Dr Alastair Graham
Senior Lecturer in Physical Geography

Research

Research interests

Alastair is an Earth Scientist studying the link between ice sheets and the geological record, from glacier margins to the deep sea. The overarching aim of his research is to better understand Earth’s icy and climate histories, and to improve knowledge of the physical processes that govern the evolution of glacial and marine environments. A current major objective is to produce records of past ice‐sheet change at the poles that are significantly longer than observations, providing a critical long‐term context for changes to our warming planet. Another key aspect is to study glacial environments using geological and geophysical tools to provide insight into modern and future ice sheet and ice‐stream behaviour.

Current research falls into five broad key themes:

1. Contemporary and historical processes at and under key Antarctic ice shelves: A line of research is focused on improving understanding of glacial processes gleaned from geophysical surveys under floating ice shelves where major Antartic ice streams come afloat. Some of this recent work has utilised AUV bathymetry to reveal how the sea-bed is shaped in difficult to reach sub-ice shelf cavities. A new NSFPLR-NERC funded project, THOR (Thwaites Offshore Research), will study the sediment record of ice and ocean change in front of Thwaites Glacier, West Antarctica, to provide a critical context for future ice loss in the ice-sheet's most vulnerable catchment.       

2. Antarctica’s glacial history: Alastair works on reconstructing ice-sheet extent, dynamics and retreat in major drainage basins through the last glacial cycle; dating ice‐sheet activity around the continent; providing geological data to steer numerical models of ice‐sheet change and to constrain the whereabouts of biological refugia.

3. Subglacial bedforms and their genesis: A major interest lies in studying the processes and products of ice‐sheet beds, including sub‐ice shelf and recently‐deglaciated grounding‐line environments, bedform geomorphology in relation to sub‐ice geology, and developing theories of landform evolution beneath ice sheets past and present.

4. Glacial and climate histories of sub‐polar regions: New research uses marine geoscientific data to understand patterns and drivers of past glacier and environmental change in rapidly-changing climatically‐sensitive regions (e.g. the sub-Antarctic islands), through ancient glaciations as well as during the Holocene, up to the present-day.

5. Polar margins and their hidden records: Projects are focused on understanding Quaternary ice dynamics in seismic data from the Antarctic continental margin, the form and evolution of sediment drifts on the Antarctic Peninsula, as well as depositional records of climatic and glacial change on continental margins in both the mid‐ and high‐latitudes.

State‐of‐the‐art and novel geophysical and geological techniques underpin each of these interests, and involve Alastair working routinely with ship‐borne bathymetric echo‐sounders, specialist autonomous and remotely‐operated underwater vehicles, industry standard 2D/3D seismic data, GIS, and physical analyses of marine sediment cores.

Research projects

Weddell Sea glacial history and changes in Antarctica’s ice sheets during the Quaternary
Marine geological and geophysical studies to determine the long-term history of the Antarctic Ice Sheet and climate in the southern Weddell Sea. Led by the British Antarctic Survey Palaeo-ice sheets group, in collaboration with colleagues at the Alfred-Wegener Institute for Polar and Marine Research.

Specific questions that we are aiming to answer through this work include: (i) how far the Antarctic Ice Sheet advanced onto the continental shelf in the Weddell Sea during the last glacial period (about 20,000 years ago); (ii) the history of glacial retreat as the climate warmed after the last glacial period; (iii) what processes occurred beneath the ice that enabled it to flow across the shelf, and how the type of material at the sea floor (e.g. hard rock or soft sediment) affected these processes; (iv) whether or not the ice sheet on West Antarctica collapsed during previous interglacial periods, which have occurred at intervals of about 100,000 years over the past 800,000 years. There is particular concern about the stability of the West Antarctic Ice Sheet because most of its bed is below sea level. If this ice sheet did collapse it would have caused global sea level to rise by more than 3 m; (v) how the ocean temperature and sea ice cover in the region have changed during glacial-interglacial cycles, and in particular since the last glacial period.

The results of these studies will be used to test and refine computer models of ice sheets that will be used to predict how much the Antarctic Ice Sheet will contribute to sea level rise in a warming climate.

Testing the extent and timing of past glaciations on the largest sub-Antarctic island, South Georgia
The sub-Antarctic islands are ideally placed to investigate past ice and climate changes, with records of their ancient glaciation important for understanding various aspects of the Earth system. Due to the islands' unique location between warm-maritime and cold-polar climates, the size of sub-Antarctic ice-cap advances provide a potentially valuable means of calibrating the sensitivity of ice-sheet models, ensuring the climate parameters used to force them are realistic and the outputs 'good' for the future. Variations in the scale and timing of glacial events can also provide critical information on the mechanisms and phasing of climate changes between regions and hemispheres. The same data constrain the whereabouts and persistence of glacial refugia, and inform biologists on the geological conditions governing the evolution and diversity of life in the Southern Ocean. To improve ice-sheet models, explain patterns of climate change, and interpret the biodiversity of the world's oceans, information on sub-Antarctica's glacial past is required. However, fundamental questions relating to the age, magnitude, and number of past glaciations remain unanswered. For the largest sub-Antarctic island, South Georgia, at least one major glacial advance is already known from ice-carved troughs and sediment ridges (moraines) found on the sea-floor of the shallow shelf surrounding the island today. Yet its age is unknown. As in other parts of Antarctica, the most recent episode of glaciation - The Last Glacial Maximum - is likely to have left behind the best record of ice-cap advance and melting. However, even here, there is no consensus, with two conflicting hypotheses prevailing: one suggesting a limited ice extent, restricted to the near-shore fjords; the other proposing that the ice cap was extensive, reaching the outer parts of the shelf around most of the island. Answers to which hypothesis is correct lie in the study of the submarine topography and sediments, which have yet to be investigated in any detail.

This project will examine the extent and timing of past glaciations on South Georgia, from a marine perspective, for the first time. I will provide a robust test of the hypotheses that, either: (i) the Last Glacial Maximum ice cap was of restricted extent and thus that one or more major ice cap glaciations that reached outer shelf limits pre-date the last glacial period; or that (ii) the Last Glacial Maximum ice cap was extensive, and a chronology of retreat is recorded in the shelf's landscape and sediments. Existing and newly-collected sonar bathymetry data will be utilised to map out the glacial features on the South Georgia shelf in unprecedented detail. Six sediment cores, among the first recovered from the shelf, will be analysed and dated. The project will target moraines marking the limits of former ice-caps, from the shelf edge to the coastal fjords. I will determine the age of the most extensive glaciation, and the age of intermediate retreat or terminal limits. Physical analyses of sediments will reconstruct environmental conditions during and since the Last Glacial Maximum, to the present day, and perhaps through older cold or warm periods. Resolving the number and extent of former shelf glaciations preserved in sub-Antarctic records will be a major outcome of the project, as will vital new information on the behaviour and reach of the Last Glacial ice cap. New records will be set in the context of Earth's climate and evolutionary histories, and form the first marine palaeo-constraints on sub-Antarctic glaciation, benefiting modellers, climate scientists and biologists. The project will also provide baseline geological data for use by habitat mapping projects and fisheries.

Depositional patterns and records in sediment drifts off the Antarctic Peninsula and West Antarctica
The biggest uncertainty in predictions of sea-level rise is what the contribution will be from the great ice sheets on Antarctica and Greenland as climate warms. The West Antarctic Ice Sheet and the Antarctic Peninsula Ice Sheet are the cause of greatest concern, as they are showing signs of significant ice loss and there are theoretical reasons for expecting them to be most vulnerable. Important sources of information for helping to predict how these ice sheets will change as climate warms are records of their response to past climate changes contained in sea bed sediments around Antarctica. Such records extend further back in time than ice cores from the ice sheets themselves. They can also show how the margins of the ice sheets interacted with changes in ocean temperature and circulation, which recent studies have identified as having an important influence on ice sheets. Although sedimentary records in the shallow seas close to Antarctica have been periodically disturbed or removed by past expansions of the ice sheets, there are places in the nearby deep ocean where sediments have accumulated continuously over millions of years. The international Integrated Ocean Drilling Program is considering a proposal to send a drilling ship to collect long sediment cores from some of these places. However, before this is done additional survey data are needed to find the sites that will provide the most continuous, detailed records and to make sure that it will be safe to drill those sites. This research project will collect this essential survey data. Work will target sea-floor sedimentary bodies, termed sediment drifts, where accumulation has been continuous and long-lived. We will acquire, process and interpret multi-channel seismic data to ‘look into’ these sediment bodies, better understand their internal form and shape, and ultimately resolve the processes that led to their formation. On the same expedition we also propose to collect short sediment cores for pilot studies to confirm that the analytical methods we intend to apply to the longer drill cores will provide reliable information about sediment ages, past climate and past ice sheet behaviour.

Grants/Funding:

Dec 2012  –  Dec 2014: NERC New Investigator Award NE/K0005271 (£99,985),
“Testing the extent and timing of past glaciations on the largest sub-Antarctic island, South Georgia”. Principal Investigator.

Oct 2014 – Oct 2016: NERC/UK-IODP Phase2 site survey grant NE/J006548/1 (£280,880),
“Depositional patterns and records in sediment drifts off the Antarctic Peninsula and West Antarctica”; Co-Investigator, PIs Larter (BAS), Hodell (Cambridge), & Hillenbrand (BAS).

Nov 2014: NERC NIGL isotope support award - actual and in-kind (£55,757)
“Determining if changes in the position of the Southern Westerly Wind belt impact the South Georgia marine ecosystem"; Co-I, with PI Leng (Nottingham), and Co-Is from BAS/Leicester/Nottingham.

Oct 2012 – Oct 2015: NERC Algorithm Studentship grant, (£9,370 + bursary)
“Reconstructing the glacial and climate history of the South Orkney Islands, NE Antarctic Peninsula”. Awarded to William Dickens (BAS). Project in collaboration with Julian Dowdeswell (Scott Polar Research Institute), and Gerhard Kuhn (Alfred-Wegener Institute, Bremerhaven). Lead proponent and supervisor.

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