Acceleration of Jakobshavn Isbræ triggered by warm subsurface ocean waters

Observations over past decades show a sudden switch of Jakobshavn Isbrae—a large outlet glacier feeding a deep-ocean fjord on Greenland’s west coast—from slow thickening to rapid thinning in 1997. This switch is associated with a doubling in glacier velocity. Hydrographic data show a concurrent sudden increase in subsurface ocean temperatures along the entire west coast of Greenland, suggesting that the changes in Jakobshavn Isbrae were triggered by the arrival of relatively warm water originating from the Irminger Sea. Observations over the past decades show a rapid acceleration of several outlet glaciers in Greenland and Antarctica1. One of the largest changes is a sudden switch of Jakobshavn Isbrae, a large outlet glacier feeding a deep-ocean fjord on Greenland’s west coast, from slow thickening to rapid thinning2 in 1997, associated with a doubling in glacier velocity3. Suggested explanations for the speed-up of Jakobshavn Isbrae include increased lubrication of the ice–bedrock interface as more meltwater has drained to the glacier bed during recent warmer summers4 and weakening and break-up of the floating ice tongue that buttressed the glacier5. Here we present hydrographic data that show a sudden increase in subsurface ocean temperature in 1997 along the entire west coast of Greenland, suggesting that the changes in Jakobshavn Isbrae were instead triggered by the arrival of relatively warm water originating from the Irminger Sea near Iceland. We trace these oceanic changes back to changes in the atmospheric circulation in the North Atlantic region. We conclude that the prediction of future rapid dynamic responses of other outlet glaciers to climate change will require an improved understanding of the effect of changes in regional ocean and atmosphere circulation on the delivery of warm subsurface waters to the periphery of the ice sheets.