Fluctuations of the Greenland Ice Sheet during past warm climates
The Arctic is currently warming more rapidly than other locations on the planet (Arctic Climate Impact Assessment, 2005), and the response of the Greenland Ice Sheet (GIS) remains uncertain. Recent changes in the GIS, such as increased velocity of outlet glaciers as well as thinning of outlet glaciers and the ice sheet, have alarmed scientists and the public alike (Zwally et al., 2002; Joughin et al., 2008). However, we do not know the sensitivity of the GIS margin on longer-term scales. In particular, determining the response of the GIS to past climate conditions as warm as or warmer than, present will significantly improve predictions of ice sheet response to future warming.
One of the best terrestrial records of GIS fluctuations during the Holocene Epoch (~11,600 years ago until present) occurs near Kangerlussuaq, western Greenland. Numerous belts of prominent, well-preserved moraines mark former ice margin positions. The ages of one set of moraines, the Orkendalen moraines, have only been broadly constrained (e.g. Forman et al, 2007) and are important for understanding the GIS response to relatively warm Holocene climate conditions. We present new ages on the Orkendalen moraines using surface exposure dating (using 10Be) of boulders atop moraines. Our data indicate these moraines are ~6,800 ± 300 yr BP and that the GIS was smaller than present from ~6,500 yrs B.P. until a few hundred years ago. We will return to Kangerlussuaq in the summer of 2011 to collect more 10Be samples to develop a more complete chronology of GIS fluctuations.