Age of the Ørkendalen moraines, Kangerlussuaq, Greenland: constraints on the extent of the southwestern margin of the Greenland Ice Sheet during the Holocene

Although Greenland ice core records register relatively stable Holocene climate conditions, the lower elevation margins of the Greenland Ice Sheet (GrIS) experienced significant Holocene fluctuations. These fluctuations include ice sheet recession during the Holocene Thermal Maximum (9–5 ka) and advance during the Little Ice Age (LIA; ∼A.D. 1350–1880). Determining the extent and timing of these fluctuations is important for understanding the response of the GrIS to interglacial climate conditions both warmer and colder than at present and for developing accurate ice sheet models. Sets of moraines marking past extents of the southwestern GrIS margin occur in the Kangerlussuaq region. We focus on the Ørkendalen moraines, a prominent moraine set located within 2 km of the modern ice margin and just outboard of the LIA moraines. We present the first 10Be ages of the Ørkendalen moraines indicating they were deposited at 6.8 ± 0.3 ka. The geomorphic relationship between the Ørkendalen and LIA moraines indicates that the ice sheet margin was inboard of its Ørkendalen extent between ∼6.8 ka and the culmination of the LIA. The age of the Ørkendalen moraines provides an important constraint on the extent of the southwestern GrIS during the middle Holocene.

► We use 10Be to date the Ørkendalen moraines, southwest Greenland, to 6.8 ± 0.3 ka. ► Our age of Greenland Ice Sheet (GrIS) extent agrees with 14C ages of past studies. ► Holocene deglaciation ages show spatial variability outside late Holocene moraines. ► The GrIS margin was behind the Ørkendalen position from 6.8 ka to end of LIA. ► The dates/positions of these moraines are useful for calibrating ice sheet models.