Modes and drivers of nonuniform outlet glacier response to seasonal meltwater forcing in Greenland

Abstract:

The Greenland Ice Sheet is losing mass due, in part, to widespread acceleration of large outlet glaciers that drain ice directly into the ocean. These glaciers can be dynamically impacted by an influx of surface meltwater to the bed, which reduces ice-bed contact area, increases basal water pressures, and results in temporary acceleration. Our understanding of the interactions between meltwater runoff and outlet glacier flow remains limited, however, due to a paucity of direct in-situ observations of meltwater drainage systems beneath fast moving glaciers. Alternatively, satellite data can be used to monitor dynamic changes and infer evolving subglacial conditions. Here we use remotely sensed observations of ice velocity and surface elevation at all large Greenland outlet glaciers and derive their main mode of seasonal velocity change. We identify three distinct patterns of seasonal change that are indicative of meltwater sensitivity and categorize our subset of glaciers accordingly. We find that mean late-summer glacier velocities across the ice sheet are significantly related to the distribution of meltwater runoff supply, but that this relationship is most robust at glaciers with limited water storage capacity. We then analyze how categorical differences in climatic and geometric variables, including hydropotential gradient, height above flotation, and catchment-scale runoff volume, influence sensitivity to runoff. Lastly, we show how changing geometric conditions, such as retreat or prolonged thinning, can impact a glacier’s typical response to seasonal meltwater injection, and discuss how the effect of summer melt on net ice sheet discharge may evolve in the future.