VARIATIONS IN LATE HOLOCENE ICE SHEET MARGIN FLUCTUATIONS IN WEST GREENLAND

Historical records reveal asynchrony in both the timing and magnitude of Greenland Ice Sheet fluctuations. This asynchrony illustrates the complex manner in which ice sheets react to climatic perturbations. We reconstruct the timing and extent of the late Holocene advance and retreat of the Greenland Ice Sheet in two study areas within the Disko Bugt region of West Greenland. The northern study area is located on the left-lateral margin of Sermeq Kujatdleq, at the head of Torsukattak Fjord in northern Disko Bugt, and the southern of our two study areas is located on the right-lateral margin of Nordenskiöld Gletscher, ~30 km south of Disko Bugt. In each study area we track past fluctuation of the Greenland ice sheet using sediment cores from proglacial-threshold lakes. Our results indicate local deglaciation at Sermeq Kujatdleq occurred at 7.6 ± 0.2 ka, with the ice margin remaining in a smaller-than present configuration until 520 ± 20 cal yr BP. The late Holocene advance continued, approaching a maximum configuration in the past 280 years, with a culmination of the advance occurring at AD 1992-1994. We find that retreat was underway at Sermeq Kujatdleq by AD 1999-2001. A similar pattern is found at Nordenskiöld Gletscher, where the Greenland Ice Sheet retreated to a smaller than present configuration at 7.2 ± 0.1 ka and remained in a restricted state until 590 ± 50 years ago. In contrast with our findings at Sermeq Kujatdleq, field and historic evidence suggest that Nordenskiöld Gletscher has been advancing or stable throughout the 20^th century and into the 21^st century. In conjunction with published Greenland Ice Sheet lake records from the Disko Bugt region, these results indicate a relatively synchronous late Holocene advance of the Greenland Ice Sheet on millennial and centennial timescales, yet asynchronous timing of the late Holocene maximum configuration and subsequent retreat when viewed on decadal timescales. Our record documents that the Greenland Ice Sheet achieved late Holocene maximum were attained after Little Ice Age. This demonstrates that a lag exists in the reaction of parts of the ice margin to climatic forcing requiring the influence of an outside mechanism, such as ice dynamics. The presence of such a lag suggests that portions of the Greenland Ice Sheet margin may have yet to react to current warming.