IAP2-22-420

Controls on CO2 storage in the glacial ocean

The cause of glacial-interglacial CO2 cycles is a first order, unsolved question in climate science. Although a number of viable mechanisms for glacial CO2 change have been proposed, suitable data to provide robust tests of these have been lacking. A major missing piece of this puzzle is the nature of CO2 storage in the deep ocean during glacial periods (Rae et al., 2018).

This project will quantify the extent and nature of deep ocean CO2 storage during the last glacial cycle, constraining the roles of changes in respired carbon, carbonate compensation, sea ice, and ocean circulation (MacGilchrist et al., 2019).

Deep ocean CO2 reconstructions will be based on the boron concentration (B/Ca) and isotope composition (11B) of benthic foraminifera (Rae et al., 2011), which record ΔCO32- and pH respectively.

To quantify CO2 storage by the biological pump, we will reconstruct deep ocean oxygen using a suite of novel trace elements in foraminifera and bulk sediments, including iodine, uranium, manganese, and cerium (e.g. Zhou et al., 2016; Gottschalk et al., 2016). This will be complemented by carbon isotope gradients between different species of benthic foraminifera (e.g. Hoogakker et al., 2015), and preserved alkenone fluxes (Anderson et al., 2019). Interpretation will be guided by a suite of experiments with simple models of the ocean carbon cycle.

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Image Captions

The Southern Ocean plays a critical role in CO2 and climate change, both past and present

Methodology

Sediment core depth profile material is already in hand from four locations in the deep Atlantic and Pacific oceans. Analyses on sediment and foraminifera will be carried out in the St Andrews Isotope Geochemistry (STAiG) lab, using techniques recently developed to improve precision on small samples. Trace elements will be measured on a new state-of-the-art triple quadrupole ICPMS, allowing removal of interferences from several key elements (e.g. REEs).

Controls on redox proxies will be further explored using sedimentary redox modelling, in collaboration with Dr Sandra Arndt at the Université Libre de Bruxelles. These may also be paired with output from the GENIE Earth system model.

The initial focus is the LGM, but it may also be possible to examine other portions of the glacial cycle and carbon release during deglaciation.

Project Timeline

Year 1

Training in clean laboratory methods and mass spectrometry, initial measurements, training in modelling, literature review

Year 2

Generate long-term records. Run model experiments. First manuscript.

Year 3

Finalize data sets, apply numerical techniques, prepare written manuscripts and write thesis.

Year 3.5

Prepare written manuscripts and write thesis.

Training
& Skills

The student will gain specific training in mass spectrometry, clean lab chemistry, and carbon cycle modelling, as well as broader education in geochemistry, oceanography, and climate science. Over the course of the PhD the student will gain transferable skills such as scientific writing, statistics and data analysis, and problem-solving, as well as time management and working towards a long-term goal.

References & further reading

Anderson et al. (2019), Global Biogeochemical Cycles 33: 301-317.
Gottschalk et al. (2016), Nature Comms. 7, 1-11
Hoogakker et al. (2015), Nature Geoscience 8.1 40
MacGilchrist, et al. (2019), Science Advances 5.8 eaav6410.
Rae et al. (2011), EPSL, 302, 403-413.
Rae, et al. (2018), Nature 562(7728), 569-573.
Zhou et al. (2016), Paleoceanography and Paleoclimatology, 31(12), 1532-1546

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