Monday 22 August 2005

P5
1400-1520 hours

079
Spatial and seasonal variability of ice-ocean interaction beneath the Amery Ice Shelf
Allison, Ian¹, Hunter, John², Craven, Michael¹
1 Australian Antarctic Division and ACE CRC, Hobart, Tasmania, Australia
2 Antarctic Climate and Ecosystems CRC, Australia
Author email: ian.allison@aad.gov.au
The Amery is a large (~60,000 km2) embayed ice shelf in East Antarctica at 70°E. Compared to the major embayed Antarctic ice shelves it is relatively narrow (decreasing from 200 km width to only 50 km at the grounding zone), but the ocean floor at the grounding zone is greater than 2500 m deep. Over the last few years processes of ice-ocean interaction for the Amery have been studied using in-situ oceanographic observations though boreholes into the cavity beneath the shelf, and along the front of the shelf; glaciological measurements of shelf dynamics and mass balance; remote-sensing observations; and numerical modelling of circulation in the ocean cavity. Very high basal melt rates occur near the grounding zone, but there is also a considerable accretion of marine ice that occurs mostly under the north-western part of the shelf. At a borehole site located 100 km back from the centre of the ice shelf front, where the shelf thickness is 480 m, the total thickness of marine ice is approximately 200 m, but the lowest 100 m of this is unconsolidated and totally porous. Core samples show considerable biological material within the marine ice, and video imagery through the borehole shows a surprisingly high level of biological activity beneath the shelf. Observations from oceanographic moorings through and off the front of the ice shelf show a strong coupling of temperature and salinity across the ice shelf front at seasonal timescales. Numerical modelling of simplified ice shelf cavities has demonstrated the importance of such seasonal cycles (due primarily to the formation and melting of sea ice) on the circulation underneath the ice shelf. In addition, the circulation is characterised by the 'ice pump' mechanism driven by melting and re-freezing of the ice shelf.

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