Contrasting evidence of Holocene ice margin retreat, south‐western Greenland

Abstract

ABSTRACTConstraining the Greenland Ice Sheet's (GrIS) response to Holocene climate change provides calibrations for ice sheet models that hindcast past ice margin fluctuations. Ice sheet models predict enhanced ice retreat in south‐western Greenland during the middle Holocene; however, few geological observations corroborating the extensive retreat are available. We present new data from lake sediment cores from the Isua region, south‐western Greenland, which provide constraints on Holocene fluctuations of the GrIS margins. Our data indicate that the main GrIS margin was 30 km west of its present‐day extent by ∼5.7k cal a BP and had retreated to within 3 km of its present‐day margin by ∼4.6k cal a BP; with subsequent re‐advances by ∼1.8 and at ∼1.7, ∼1.3 and ∼0.5k cal a BP. Times of ice retreat are coeval with increasing temperatures in western Greenland, suggesting that temperature was a dominant factor in ice retreat. The late retreat at Isua is in contrast to the early retreat observed in the Godthåbsfjord area and is probably related to the lack of fjords extending to the present Isua ice margin. Our data are not consistent with current ice sheet models that overestimate the middle Holocene ice retreat in the Isua region of south‐western Greenland.