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C317: Constraining the ocean’s role in past atmospheric CO2 change: a geochemical fingerprinting approach (Lead Supervisor: Luke Skinner, Earth Sciences)

Supervisors: Luke Skinner (Earth Sciences) and Sambuddha Misra (Earth Sciences)

Importance of the area of research:

The ocean represents a vast and dynamic reservoir of carbon and heat.  Changes in the ocean’s overturning circulation may drastically alter regional and global climate, both directly through changes in heat transport and indirectly through changes in the carbon cycle and atmospheric CO2.  Indeed, the overturning circulation is believed to have played a key role in glacial-interglacial regional- and global climate change over at least the last ~2 million years, principally via its impact on atmospheric CO2.  After over a century of investigations, and despite much progress, it remains unclear exactly what processes and feedbacks were able to motivate glacial-interglacial ‘mode shifts’ in the ocean’s ability to stock CO2.  Resolving this long-standing question will help us to better understand global and regional climate-carbon cycle feedbacks, as well as their role in non-linear climate dynamics on millennial timescales.

Project summary:

This project will make use of a range of cutting-edge geochemical proxies in order to constrain the ocean’s role in glacial-interglacial atmospheric CO2 change. Geochemical measurements on foraminifera will be used to reconstruct the global marine distribution of carbonate chemistry (carbonate ion saturation and pH), oxygenation and ‘radiocarbon ventilation’ at the Last Glacial Maximum.  The temporal evolution of these chemical properties will also be reconstructed at several key locations, both leading up to the glacial maximum, and leading out of the glacial period to the Holocene. This work will thus determine how changes in the efficiency of the marine biological ‘carbon pumps’ and ocean-atmosphere gas exchange have contributed to past CO2 variability.

What the student will do:

The student will prepare sediment and foraminifer samples for subsequent clean laboratory cleaning and analysis by IR-MS, solution ICP-MS and laser ablation (LA-) ICP-MS.  Samples will be selected from a range of cores from around the world, and will target a time-slice study of the Last Glacial Maximum (LGM).  Proxy measurements will include stable (oxygen and carbon) isotopes, trace element composition (e.g. U, Mn, Mg, B) and trace element isotopes (e.g. δ11B) on planktonic- and benthic foraminifera.  Samples will also be cleaned, graphitised and pressed into cathode targets for radiocarbon analysis by AMS.  This project mainly consists of foraminiferal picking, clean lab manipulations and geochemical analyses; however, the project ultimately strives to understand the synergy of biological and ocean dynamical processes that have been responsible for past marine carbon cycle change and therefore will also benefit from comparisons with simple biogeochemical box-models and other numerical model outputs.

Please contact the lead supervisor directly for further information relating to what the successful applicant will be expected to do, training to be provided, and any specific educational background requirements.

References:

Skinner, L. C., Fallon, S., Waelbroeck, C., Michel, E., and Barker, S., 2010. Ventilation of the deep southern ocean and deglacial CO2 rise. Science, vol. 328, pp.1147-1151.

Sigman, D. M., Hain, M. P., and Haug, G. H., 2010, The polar ocean and glacial cycles in atmospheric CO2: Nature, vol. 466, pp.47-55.

Freeman, E., Skinner, L., Waelbroeck, C., Hodell, D., 2016. Radiocarbon evidence for enhanced respired carbon storage in the deep Atlantic at the Last Glacial Maximum. Nature Communications 7.

Follow this link to find out about applying for this project

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