|Autosub is an AUV (Automated Underwater Vehicle), designed, developed and built at the National Oceanography Centre in Southampton with funding from the Natural Environment Research Council.|
|Autosub3 has a maximum range of 400km and is powered by 5,000 ordinary D-cell batteries. The batteries are packed in bundles in pressure-tested housings. Either end of the seven-meter sub there are free-flooding areas where the payload of instruments are installed.|
|It carries a multibeam sonar system that builds up a 3D map of the ice above and the seabed below. It also carries precision instruments for measuring the salinity, temperature, and oxygen concentrations in the sea water within the ice cavity, which are vital to understanding the flow of water within the ice cavity and the rate of melting.|
|Autosub is 7m long and weighs 3.5 tonnes. Travelling at 6km/h it is capable of diving up to 1600m deep, and can operate for 72 hours (400 km) between battery changes.|
Thinning ice in West Antarctica is currently contributing nearly 10% of global sea level rise and scientists have identified Pine Island Glacier (PIG) as a major source. Using Autosub (an autonomous underwater vehicle) to dive deep and travel far beneath the pine Island Glacier’s floating ice shelf, the scientists captured ocean and sea-floor measurements, which revealed a 300m-high ridge (mountain) on the sea floor.
Pine Island Glacier was once grounded on (sitting on top of) this underwater ridge, which slowed its flow into the sea. However, in recent decades it has thinned and disconnected from the ridge, allowing the glacier to move ice more rapidly from the land into the sea.
This also permitted deep warm ocean water to flow over the ridge and into a widening cavity that now extends to an area of 1,000 km² under the ice shelf. The warm water, trapped under the ice, is causing the bottom of the ice shelf to melt, resulting in continuous thinning and acceleration of the glacier.
The discovery of the ridge has raised new questions about whether the current loss of ice from Pine Island Glacier is caused by recent climate change or is a continuation of a longer-term process that began when the glacier disconnected from the ridge.
We do not know what kick-started the initial retreat from the ridge, but we do know that it started some time prior to 1970. Since detailed observations of Pine Island Glacier only began in the 1990s, we now need to use other techniques such as ice core analysis and computer modelling to look much further into the glacier’s history in order to understand if what we see now is part of a long term trend of ice sheet contraction. This work is vital for evaluating the risk of potential wide-spread collapse of West Antarctic glaciers.
—Lead author Dr Adrian Jenkins of British Antarctic Survey
Since our first measurements in the Amundsen Sea, estimates of Antarctica’s recent contributions to sea level rise have changed from near-zero to significant and increasing. Now finding that the PIG’s grounding line has recently retreated more than 30 km from a shallow ridge into deeper water, where it is pursued by a warming ocean, only adds to our concern that this region is indeed the ‘weak underbelly’ of the West Antarctic Ice Sheet. Increased melting of continental ice also appears to be the primary cause of persistent ocean freshening and other impacts, both locally and downstream in the Ross Sea.
—Co-author Stan Jacobs
Adrian Jenkins, Pierre Dutrieux, Stanley S. Jacobs, Stephen D. McPhail, James R. Perrett, Andrew T. Webb & David White (2010) Observations beneath Pine Island Glacier in West Antarctica and implications for its retreat. Nature Geoscience. doi: 10.1038/ngeo890