Runoff Routing Beneath Marine-terminating Glaciers in Central West Greenland

Abstract:

Subglacial discharge at the grounding line of marine-terminating glaciers plays an important role in subaqueous melting, calving and, in turn, ice dynamic change from back-stress perturbations. Subglacial discharge (or runoff) can directly melt glacier termini as freshwater plumes rise buoyantly and entrain warm seawater at depth. Runoff can also impact fjord circulation and thus heat transport to the terminus face. As a result, it is important to understand the spatio-temporal distribution in submarine runoff at the grounding line of marine-terminating glaciers. This information may prove critical for predicting changes in the terminus position and shape through time, as the rate of submarine melt is predicted to vary nonlinearly on the maximum subglacial discharge, and not just its annual volume. Here, we link a predictive model of subglacial water routing to observations of subglacial discharge (both from satellite remote sensing and multibeam bathymetry) for three tidewater glaciers in central West Greenland. Our predictive model identifies the location of several large subglacial channels as point sources for discharge at the grounding line. Channel locations are confirmed through observations of turbid sediment plume formation, polynya formation within the ice mélange, localized thermal undercutting of the calving face and bathymetric morphology of the terminus face and sea floor. We examine the identified subglacial channels in terms of their impact on ice front position over six melt seasons and find that for some glaciers the largest seasonal ice front retreat occurs in sectors that have the most active subglacial discharge. Overall, we find that while subglacial water is routed through complex paths inland, its outlet at the terminus is ultimately controlled by the geometry of the near-terminus region. The outlets remain fixed in space over long time periods for those glaciers not experiencing rapid retreat.