Bathymetric control of tidewater glacier mass loss in northwest Greenland

It has been suggested that fjord geometry could be an important contributor to the observed mass loss variability in Greenland by modulating the flow of warm water to marine-terminating glaciers. New gravity-derived bathymetry of Greenlandic fjords confirms the link between the grounding line depth and rates of glacier mass loss, a relationship previously predicted only in ice models. We focus on two neighboring glaciers to minimize differences in external forcing and therefore isolate the role of the fjord bathymetry. Tracy Glacier has a deeper grounding line and has been retreating since 1892 with a contemporary mass budget of −1.63 Gt a−1. Heilprin Glacier has a shallower grounding line depth, a stable ice terminus, and a mass budget of only −0.53 Gt a−1. Because of its deeper grounding line, Tracy has more ice in contact with warm subsurface water, leaving it more vulnerable to changes in ocean forcing and therefore mass loss. •We focus on a pair of neighboring glaciers in NW Greenland with similar forcings.•Lidar data indicate Tracy Glacier is losing three times more mass than Heilprin.•Aerogravity data is inverted to obtain new bathymetry of these fjords.•A deeper grounding line exposes more ice to warm subsurface water.•For this pair, the glacier with a deeper grounding line is losing more mass.