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Cambridge NERC Doctoral Training Partnerships

Graduate Research Opportunities

Lead supervisor: Luke Skinner, Earth Sciences

Co-supervisor: Matt Osman, Geography

Brief summary: 
This project aims to develop the use of habitat biases that are inherent in foraminifer-based proxies to investigate the impacts of past abrupt climate change on detailed aspects of the North Atlantic hydroclimate system, such as water column structure, seasonality and interannual climate variability. Such reconstructions may provide a more direct basis for comparison with climate model outputs and have the potential to inform on aspects of the climate system that are of more direct relevance to society and ecosystems alike.
Importance of the area of research concerned: 
Planktonic foraminifera occupy a diversity of habitats both during a given species’ life cycle and between different individual species. The memory of these different microhabitats is recorded in the geochemistry of a foraminifer’s test. Palaeoceanographic proxy measurements typically seek to average out the biases associated with a given species, individual foraminifer, or ‘ontogenic’ (life cycle) stages. However, it is probable that such biases can never be avoided entirely. An alternative approach aims to characterise the biases that affect ‘habitat selective’ foraminifer species and to then use these biases as a novel source of information for interpreting past seasonality, inter-annual variability or extreme event occurrence. By looking at the evolution of these biases over time, including across important abrupt regional climate change events, we further stand to learn a great deal about the impacts of global or regional-scale climate change on past ecosystem and societial resiliance.
Project summary : 
This project aims to use novel geochemical and statistical analysis methods to unravel the habitat biases recorded in different planktonic foraminifer species in the Northeast Atlantic. These biases will be investigated in terms foraminifer habitat selectivity and their associations with seasonality, water depth, nutrient loading. The project will use both modern and ancient Iberian Margin sediments spanning a range of hydrographic regimes and water depths to differentiate between secondary diagenetic and primary habitat biases. By pairing these new insights against both modern observations and paleoclimate model simulations, the evolution of habitat biases and their controls will be investigated across a suite of past abrupt climate transitions (e.g., Dansgaard-Oeschger, Heinrich events) to generate new insights into regional hydroclimate impacts of past abrupt climate change.
What will the student do?: 
The student will pick and prepare (i.e. clean, mount) foraminifer samples for geochemical analysis using standard isotope ratio mass spectrometry (IRMS) techniques, as well as solution- and laser-ablation ICP-MS measurements. Stable carbon and oxygen isotopes will be analysed along with a range of trace- and minor elemental ratios (Mg/Ca, Sr/Ca etc.). The student will work to develop new calibrations (i.e., “proxy system models”) of foraminifer seasonal biasing using novel statistical methods. Using these novel data and methods, detailed time-series for a suite of abrupt events will be compared alongside regional reconstructions (from ice cores and speleothems in particular) and numerical global climate model outputs to invoke different triggering mechanisms for 'stadial-interstadial' like variability.
References - references should provide further reading about the project: 
Kretschmer, K., et al. (2018). "Modeling seasonal and vertical habitats of planktonic foraminifera on a global scale." Biogeosciences 15(14): 4405-4429.
Sadekov, A., Eggins, S. M., De Deckker, P., Ninnemann, U., Kuhnt, W., and Bassinot, F.: Surface and subsurface seawater temperature reconstruction using Mg/Ca microanalysis of planktonic foraminifera globigerinoides ruber, globigerinoides sacculifer, and pulleniatina obliquiloculata, Paleoceanography, 24, 17, Pa3201 10.1029/2008pa001664, 2009.
Skinner, L. C., and Elderfield, H.: Constraining ecological and biological bias in planktonic foraminiferal Mg/Ca and d18Occ: A multi-species approach to proxy calibration testing, Paleoceanography, 20, 1-15, 2005.
You can find out about applying for this project on the Department of Earth Sciences page.