The largest uncertainty in estimates of future sea level rise is the response of the Antarctic ice shelves to the warming of the surrounding oceans (Church et al., 2013). Increased melt at the base of the fringing ice shelves results in more rapid mass loss from the Antarctic Ice Sheet and faster sea level rise. However, the processes regulating melting of ice shelves are poorly known. A better understanding of the mechanisms that drove ice retreat and sea-level rise (by 120-130m on average) since the Last Glacial Maximum (LGM), about 20,000 years ago, can reduce the uncertainty in future projections (Bentley, 2010). During the last deglaciation global sea-level rose abruptly in two phases, or ‘meltwater pulses’. The hemispheric origin of the meltwater pulses, particularly “pulse 1A”, at ~ 14.5 thousand years before present, remains uncertain. One hypothesis to explain these pulses of abrupt sea-level rise invokes accelerated melting of the Antarctic ice sheet in response to reduced Southern Ocean overturning (Golledge et al., 2014). According to this model, Antarctic melting is initiated by the rapid recovery of the Atlantic Meridional Overturning Circulation (AMOC) around 14,000 years ago, following a near shut-down several thousand years earlier (McManus et al., 2004). Increased AMOC reduces the strength of the Southern overturning cell, notably the production of cold, salty Antarctic Bottom Water, which forms on the Antarctic shelf. This in turn leads to cooling of Antarctica and decreased sea surface temperatures around Antarctica, leading to more sea-ice, and less AABW production. The reduction in AABW, and increase in warmer, northern-sourced Circumpolar Deep Water (CDW) leads to a subsurface warming on the Antarctic shelf, which melts the base of the ice shelf. The ocean stratification that results from the melting then further reduces AABW formation, driving a feedback that results in accelerated ice sheet retreat.
This project will use marine sediment cores recovered from the slope of the Mertz glacier region to test the ice-ocean feedback mechanism. This is an important region for AABW formation, and will be sensitive to changes in AABW production over glacial cycles. Hydrographic data and seawater samples proximal to Mertz Glacier will constrain the present day ice-sheet-ocean configuration as well as geochemical characteristics of AABW and CDW. The project will involve a multi-proxy reconstruction of ocean properties to test the sequence of events thought to drive rapid melting. Preliminary assessment of the sediment cores reveals sections of finely laminated sandy/silts including dropstones, and sections of intensely bioturbated muds and sandy muds. The age models will be fine-tuned using bulk radiocarbon dating methods.
Other advisors on this project will be Dr Taryn Noble (UTAS), Dr Steve Rintoul (CSIRO, ACE CRC) and Dr Helen Bostock (National Institute of Water and Atmospheric Research, NZ).
This project is supported by the Australian Research Council (ARC) Special Research Initiative for Antarctic Gateway Partnership. For information about the Antarctic Gateway Partnership visit the Institute for Marine and Antarctic Studies (IMAS) web page.
The ARC Antarctic Gateway Partnership is seeking applications from suitably qualified graduates for living allowance Scholarships to undertake PhD projects.
The UTAS Graduate Research Office provides detailed information about scholarships including eligibility, award conditions and application processes.
To be considered for an ARC Antarctic Gateway Partnership living allowance Scholarship it is necessary to specify this on the Admissions and Scholarship Application Part 9.1.
Tuition fees apply to all international candidates. Limited numbers of UTAS tuition fee scholarships are also available on a competitive basis to candidates undertaking projects closely aligned with the ARC Antarctic Gateway Partnership's research objectives.
Bentley, M.J., 2010. The Antarctic palaeo record and its role in improving predictions of future Antarctic Ice Sheet change. J. Quaternary Sci. 25, 5–18. doi:10.1002/jqs.1287
Church JA, and others. Sea Level Change. In: Climate Change 2013. The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change (Stocker TF, et al. eds). Cambridge University Press, 2013
Cofaigh, C.O., 2012. Ice sheets viewed from the ocean: the contribution of marine science to understanding modern and past ice sheets. Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 370, 5512–5539. doi:10.1130/G32153.
Golledge, N.R., Menviel, L., Carter, L., Fogwill, C.J., England, M.H., Cortese, G., Levy, R.H., 2014. Antarctic contribution to meltwater pulse1A from reduced Southern Ocean overturning. Nat Comms 5, 1–10. doi:10.1038/ncomms6107
Harris, P.T., Brancolini, G., Armand, L., Busetti, M., Beaman, R.J., Giorgetti, G., Presti, M., Trincardi, F., 2001. Continental shelf drift deposit indicates non-steady state Antarctic bottom water production in the Holocene. Mar. Geol. 179, 1–8.
Shevenell, A.E., Ingalls, A.E., Domack, E.W., Kelly, C., 2012. Holocene Southern Ocean surface temperature variability west of the Antarctic Peninsula. Nature 470, 250–254. doi:10.1038/nature09751