suggests that the LTSR are moribund tidally remobilised sediments representing the transgressive systems tract. This interpretation is supported by two-dimensional finite-difference model reconstructions of the M2 tide, forced using the output from a glacial isostatic adjustment model to derive palaeotopography, and a global ocean model to derive the tides on the ocean boundary, used here to reconstruct peak bed stress vectors for the Celtic Sea for timesteps covering the transgression since the Last Glacial Maximum (last 21 ka). These data are coupled with interpretation of recent published observations on the outer shelf depocentres of the Fleuve Manche and the Irish Sea Ice Stream (ISIS) to confirm that the LTSR distribution is consistent with modelled sand transport paths during transgression. The main phase of LTSR growth was between 20 cal ka and 12 cal ka. Ridge axis orientations reflect the final phase of LTSR construction around 12 cal ka, with some later growth of the most southerly LTSR as late as 10 cal ka. LTSR growth was from the SW across the shelf towards the NE. Strong tidal pumping of sediments into slope canyon heads on the outer shelf occurred between 20 cal ka and 12 cal ka, contributing to turbidite activity and the growth of the Celtic and Armorican deep sea fans. It is proposed that 1. the Fleuve Manche shelfal estuary-delta, and the Irish Sea Ice Stream (ISIS) shelf fan, were the main sediment depocentres supplying the growing LTSR, 2. the lack of sediments available in the western Channel limited LTSR growth in this area, and that the easterly termination of the LTSR in this sector results from sediment starvation, and 3. the northeasterly termination in the Celtic Sea sector is a function of declining peak bed stresses rather than sediment starvation. The Celtic Sea margin represents a passive margin depositional system transitional between true glacial ice stream-trough mouth fan systems (to the north) and the fluvial canyon systems characteristic of the margin to the south. This interpretation therefore complements studies of macroscale sedimentation linked to glaciation on the continental margins of the North Atlantic. © 2009 Elsevier B.V. All rights reserved.
Abstract.
(2009). Changes in wave climate over the northwest European shelf seas during the last 12,000 years.
Journal of Geophysical Research: Oceans,
114(6).
Abstract:
Changes in wave climate over the northwest European shelf seas during the last 12,000 years
Because of the depth attenuation of wave orbital velocity, wave-induced bed shear stress is much more sensitive to changes in total water depth than tidal-induced bed shear stress. The ratio between wave- and tidal-induced bed shear stress in many shelf sea regions has varied considerably over the recent geological past because of combined eustatic changes in sea level and isostatic adjustment. In order to capture the high-frequency nature of wind events, a two-dimensional spectral wave model is here applied at high temporal resolution to time slices from 12 ka BP to present using paleobathymetries of the NW European shelf seas. By contrasting paleowave climates and bed shear stress distributions with present-day conditions, the model results demonstrate that, in regions of the shelf seas that remained wet continuously over the last 12,000 years, annual root-mean-square (rms) and peak wave heights increased from 12 ka BP to present. This increase in wave height was accompanied by a large reduction in the annual rms wave-induced bed shear stress, primarily caused by a reduction in the magnitude of wave orbital velocity penetrating to the bed for increasing relative sea level. In regions of the shelf seas which remained wet over the last 12,000 years, the annual mean ratio of wave- to (M2) tidal-induced bed shear stress decreased from 1 (at 12 ka BP) to its present-day value of 0.5. Therefore compared to present-day conditions, waves had a more important contribution to large-scale sediment transport processes in the Celtic Sea and the northwestern North Sea at 12 ka BP. Copyright 2009 by the American Geophysical Union.
Abstract.
(2009). Continuous marine radiocarbon reservoir calibration and the<sup>13</sup>C Suess effect in the Irish Sea: Results from the first multi-centennial shell-based marine master chronology.
Earth and Planetary Science Letters,
279(3-4), 230-241.
Abstract:
Continuous marine radiocarbon reservoir calibration and the13C Suess effect in the Irish Sea: Results from the first multi-centennial shell-based marine master chronology
The identification in various proxy records of periods of rapid (decadal scale) climate change over recent millennia, together with the possibility that feedback mechanisms may amplify climate system responses to increasing atmospheric CO2, highlights the importance of a detailed understanding, at high spatial and temporal resolutions, of forcings and feedbacks within the system. Such an understanding has hitherto been limited because the temperate marine environment has lacked an absolute timescale of the kind provided by tree-rings for the terrestrial environment and by corals for the tropical marine environment. Here we present the first annually resolved, multi-centennial (489-year), absolutely dated, shell-based marine master chronology. The chronology has been constructed by detrending and averaging annual growth increment widths in the shells of multiple specimens of the very long-lived bivalve mollusc Arctica islandica, collected from sites to the south and west of the Isle of Man in the Irish Sea. The strength of the common environmental signal expressed in the chronology is fully comparable with equivalent statistics for tree-ring chronologies. Analysis of the14C signal in the shells shows no trend in the marine radiocarbon reservoir correction (ΔR), although it may be more variable before ∼ 1750. The δ13C signal shows a very significant (R2= 0.456, p < 0.0001) trend due to the13C Suess effect. © 2009 Elsevier B.V. All rights reserved.
Abstract.
(2009). Dinoflagellates in a fast-ice covered inlet of the Riiser-Larsen Ice Shelf (Weddell Sea).
Polar Biology,
32(9), 1331-1343.
Abstract:
Dinoflagellates in a fast-ice covered inlet of the Riiser-Larsen Ice Shelf (Weddell Sea)
A short-term (3-15 days) multiple and single sediment-trap array deployed in Drescher Inlet (Eastern Weddell Sea) during austral summer 1998 showed well preserved and relatively diverse dinoflagellate assemblages comprised of 13 taxa. Consistent with other Antarctic studies, large Protoperidinium species were dominating whereas Preperidinium and Dinophysis showed minor frequencies. Athecates were not observed, possibly due to their poor preservation status. The majority of dinoflagellates were heterotrophic species, likely feeding on previously recorded abundant diatoms at the study site. Assemblage structures varied according to depth (Protoperidinium antarcticum and P. rosaceum at 10 m depth vs. P. macrapicatum and Preperidinium granulosum at 360 m depth) and collection period (first period: P. antarcticum; second period: Protoperidinium sp. C). Sediment-trap dinoflagellates were either derived from a flux out of the overlying fast ice, platelet ice, or the water column but given their high mobility, migration between these media cannot be ruled out. © Springer-Verlag 2009.
Abstract.
(2009). Discussion on 'An analysis of Cotswold topography: Insights into the landscape response to denudational isostasy'. Journal of the Geological Society, 166(3).
(2009). Growth, dynamics and deglaciation of the last British-Irish ice sheet: the deep-sea ice-rafted detritus record.
Quaternary Science Reviews,
28(27-28), 3066-3084.
Abstract:
Growth, dynamics and deglaciation of the last British-Irish ice sheet: the deep-sea ice-rafted detritus record
The evolution and dynamics of the last British-Irish Ice Sheet (BIIS) have hitherto largely been reconstructed from onshore and shallow marine glacial geological and geomorphological data. This reconstruction has been problematic because these sequences and data are spatially and temporally incomplete and fragmentary. In order to enhance BIIS reconstruction, we present a compilation of new and previously published ice-rafted detritus (IRD) flux and concentration data from high-resolution sediment cores recovered from the NE Atlantic deep-sea continental slope adjacent to the last BIIS. These cores are situated adjacent to the full latitudinal extent of the last BIIS and cover Marine Isotope Stages (MIS) 2 and 3. Age models are based on radiocarbon dating and graphical tuning of abundances of the polar planktonic foraminifera Neogloboquadrina pachyderma sinistral (% Nps) to the Greenland GISP2 ice core record. Multiple IRD fingerprinting techniques indicate that, at the selected locations, most IRD are sourced from adjacent BIIS ice streams except in the centre of Heinrich (H) layers in which IRD shows a prominent Laurentide Ice Sheet provenance. IRD flux data are interpreted with reference to a conceptual model explaining the relations between flux, North Atlantic hydrography and ice dynamics. Both positive and rapid negative mass balance can cause increases, and prominent peaks, in IRD flux. First-order interpretation of the IRD record indicates the timing of the presence of the BIIS with an actively calving marine margin. The records show a coherent latitudinal, but partly phased, signal during MIS 3 and 2. Published data indicate that the last BIIS initiated during the MIS 5/4 cooling transition; renewed growth just before H5 (46 ka) was succeeded by very strong millennial-scale variability apparently corresponding with Dansgaard-Oeschger (DO) cycles closely coupled to millennial-scale climate variability in the North Atlantic region involving latitudinal migration of the North Atlantic Polar Front. This indicates that the previously defined "precursor events" are not uniquely associated with H events but are part of the millennial-scale variability. Major growth of the ice sheet occurred after 29 ka with the Barra Ice Stream attaining a shelf-edge position and generating turbiditic flows on the Barra-Donegal Fan at ∼27 ka. The ice sheet reached its maximum extent at H2 (24 ka), earlier than interpreted in previous studies. Rapid retreat, initially characterised by peak IRD flux, during Greenland Interstadial 2 (23 ka) was followed by readvance between 22 and 16 ka. Readvance during H1 was only characterised by BIIS ice streams draining central dome(s) of the ice sheet, and was followed by rapid deglaciation and ice exhaustion. The evidence for a calving margin and IRD supply from the BIIS during Greenland Stadial 1 (Younger Dryas event) is equivocal. The timing of the initiation, maximum extent, deglacial and readvance phases of the BIIS interpreted from the IRD flux record is strongly supported by recent independent data from both the Irish Sea and North Sea sectors of the ice sheet. © 2009 Elsevier Ltd. All rights reserved.
Abstract.
(2009). Late-glacial remains of woolly mammoth (Mammuthus primigenius) from Shropshire, UK: Stratigraphy, sedimentology and geochronology of the Condover site.
Geological Journal,
44(4), 392-413.
Abstract:
Late-glacial remains of woolly mammoth (Mammuthus primigenius) from Shropshire, UK: Stratigraphy, sedimentology and geochronology of the Condover site
In 1986 remains of an adult woolly mammoth, Mammuthus primigenius (Blumenbach), were discovered at Norton Farm Pit, Condover, south of Shrewsbury, UK. Preliminary stratigraphical investigations indicated that this individual dated to the Devensian Late-glacial Interstadial, then the first evidence for survival of mammoth in Britain following the Last Glacial Maximum. Initial radiocarbon analysis confirmed this interpretation. Subsequent excavations in 1987/1988 recovered the remains of a further three juvenile mammoth individuals. All of these remains were found in the spoil heaps of overburden (ex situ) and their true stratigraphical context had to be reconstructed from the remnants surviving in the Pit. The 1987/1988 excavations enabled stratigraphical investigation of the site and submission of samples for radiocarbon (14C) dating, including the use of ultrafiltration pretreatment for bone samples, with the aims of reconstructing the geological and palaeoenvironmental evolution of the site and the sedimentary context of the unstratified mammoth remains. These results are presented here. This investigation indicates that the woolly mammoth remains at Condover derive from a dead-ice landscape dominated by eskers, kames and kettle-hole basins, and that the sedimentary sequence in which the mammoth remains were found forms the infilling of a kettle-hole basin. The sedimentary infilling and formation of the kettle-hole basin through ice block melt-induced subsidence were syngenetic. 14C determinations indicate that basin infill was initiated prior to Greenland Interstadial 1, and probably in Greenland Stadial 2 i.e. before 14.7 ka BP and that it continued until the early Holocene, around 8ka BP. The sedimentological and 14C data indicate that the unstratified mammoth remains can be attributed to a dark grey clayey sandy silt (Unit C1), which accumulated during the earlier part of Greenland Interstadial 1 (14 to 14.5 ka BP) within an actively subsiding slow-flowing, beaded, fluvial network characterized by channels and pools/lakes, and with relatively shallow marginal slopes. The sedimentary architecture indicates survival of the buried ice block into Greenland Interstadial 1 and final melting only towards the end of the Interstadial at ca. 12.65 ka BP. © 2009 John Wiley & Sons, Ltd.
Abstract.
(2009). Palaeoenvironmental context of the Late-glacial woolly mammoth (Mammuthus primigenius) discoveries at Condover, Shropshire, UK.
Geological Journal,
44(4), 414-446.
Abstract:
Palaeoenvironmental context of the Late-glacial woolly mammoth (Mammuthus primigenius) discoveries at Condover, Shropshire, UK
In 1986/1987 the remains of several mammoths, Mammuthus primigenius (Blumenbach), were discovered on the spoil heap of an actively working gravel pit at Condover, Shropshire, England. The discovery of the remains posed two questions that could be addressed by analyses of biological proxies. First, as none of the bones was found in situ it was necessary to confirm the stratum in which the remains occurred. Second, what was the environment in which these animals lived and died? a range of biological indicators was used to address these questions, including pollen, spore and algal, plant macrofossil, invertebrate, anuran and biological mineral analyses. Multivariate statistical analyses of palynological and Pediastrum data, along with evidence from the Coleopteran assemblages, support the attribution of the mammoth bones to a unit of dark grey clayey sandy silt, although they may have lived at the time of the overlying green detritus mud. The palaeobiological data supports the correlation of these sediments to the Devensian Late-glacial. The mammoths entered this basin at the start of the Late-glacial Interstadial (Greenland Interstadial 1e) (ca. 14 830-3930 cal. year BP; 12 300±11014C year BP) and became mired in soft cohesive sediments. Palaeotemperature reconstructions, based on the Coleopteran assemblages, from the time when the mammoths actually became mired, show that the climate was temperate with mean July temperatures between 15 and 19°C and mean January temperatures between - 13 and +6°C. Biological indicators from the sediments encasing the mammoths indicate that the landscape surrounding the basin was treeless and dry, contrasting with rich vegetation within the basin itself that had possibly attracted the mammoths to the site. Evidence of sedimentary disturbance suggests that the mammoths caused large-scale bioturbation of the deposits making palaeoenvironmental interpretations difficult. Fossils of terrestrial blowflies, carcass and dung beetles show that some of the decaying corpses must have lain exposed on the land surface for sufficient time for the soft parts to have rotted away and skin and bones to have become desiccated before many of them sank into the dark grey clayey sandy silt. ©2009 John Wiley & Sons, Ltd.
Abstract.
(2009). Persistent positive north atlantic oscillation mode dominated the medieval climate anomaly.
Science,
324(5923), 78-80.
Abstract:
Persistent positive north atlantic oscillation mode dominated the medieval climate anomaly
The Medieval Climate Anomaly (MCA) was the most recent pre-industrial era warm interval of European climate, yet its driving mechanisms remain uncertain. We present here a 947-year-long multidecadal North Atlantic Oscillation (NAO) reconstruction and find a persistent positive NAO during the MCA. Supplementary reconstructions based on climate model results and proxy data indicate a clear shift to weaker NAO conditions into the Little Ice Age (LIA). Globally distributed proxy data suggest that this NAO shift is one aspect of a global MCA-LIA climate transition that probably was coupled to prevailing La Niña-like conditions amplified by an intensified Atlantic meridional overturning circulation during the MCA.
Abstract.
Van Landeghem KJJ, Uehara K, Wheeler AJ, Mitchell NC, Scourse JD (2009). Post-glacial sediment dynamics in the Irish Sea and sediment wave morphology: Data-model comparisons.
Continental Shelf Research,
29(14), 1723-1736.
Abstract:
Post-glacial sediment dynamics in the Irish Sea and sediment wave morphology: Data-model comparisons
The irregular seafloor of the narrow Irish Sea on the NW European Shelf has been documented over several decades. From recently collected swath bathymetry data, very large trochoidal, nearly symmetrical sediment waves are observed in many parts of the Irish Sea and appear similar to those described from other continental shelf seas in North America that were covered by glacigenic sediments during the Last Glacial Maximum. Swath multibeam and single beam bathymetry data, backscatter intensity, shallow seismic imagery, video footage and sediment cores from the Irish Sea high sediment waves have been integrated to identify their genesis with reference to present and past hydrodynamic variability. From cross-sectional profiles over asymmetrical sediment waves in the Irish Sea the direction of asymmetry is used to map residual bed stress directions and associated bedload transport paths. Irish Sea peak bed stress vectors were generated using a two-dimensional palaeo-tidal model for the NW European shelf seas and compare well with the observations. Tidally induced bed stresses are modelled to have increased between 7-10 ka BP, to be nearly symmetrical in magnitude and to have reversed in dominant direction on a millennial scale. These environmental conditions during the post-glacial marine transgression are suggested here to help comprehend the construction of the very large sediment waves, with local variations due to differences in sediment grain size, sediment supply, water depth and intensified currents due to seafloor slopes. Model parameterisation using an open ocean boundary with time-dependent tidal changes and the implementation of high-resolution bathymetric information will improve future models of small-scale bed shear stress patterns and improve the predictive value of such modelling efforts. © 2009 Elsevier Ltd. All rights reserved.
Abstract.
(2009). The formation of headland/island sandbanks.
Continental Shelf Research,
29(18), 2167-2177.
Abstract:
The formation of headland/island sandbanks
There are four extensive sandbanks in the vicinity of the Isle of Portland, a headland in the English Channel. The formation and maintenance of the two most prominent of these sandbanks (one on either side of the headland) can largely be explained by net bedload convergence, driven by instantaneous headland eddies generated by tidal flow past the headland. However, there are also two less prominent sandbanks (again, one on either side of the headland), which are not located in zones of bedload convergence. It is suggested here that these latter two sandbanks were formed when the Isle of Portland was isolated from the mainland by a tidal strait. Relative sea-level data and radiocarbon dates indicate that this would have occurred ca. 9-7 ka BP, prior to the closure of the strait by sedimentation. Tidal flow through this strait generated eddy systems in addition to the headland eddies, leading to the formation of associated headland/island sandbanks. At 7 ka BP, sedimentation resulted in closure of the strait, leading to the present-day headland configuration, and subsequent reworking of these now moribund sandbanks formed by the strait. A series of idealised morphological model experiments, parameterised using bedrock depths and glacial isostatic adjustment model output of relative sea level, are here used to simulate this hypothesised sequence of sandbank evolution over the Holocene. The results of the model experiments are corroborated by in situ observations of bedforms and sediment characteristics, and by acoustic Doppler current profiler (ADCP) data applied to predictions of bedload transport over the sandbanks. In addition to demonstrating the mechanism which leads to the formation of sandbanks by tidal flow through a strait, the model results show that upon subsequent closure of such a strait, these sandbanks will no longer be actively maintained, in contrast to sandbanks which are continuously maintained by headland eddies. © 2009 Elsevier Ltd. All rights reserved.
Abstract.
(2009). Tidal mixing and the meridional overturning circulation from the Last Glacial Maximum.
Geophysical Research Letters,
36(15).
Abstract:
Tidal mixing and the meridional overturning circulation from the Last Glacial Maximum
Using a global tidal model it is shown that the supply of tidal energy to the deep ocean was larger during the Last Glacial Maximum (LGM; 18,000-22,000 years BP). The results were used to modify the rate of vertical mixing in a coupled ocean-atmosphere model set up for the present and LGM oceans. The increased levels of mechanical energy during the LGM were countered by a fresher upper North Atlantic, which led to a reduced circulation and deep water formation in spite of a trebling of the implicit mixing energy. This identifies the significance of accurately representing vertical mixing in climate models to estimate the recovery time-scales and timings of rapid catastrophic paleoceanographic events. From the estimated levels of implicit energy in the vertical mixing scheme an amendment to diffusivity based mixing schemes is suggested. Copyright 2009 by the American Geophysical Union.
Abstract.
2008
(2008). Impact of sea-level rise over the last deglacial transition on the strength of the continental shelf CO<inf>2</inf> pump.
Geophysical Research Letters,
35(24).
Abstract:
Impact of sea-level rise over the last deglacial transition on the strength of the continental shelf CO2 pump
Although shelf seas account for only 7% of the oceanic surface area, recent observations demonstrate that they host significant ocean-atmosphere CO 2 fluxes. A mechanism implicated in driving a significant CO 2 sink in the temperate shelf seas is the Continental Shelf Pump. Here we present an analysis of the impact of sea-level rise, and the consequent flooding of continental shelves, on the growth of the continental shelf CO 2 pump over the last deglacial transition. Wc combine reconstructions of shelf palaeogeography, bathymetry and tides, with contemporary shelf sea - atmosphere CO2 flux estimates, to demonstrate the potential of the expanding shelf seas to have impacted on the global carbon cycle, via the continental shelf CO2 pump, over the past 21,000 years and, by inference, earlier glacial-interglacial cycles. Copyright 2008 by the American Geophysical Union.
Abstract.
(2008). Marine production in the Congo-influenced SE Atlantic over the past 30,000 years: a novel dinoflagellate-cyst based transfer function approach.
Marine Micropaleontology,
68(1-2), 198-222.
Abstract:
Marine production in the Congo-influenced SE Atlantic over the past 30,000 years: a novel dinoflagellate-cyst based transfer function approach
The sediments from the Congo deep-sea fan contain valuable information about past environmental conditions of the east equatorial Atlantic during the transition from the Last Glacial Maximum (LGM) to present-day climatic conditions. The high-resolution marine (organic-walled dinoflagellate cysts = dinocysts) and terrestrial (pollen) palynological records from two cores off equatorial West Africa, covering the last 30,000 years, document three major phases in surface productivity. (1) During the LGM relative sea level was low, nutrient enrichment due to seasonal coastal upwelling prevailed off the Congo mouth and high aridity prevailed in the catchment area. (2) at around 15.2 cal ka BP, monsoonal precipitation strengthened over the Congo Basin, generating high river discharges, river-induced upwelling, and increased nutrient flux to the ocean. In parallel, erosion of shelf sediments during shelf transgression further enhanced nutrient flux. (3) at around 9-8 cal ka BP, rainforest vegetation inhibited soil erosion, depleted nutrient supply, and restricted marine productivity to its modern levels. The study presents the application of modern analogues and a dinocyst transfer function to the reconstruction of primary palaeoproductivity (PP) in a region of freshwater influence. A database of recent dinocyst assemblages comprising of 208 sites in the equatorial Atlantic enabled the reconstruction of sea-surface annual PP 1.3 times higher during the LGM and also during the deglaciation, between 15.2 and 13.2 cal ka BP. The reconstruction is independent of, and thus provides corroboration for, other biological and geochemical proxies. © 2008 Elsevier B.V. All rights reserved.
Abstract.
(2008). Very long lived mollusks confirm 17th century AD tephra based radiocarbon reservoir ages for north Icelandic shelf waters.
Radiocarbon,
50(3), 399-412.
Abstract:
Very long lived mollusks confirm 17th century AD tephra based radiocarbon reservoir ages for north Icelandic shelf waters
Marine sediment records from the north Icelandic shelf, which rely on tephrochronological age models, reveal an average ΔR (regional deviation from the modeled global surface ocean reservoir age) of approximately 150 yr for the last millennium. These tephra-based age models have not hitherto been independently verified. Here, we provide data that corroborate ΔR values derived from these sediment archives. We sampled the youngest portion (ontogenetic age) of a bivalve shell, Arctica islandica (L.), for radiocarbon analysis, which was collected alive in 2006 from the north Icelandic shelf in ~80 m water depth. Annual band counting from the sectioned shell revealed that this clam lived for more than 405 yr, making it the longest-lived mollusk and possibly the oldest non-colonial animal yet documented. The14C age derived from the umbo region of the shell is 951 ± 27 yr BP. Assuming that the bivalve settled onto the seabed at AD 1600, the corresponding local value of ΔR is found to be 237 ± 35 yr by comparison of the14C age with the Marine04 calibration curve (Hughen et al. 2004) at this time. Furthermore, we cross-matched a 287-yr-old, dead-collected, A. islandica shell from AD 1601 to 1656 from the same site with the live-caught individual.14C analysis from the ventral margin of this shell revealed a ΔR of 186 ± 50 yr at AD 1650. These values compare favorably with each other and with the tephra-based ΔR values during this period, illustrating that14C from A. islandica can effectively record14C reservoir changes in the shelf seas.© 2008 by the Arizona Board of Regents on behalf of the University of Arizona.
Abstract.
2007
(2007). A 3D visualisation environment modelling the evolution of north-west Europe since the Last Glacial Maximum.
Abstract:
A 3D visualisation environment modelling the evolution of north-west Europe since the Last Glacial Maximum
Abstract.
(2007). Compositional variability of ice-rafted debris in Heinrich layers 1 and 2 on the northwest European continental slope identified by environmental magnetic analyses.
Journal of Quaternary Science,
22(2), 163-172.
Abstract:
Compositional variability of ice-rafted debris in Heinrich layers 1 and 2 on the northwest European continental slope identified by environmental magnetic analyses
The composition of ice-rafted debris (IRD) within a sediment core from the European continental slope (core OMEX-2K; 49° 5′ N, 13° 26′ W) has been examined using environmental magnetic analyses. The data demonstrate compositional variability of the IRD within Heinrich layers 2 (H2) and 1 (H1) and these differences are most readily explained by changes in the contribution of different IRD sources to the core site. Some IRD within the main Heinrich layers show magnetic signatures that are similar to IRD derived from the Laurentide ice sheet found in cores from within the main North Atlantic IRD-belt. In contrast, other IRD-rich layers, both prior to and within the main Heinrich layers, demonstrate different magnetic behaviour, suggesting a contribution from a non-Laurentide sourced IRD, most likely derived from ice streams discharging from northeast Atlantic ice sheets such as the British and Fennoscandian ice sheets. These data are consistent with published compositional data from the same core and, given the rapid, highly sensitive and non-destructive nature of the method, suggest that environmental magnetic analysis has considerable potential for characterising IRD materials within Heinrich layers for the purposes of defining provenance. Copyright © 2006 John Wiley & Sons, Ltd.
Abstract.
Eynaud F, Zaragosi S, Scourse JD, Mojtahid M, Bourillet JF, Hall IR, Penaud A, Locascio M, Reijonen A (2007). Deglacial laminated facies on the NW European continental margin: the hydrographic significance of British-Irish Ice Sheet deglaciation and Fleuve Manche paleoriver discharges.
Geochemistry, Geophysics, Geosystems,
8(6).
Abstract:
Deglacial laminated facies on the NW European continental margin: the hydrographic significance of British-Irish Ice Sheet deglaciation and Fleuve Manche paleoriver discharges
We have compiled results obtained from four high sedimentation rate hemipelagic sequences from the Celtic sector of the NW European margin (NE Atlantic) to investigate the paleoceanographic and paleoclimatic evolution of the area over the last few climatic cycles. We focus on periods characteristic of deglacial transitions. We adopt a multiproxy sedimentological, geochemical, and micropaleontological approach, applying a sampling resolution down to ten microns for specific intervals. The investigation demonstrates the relationships between the Bay of Biscay hydrography and the glacial/deglacial history of both the proximal British-Irish Ice Sheet (BIIS) and the western European continent. We identify recurrent phases of laminae deposition concurrent with major BIIS deglacial episodes in all the studied cores. Evidence for abrupt freshwater discharges into the open ocean highlights the influence of such events at a regional scale. We discuss their impact at a global scale considering the present and past key location of the Bay of Biscay versus the Atlantic Meridional Overturning Circulation (AMOC). Copyright 2007 by the American Geophysical Union.
Abstract.
(2007). Progressive reduction in NE Atlantic intermediate water ventilation prior to Heinrich events: Response to NW European ice sheet instabilities?.
Geochemistry, Geophysics, Geosystems,
8(1).
Abstract:
Progressive reduction in NE Atlantic intermediate water ventilation prior to Heinrich events: Response to NW European ice sheet instabilities?
We present high-resolution benthic δ13C records from intermediate water depth core site MD01-2461(1153 m water depth), from the Porcupine Seabight, NE Atlantic, spanning 43 to 8 kyr B.P. At an averageproxy time step of 160 ± 56 years this core provides information on the linkage between records from the Portuguese Margin and high-latitude North Atlantic basin, allowing additional insights into North Atlantic thermohaline circulation (THC) variability during millennial-scale climatic events of the last glacial. Together, these records document both discrete and progressive reductions in Glacial North Atlantic Intermediate Water (GNAIW) formation preceding Heinrich (H) events 1, 2, and 4, recorded through the apparent interchange of glacial northern and southern-sourced intermediate water signatures along the European Margin. Close coupling of NW European ice sheet (NWEIS) instability and GNAIW formation is observed through transient advances of SCW along the European margin concurrent with pulses of icerafted debris and meltwater release into the NE Atlantic between 27 and 16 kyr B.P. when the NWEIS was at maximum extent and proximal to Last Glacial Maximum convection zones in the open North Atlantic. It is such NWEIS instability and meltwater forcing that may have triggered reduced North Atlantic THC prior to collapse of the Laurentide ice sheet at H1 and H2. Precursory reduction in GNAIW formation prior to H4 may also be inferred. However, limited NWEIS ice volume prior to H4 and convection occurring in the Norwegian-Greenland Sea require that if a meltwater trigger is invoked, as appears to be the case at H1 and H2, the source of meltwater prior to H4 is elsewhere, likely higher-latitude ice sheets. Clarification of the sequencing and likely mechanisms of precursory decrease of the North Atlantic THC support theories of H event initiation relating to ice shelf growth during cold periods associated with reduced North Atlantic THC and subsequent ablation through subsurface warming and sea level rise associated with further reductions in meridional overturning. Copyright 2007 by the American Geophysical Union.
Abstract.
Turney CSM, Scourse J, Rodbell D, Caseldine C (2007). Quaternary climatic, environmental and archaeological change in Australasia.
JOURNAL OF QUATERNARY SCIENCE,
22(5), 421-422.
Author URL.
(2007). The Holocene vegetation history of the Arfon Platform, North Wales,UK.
Boreas,
36(2), 170-181.
Abstract:
The Holocene vegetation history of the Arfon Platform, North Wales,UK
Detailed pollen, charcoal and loss on ignition profiles were analysed from Llyn Cororion, North Wales, UK. The chronology was based on 11 radiocarbon dates. This site is particularly important for this region because its high-resolution record improves the spatial and temporal resolution of records of Holocene vegetation change in an area characterized by a highly variable environment. An early Holocene phase of Juniperus-Betula scrub was succeeded by Betula-Corylus woodland. Quercus and Ulmus were established by c. 8600 14C yr BP, with Pinus dominating at c. 8430 14C yr BP. Local disturbance then allowed the spread of Alnus; Tilia was a common component of the forest by 5650 14C yr BP. Charcoal and pollen records suggest that by c. 2600 14C yr BP there was progressive deforestation, increased use of fire and spread of grassland; the first cereal grain was recorded at c. 2900 14C yr BP. Compared with data from upland Snowdonia, the results show that within a topographically diverse region there were significant local variations in forest composition. These variations developed as a response to interactions between many environmental parameters and were further complicated by the influence of human activity. In an area such as North Wales it is therefore unlikely that one site can be representative of regional Holocene vegetational development. The site is additionally important because it contributes to the data available for meta-analyses of environmental change in the North Atlantic region, particularly as detailed pollen diagrams from coastal lake sites around estern Europe are rare.
Abstract.
(2007). The relationship of Heinrich events and their European precursors over the past 60 ka BP: a multi-proxy ice-rafted debris provenance study in the North East Atlantic.
Quaternary Science Reviews,
26(7-8), 862-875.
Abstract:
The relationship of Heinrich events and their European precursors over the past 60 ka BP: a multi-proxy ice-rafted debris provenance study in the North East Atlantic
High resolution, multi-proxy records of ice-rafted debris (IRD) flux and provenance in the NE Atlantic detail the development, variability and decline of marine margins of the last glacial circum-North Atlantic ice sheets. Coupled lithological identification, Sr and Nd isotopic composition and 40Ar/39Ar ages of individual hornblende grains reduce ambiguity as to IRD potential source region, allowing clear differentiation between Laurentide (LIS), Icelandic and British (BIS) ice sheet sources (the Icelandic and BIS are collectively referred to as the NW European ice sheet, NWEIS). A step-wise increase in the flux of IRD to the core site at ∼26.5 ka BP documents BIS advance and glaciation of Ireland. Millennial-scale variability of the BIS at a ∼2 ka periodicity is inferred through clusters of pulsed IRD fluxes throughout the late glacial (26.5-10 ka BP). Combination of these European IRD events and the ∼7 ka periodicity of LIS instability is thought to account for quasi-synchronicity of the NWEIS and LIS IRD pulses at Heinrich event (H) 2 and H1, previously suggested to represent the possible involvement of the NWEIS in the initiation of H events. Furthermore, the lack of extensive NWEIS marine margin is inferred prior to H3 (31.5 ka BP), such that no 'European precursor' event is associated with either H5 or H4. This suggests that 'precursor events' were not directly implicated in the collapse of the LIS, and the persistent instabilities of the BIS that are clustered at a 2 ka periodicity are incompatible with the concept that both H events and their 'precursors' are independent responses to a common underlying trigger. © 2007 Elsevier Ltd. All rights reserved.
Abstract.
2006
(2006). Climatic instability in west equatorial Africa during the Mid- and Late Holocene.
Quaternary International,
150(1), 71-81.
Abstract:
Climatic instability in west equatorial Africa during the Mid- and Late Holocene
Millennial-scale climatic variations have punctuated the Holocene characterised by abrupt changes from warm to cool or wetter to drier conditions. Amongst these climatic events, there is increased evidence for an abrupt multicentennial shift of climatic conditions around 3.8/3.7 kyr BP (4.1 cal. kyr BP) in mid- to low-latitude regions which had a profound impact on landscape and population migration. In the Mediterranean region, subtropical, tropical and equatorial Africa, a number of continental proxies (lake-levels, pollen sequences, stable isotopes) record this abrupt change towards drier conditions. However, regionalism in climatic conditions is reflected in the vegetation records, possibly in relation to orographic conditions and the influence of sea-surface conditions. Hitherto there have been very few marine sequences that record this particular climatic shift at high-resolution. We present here new data from the Congo deep-sea fan containing integrated marine and terrestrial proxies. Around 5-4 cal. kyr BP, shifts in surface conditions off the Congo River mouth are observed, with possible establishment of seasonal coastal upwelling, and lower sea-surface temperatures. In parallel, pollen data indicate fluctuations of herbaceous, afromontane taxa and charred grass cuticles, suggesting more open vegetation in the lowland regions and an increase in cloud forest and/or afromontane vegetation at higher altitudes within the Congolese region. © 2006 Elsevier Ltd and INQUA.
Abstract.
(2006). Comment on: Numerical 230Th/U dating and a palynological review of the Holsteinian/Hoxnian Interglacial by Geyh and Müller. Quaternary Science Reviews, 25(21-22), 3070-3071.
(2006). Editorial: Late Holocene oceanographic and climate change from the western European margin: the results of the HOLSMEER project.
Holocene,
16(7), 931-935.
Abstract:
Editorial: Late Holocene oceanographic and climate change from the western European margin: the results of the HOLSMEER project
The underlying aim of the HOLSMEER project has been to improve our understanding of natural climate variability through the search for, interpretation and quantification of, climatic variability in very high-resolution shallow marine records from Atlantic Europe covering the last 2000 years. This has been achieved through detailed analyses of a series of coastal and shallow marine sites spanning the Atlantic seaboard from Iberia to western Norway, and extending across to Iceland. HOLSMEER partners have documented pronounced instability in the thermohaline circulation (THC) during the period immediately prior to the recent significant anthropogenic impact on the environment. For the first time we have been able to document that these changes in the coastal ocean are correlated with significant changes in terrestrial palaeoclimate proxies, notably during the last 1000 years. The notable changes are the significance of warm sea surface temperatures (SST) associated with active THC between AD 700 and 1000, a transition phase to much colder SST and reduced THC between AD 1000 and AD 1300, colder SST through to AD 1900 followed by an active re-establishment of warm surface water circulation during the twentieth century. These switch-like reorganizations of the climate system have influenced the entire seaboard from western Iberia to western Norway, and have forced changes in ocean productivity, iceberg frequency and sea ice coverage. These changes have also directly influenced sea level through steric effects. The project has also resulted in significant advances in the establishment of new palaeoclimate proxies, including transfer functions related to benthic foraminifera, diatoms and dinoflagellate cysts. Annual growth band series from fossil specimens of the long-lived bivalve mollusc Arctica islandica from the northern North Sea have been successfully cross-matched, and independently verified by radiocarbon dating, to provide the longest Arctica chronology, and the first floating chronology constructed entirely from marine fossils. © 2006 SAGE Publications.
Abstract.
Scourse J, Richardson C, Forsythe G, Harris I, Heinemeier J, Fraser N, Briffa K, Jones P (2006). First cross-matched floating chronology from the marine fossil record: data from growth lines of the long-lived bivalve mollusc Arctica islandica.
HOLOCENE,
16(7), 967-974.
Author URL.
(2006). High resolution evidence for linkages between NW European ice sheet instability and Atlantic Meridional Overturning Circulation.
Earth and Planetary Science Letters,
243(3-4), 476-488.
Abstract:
High resolution evidence for linkages between NW European ice sheet instability and Atlantic Meridional Overturning Circulation
Published studies show that ice rafted debris (IRD) deposition preceding Heinrich (H) events H1 and H2 in the NE Atlantic was derived from the NW European ice sheets (NWEIS), possibly offering clues about ice sheet sensitivity and stability, and the mechanisms that caused periodic collapse of the Laurentide Ice Sheet (LIS). We present detailed lithological and geochemical records, including radiogenic isotope fingerprinting, of IRD deposits from core MD01-2461, proximal to the last glacial British Ice Sheet (BIS), demonstrating persistent instability of the BIS, with significant destabilisation occurring 1.5-1.9 kyr prior to both H1 and H2, dated at 16.9 and 24.1 kyr BP, respectively, in the NE Atlantic. Paired Mg/Ca and δ18O data from the surface dwelling Globigerina bulloides and subsurface dwelling Neogloboquadrina pachyderma sinistral are used to determine late-glacial variability of temperature, salinity and stratification of the upper water column. A picture emerges that the BIS was in a continuing state of readjustment and never fully reached steady state. Increased sea surface temperatures appear to have triggered the episode of NWEIS instability preceding H1. It seems most probable that the so-called 'precursor' events were not linked to the H events. However, if response to a common thermal forcing is considered, an increased response time of the LIS, up to ∼2 kyr longer than the NWEIS, may be inferred. Negative salinity excursions of up to 2.6 indicate significant incursions of melt water associated with peaks in NWEIS instability. Decreased surface density led to a more stable stratification of the upper water column and is associated with reduced ventilation of intermediate waters, recorded in depleted epibenthic δ13 C (Cibicidoides wuellerstorfi). We suggest that instability and meltwater forcing of the NWEIS temporarily weakened Atlantic Meridional Overturning Circulation, allowing transient advance of southern-sourced waters to this site, prior to H events 1 and 2. © 2006 Elsevier B.V. All rights reserved.
Abstract.
(2006). Mid-latitude shelf seas: a NW European perspective on the seasonal dynamics of temperature, salinity and oxygen isotopes.
Holocene,
16(7), 937-947.
Abstract:
Mid-latitude shelf seas: a NW European perspective on the seasonal dynamics of temperature, salinity and oxygen isotopes
Pronounced seasonal variability, particularly in the surface ocean heat flux, imparts an important control that drives thermal stratification of the tide-dominated middle- and high-latitude shelf seas. Bottom water temperature and salinity data, resolved on a grid 20′ latitude by 30′ longitude, were combined with a regional synthesis of the salinity:δ18O relationship in order to generate a spatial and temporal understanding of oxygen isotopes in seawater around the shelf seas of NW Europe. The data are expressed according to equilibrium calcite (δ18OEq.calcite) and, in the shallow mixed water column, exhibit large seasonal changes that are primarily driven by bottom water temperature. Annual bottom water temperature varies from < 3°C to > 17°C in the southern North Sea, generating a seasonal δ18OEq.Calcitesignal of up to 3.2‰. The amplitude of the seasonal δ18OEq.calcitesignal is significantly damped (0.1-0.2‰) in deeper, thermally stratified shelf waters. Maps of the monthly distribution δ18OEq.calciteprovide the first systematic overview of the spatial and temporal changes on the NW European shelf and highlight the importance of understanding seasonal growth on the incorporation of geochemical signatures into marine organisms. © 2006 SAGE Publications.
Abstract.
(2006). New evidence for a grounded Irish Sea glaciation of the Isles of Scilly, UK.
Abstract:
New evidence for a grounded Irish Sea glaciation of the Isles of Scilly, UK
Abstract.
(2006). Tidal evolution of the northwest European shelf seas from the Last Glacial Maximum to the present.
Journal of Geophysical Research: Oceans,
111(9).
Abstract:
Tidal evolution of the northwest European shelf seas from the Last Glacial Maximum to the present
Two-dimensional paleotidal simulations have been undertaken to investigate tidal and tide-dependent changes (tidal amplitudes, tidal current velocities, seasonal stratificafion, peak bed stress vectors) that have occurred in the NW European shelf seas during the last 20 ka. The simulations test the effect of shelf-wide isostatic changes of sea level by incorporating results from two different crustal rebound models, and the effect of the ocean-tide variability by setting open boundary values either fixed to the present state or variable according to the results of a global paleotidal model. The use of the different crustal rebound models does not affect the overall changes in tidal patterns, but the timing of the changes is sensitive to the local isostatic effects that differ between the models. The incorporation of ocean-tide changes greatly augments the amplitude of tides and tidal currents in the Celtic and Malin seas before 10 ka BP, and has a large impact on the distribution of seasonally stratified conditions, magnitude of peak bed stress vectors and tidal dissipation in the shelf seas. The predictions on seasonal stratification are supported by well-dated evidence on tidal mixing front migration in the Celtic Sea. Additional experiments using the global model suggest that the variability of offshore tides has been caused mainly by changes of eustatic sea level and ice-sheet extent. In particular, a large decrease observed at 10-8 ka BP is attributed to the opening of Hudson Strait accompanied by the retreat of the Laurentide Ice Sheet. Copyright 2006 by the American Geophysical Union.
Abstract.
2005
Scourse JD, Clarke L, Marret F (2005). Editorial. Journal of Quaternary Science, 20(5).
(2005). High-resolution last deglaciation record from the Congo fan reveals significance of mangrove pollen and biomarkers as indicators of shelf transgression.
Quaternary Research,
64(1), 57-69.
Abstract:
High-resolution last deglaciation record from the Congo fan reveals significance of mangrove pollen and biomarkers as indicators of shelf transgression
High abundances of mangrove pollen have been associated with transgressive cycles on tropical margins, but the detailed relations between systems tracts and the taphonomy of the pollen are unclear. We report here the occurrence and high abundance of Rhizophora pollen, in association with taraxerol, a Rhizophora-sourced biomarker, from a high-resolution Congo fan core covering the last deglaciation. An age model based on14C dates enables the temporal changes in taraxerol content and the percentage frequencies and flux (pollen grains (pg) cm-2(103yr)-1) of mangrove pollen to be compared quantitatively with the lateral rate of transgression across the flooding surface (derived from glacio-hydro-isostatic model output and the bathymetry of the margin). Rhizophora pollen concentrations and taraxerol content of the sediment are very strongly positively correlated with the lateral rate of transgression and indicate, independently of any sequence stratigraphic context, that mangrove pollen spikes are associated with the transgressive systems tract rather than the highstand systems tract or maximum flooding surface. Lower-resolution longer-term records from this margin indicate an association between taraxerol concentrations and transgressive rather than regressive phases. The flux of these materials to the Congo fan is interpreted as a function of the erosion of flooded mangrove swamp on the shelf and, less importantly, changing extent of mangrove habitat, during sea-level rise. Congo River palaeoflood events also result in reworking of mangrove pollen and supply to the fan, but this mechanism is subdominant. Rhizophora pollen has been underestimated in many palynological studies undertaken on cores from the African margin because of inappropriate sieve mesh size used during laboratory preparation. © 2005 University of Washington. All rights reserved.
Abstract.
(2005). Palaeoclimatology and palaeohydrography of the glacial stages on Celtic and Armorican margins over the last 360 000 yrs.
Marine Geology,
224(1-4), 57-82.
Abstract:
Palaeoclimatology and palaeohydrography of the glacial stages on Celtic and Armorican margins over the last 360 000 yrs
Core MD03-2692 was retrieved in a water-depth of 4064 m on the Celtic margin (Bay of Biscay) during the SEDICAR cruise onboard the RV Marion Dufresne II. It covers the last 360 ka in a total length of 39 m. Multidisciplinary analyses have been applied to this sequence with the aim of studying the palaeoclimatic and palaeoenvironmental signals of the last few climatic cycles. The analyses undertaken include: (1) non-destructive logging with: physical properties (magnetic susceptibility, sediment colour), X-ray radiography and measurement of the major elements by X-ray-fluorescence, (2) analyses of planktonic and benthic foraminifera, lithic grains and stable isotopic measurements (oxygen and carbon). We have focused on the long-term evolution of glacial stages (with special attention to terminations and Heinrich events). The results obtained confirm the close correlation between deep-sea sedimentation recorded on the Celtic margin and changes in the terrestrial environment of the adjacent continent. Heinrich layers have been identified in MIS 2, 3, 6 and 8. We note the occurrence of laminated facies within deglacial sequences deposited during Termination I and MIS 6. These facies are closely linked to disintegration phases of the British-Irish Ice Sheet (BIS). The laminations contain lower ice-rafted detritus (IRD) concentrations than the equivalent Heinrich layers and are linked to abrupt changes in sea-surface palaeotemperatures. We suggest that the laminations are formed by an annual cycle of meltwater and iceberg release from the disintegrating BIS generating cascading plumes of dense turbid meltwater coeval with IRD release. © 2005 Elsevier B.V. All rights reserved.
Abstract.
2004
(2004). Distribution of dinoflagellate cyst assemblages in surface sediments from the northern and western shelf of Iceland.
Abstract:
Distribution of dinoflagellate cyst assemblages in surface sediments from the northern and western shelf of Iceland
Abstract.
(2004). Holocene shelf-sea seasonal stratification dynamics: a dinoflagellate cyst record from the Celtic Sea, NW European shelf.
Holocene,
14(5), 689-696.
Abstract:
Holocene shelf-sea seasonal stratification dynamics: a dinoflagellate cyst record from the Celtic Sea, NW European shelf
Published records of the Holocene evolution of seasonal stratification in the Celtic Sea (NW European shelf) have been based on benthic proxies, notably benthic foraminifera and associated stable isotopic data. We have investigated organic-walled dinoflagellate cyst assemblages from a well-dated Holocene sequence from the central Celtic Sea in order to assess the signal from this planktonic proxy and to reconstruct paired bottom- and surface-water conditions through time. This sequence has, on the basis of the benthic proxies, been interpreted previously as a record of the replacement of tidally mixed water by stratified water associated with tidal-front migration during the early Holocene. Interpretation of the dinocyst record has been facilitated by a parallel study of the distribution of cysts from Celtic Sea surface sediments and their relationship with seasonal water masses. The dinocyst stratigraphy indicates mixed-water conditions during the early Holocene consistent with reduced water depths (hence lowered sea level) over the core site. The first significant change in the dinocyst assemblages is recorded at around 6650 cal. years BP and indicates a transition from mixed-frontal conditions to seasonal stratification. This interpretation of frontal migration is consistent with changes in the benthic foraminiferal assemblages and associated stable isotopes at the same core depth. From 6650 to 3600 cal. years BP, the significant occurrence of Bitectatodinium tepikiense accompanied by Spiniferites elongatus is attributed to strong seasonality, with winter sea-surface temperatures possibly below 5°C. Another transition at 3600 cal. years BP is attributed to a reduction in seasonality generated by milder winter conditions linked to a stronger influence of the thermohaline circulation over the studied area. This transition is not recorded by the benthic proxies and is attributed to climate forcing rather than to any change in tidal dynamics. It is notable that many mires in western Britain record distinct wet shifts contemporary with this change.
Abstract.
Barker PA, Talbot MR, Street-Perrott FA, Marret F, Scourse J, Odada EO (2004). Late quaternary climatic variability in intertropical Africa.
Author URL.
(2004). Stable isotopic analyses of modern benthic foraminifera from seasonally stratified shelf seas: Disequilibria and the 'seasonal effect'.
Holocene,
14(5), 747-758.
Abstract:
Stable isotopic analyses of modern benthic foraminifera from seasonally stratified shelf seas: Disequilibria and the 'seasonal effect'
Previously published stable isotopic data on benthic foraminiferal species from a Holocene sequence in the Celtic Sea have been interpreted in terms of the progressive replacement of a tidally mixed by a stratified water mass. Offsets in the δ18O data between Ammonia batavus and Quinqueloculina seminulum were attributed to a 'seasonal effect' in which these two species were hypothesized to have calcified at different times of the year. The aims of this study were to test the hypotheses (1) that benthic foraminiferal stable isotope records from across the Celtic Sea front reflect seasonal stratification and (2) that offsets in the oxygen isotope record between different species are the result of the postulated seasonal effect. Hypothesis I was tested through investigation of live and dead benthic foraminiferal and bottom-water δ18O and δ13C sampled in transects across the Celtic Sea front from mixed through frontal to stratified water masses. Measurements of bottom-water salinity enabled a mixing-line equation to be developed for this area enabling quantitative reconstructions of bottom-water temperature from the isotopic data. Samples from stratified settings are characterized by heavier δ18Oforam and lighter δ13Cforam values than the mixed samples. Offsets in δ18Oforam between A. batavus and Q. seminulum support the notion of the seasonal effect. A. batavus produces values close to equilibrium while Q. seminulum overestimates temperature by up to 2°C and this might explain some of the offset observed between the two species observed in the palaeodata. Comparison of the δ18Oforam data with measured seasonal temperature cycles from mixed and stratified localities in the Celtic Sea demonstrates that, while most foraminifera calcify during the summer months, different species calcify at, or are preserved from, different times within this warm part of the seasonal cycle; Q. seminulum calcifies during September when peak bottom-water temperatures occur, while A. batavus calcifies during September in stratified localities, but during spring or early summer in mixed localities. This study confirms the interpretation of the δ18O palaeodata from the Celtic Sea as a palaeostratification record and demonstrates that δ18O data from shelf-sea cores can be used to supplement benthic foraminiferal assemblages as a tool for reconstructing the long-term dynamics of seasonal stratification.
Abstract.
Scourse J (2004). Untitled.
JOURNAL OF QUATERNARY SCIENCE,
19(1), 1-1.
Author URL.
2003
(2003). Control of modern dinoflagellate cyst distribution in the Irish and Celtic seas by seasonal stratification dynamics.
Marine Micropaleontology,
47(1-2), 101-116.
Abstract:
Control of modern dinoflagellate cyst distribution in the Irish and Celtic seas by seasonal stratification dynamics
Surface sediments from seven stations located in the seasonally stratified, frontal and mixed water regions in the Celtic and Irish seas have been analysed for their dinoflagellate cyst assemblages and dinosterol content. A total of 45 dinoflagellate cyst taxa have been identified and the assemblages related to surface and sediment conditions. Sediments from the mixed water region, at 30 m water depth, are characterised by a relatively low cyst concentration (∼2300 cysts/g dry weight) and high relative abundances of Lingulodinium machaerophorum accompanied by Spiniferites membranaceus, Brigantedinium spp. and Dubridinium caperatum. Assemblages from stratified and frontal water stations are dominated by Spiniferites ramosus associated with Operculodinium centrocarpum, Brigantedinium spp. cysts of Polykrikos schwartzii and Selenopemphix quanta. Ordination techniques performed on a restricted number of 35 taxa from the assemblages differentiated the stratified and frontal assemblages based on the abundance of the less abundant species Bitectatodinium tepikiense and Spiniferites elongatus. Among the environmental parameters (sea-surface temperature and salinity, stratification index, chlorophyll concentration and sediment grain-size classes), the seasonal stratification and sedimentological context, itself a function of tidal dynamics, explain most of the variance in the environmental conditions. These results indicate that dinoflagellate cyst analyses of shelf sediment records can be used to document the planktonic signal of seasonal stratification dynamics. © 2002 Elsevier Science B.V. All rights reserved.
Abstract.
(2003). The distribution of benthic foraminifera in the Celtic Sea: the significance of seasonal stratification.
Journal of Foraminiferal Research,
33(1), 32-61.
Abstract:
The distribution of benthic foraminifera in the Celtic Sea: the significance of seasonal stratification
Seasonal stratification is an important phenomenon in tidally-stirred shelf seas, influencing biological productivity, sedimentation rates, the organic content of shelf sediments, and the climate of surrounding landmasses. Previous micropaleontological and stable isotopic investigation investigation of a Holocene sequence from the Celtic Sea suggests that benthic foraminiferal distributions are linked to the physical and biological oceanographic characteristics associated with stratification. We have tested this hypothesis by analyzing the living and dead foraminiferal faunas from surface samples collected during across-frontal cruises during the summers of 1995 and 1996. Foraminiferal and environmental data for 56 samples are presented. Live and dead foraminiferal data were analyzed by factor analysis and, along with the environmental data, canonical correspondence analysis (CCA). Four distinct assemblages were identified from factor analysis of the live data: (1) a frontal assemblage characterized by Stainforthia fusiformis, (2) a mixed water assemblage characterized by Cibicides lobatulus, Textularia bockii, Spiroplectammina wrightii, Ammonia batavus and Quinqueloculina seminulum, (3) a stratified assemblage characterized by Bulimina marginata, Hyalinea balthica, Adercotryma wrighti and Nonionella turgida, and (4) an eastern assemblage dominated by Bulimina gibba, Elphidium excavatum and Eggerelloides scaber. Factor analysis of the dead data reproduces all groupings except the frontal assemblage. These data therefore support interpretations based on earlier stratigraphic data, and highlight the significance of benthic foraminifera as faunal indicators of paleostratification in shelf seas. The distributions also support predicted cross-frontal transfer of nutrients and the existence of surface converging circulation cells. Statistical analyses indicate the significance of unmeasured ecological variables which we speculate might be food supply, and oxygen concentration of bottom and sediment pore waters.
Abstract.
Scourse J (2003). Untitled.
JOURNAL OF QUATERNARY SCIENCE,
18(1), 1-1.
Author URL.
2002
(2002). Holocene evolution of seasonal stratification in the Celtic Sea: Refined age model, mixing depths and foraminiferal stratigraphy.
Marine Geology,
191(3-4), 119-145.
Abstract:
Holocene evolution of seasonal stratification in the Celtic Sea: Refined age model, mixing depths and foraminiferal stratigraphy
Published stable isotopic (oxygen, carbon) and preliminary foraminiferal data from a Holocene vibrocore from the Celtic Sea (Northwest European continental shelf) have been interpreted in terms of the progressive replacement of tidally mixed by seasonally stratified water, the first study of the long-term dynamics of seasonal stratification. This study was hampered by poor age control and the foraminiferal data were based on processing with a 125-μm sieve which has been shown not to recover critical small taxa. We present here a new age model for this vibrocore (BGS 51/-07/199) based on 12 accelerator mass spectrometry 14C dates on foraminifera and molluscs, radionuclide (137Cs, 40K) profiles from the vibrocore and juxtaposed multicores, and a complete foraminiferal stratigraphy based on sieving at 63 μm. Together, the three datasets enable a mixing model to be proposed which clarifies the resolution of the record which is confirmed as extending from the Late-Glacial to the late Holocene. Correction for autocompaction reveals an increase in sedimentation rate and mixing depth from the early to the late Holocene. A temporary increase in sedimentation rate at 6650 yr cal BP is attributed to migration of the productive frontal zone across the core site. Some time after 3000 yr cal BP sedimentation either slowed abruptly or ceased completely, giving the modern mixed layer an apparent age of ∼ 3000 yr cal BP. The mixed layer depth indicates strongly that the apparent transition to stratification during the early Holocene is primarily a threshold change attenuated by bioturbation; secondary attentuation is related to reworking. The mixed layer model adopted suggests that this isotopic transition occured between 8990 and 8440 yr cal BP (8720±2σ). The foraminiferal analyses, in the light of modern foraminiferal distributional data, support the inference that the succession can be interpreted as a response to the progressive seasonal stratification of the Celtic Sea during the Holocene. The data highlight the value of key taxa as indicators of shelf palaeostratification in the geological record, notably of Textularia bocki and Stainforthia fusiformis as mixed-frontal and frontal-stratified indicators, respectively. The critical change to this frontal assemblage occurs at the same depth as the isotopic threshold, based on the mixing model. These data affirm the earlier interpretation of the isotopic record as registering bottom water temperature and water column productivity changes driven by the evolution of seasonal stratification. The clear association between grain size and sedimentation, as well as these isotopic and faunal data, indicates that the shelf record of highstand sedimentation is preferentially biased towards the preservation of sequences deposited under seasonally stratified rather than mixed water masses. © 2002 Elsevier Science B.V. All rights reserved.
Abstract.
(2002). Quaternary shelf sea palaeoceanography: Recent developments in Europe.
Marine Geology,
191(3-4), 87-94.
Abstract:
Quaternary shelf sea palaeoceanography: Recent developments in Europe
High-quality palaeoceanographic reconstructions based on sequences preserved in shallow marine environments demonstrate that these constitute significant archives of climatic and oceanographic change. Such sequences are important, first, because their often very high-resolution, sometimes laminated, nature enables high-frequency cycles to be resolved and provides the basis for establishing spatial and temporal variability in the marine radiocarbon reservoir effect. Second, sea-level index points from shelves are important for the validation of glacio-hydro-isostatic geophysical models and for understanding sea-level change during early deglaciation. Third, shallow marine sequences contain excellent records of land-ocean interaction, often preserving paired terrestrial-marine proxies in the same stratigraphic sequence. A new development in shelf sea palaeoceanography is documenting the long-term dynamics of shelf sea stratification. This is the dominant hydrodynamic phenomenon of tide-dominated shelf seas in the middle and high latitudes and has a profound influence on productivity and therefore global change through the carbon cycle. Detailing the evolution of seasonal stratification during eustatic highstands is therefore of relevance to the climate system. © 2002 Elsevier Science B.V. All rights reserved.
Abstract.
Scourse J (2002). Untitled.
JOURNAL OF QUATERNARY SCIENCE,
17(1), 1-1.
Author URL.
2001
(2001). A critical review of the glaciomarine model for Irish sea deglaciation: Evidence from southern Britain, the Celtic shelf and adjacent continental slope.
Journal of Quaternary Science,
16(5), 419-434.
Abstract:
A critical review of the glaciomarine model for Irish sea deglaciation: Evidence from southern Britain, the Celtic shelf and adjacent continental slope
In support of their 'glaciomarine' model for the deglaciation of the Irish Sea basin, Eyles and McCabe cited the occurrence of distal glaciomarine mud drapes onshore in the Isles of Scilly and North Devon, and of arctic beach-face gravels and sands around the shores of the Celtic Sea. Glacial and sea-level data from the southern part of the Irish Sea in the terminal zone of the ice stream and the adjacent continental slope are reviewed here to test this aspect of the model. The suggestion that the glacial sequences of both the Isles of Scilly and Fremington in North Devon are glaciomarine mud drapes is rejected. An actively calving tidewater margin only occurred early in the deglacial sequence close to the terminal zone in the south-central Celtic Sea. Relative sea-levels were lower, and therefore glacio-isostatic depression less, than envisaged in the glaciomarine model. Geochronological, sedimentological and biostratigraphical data indicate that the raised beach sequences around the shores of the Celtic Sea and English Channel were deposited at, or during regression soon after, interglacial eustatic highstands. Evidence for ice-rafting at a time of high relative sea-levels is restricted to a phase(s) earlier than the Late Devensian. These data indicate that the raised beach sequences have no bearing on the style of Irish Sea deglaciation. Copyright © 2001 John Wiley & Sons, Ltd.
Abstract.
(2001). Integrated marine and terrestrial evidence for abrupt Congo River palaeodischarge fluctuations during the last deglaciation.
Journal of Quaternary Science,
16(8), 761-766.
Abstract:
Integrated marine and terrestrial evidence for abrupt Congo River palaeodischarge fluctuations during the last deglaciation
We present a high-resolution reconstruction of tropical palaeoenvironmental changes for the last deglacial transition (18 to 9 cal. kyr BP) based on integrated oceanic and terrestrial proxies from a Congo fan core. Pollen, grass cuticle, Pediastrum and dinoflagellate cyst fluxes, sedimentation rates and planktonic foraminiferal δ18O ratios, uK'37 sea-surface temperature and alkane/alkenone ratio data highlight a series of abrupt changes in Congo River palaeodischarge. A major discharge pulse is registered at around 13.0 cal. kyr BP which we attribute to latitudinal migration of the Intertropical Convergence Zone (ITCZ) during deglaciation. The data indicate abrupt and short-lived changes in the equatorial precipitation regime within a system of monsoonal dynamics forced by precessional cycles. The phases of enhanced Congo discharge stimulated river-induced upwelling and enhanced productivity in the adjacent ocean. Copyright © 2001 John Wiley & Sons, Ltd.
Abstract.
(2001). Workshop explores debris transported by icebergs and paleoenvironmental implications. Eos, 82(35), 382-386.
2000
(2000). The origin of Heinrich layers: Evidence from H2 for European precursor events.
Earth and Planetary Science Letters,
182(2), 187-195.
Abstract:
The origin of Heinrich layers: Evidence from H2 for European precursor events
Recent well-dated isotopic (Sr-Nd) fingerprinting of Heinrich layer ice-rafted detritus (IRD) on the European margin indicates supply from European ice sheets as precursors to Laurentide Ice Sheet (LIS) supply [F.E. Grousset et al. Geology 28 (2000) 123-126, H. Snoeckx et al. Mar. Geol. 158 (1999) 197-208]. These precursor events lead LIS input by up to 1.5 ka [F.E. Grousset et al. Geology 28 (2000) 123-126] and have been interpreted to indicate LIS collapse during Heinrich events stimulated by events originating on the European side of the Atlantic [F.E. Grousset et al. Geology 28 (2000) 123-126]. Such phasing of IRD supply from different sources within Heinrich layers therefore has implications for the origin and mechanics of Heinrich events. We present evidence here that the IRD comprising Heinrich layer 2 (H2; ~20-21 14C ka BP) on the European continental margin contains detrital Campanian Upper Chalk deriving from bedrock sources eroded on the Celtic shelf by the British Ice Sheet (BIS) in addition to lithic material sourced from the LIS. High-resolution radiocarbon chronology indicates chalk grain deposition as discrete pulses both before and coincident with supply of LIS-sourced detritus. The specificity of the chalk fingerprint to the BIS enables a 700-1000 yr lag between the BIS and LIS events to be identified. This phasing indicates a more rapid response of the outlet lobes draining the smaller BIS than those draining the LIS and implicates external climatic forcing of Heinrich events. It is unlikely that this precursor event represents IRD event 18, the recently identified 1-2 ka IRD cycle event which immediately precedes H2, because the lag between precursor and main event is here less than 1.5 ka and because such pervasive periodicity is not apparent in European continental margin IRD records. The later synchroneity between the BIS and LIS input in H2 identifies glacio-eustatic sea-level rise associated with LIS discharges as a possible feedback mechanism causing destabilisation of ice streams elsewhere during Heinrich events. (C) 2000 Elsevier Science B.V. All rights reserved.
Abstract.
Scourse J (2000). Untitled.
JOURNAL OF QUATERNARY SCIENCE,
15(1), 1-1.
Author URL.
1999
Marret F, Scourse J, Jansen JHF, Schneider R (1999). Climate and palaeoceanographic changes in west Central Africa during the last deglaciation: Palynological investigation.
Comptes Rendus de l'Academie de Sciences - Serie IIa: Sciences de la Terre et des Planetes,
329(10), 721-726.
Abstract:
Climate and palaeoceanographic changes in west Central Africa during the last deglaciation: Palynological investigation
Palynological analyses of two marine cores recovered from the Congo fan provide a high-resolution record of palaeoclimatic changes that have taken place on the adjacent continent and the margin since the Late Pleistocene. Between 27 and 1414C kyr BP, the basin was characterized by well-developed grasslands, and the coastal area was under the influence of seasonal coastal upwellings. From 14-1314C kyr BP, significant changes in the rainforest and coastal vegetation are recorded, characterized by an increase of the rainforest until 5-414C kyr BP, followed by the development of herbaceous vegetation. Sea level fluctuations are documented by Rhizophora frequencies.
Abstract.
(1999). Foraminiferal isoleucine epimerization determinations from the Nar Valley Clay, Norfolk, UK: Implications for Quaternary correlations in the southern North Sea basin.
Geological Magazine,
136(5), 543-560.
Abstract:
Foraminiferal isoleucine epimerization determinations from the Nar Valley Clay, Norfolk, UK: Implications for Quaternary correlations in the southern North Sea basin
Fully temperate freshwater, brackish and marine sediments overlying Anglian till and glacilacustrine sediments in the Nar Valley area of northwest Norfolk, UK, have been attributed to the Middle Pleistocene Hoxnian temperate stage on palynological grounds, and basal peats associated with this sequence have been recently correlated with oxygen isotope stage 9 on the basis of a series of 230Th/238U dates (mean 317 ± 14 ka). At Tottenhill these sediments (Nar Valley Freshwater Beds, Nar Valley Clay) underlie a deltaic complex attributed to the Wolstonian ice margin. The lithostratigraphical relations between the major formations in the Nar Valley, and the pollen stratigraphy of the fully temperate sequence, are very similar to the Pleistocene sequence in the Inner Silver Pit area of the southern North Sea, and correlation has been proposed between the successions described from these two localities. However, the Inner Silver Pit sequence has yielded aminostratigraphic data consistent with isotopic stage 11. Benthic foraminiferal assemblages and foraminiferal amino-acid determinations have been investigated from the Nar Valley Clay in order to test further the palaeoenvironmental setting of the sequence and to help resolve the age of the sequence and correlation with the Inner Silver Pit interglacial. The foraminiferal assemblages support previous sedimentological and palaeontological evidence for a transgressive tendency within this sequence. Multiple isoleucine epimerization determinations on Ammonia beccarii and Aubignyna perlucida from five levels within the Nar Valley Clay give mean aIle/Ile ratios of 0.135 and 0.111, respectively. The A. beccarii ratios are much lower than mean aIle/Ile ratios on equivalent species from the interglacial sequence in the Inner Silver Pit (upper Sand Hole Formation), which are close to 0.2, and the two datasets fail to overlap at the 1 σ level. The new aminostratigraphic ratios indicate correlation of the Nar Valley Clay with oxygen isotope stage 9, and therefore support the pre-existing 230Th/238U data. These results suggest that two temperate stages of Hoxnian palynological affinity are present in the Quaternary record of East Anglia and the southern North Sea basin, a conclusion consistent with independent new U-series data from other Hoxnian sites in East Anglia. An alternative model in which the amino-acid ratios are explained as a function of different post-depositional thermal histories, related to length of cover by ice and water, is discussed but considered unlikely. The conclusions have important implications for the timing and number of glacial events in and around the southern North Sea basin, and help to resolve discrepancies in relative sea-level histories and biogeography in temperate sequences hitherto accommodated within a single stage.
Abstract.
1998
(1998). A middle pleistocene shallow marine interglacial sequence, inner silver pit, Southern North Sea: Pollen and dinoflagellate cyst stratigraphy and sea-level history.
Quaternary Science Reviews,
17(9-10), 871-900.
Abstract:
A middle pleistocene shallow marine interglacial sequence, inner silver pit, Southern North Sea: Pollen and dinoflagellate cyst stratigraphy and sea-level history
The Sand Hole Formation is a Pleistocene seismic-stratigraphic unit of restricted distribution in the Inner Silver Pit, southern North Sea. Pollen and dinoflagellate cyst analyses of this formation, penetrated by British Geological Survey borehole 81/52A and three juxtaposed vibrocores, enables division of the formation into two sequences of contrasting palaeoclimatic affinity. The lower sequence contains poorly-preserved pollen assemblages of low concentration dominated by residual reworked elements, and is coincident with cold, shallow marine dinoflagellate cyst and foraminiferal assemblages. This sequence overlies till and glacimarine sediments of the Anglian/Elsterian Swarte Bank Formation, and is also interpreted as late Anglian/Elsterian in age. The upper sequence contains well-preserved, high concentration, pollen spectra recording the latter half of an interglacial stage with Hoxnian affinities. The strong terrigenous signal preserved in this sequence suggests a subtidal depositional setting within a region of freshwater influence; correlation of the vibrocores with the longer record preserved in borehole 81/52A indicates that interglacial sedimentation rates increase southwards towards a suggested terrigenous source in the Wash area. The first half of the interglacial cycle is missing, indicating that a hiatus is present between the two sequences preserved within the Sand Hole Formation, but the termination of the interglacial is clearly preserved. The spatial and temporal distribution of the sediments and bounding unconformities in the region are consistent in recording the transgressive ravinement surface, highstand systems tract and subsequent regression within an interglacial eustatic cycle. The character, age and elevation of the preserved facies is typical of a glacio-isostatically controlled emergence cycle and lends support to the notion that this temperate stage (oxygen isotope stage 9) immediately followed extensive glaciation during the late Anglian/Elsterian.
Abstract.
(1998). Observations on selected salt-marsh and shallow-marine species of agglutinating foraminifera: Grain size and mineralogical selectivity.
Journal of Foraminiferal Research,
28(4), 261-267.
Abstract:
Observations on selected salt-marsh and shallow-marine species of agglutinating foraminifera: Grain size and mineralogical selectivity
Two species of surface salt-marsh agglutinating foraminifera from sites around Britain have been investigated using SEM/EDX to examine for grain size and mineralogical selectivity of their adventitious test wall particles. Grain size and elemental measurements on test constituents of Trochammina inflata and Jadammina macrescens, from the same sites, when compared with substrate grain size distributions, suggest a high degree of grain size and mineralogical selectivity. Trochammina inflata tests are dominated by relatively small (modal class 1-3 μm) quartz grains, whereas those of J. macrescens are characterized by larger (modal class 4-9 μm) platy aluminosilicate minerals. In addition, four species of surface/subsurface agglutinating foraminifera from around Britain and Ireland were examined for mineralogical selectivity. Eggerelloides scabrus and Ammoscalaria runiana are dominated by quartz, whereas Haplophragmoides wilberti is predominantly composed of aluminosilicate minerals. Miliammina fusca does not appear to select grains by size, shape or mineralogy.
Abstract.
(1998). Quaternary Science Reviews: Preface. Quaternary Science Reviews, 17(9-10), 799-800.
1997
(1997). Evolution of seasonal stratification in the Celtic Sea during the Holocene.
Journal of the Geological Society,
154(2), 249-256.
Abstract:
Evolution of seasonal stratification in the Celtic Sea during the Holocene
Seasonal thermocline development in the shelf seas of NW Europe results in the formation of pronounced frontal regions which separate stratified from well-mixed water. Numerical M2palaeotidal modelling of the NW European continental shelf during successive stages of the Holocene transgression indicates that seasonal stratification started to develop in the central Celtic Sea once a critical threshold water depth had been exceeded at around 9000 years BP. This hypothesis has been tested through faunal, isotopic and geochemical analysis of an AMS14C-dated British Geological Survey vibrocore from the Celtic Deep bathymetric basin; a record which spans the last 12 000 years. Marked positive trends in the stable oxygen isotopic data from the benthic foraminifera Ammonia batavus and Quinqueloculina seminulum between 9000 and about 5000 years BP represent a 4-5°C cooling in summer bottom water temperature caused by the progressive replacement of tidally well-mixed by stratified water. Stable carbon isotopic data from the same species, measured through the same core intervals, show a negative trend consistent with net oxygen utilization and decomposition of organic matter beneath the productive frontal zone. These geological data indicate the progressive evolution of seasonally stratified water in the Celtic Sea during the earlier part of the Holocene. Modern shelf sea frontal and thermocline development are known to influence biological productivity, sedimentation rates, the organic content of shelf sediments and the climate of surrounding landmasses. Hence these palaeodata have significance in defining the role ot shelf sea environments in the climate system.
Abstract.
1996
(1996). Late quaternary relative sea-level changes and the role of glaciation upon continental shelves.
Terra Nova,
8(3), 213-222.
Abstract:
Late quaternary relative sea-level changes and the role of glaciation upon continental shelves
Sea levels of the past 20 kyr are largely determined by the response of the Earth to the last ice age. Consequently, sea-level indicators are an important source of information about the interaction between cryosphere and hydrosphere and the solid Earth. Based on the material presented at a recent European Science Foundation conference, the present paper pin-points some of the topics currently under discussion with respect to sea-level evidence found on continental shelves. These topics include possible effects of erosion and changes in palaeotidal ranges on indicators of former relative sea levels as well as the problems involved in the determination of palaeo-water depth in addition to former sea levels. More evidence is being gathered for substantial small-scale patterns in the sea-level changes at or nearby to the former ice margins. These patterns are not reproduced by the available geophysical models, which reconcile on first-order level only the large-scale pattern.
Abstract.
Scourse J (1996). Trace fossils of talitrid sandhoppers in interglacial littoral calcareous sandstones, Cornwall, U.K.
Quaternary Science Reviews,
15(5-6), 607-615.
Abstract:
Trace fossils of talitrid sandhoppers in interglacial littoral calcareous sandstones, Cornwall, U.K.
Small (
Abstract.
1995
(1995). Notice of raised beach deposits at Llanddona, Anglesey, North Wales.
Quaternary Newsletter,
77, 1-5.
Abstract:
Notice of raised beach deposits at Llanddona, Anglesey, North Wales
Raised beach deposits are common in the coastal Pleistocene sequences of South and south-west Wales. However, outcrops in North Wales are much more limited, and two principal localities have been identified - at Red Wharf Bay, Anglesey, and Porth Oer, Llyn. The QRA visited Porth Oer in 1990 and some members threw considerable doubt on previous interpretations of the deposits there as interglacial raised beach sediments. This left Red Wharf Bay as the only North Wales locality where in situ raised beach sediments of pre-Holocene age were believed to be preserved; even these are poorly developed, allegedly unfossiliferous and of disputed origin. Despite this, the deposits at Porth Oer and Red Wharf Bay have formed the basis for correlating the drift deposits of North and South Wales. -from Authors
Abstract.
(1995). Palaeotidal modelling of continental shelves: Marine implications of a land-bridge in the Strait of Dover during the Holocene and Middle Pleistocene.
Geological Society Special Publication,
96, 75-88.
Abstract:
Palaeotidal modelling of continental shelves: Marine implications of a land-bridge in the Strait of Dover during the Holocene and Middle Pleistocene
Numerical models of the tide on the NW European continental shelf are useful in predicting basic tidal dynamics (amplitude, current, bed stress, mixing) from bathymetry, coastline configuration and a known ocean tide at the shelf edge. Using the M. 2 constituent of the ocean tide, a numerical model has been used to investigate the tidal regime of the English Channel/southern North Sea at successive stages during the Holocene transgression, and also during the maximal sea-levels of Middle Pleistocene temperate stages, by incorporating palaeogeographical interpretations of geological data from these time-slices. Prior to the breaching of the Strait of Dover in the early Holocene, the Southern Bight of the North Sea was a quiet, shallow embayment of low M. 2 tidal amplitude (
Abstract.
(1995). Palaeotidal modelling of continental shelves: marine implications of a land-bridge in the Strait of Dover during the Holocene and Middle Pleistocene.
Island Britain: a Quaternary perspective, 75-88.
Abstract:
Palaeotidal modelling of continental shelves: marine implications of a land-bridge in the Strait of Dover during the Holocene and Middle Pleistocene
Prior to the breaching of the Strait of Dover in the early Holocene, the Southern Bight of the North Sea was a quiet, shallow embayment of low M2 tidal amplitude (
Abstract.
1994
Scourse JD, Austin WEN (1994). A Devensian late-glacial and Holocene sea-level and water depth record from the central Celtic Sea.
Quaternary Newsletter,
74, 22-29.
Abstract:
A Devensian late-glacial and Holocene sea-level and water depth record from the central Celtic Sea
Describes evidence from a deep hollow at the southern end of the Irish Sea/Celtic Sea. Water depth is currently 118m and the stratigraphy suggests that water depth here was 30m in Zone 1 and more than 60m in Zone 3. The implied sea level is lower than most sea-level curves suggest, and may reflect subsidence related to ice loading by a northerly-migrating forebulge. -K.Clayton
Abstract.
1993
Ekman SR, Scourse JD (1993). Early and middle pleistocene pollen stratigraphy from British geological survey borehole 81/26, Fladen Ground, central North Sea.
Review of Palaeobotany and Palynology,
79(3-4), 285-295.
Abstract:
Early and middle pleistocene pollen stratigraphy from British geological survey borehole 81/26, Fladen Ground, central North Sea
Eight pollen assemblage zones are identified in a 200 m deep borehole (BH 81/26) from the Fladen Ground in the North Sea (British sector). Pollen stratigraphical data support interpretations of this core based on a previous multidisciplinary study (Sejrup et al. 1987). Pollen zones II to IV, which occur below the Bruhnes/Matuyama boundary, may correlate with the Bavelian complex and possibly include two interglacial stages, while pollen zones V to VIII indicate predominantly cold conditions. © 1993.
Abstract.
1991
(1991). Annual field meeting report: central East Anglia and the Fen Basin 9- 12 April 1991.
Quaternary Newsletter,
64, 6-10.
Abstract:
Annual field meeting report: central East Anglia and the Fen Basin 9- 12 April 1991
This field meeting visited the following sites: Warren Hall, High Lodge at Ingham; Beeches Pit, Knettishall Pit and Quidenham and Hockham Meres; Somersham, Mepal Fen, Shouldham Thorpe, Tottenhill; Northam Pit, Maxey at Tanholt Farm. The field guide will be fully abstracted in a later issue. -K.Clayton
Abstract.
(1991). Glacial deposits of the Isles of Scilly.
Glacial deposits in Great Britain and Ireland, 291-300.
Abstract:
Glacial deposits of the Isles of Scilly
Erratics have been known from the islands of Scilly since 1958, and were interpreted as glacial in 1882. The dating of the glacial material is heavily dependent on the number and age of nearby raised beach units. Here the stratigraphy is described in terms of a northern glacial and southern extra glacial region. Traditionally the till has been interpreted as Wolstonian in age, but here it is thought to be Devensian: it is till rather than head. -K.Clayton
Abstract.
Scourse J, Robinson E, Evans C (1991). Glaciation of the central and southwestern Celtic Sea.
Glacial deposits in Great Britain and Ireland, 301-310.
Abstract:
Glaciation of the central and southwestern Celtic Sea
Glaciogenic sediments have been recovered from 14 coring sites WSW and S of the Scilly Isles. The stratigraphy shows Melville Formation underlain by the early Pleistocene Little Sole Formation and overlain by recent sediments. Most of the glacigenic samples overlie Neogene strata. Penetration was difficult, itself emphasising the glacigenic character of the material which occurs in isolated patches or mounds. Sedimentary evidence shows that deposition occurred after the formation of tidal sand ridges which themselves were formed when sea level was 100 m below present level, showing that the Melville Formation is ice rafted and is of late Devensian age. -K.Clayton
Abstract.
(1991). Late Pleistocene stratigraphy and palaeobotany of the Isles of Scilly.
Philosophical Transactions - Royal Society of London, B,
334(1271), 405-448.
Abstract:
Late Pleistocene stratigraphy and palaeobotany of the Isles of Scilly
A re-evaluation of the Pleistocene stratigraphy of the Isle of Scilly has enabled the formal definition of eight lithostratigraphic units of member status grouped into two formations. A chronology of events has been provided by radiocarbon (14C) determinations, optical and thermoluminescence (TL) dates. Intersite correlations have been strengthed by palynology, which has aided palaeoenvironmental reconstruction. The defined units have been incorporated into two lithostratigraphic models, one for the "northern' (glacial) Scillies and one for the "southern' (extra-glacial) Scillies. Raised beach sediments of the Watermill Sands and Gravel in the southern Scillies are overlain by the Porthloo Breccia, a unit of soliflucted material derived exclusively from the weathering of local granite. In the northern Scillies, the Porthloo Breccia is overlain by three units that are all related to a single glacial event. The Scilly Till, a massive, poorly sorted, clay-rich pale brown diamicton containing abundant striated and faceted erratics of northern derivation, occurs at Bread and Cheese Cove, and Pernagie and White Island Bars. This sediment is of uncertain depositional facies, although the available data suggest that it may be a lodgement till. The distributional relation between the glacially derived sediments, marine bars and morphological varieties of granite tors suggest that some of the bars may be remnant moraines, and that the glacier was erosive in the northern Scillies. Ice advanced at least as far as the northern Isles of Scilly during the Dimlington Stadial of the late Devensian Substage. This conflicts with previous interpretations which place the glacial deposits within the Wolstonian Stage. However, the late Devensian event was probably not the first glacial event to have influenced the Islands because erratics are widespread in some exposures of the Watermill Sands and Gravel; the age of this earlier event remains uncertain. -from Author
Abstract.
1990
Dowdeswell JA, Scourse JD (1990). Glacimarine environments: processes and sediments.
Glacimarine environments: processes and sedimentsAbstract:
Glacimarine environments: processes and sediments
22 papers on both modern and ancient environments given at a two-day meeting held in London in March 1989. All the papers are abstracted separately. There are two indexes of subject and geographical. -K.Clayton
Abstract.
(1990). Glacimarine environments: processes and sediments.
Glacimarine environments: processes and sedimentsAbstract:
Glacimarine environments: processes and sediments
22 papers on both modern and ancient environments given at a two-day meeting held in London in March 1989. All the papers are abstracted separately. There are two indexes of subject and geographical. -K.Clayton
Abstract.
(1990). On the description and modelling of glacimarine sediments and sedimentation.
Geological Society Special Publication,
53, 1-13.
Abstract:
On the description and modelling of glacimarine sediments and sedimentation
Models of glacimarine environments fall into two categories: (a) qualitative summaries of the depositional record; and (b) quantitative models of the physical processes of glacimarine sedimentation and their rates of operation. Qualitative approaches include descriptive vertical lithofacies profiles and models derived from observations of two- or three-dimensional sedimentary or seismic facies changes. Qualitative models are based on observations in modern glacimarine environments where the processes and settings are relatively well constrained, or on sedimentary or seismic investigations of Cenozoic and pre-Cenozoic successions. Some represent hypothetical sedimentary facies associations based on intuitive reasoning in the absence of observations (e.g. beneath ice shelves). Quantitative process and rate models can be based on theory or empirical data. The nature and rate of sedimentation beneath ice shelves has been modelled quantitatively. Scaled-down laboratory models, for example of iceberg melting, have also been used experimentally. Process models linking different parts of the glacimarine system are an important future research area. © 1990 the Geological Society.
Abstract.
(1990). On the description and modelling of glacimarine sediments and sedimentation.
Glacimarine environments: processes and sediments, 1-13.
Abstract:
On the description and modelling of glacimarine sediments and sedimentation
Models of glacimarine environments fall into two categories: qualitative summaries of the depositional record; and 2) quantitative models of the physical processes of glacimarine sedimentation and their rates of operation. Quantitative process and rate models can be based on theory or empirical data. The nature and rate of sedimentation beneath ice shelves has been modelled quantitatively. Scaled-down laboratory models, for example of iceberg melting, have also been used experimentally. Process models linking different parts of the glacimarine system are an important future research area. -from Authors
Abstract.
(1990). Sedimentology and micropalaeontology of glacimarine sediments from the Central and Southwestern Celtic Sea.
Geological Society Special Publication,
53, 329-347.
Abstract:
Sedimentology and micropalaeontology of glacimarine sediments from the Central and Southwestern Celtic Sea
Thin discontinuous glacigenic sediments occur at or close to the sea bed as far south as 49°N in the Celtic Sea. The northern samples (facies A) are clast-rich, overconsolidated lodgement tills or proximal glacimarine sediments containing sparse reworked microfaunas. The southern samples (facies B) are distal glacimarine plastic silty clays containing abundant cold water microfaunas. Both these facies are correlated with the Late Devensian Scilly Till, enabling a quantitative reconstruction of ice thicknesses, grounding line, sea-level and shoreline elevations in the Celtic Sea at 19 000 years BP. The ice advance terminated in marine waters towards the shelf edge break, and is likely to have constituted a thin lobate surge over deformable marine sediments. © 1990 the Geological Society.
Abstract.
(1990). Sedimentology and micropalaeontology of glacimarine sediments from the central and southwestern Celtic Sea.
Glacimarine environments: processes and sediments, 329-347.
Abstract:
Sedimentology and micropalaeontology of glacimarine sediments from the central and southwestern Celtic Sea
Thin discontinuous glacigenic sediments occur at or close to the sea bed as far south as 49°N in the Celtic Sea. The northern samples (facies A) are clast-rich, overconsolidated lodgement tills or proximal glacimarine sediments containing sparse reworked microfaunas. The southern samples (facies B) are distal glacimarine plastic silty clays containing abundant cold water microfaunas. Both these facies are correlated with the Late Devensian Scilly Till, enabling a quantitative reconstruction of ice thicknesses, grounding line, sea-level and shoreline elevations, in the Celtic Sea at 19 000 years BP. -from Authors
Abstract.
Knudsen KL, Penney DN (1990). The Pleistocene sea-level and neotectonic history of the eastern Solent, southern England.
Philosophical Transactions - Royal Society of London, B,,
328(1249), 425-477.
Abstract:
The Pleistocene sea-level and neotectonic history of the eastern Solent, southern England
In the eastern extremity of the Isle of Wight, near Bembridge, marine interglacial deposits occur at a variety of different elevations. The highest of these, the Steyne Wood Clay, is an estuarine deposit that lies between 38 and 40 m O.D. and rests on Bembridge Marls (Lower Oligocene). The Steyne Wood Clay, which had previously been assigned to the post-temperate substage of a Middle Pleistocene interglacial, has now yielded a diverse coccolith assemblage dominated by Gephyrocapsa oceanica and G. caribbeanica. The absence of both Pseudoemiliania lacunosa, with a last occurrence datum at ca. 0.475 Ma BP. and Emiliania huxleyi, with a first occurrence datum at ca. 0.275 Ma BP, suggests deposition during this time interval. The dating of the Steyne Wood Clay is further constrained by palaeomagnetic data, indicating normal geomagnetic polarity, and by amino acid ratios consistent with an early Middle Pleistocene age. The low-level interglacial deposits make up the Bembridge Raised Beach, here formally defined as consisting of high-energy beach gravels, intertidal sands and organic muds, which represent a single fining-upwards sequence. Pollen analysis of the organic muds indicates that these accumulated during the early and late-temperate substages of the Ipswichian interglacial (Ip IIb-III). The relationship of these marine deposits to those occurring on the adjacent mainland are considered. The Steyne Wood Clay is correlated with the Slindon Sands at Boxgrove, part of the Goodwood-Slindon Raised Beach, which occur at an identical elevation and have produced a similarly diverse coccolith assemblage. Additional palaeontological evidence from Boxgrove suggests that the interglacial deposits should be assigned to a temperate stage falling in the latter part of the "Cromerian Complex' Correlation of the Steyne Wood Clay and Slindon Sands with oxygen isotope stage 9, 11 or 13 seems very probable. -from Authors
Abstract.
1987
(1987). Periglacial sediments and landforms in the Isles of Scilly and West Cornwall.
Periglacial processes and landforms in Britain and Ireland, 225-236.
Abstract:
Periglacial sediments and landforms in the Isles of Scilly and West Cornwall
The Pleistocene stratigraphy of the Isles of Scilly and West Cornwall is dominated by solifluction sediments deposited under periglacial conditions. Periglacial structures, including thermal contraction cracks, ice fissures, involutions and festooning are described from areas of slate bedrock, especially the Camel Estuary. Reasons for the absence of such structures from areas of granite bedrock are discussed. -from Author
Abstract.
(1987). Pleistocene sea-level history in the Bembridge area of the Isle of Wight.
Wessex and the Isle of Wight. Field guide, 136-149.
Abstract:
Pleistocene sea-level history in the Bembridge area of the Isle of Wight.
Evidence includes Steyne Wood clay, an estuarine ?Middle Pleistocene clay at 38-40 m OD; it may be of Hoxnian age. Other sites described are Priory Bay (Lower Palaeolithic artefacts) the Bembridge raised beach (up to 18 m) and organic deposits from the Bembridge foreland and also at Lane End, the former being Ipswichian in age. -K.Clayton
Abstract.
1986
(1986). A review of fine gravel analysis.
Technical Guide - Quaternary Research Association,
3Abstract:
A review of fine gravel analysis.
The main value of fine gravel analysis is that it requires only a small sample size and so can be applied to borehole material. Various size ranges have been chosen, but all include at least part of the granule (2-4 mm) fraction. The most common method is Dutch which involves the analysis of the 3-5 mm fraction.-K.Clayton
Abstract.
(1986). The Isles of Scilly - field guide.
Abstract:
The Isles of Scilly - field guide.
The first part presents reviews of the three major themes covered by the excursion, the Pleistocene stratigraphy, Flandrian vegetational history, and archaeology. The second part deals with the individual sites to be visited on the excursion and is divided into three reflecting the respective islands visited on the three days of the excursion, the first part dealing with St. Mary's, the second St. Martin's and Nornour, and the third day Tresco and Samson. -from Editor
Abstract.
Scourse JD (1986). The Isles of Scilly - field guide.
Abstract:
The Isles of Scilly - field guide.
The first part presents reviews of the three major themes covered by the excursion, the Pleistocene stratigraphy, Flandrian vegetational history, and archaeology. The second part deals with the individual sites to be visited on the excursion and is divided into three reflecting the respective islands visited on the three days of the excursion, the first part dealing with St. Mary's, the second St. Martin's and Nornour, and the third day Tresco and Samson. -from Editor
Abstract.
1985
(1985). The Trewornan ' lake flat': a reinterpretation.
Quaternary Newsletter,
46, 11-18.
Abstract:
The Trewornan ' lake flat': a reinterpretation.
Pollen analysis of alluvial sediments supposed to underlie a pro-glacial lake flat leads to the rejection of the glacial hypothesis as the sediment is of Flandrian age. -K. Clayton
Abstract.
