Abstract
ABSTRACT The response of the Greenland Ice Sheet to future climate change is relatively unconstrained. Determining the extents and rates of ice-margin fluctuations during the Holocene provides a longer-term perspective on ice-sheet changes and offers an analogue of how the ice-sheet may respond to future changes. Here, we present sixteen new 10Be ages of boulders on moraines, boulders perched on bedrock, and bedrock surfaces that mark the timing of ice-margin fluctuations during the Holocene in the Kangerlussuaq region of southern west Greenland. We show that the Keglen moraines date to 8.0 ± 0.3 ka (n = 6) and that the average ice-margin retreat rate slowed from about 49 to 13 m yr−1 after about 8.0 ka, likely in response to the ice margin retreating onto land at the head of the fjord Kangerlussuaq at this time. The average retreat rate further slowed to less than 1 m yr−1 between 6.8 ka and 4.2 cal kyr BP, a time when nearby paleoclimate records document warm summers and increased precipitation. Finally, we show that the historical advances of the ice margin occurred during the past 200 years, likely in response to cooler summer temperatures.
Highlights
Global sea level is predicted to rise 0.5–1.2 m (Stocker et al 2013) by the end of the twenty-first century and contributions from the Greenland Ice Sheet (GrIS) are projected to be 8–22 cm by AD 2100 (Bindschadler et al 2013)
We suggest that the 8.2 ka event may have involved a decrease in summer temperatures, and early Holocene summer temperature reconstructions extending beyond 8 ka along the western GrIS margin would provide valuable data
We present sixteen new 10Be ages that further constrain the Holocene extents of the western margin of the GrIS east of Kangerlussuaq
Summary
Global sea level is predicted to rise 0.5–1.2 m (Stocker et al 2013) by the end of the twenty-first century and contributions from the Greenland Ice Sheet (GrIS) are projected to be 8–22 cm by AD 2100 (Bindschadler et al 2013). We present sixteen new 10Be ages of boulders on moraines, boulders perched on bedrock, and bedrock surfaces that constrain the Holocene extents and thicknesses of the western GrIS margin fluctuations near Kangerlussuaq, Greenland. The Kangerlussuaq region of southern west Greenland hosts an exceptional record of Holocene GrIS extents in the form of north-south trending moraines (Figure 1) These well-preserved moraines exist from the coast near Sisimiut to the present-day ice margin, and mark stillstands or readvances of the ice-sheet margin (Ten Brink 1975; Ten Brink and Weidick, 1974; van Tatenhove, van der Meer, and Koster 1996). We focus on the region between Kangerlussuaq and the present-day ice margin where e1414477-2
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