Changes in ice volume and ocean stratification across the Mid Pleistocene Transition: A multiproxy paleoceanographic study on the Agulhas Plateau

Explanations of the glacial–interglacial and millennial timescale variations in atmospheric pCO2 invoke an important role for the deep ocean in the storage of CO2. Deep-ocean density stratification has been proposed as a mechanism to promote the storage of CO2 in the deep ocean during glacial times. Little is known, however, about how ocean stratification might have evolved across much of the Pliocene–Pleistocene and therefore its potential role in regulating atmospheric pCO2.

The recent International Ocean Discovery Program (IODP) Expedition 361 drilled six sites on the southeast African margin and in the Indian-Atlantic ocean gateway (IAOG), southwest Indian Ocean during spring 2016 (Hall et al., 2016; Figure 1). This project, which will be collaborative with an international team, intends to utilise material collected during EXP 361 to provide quantitative reconstructions of water-column hydrography, dynamics, sediment provenance and relative export production in the Subantarctic Zone (SAZ) and IAOG during key intervals of climate change over the past ~5 Ma. Will we also assess changes in the oxygen isotopic composition of seawater as a proxy for ice volume.

The project will initially focus the on the Early Middle Pleistocene Transition (EMPT; 1.4-0.4 Ma) - which marks a fundamental shift in the Earth’s climate state with a progressive increase in the amplitude of glacial-interglacial oscillations and a shift towards a quasi-100 kyr frequency - to investigate (i) the extent of changes in ocean stratification during the EMPT (ii) the response of the soft-tissue biological pump to the increased iron deposition observed during the onset of the EMPT (iii) the intensity of oceanic CO2 leakage from the SAZ and (iv) these processes in the context of changes in ice volume and meridional overturning circulation on a regional and global scale. These records will then be compared to similar reconstructions across other key Pliocene glacial events, which may have been global and occurred at ~4.9-4.8 Ma, ~4.0 Ma, ~3.6 Ma and ~3.3 Ma. It is anticipate that this study will provide a valuable contribution to our understanding of the processes that resulted in lower glacial atmospheric pCO2 in the post-EMPT world.

The PhD project will involve a range of palaeoceanographic and geochemical techniques. The student will work within a very active and dynamic research environment and will be trained fully in laboratory techniques. The project will also involve a visit to Lamont-Doherty Earth Observatory (Columbia University, New York) for 40Ar/39Ar and K/Ar analyses. This project would suit a student with an analytical geochemistry/sedimentology background and a strong interest in Earth science and climate change. It is envisaged that the student will gain seagoing experience.