10Be chronology of the Drygalski Moraines, central western Greenland

Ice sheet margin fluctuations throughout the Holocene are increasingly well documented in Greenland, but fundamental gaps still exist. The Drygalski Moraines on the Nuussuaq Peninsula, central western Greenland, represent one of the few locations on Greenland where potential early Neoglacial (~2-5 ka) moraines have been identified. We used cosmogenic 10Be exposure dating of moraine boulders to test the hypothesis that the Drygalski Moraines are early Neoglacial in age, as was previously estimated using cross-cutting relationships with relative sea level. Alternative hypotheses are that the Drygalski Moraines represent the northern extent of the Ørkendalen Moraine (6.8 × 0.3 ka) or the Fjord Stade Moraines (~9.3 and ~8.2 ka). Results from 10Be dating of perched erratics outboard of the Drygalski Moraines suggest that deglaciation of the area occurred between ~10.4 × 0.3 ka and 9.5 × 0.3 ka. We dated three different crests of the Drygalski Moraine complex, which have mean ages of 8.6 × 0.4 ka (n=2), 8.5 × 0.2 ka (n=3), and 7.6 × 0.1 ka (n=2) from outer to inner. Perched erratics between the younger two moraines average 7.8×0.1 ka (n=2) and are consistent with the nearby moraine ages. These results allow us to reject the early Neoglacial and Ørkendalen hypotheses and generally support the Fjord Stade Moraine hypothesis because the Drygalski and Fjord Stade moraines are both early Holocene in age. However, we propose that the Drygalski and Fjord Stade moraines represent a different ice sheet response to early Holocene climate history. This may be attributed to the fast-flowing, marine-terminating nature of Jakobshavn Isbræ (the outlet glacier that deposited the Fjord Stade Moraines) in contrast with the land-based and slower-flowing lobe that deposited the Drygalski Moraines. Evidence suggests that Jakobshavn Isbræ is extremely sensitive to changes in climate, even on the centennial to decadal scale. As a result, Jakobshavn Isbræ may create discrete moraines in response to short-lived climate events (i.e. the 9.3 and 8.2 ka climate events). In contrast, the Drygalski Moraines may archive the centennial- to millennial-scale climate variability during the early Holocene and do not seem to be associated with specific early Holocene climate events.