Using an autonomous underwater vehicle known as Autosub, the scientists were able to gather data on the topography of the sea floor beneath the glacier’s floating ice shelf, which revealed the presence of a 300-metre-high ridge. The glacier was, at one time, grounded on this ridge; however, recent thinning has caused it to become disconnected from the ridge, allowing it to flow more rapidly into the sea. The disconnection also permitted warmer ocean water to flow over the ridge and under the ice shelf, where it’s causing the bottom of the shelf to melt.

‘We don’t know what kick-started the initial retreat from the ridge, but we do know that it started some time prior to 1970,’ said the study’s lead author, Adrian Jenkins of the BAS. ‘Since detailed observations of the 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 in ice-sheet contraction.’

August 2010