NEW INSIGHTS IN THE LATEGLACIAL AND HOLOCENE GLACIAL HISTORY OF THE SOUTHWEST GREENLAND ICE SHEET

In this study, we have used a combination of ¹⁰Be exposure ages and threshold lakes to constrain the ice sheet history in southwest Greenland (63-64ºN) during the Lateglacial and Holocene. The ¹⁰Be cosmogenic exposure ages have been used to quantify both the ice retreat and thinning of the southwest Greenland Ice Sheet in 3 transects from the coast to the present ice margin. Preliminary results (n=47) indicate initial deglaciation of coastal areas around 11 ka in concert with existing radiocarbon chronology, followed by a rapid retreat from the outer coast to the present ice margin around 10 ka. Boulder samples from the highest peaks demonstrate that the ice was warm-based whereas bedrock samples often contains an inherited signal and are to old. These results may have implications for other studies in Greenland, which have inferred thin LGM ice based on ¹⁰Be ages of bedrock samples. We have constrained the Holocene glaciation record using threshold lakes, which record episodes when the ice sheet was close-to-the present extent, represented by beds of clastic sediments whereas gyttja-deposition reflects periods when the glacier was behind the threshold, and no glacial meltwater input. Our results demonstrates that following the initial deglaciation the ice margin remained close to the present ice margin until around 7 cal. ka BP before it retreated behind the present extent during the Holocene Thermal Maximum (HTM). In some areas the ice sheet readvanced to the present extent around 2-3 cal. ka BP after it was retracted during the Roman and Medieval Warm Periods until the Little Ice Age (LIA) around 0.5 cal. ka BP. In other areas the ice sheet remained retracted from around 7 cal. ka BP until the LIA. Our results show that the ice sheet was retracted in a more restricted period compared to previous reconstructions and this implies that it probably is less sensitive to Holocene climate changes.