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Cambridge NERC Doctoral Training Partnerships

Graduate Research Opportunities

Lead Supervisor: Luke Skinner, Earth Sciences

Co-Supervisor: Oscar Branson, Earth Sciences

Brief summary: 
This project seeks to develop and apply novel oxygenation proxies, e.g. based on Rare Earth Elements (REE) and uranium, with the ultimate aim of understanding, and potentially to quantify, past changes in deep ocean carbon storage associated with global climate change.
Importance of the area of research concerned: 
This project aims to use novel proxies for deep ocean oxygenation to look at changes in ocean circulation and carbon cycling across the last glacial period. The cycling of oxygen, nutrients and carbon are tightly connected in the marine environment, making deep ocean oxygenation a key parameter for understanding past changes in carbon respiration and CO2 sequestration from the atmosphere, and therefore global climate change. Using a novel laser-ablation microanalysis approach it can be shown that the Rare Earth Element (REE) composition of early diagenetic ‘coatings’ on foraminifera is strongly influenced by changes in pore-water chemistry near the sediment-water interface, including the impacts of redox changes in particular. This raises the possibility of using foraminifer ‘Cerium enrichment’ as an indicator of deep-ocean oxygen supply to sediments. However, this potential redox proxy has never been tested or compared with other redox proxies (uranium, Dd13C, I/Ca) , either using core-top material or in down-core records.
Project summary : 
The goal of this project is to fully assess a suite of 'diagensis-based' oxygenation proxies in parallel, using sub-modern sediments and seawater/pore-water samples, as well as down-core records of the last glacial cycle. To this end, analyses will be performed on sub-modern sediments from three depth transects located in the North Atlantic, South Atlantic and Indian Ocean basins, as well as a suite of sediment cores that span the last glacial cycle. The latter, arranged in a depth transect in the Atlantic Ocean, will be used to assess the timing and also the magnitude of past deep ocean oxygenation changes related to respired carbon accumulation, and CO2 sequestration across the last glacial cycle. This project aims to provide a major advance in our ability to reconstruct past seawater oxygenation, and to shed new light on the mechanisms of glacial-interglacial CO2 change.
What will the student do?: 
The student pick small samples of foraminifera in a range of sediment samples, for cleaning, mounting and analysis of e.g. U and REE by laser-ablation (LA) ICP-MS. Monospecific samples of planktonic foraminifera will be picked (~30 individuals), cleaned and prepared for analysis by laser-ablation for authigenic coating trace element composition. These analyses will be combined with existing sediment property and pore-water data, including organic- and inorganic carbon content, approximate sedimentation rates, and in situ oxygenation. Ideally, the student would also engage with simple biogeochemical mass balance models, and biogeochemical numerical modelling outputs, in order to explore further the inferred magnitudes of past oxygen and respired carbon change, as well as the likely impacts on ocean-atmosphere CO2 partitioning.
References - references should provide further reading about the project: 
Haley, B.A., Klinkhammer, G. and McManus, J. (2004) Rare earth elements in pore waters of marine sediments. Geochimica et Cosmochimica Acta 68, 1265-1279.
Gottschalk, J., Skinner, L.C., Lippold, J., Vogel, H., Frank, N., Jaccard, S.L. and Waelbroeck, C. (2016) Biological and physical controls in the Southern Ocean on past millennial-scale atmospheric CO2 changes. Nature Communications 7, 11539.
Skinner, L., Sadekov, A., Brandon, M., Greaves, M., Plancherel, Y., de la Fuente, M., . . . Scrivner, A. E. (2019). Rare Earth Elements in the service of palaeoceanography: a novel microanalysis approach. Geochimica et Cosmochimica Acta, 245, 118-132.
You can find out about applying for this project on the Department of Earth Sciences page.
Dr Oscar Branson
Department of Earth Sciences Graduate Administrator
Dr Luke Skinner