Washington Land, Petermann Glacier, Greenland, Late Pleistocene to Holocene Beryllium-10 Moraine Ages, 2015 -2018

Terrestrial chronologies from southern Greenland provide a detailed deglacial history of the Greenland Ice Sheet (GIS). The northern GIS margin history, however, is less established. Here we present surface exposure ages from moraines associated with two large outlet glaciers, Petermann and Humboldt, in the northwestern sector of the GIS. The research took place from 2015 to 2018. These moraine chronologies indicate a Little Ice Age advance of the ice sheet margin before ~0.3 kiloannum (ka) and a possible equivalent advance of similar magnitude prior to ~2.8 ka. An early Holocene moraine at Humboldt Glacier was abandoned by 8.3 ± 1.7 ka and is contemporaneous with other moraines deposited along the entire western GIS margin. This widespread ice margin stability between ~9 and 8 ka indicates that while this margin was influenced by warming atmospheric temperatures during the early Holocene, the warming was likely overprinted with the effect of the abrupt climate cooling at 9.3 and 8.2 ka.