Can we see through the ice of Greenland’s outlet glaciers? A helicopter-borne GPR investigation in southern Greenland

The Greenland Ice Sheet (GrIS) presently loses mass at a rate of ~200 Gt/yr, impacting anything from ocean circulation and sea levels, over sea-ice extents and surface albedo, to the functioning of local ecosystems and human activities. Half of the loss is due to surface melt, while the other half stems from direct ice discharge into the ocean. The latter is essentially the product of the ice flow velocity and the ice thickness of so-called outlet glaciers, i.e. glaciers that transport ice from the GrIS’s interior to the ocean. While ice flow velocity can be determined via remote sensing, the ice thickness is much harder to constrain. This is particularly true in the southern Greenland, where ice thickness surveys have been rare and often unsuccessful in the past.

Here, we report on a pilot project by which ETH Zurich’s Airborne Ice penetrating Radar (AIRETH) was deployed over four outlet glaciers using Narsarsuaq airport, southern Greenland, as base for the operation. More specifically, we used AIRETH’s 25MHz configuration to conduct a set of dedicated, helicopter-borne GPR surveys over (i) Qooqqup Sermia, (ii) an unnamed glacier terminating into Lake Motzfeldt, (iii) Eqalorutsit Kangilliit Sermiat, and (iv) Sermilik Bræ. These sites are of specific interest in the frame of ongoing partner projects and had seen unsuccessful airborne GPR investigations in the past. Our contribution will provide details on the used GPR system and present first results, particularly focusing on both the encountered challenges and the interpretation of the retrieved data. A comparison to previously-existing, model-based ice thickness estimates will be presented too, providing hints on the need of further investigations.