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

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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.