Robot sub studies signs of melting deep into an Antarctic ice shelf cavity

Science Daily: Autosub, a robot submarine built and developed by the UK's National Oceanography Centre, Southampton, has successfully completed a high-risk campaign of six missions travelling under an Antarctic glacier. Autosub has been exploring Pine Island Glacier, a floating extension of the West Antarctic ice sheet, using sonar scanners to map the seabed and the underside of the ice as it juts into the sea. Scientists hope to learn why the glacier has been thinning and accelerating over recent decades. Pine Island Glacier is in the Amundsen Sea, part of the South Pacific bordering West Antarctica. Changes in its flow have been observed since the early 1970s, and together with neighbouring glaciers it is currently contributing about 0.25 mm a year to global sea level rise.

Steve McPhail led the Autosub team during the ten-day survey. He said: "Autosub is a completely autonomous robot: there are no connecting wires with the ship and no pilot. Autosub has to avoid collisions with the jagged ice overhead and the unknown seabed below, and return to a pre–defined rendezvous point, where we crane it back onboard the ship. "Adding to the problems are the sub zero water temperatures and the crushing pressures at 1000 m depth. All systems on the vehicle must work perfectly while under the ice or it would be lost. There is no hope of rescue 60 km in, with 500 metres of ice overhead."

An international team of scientists led by Dr Adrian Jenkins of British Antarctic Survey and Stan Jacobs of the Lamont-Doherty Earth Observatory, Columbia University, New York on the American ship, the RVIB Nathaniel B Palmer, has been using the robot sub to investigate the underside of the ice and measure changes in salinity and temperature of the surrounding water. After a test mission in unusually ice-free seas in front of the face of the glacier, they started with three 60km forays under the floating glacier and extended the length of missions to 110km round-trip. In all, a distance over 500km beneath the ice was studied.

NASA image of the Pine Island Glacier ice shelf