Aims

The project will determine the timing and rate of retreat of the edge of the Antarctic ice sheet across the Ross continental shelf since the last glacial maximum 20,000 years ago to resolve the present substantial differences of opinion. This will involve coring from fast sea ice off the Victoria Land coast in Granite Harbour and northwards, and from a ship in the central Ross Sea.

The cores will penetrate the recent layer of mud, deposited under sea ice/open water conditions like today's, and into diamictite beneath, deposited when the shelf was covered by the extended ice sheet. The corer has been designed to penetrate and recover up to 6 m of both soft mud and diamictite in water depths to 1000 m. The timing of glacial retreat is obtained from carbon dating contemporaneous shell material and organic carbon in organic rich sediment just above the diamictite. Thorium 230 dating by mass spectrometry on suitable carbonate materials may also be attempted.

The main objective of the 1992-93 sea ice based programme was to obtain cores from the sea floor in Granite Harbour. This part of the programme was not successful because of deployment and operational problems with our new coring equipment (vibracorer). The corer performed correctly in 700 m deep water but was unstable on the very soft sea floor and no useful core was recovered.

A ship based programme in February 1993 was very successful, with over 450 nautical miles of 3.5 kHz sea floor profiling data collected from the USCGC Polar Star off the South Victoria Land Coast (Figure 1). Data collected in Granite Harbour and off the Nordenskjold Ice Tongue will be used to map the extent and thickness of the Holocene mud blanket. The data collected offshore of Cape Roberts will be used to characterise the sea floor and compile a high resolution bathymetry map for future proposed drill sites in the area.