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Cambridge NERC Doctoral Training Partnerships

Graduate Research Opportunities
 

Lead Supervisor: Luke Skinner, Earth Sciences

Brief summary: 
This project will produce a detailed analysis of the evolution of deep ocean radiocarbon ‘ventilation’ across a suite of Heinrich events that preceded the LGM, thus providing a first insight into marine radiocarbon cycling across episode of abrupt change, and leading up to peak glacial conditions, with implications for the closure of the ocean-atmosphere radiocarbon (and carbon) budgets across the last glacial cycle.
Importance of the area of research concerned: 
The prevailing account of past glacial-interglacial atmospheric CO2 change attributes a major role to ‘ocean ventilation’ (i.e. overturning rates and air-sea gas exchange efficiency). Marine radiocarbon data spanning the last ~20,000 years, from the Last Glacial Maximum (LGM) to the current interglacial period, support this paradigm: they indicate a drop in marine radiocarbon ventilation ages across the last deglaciation, suggesting enhanced exchange of the marine- and atmospheric carbon pools. However, it has not been possible to reconcile this theory with a complete closure of the global radiocarbon- and carbon cycles since the last glacial period. Furthermore, it is not even known if reduced ocean ventilation persisted prior to the LGM, when atmospheric CO2 was already near minimum glacial levels, or now it may have varied across episodes of abrupt climate change associated with so-called ‘Dansgaard-Oeschger cycles’ and ‘Heinrich events’. An urgent need thus arises to close this major gap in our observations and our understanding of marine carbon cycling across the last glacial cycle.
Project summary : 
This project seeks to confront the prevailing paradigm of CO2 rise after the LGM, with new data from the onset of the LGM, while also providing new insights into the evolution of marine radiocarbon ventilation across abrupt climate perturbations associated with so-called ‘Heinrich events’. The project aims to test the hypothesis that ocean ventilation was not significantly different from modern during the 20,000 years that preceded the LGM, when atmospheric CO2 was already close to minimum levels. The project will further test the hypothesis that changes in ocean-atmosphere carbon exchange played a central role in sub-millennial atmospheric radiocarbon and CO2 anomalies that occurred during the last glacial period. We will generate the first marine radiocarbon dataset capable of testing these hypotheses, both through qualitative- and quantitative numerical model-supported analyses.
What will the student do?: 
The student will pick benthic and planktonic foraminifera from a suite of marine sediment cores distributed across the globe (N. Atlantic, S. Ocean, and Pacific) for subsequent preparation and graphitisation prior to radiocarbon dating. Additional work will be required to place these sediment cores on robust chronostratigraphic age-models, aligned to the Greenland and Antarctic ice-core chronologies. Due to the challenging nature of the radiocarbon dates being performed, it is foreseen that a significant amount of work will be needed to assess and eliminate as far as possible contamination and diagenetic overprinting of the foraminifer samples, prior to radiocarbon dating. This work will be done in collaboration with the Oxford and Belfast radiocarbon laboratories, using novel leaching and gas-source AMS techniques. The student will also engage with simple box-model simulations and more complex numerical model runs, in order to assess the implications of the newly collected data for the global carbon/radiocarbon cycles.
References - references should provide further reading about the project: 
Skinner, L., Freeman, E., Hodell, D., Waelbroeck, C., Vasquez Riveiros, N., & Scrivner, A., 2021. Atlantic Ocean ventilation changes across the last deglaciation and their carbon cycle implications. Paleoceanography and Paleoclimatology.
Bauska, T. K., Marcott, S. A., & Brook, E. J., 2021. Abrupt changes in the global carbon cycle during the last glacial period. Nature Geoscience, 14(2), 91-96. doi:10.1038/s41561-020-00680-2
Dinauer, A., Adolphi, F., & Joos, F., 2020. Mysteriously high ∆14C of the glacial atmosphere: Influence of 14C production and carbon cycle changes. Clim. Past Discuss., 2020, 1-46. doi:10.5194/cp-2019-159
Applying
You can find out about applying for this project on the Department of Earth Sciences page.
Department of Earth Sciences Graduate Administrator
Dr Luke Skinner