Overview
After transferring from Queen Mary University of London, I graduated in 2015 with a BSc in Geography (with proficiency in Spanish) from the University of Exeter.
My undergraduate dissertation at Exeter led me to conduct 8 weeks of lab work at Bangor University’s School of Ocean Sciences at the invitation of Professor Chris Richardson (Head of SOS). During the stay, I learned techniques for preparing and processing bivalve shells for sclerochronology - the study of the growth lines on bivalve molluscs analogous to dendrochronology. The final project entitled “A sclerochronology of the English Channel – using the annually-resolved growth increments of Glycymeris glycymeris to infer recent marine palaeoenvironment” produced the first ever sclerochronology of the English Channel and added to the limited number of bivalve proxies in the UK and worldwide.
In my final year at Exeter I was offered a PhD with the University of Exeter, Bangor University and CEFAS. The aim of the project is to better understand the shelf sea environment with the aid of ecosystem models and the proxy records of long-lived bivalve molluscs.
Qualifications
BSc Geography with proficiency in Spanish (University of Exeter)
Research
Research projects
Project Title: Using annually resolved bivalve records and biogeochemical models to understand and predict climate impacts in coastal oceans
Supervisors: Dr Paul Halloran, Prof. Chris Perry (Exeter University), Dr Paul Butler (Bangor University) and Dr Johan van der Molen (CEFAS).
Funding Body: NERC and CEFAS (NERC Industrial CASE Studentship)
Project Description:
The shelf seas are disproportionally productive compared to the open ocean, sustaining over 90% of global fisheries. It is therefore very important to understand both past and future processes in these coastal oceans, especially in lieu of climate change, which threatens eutrophication, anoxia, ocean warming and more. Biogeochemical or ecosystem modelling has the capacity to reconstruct shelf sea processes, both hindcasting and forecasting, but spatial and temporal limitations in observational data of the ocean is restricting our ability to test model accuracy.
This PhD study aims to create and use proxy records of the bivalve mollusc Arctica islandica in the North Sea to validate and improve the benthic component of ecosystem models, in particular the CEFAS version of the European Regional Seas Ecosystem Model (ERSEM). The research may then be able to advance predictions of how future shelf seas will respond to climate change, influencing the advice given to policy-makers and stakeholders as well as contributing to the wider modelling, sclerochronology and climate/ocean science community.
Publications
Key publications | Publications by category | Publications by year
Publications by year
2023
Holmes S (2023). Sclerochronology and modelling: combining annually resolved bivalve records and biogeochemical models to understand the shelf seas.
Abstract:
Sclerochronology and modelling: combining annually resolved bivalve records and biogeochemical models to understand the shelf seas
The shelf seas are extremely vulnerable to the effects of climate change. Projected to warm at substantially greater rates than the open ocean, understanding how shelf sea systems operate and how they will respond to future change is of vital importance. Policy decision-makers rely on high quality information to ensure the protection of marine habitats and ecosystem services. While model studies can provide such data, they require spatially and temporally-extensive datasets for verification. Currently, this type of data is highly limited for the shelf seas, particularly at depth.
Sclerochronology of bivalve molluscs has shown great potential to extend instrumental data for the shelf seas, providing absolutely-dated, multi-centennial, annually-resolved archives of past ocean environment, analogous to dendrochronology in terrestrial environments. Bivalve molluscs have a wide distribution, and can be found on the shelf environments living at depth on the sea floor. Yet sclerochronology is a developing field with a number of fundamental research gaps limiting the use of sclerochronology as a valuable marine proxy. This thesis addresses three of those gaps:
Chapter 2 (Methods Development: Imaging shells for sclerochronology) presents a novel and non-destructive method for imaging the internal growth bands of bivalves used in sclerochronology – micro computed tomography (micro-CT). Micro-CT uses x-rays to create 3D high resolution images of the internal structure of specimens. Experiments evaluated whether density or resolution could limit bivalves from being imaged and showed that subtle microstructural features can be seen in the micro-CT images of even the most dense bivalve species. The research suggested that with future development in micro-CT technology including increased resolution and power, analysis of bivalve growth bands via micro-CT may be possible, significantly reducing the time required to produce highly valuable sclerochronology records and allowing more records to be constructed.
Chapter 3 (Sclerochronology and 1D modelling: a novel study using a 1D ecosystem model to better interpret sclerochronology records) focuses on a fundamental problem in sclerochronology - the lack of understanding regarding the mechanistic drivers of shell growth. Here, a 1D ecosystem model GOTM-ERSEM- BFM was used explore these mechanisms. The model was able to simulate the shell growth of a central North Sea composite chronology which allowed exploration of ecosystem processes to understand the mechanisms that lead to growth. Experiments manipulating the meteorological inputs to the model mechanistically attributed variability in surface heating and wind temperature as key controls on shell growth in the central North Sea.
Chapter 4 (Southern North Sea sclerochronologies: using shell records to test hypotheses across hydrological and biological gradients) addresses the scarcity of long-term productivity information in the North Sea which currently limits an understanding of historical variability. In particular, accurate measurements of North Sea productivity are limited by the poor quantification of sub-surface chlorophyll which cannot be measured by remote sensing or surface phytoplankton surveying. 12 new sclerochronology records of the bivalve mollusc Arctica islandica were produced from 4 locations in the southern North Sea to test if bivalve growth differs across productivity and hydrography gradients, and investigate whether shell records capture sub-surface chlorophyll variability. Differences in the rate of raw growth of Arctica islandica was demonstrated between regions of high and low productivity, supported by variations in synchronicity (estimated population signals) of multiple composite chronologies constructed using the shells records. These results suggest that sub surface chlorophyll may play a role in Arctica islandica shell growth but how this interacts with stratification regimes in the North Sea is difficult to quantify due to complex interactions of biology and other hydrographical features in the region. Further research is required in other locations to better understand impact of stratification and sub-surface productivity on shell growth and subsequently North Sea ecosystems.
The novel research presented in this thesis has advanced the fields of sclerochronology and ecosystem modelling and has laid the foundation for transformative approaches to sclerochronology. By developing the methods needed to understand long-term variability of shelf sea environments, particularly at depth, this work has contributed to improving the understanding of past and future climate change in the shelf seas.
Abstract.
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