Ocean Melting Greenland (OMG) bathymetric survey of northwest Greenland and implications for the recent evolution of its glaciers

Abstract:

Oceans Melting Greenland (OMG) is a five-year Earth Ventures Suborbital Mission funded by NASA to investigate the role of the oceans in ice loss around the margins of the Greenland Ice Sheet, which includes measurements of seafloor bathymetry from multibeam surveys and airborne gravity, glacier surface elevation from high-frequency radar interferometry, and temperature/salinity/depth from vessels and airborne-dropped probes. Here, we describe the results of the 2016 bathymetry survey of northwest Greenland that took place in the summer of 2015: july 22-August 19 and Sept 2-Sept 16 spanning from Ilulissat to Thule AFB in north Greenland, and to be complemented by a survey of southeast Greenland in 2016. We deployed a multibeam Reson 7160 with 512 beams installed on the hull of the Cape Race vessel, with enhanced capabilities for fjord wall and ice face mapping. The survey tracks were optimized based on the IBCAO3 database, recent cruises, airborne gravity data collected by NASA Operation IceBridge which indicated the presence of troughs, bed topography mapped inland using a mass conservation approach, the spatial distribution of ice discharge to locate the largest outlets and maximizing the number of major fjords sampled during the survey, with the goal to identify all troughs that are major pathways for subsurface ocean heat, and constrain as many glacier ice front thickness as permitted by time and the practicality of navigating the ice-choked fjords. The data reveal many deep, U-shaped, submarine valleys connected to the glaciers, intercut with sills and over deepened in narrower passages where former glaciers and ice streams merged into larger units; as well as fjords ending in shallow plateaus with glaciers in retreated positions. The presence of warm, salty water of Atlantic origin (AW) in the fjords is documented using CTD. Some glaciers sit on shallow plateaus in cold, fresh polar waters (PW) at the end of deep fjords, while others are deeper and standing in AW. We compare the results to the recent history of deglaciation of this sector of Greenland using satellite imagery from 1962 to 2015, complemented by results from aerial surveys for earlier periods to illustrate how the evolution of the glaciers under ocean thermal forcing has been modulated by the presence and/or absence of natural pathways for AW.