The Antarctic ice sheet, which represents the largest of all potential contributors to sea level rise, appears to be losing mass at a rate that has accelerated over recent decades.
Ice loss is focussed in a number of key drainage basins where dynamical changes in the outlet glaciers have led to increased discharge. The synchronous response of several independent glaciers, coupled with the observation that thinning is most rapid over their floating termini, is generally taken as an indicator that the changes have been driven from the ocean. The deeper parts of the Amundsen Sea continental shelf are flooded by Circumpolar Deep Water (CDW) with a temperature around 1ºC, which potentially drives rapid melting of the floating ice.
Some of the most significant changes have been observed on Pine Island Glacier, where thinning, acceleration and grounding line retreat have all been observed, primarily through satellite remote sensing. Even during the relatively short satellite record, rates of change have been observed to increase.
Between 20th and 30th January 2009 the Natural Environment Research Council's autonomous underwater vehicle, Autosub3, was deployed on six sorties into the ocean cavity beneath Pine Island Glacier. Total track length was 887 km (taking 167 hours) of which 510 km (taking 94 hours) were beneath the glacier. Specific aims were to investigate how CDW flows beneath Pine Island Glacier and determines its melt rate, and to map both the seabed beneath and the underside of the glacier. The instruments carried by Autosub-3 were a Seabird CTD, with dual conductivity and temperature sensors plus a dissolved oxygen sensor and a transmissometer, a multi-beam echosounder that could be configured to look up or down, and two Acoustic Doppler Current Profilers (ADCP's): an upward-looking 300 kHz instrument and a downward-looking 150 kHz instrument, providing a record of ice draft and seabed depth along the vehicle track in addition to horizontal current velocity profiles.
This work is done in collaboration with :
Adrian Jenkins, British Antarctic Survey, Cambridge, U.K.
The AUTOSUB team, National Oceanography Centre, Southampton, U.K.
Stan Jacobs, Lahmont-Doherty Earth Observatory, Palisades, New York, U.S.A.
Stanley S. Jacobs, Adrian Jenkins, Claudia Giulivi and Pierre Dutrieux, Stronger ocean circulation and increased melting under Pine Island Glacier ice shelf, Nature Geoscience advance online publication (26 June 2011) doi:10.1038/NGEO1188
Observations beneath Pine Island Glacier in West Antarctica and implications for its retreat Adrian Jenkins, Pierre Dutrieux, Stanley S. Jacobs, Stephen D. McPhail, James R. Perrett, Andrew T. Webb, David White, Nature Geoscience 3, 468-472 (20 June 2010) doi:10.1038/ngeo890
A consistent dataset of Antarctic ice sheet topography, cavity geometry, and global bathymetry, Timmermann, R., Le Brocq, A., Deen, T., Domack, E., Dutrieux, P., Galton-Fenzi, B., Hellmer, H., Humbert, A., Jansen, D., Jenkins, A., Lambrecht, A., Makinson, K., Niederjasper, F., Nitsche, F., Nøst, O. A., Smedsrud, L. H., and Smith, W. H. F., Earth Syst. Sci. Data, 2, 261-273, 2010, doi:10.5194/essdd-3-231-2010