Over the last few decades, melting of West Antarctic glaciers has contributed significantly to global sea-level rise. Since 1992, two major outlet glaciers have experienced up to 25 km of landward retreat of their "grounding line," the position at which the glacier margin starts to float.
Both glaciers rest on a bed far below sea level, so their grounding line may undergo further rapid retreat over coming decades. Until today, the long-term context of the "snapshot" of ice-sheet history recorded over the last 20 years was poorly understood. This context is crucial for predicting future ice loss and resulting sea-level rise.
In this new study, scientists from the United Kingdom, Germany, and Norway have reconstructed the timing of grounding-line retreat since the end of the last ice age about 12,000 years ago. The research team analyzed marine sediment cores recovered from the seabed offshore from the two glaciers.
Their results demonstrate that the grounding line has been located within 110 km of its modern position for the last 10,000 years. Currently, there is no evidence that the glaciers ever re-advanced. Thus, the data imply that the fast retreat observed today is exceptional, if not unprecedented, over the last ten millennia.
Claus-Dieter Hillenbrand et al., British Antarctic Survey, High Cross, Madingley Road, Cambridge CB3 0ET, UK. Posted online 19 October 2012; doi: 10.1130/G33469.1.