| Summary: | Early Holocene summer warmth drove dramatic Greenland ice sheet (GIS) retreat. Subsequent insolation-driven cooling caused GIS margin readvance to late Holocene maxima, from which ice margins are now retreating. We use Be-10 surface exposure ages from four locations between 69.4 deg N and 61.2 deg N to date when in the early Holocene south to west GIS margins retreated to within these late Holocene maximum extents. We find that this occurred at 11.1 +/- 0.2 ka to 10.6 +/- 0.5 ka in south Greenland, significantly earlier than previous estimates, and 6.8 +/- 0.1 ka to 7.9 +/- 0.1 ka in southwest to west Greenland, consistent with existing Be-10 ages. At least in south Greenland, these Be-10 ages likely provide a minimum constraint for when on a multicentury timescale summer temperatures after the last deglaciation warmed above late Holocene temperatures in the early Holocene. Current south Greenland ice margin retreat suggests that south Greenland may have now warmed to or above earliest Holocene summer temperatures.
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