Rapid ice retreat in Disko Bugt supported by 10Be dating of the last recession of the western Greenland Ice Sheet

Abstract

Due to rising sea levels and warming ocean currents, marine-based sectors of the Greenland and Antarctic ice sheets are particularly vulnerable to warming climate. Reconstructions of the timing of marine-based ice margin fluctuations in Greenland during the early Holocene can provide context for historical and modern observations of ice-sheet change. Here, we generate a 10Be chronology of ice-sheet retreat through Disko Bugt, western Greenland. Our new chronology, consisting of twelve 10Be ages from sites surrounding and within Disko Bugt, fills a gap in the history of the western margin of the Greenland Ice Sheet and allows for a continuous composite record of ice-margin recession between the continental shelf break and the current margin. We constrain the onset of ice-margin retreat from outer Disko Bugt to 10.8 ± 0.5 ka. When combined with previous chronologies, these results place the final Greenland Ice Sheet retreat out of Disko Bugt onto land at Jakobshavn Isfjord and Qasigiaanguit at 10.1 ± 0.3 ka, and later at 9.2 ± 0.1 ka in southeastern Disko Bugt. The rate of retreat during this time period is between ∼50–450 m a−1 for central Disko Bugt and ∼50–70 m a−1 along the southern coast of Disko Bugt. Deglaciation of Disko Bugt occurred ∼1000 years later than in neighboring Uummannaq Fjord to the north. This asynchrony in the timing of deglaciation suggests that local ice dynamics played an important role in the retreat of the Greenland Ice Sheet from large marine embayments in western Greenland.