Investigating the Controlling Factors of Transient Speed Variations in Upernavik Isstrøm Outlet Glaciers Through the Community Ice Sheet Model

Abstract:

Greenland outlet glaciers currently experience speeding up, thinning, and retreating under the warming climate in general. In particular, it is observed that in late 2010 summer, one of the outlet glaciers at Upernavik Isstrøm, northwest Greenland, showed abrupt change in speed. It accelerated from 4.5 km/yr to 6 km/yr. In this study, we attempt to explain this sudden speed up by investigating the factors that would affect short-term variation of speed in tidewater glaciers through numerical modeling. We have adopted the Community Ice Sheet Model (CISM) with high spatial (100 m) and high temporal resolutions (5 days) to simulate these effects on glacial speed. We find that the potential reasons could include enhanced surface melting induced by an atmospheric warming trend; changes in ice-ocean boundary condition; and change in terminus stability from grounding line migration. Ice loss through calving and submarine melting taking place along terminus and grounding position strongly alters the inside stress balance. Changes in surface melting affects melt water supply to the base and hence account for basal hydrological responses. These factors therefore in turn have impact on glacial speed, which we are quantitatively assessing using the CISM. Our study emphasizes on obtaining insights on the factors controlling transient speed variation in tidewater glaciers, which would be helpful in further understanding their seasonal and inter-annual variability and reducing the uncertainties in projections of future sea level rise.