Subglacial discharge as a driver of fjord circulation in Ilulissat Icefjord

Abstract

The ice-ocean interface of Greenlandic outlet glaciers is the main source of uncertainty in the sea level contribution estimates from the Greenland ice sheet in the coming century. Subglacial discharge of surface meltwater is a currently understudied process that connects atmospheric forcing to the marine terminus. At the terminus, subglacial discharge drives buoyant plumes that enhance melt of the glacier. Surface meltwater from the ice sheet is often assumed to be directly and instantaneously transported to the gounding line as subglacial discharge. However, the subglacial drainage network evolves as a response to changes in surface meltwater volume, thus moderating and distributing the discharge along the grounding line. The early-season and late-season networks are likely to have different transport properties, leading to different properties of the buoyant subglacial discharge plume, and the accompanying melt rate.We model the subglacial hydrologic network of Sermeq Kujalleq (Jakobshavn Isbræ) glacier in West Greenland with GlaDS in ISSM. We characterize the evolution of subglacial discharge into the fjord throughout the runoff season, and compare different runoff years. Furthermore, we use the MITgcm ocean model of Ilulissat Icefjord to characterize the impact of seasonality of the subglacial discharge to fjord properties, circulation and submarine melt of the glacier front.