Ocean Forcing of Ice Sheet Evolution in the Marine Basins of East Antarctica

Sea levels around the world are currently rising, threatening populations living near the coast with flooding and increased coastal erosion. Evaluating the future threat requires a better understanding of the physical processes responsible for driving changes in the Earth's ice sheets. Recent observations show that in some key locations around the ice sheets' margins, rapid thinning is currently contributing 1.3 mm/yr to global sea level rise, and that that number has risen dramatically in recent years. Most of the attention has been focussed on the Greenland and West Antarctic ice sheets, where the thinning is most widespread and rapid. It is generally assumed that the culprit is a warming of the ocean waters that come into contact with the ice sheet. Increased melting of the floating ice shelves and tidewater glaciers has caused them to thin, forcing the grounding line or calving front to retreat and allowing the inland ice to flow faster towards the coast.

Although thinning of the East Antarctic Ice Sheet (EAIS) is currently much less widespread and dramatic than that observed in West Antarctica, a large sector of the EAIS is grounded below sea level and is thus potentially vulnerable to the same process of ice shelf thinning, grounding line retreat and ice stream acceleration. In addition, analogous ocean forcing to that in West Antarctica could influence the marine-based sector of the EAIS. In both regions the Antarctic Circumpolar Current brings warm Circumpolar Deep Water (CDW) close to the continental slope. While CDW may already be influencing Totten Glacier, which now shows the strongest thinning signature over the entire EAIS, other glaciers in the region, most notably Mertz Glacier, may be protected by the formation of dense, cold Shelf Water in local polynyas. However, our knowledge of the oceanography of the continental shelf and of the waters that circulate beneath and interact with the floating ice shelves is presently insufficient to understand what processes are driving the change on Totten Glacier and how vulnerable its near neighbours such as Mertz Glacier might be. Our ability to project the future behaviour of these outlet glacier systems is severely limited as a result.

To address this deficiency, this project will make observations of the critical processes that take place beneath the floating ice shelves, to determine how the topography beneath the ice and the oceanographic forcing from beyond the cavity control the rate at which the ice shelves melt. The key tool with which the necessary observations will be made is an Autonomous Underwater Vehicle (Autosub3), configured and run in a manner analogous to that used for an earlier, highly successful campaign in which it completed 500 km of along-track observations beneath the 60-km long floating tongue of Pine Island Glacier in West Antarctica. We will use these data to validate a numerical model of ocean circulation beneath the ice shelves and use the computed melt rates to force a numerical model of ice flow, in order to investigate the response of the glaciers to a range of climate forcing. A detailed understanding of ocean circulation and melting beneath Totten and Mertz glaciers will generate insight into ocean-ice interactions that will be relevant to many other sites in Greenland and Antarctica, and will advance our developing knowledge of ice sheet discharge and its future effect on sea-level rise.

This work forms part of an intensive observational campaign focused on ocean-ice shelf interactions in East Antarctica. The collaborative, interdisciplinary effort consists of coordinated ocean and glacier studies conducted by groups at Australian, French, UK and US institutions.

The results of this research will have an impact beyond the academic community. Beneficiaries from this broader community include:

1) UK and international policy makers concerned with the impacts of climate change and their mitigation.
The primary vehicle for communication of the outcomes of climate change research to policy makers is the series of Assessment Reports produced by the Intergovernmental Panel on Climate Change (IPCC). The main results of this project will be published in time to influence the writing of the Sixth Assessment Report.

2) The UK Met Office.
While the climate model development teams at the Met Office are academic beneficiaries, the Climate, Cryosphere and Oceans group have specific needs that will be addressed more directly than is possible via the usual routes of publications and conference presentations used to communicate results to academics. At present they are working on coupling an evolving ice sheet model with the atmosphere and ocean component models being developed for the next climate and earth system models. A joint effort by the Met Office and BAS to prepare the ocean component (NEMO) for coupling with an ice sheet, by modifying the code such that it can simulate the circulation beneath ice shelves, started in September 2012. The observation and modelling work of this project will generate invaluable datasets for testing such ocean models and improved parameterisations of key processes should be readily transferable to NEMO. We will also visit the Met Office at the end of the project to present the results of our research that are of particular relevance for the development of climate and earth system models.

3) Postgraduate students and early career scientists.
The environmental sciences need to attract the very best of the next generation of physical scientists to meet the challenges presented by the need to understand our changing climate. The combination of cutting edge technology, a remote and pristine natural environment and the adventurous nature of the work proposed here should provide suitable inspiration to attract promising young people into the environmental sciences. The outcomes of this research will be incorporated into lectures given at summer schools attended by the pick of new postgraduate students internationally.

4) General public.
The challenges of working in remote and hostile environments, and the futuristic capabilities of advanced technology are themes that often generate interest in the general public. These elements of the work proposed here should help to draw a very wide audience to an awareness of the outcomes of NERC-funded research. Our primary means of communicating with the general public will be through the BAS press office, and we will aim to raise public awareness of change in the Antarctic Ice Sheet and increase the general level of understanding about the key drivers of that change.