DEGLACIATION OF NARES STRAIT AND WASHINGTON LAND, NORTHWEST GREENLAND

Petermann Glacier is an arctic tidewater glacier in northwest Greenland that terminates into Nares Strait and drains roughly 6% of the Greenland Ice Sheet (GIS). Erratic boulders, moraines, and other glacial features across the adjacent, and presently ice free, Washington Land and islands within Nares Strait demonstrate a more extensive ice sheet at the Last Glacial Maximum. Little chronologic control, however, exists for the timing of the ice retreat during the last deglaciation, despite the importance of such a chronology to help deduce the underlying mechanisms responsible for the ice retreat in this sector of GIS. Here we present 80 new ¹⁰Be cosmogenic exposure dates awaiting final AMS measurements together with 30 existing ages from moraines along the margins of Petermann and Humboldt Glaciers (Reusche et al. submitted) to better constrain the timing of the glacial retreat over the past ~12 ka.

Washington Land and the islands within Nares Strain are composed of flat-lying carbonate bedrock overlain with large (>1m) erratic boulders, many of which are of granitic or sandstone lithology and from the interior of the GIS. As part of a multidiscplinary field campaign in 2015, we collected 115 samples from these erratic boulders for ¹⁰Be cosmogenic surface exposure dating. The samples come from three islands in Nares Strait and multiple locations along the coast and interior of Washington Land. Sample elevations range from 100-600 m.a.s.l. and span an area of ~9500 km². Ages from the erratic boulders from the islands will resolve the timing of separation of the GIS from the Canadian coast and opening of Nares Strait, while the ages across Washington Land will document both the timing and thinning of the GIS to its present margins. Both our terrestrial based work and the paleoceanographic data being collected as part of the larger multidisciplinary research project of Petermann Glacier, will provide further insight into the timing and mechanisms leading to deglaciation of this sector of the GIS following the Last Glacial Maximum.