Stability of Barnes Ice Cap, Baffin Island, Canada

Abstract:

Barnes Ice Cap is a modern remnant of the Laurentide Ice Sheet, which covered much of North America during the Last Glacial Maximum. Moraine chronology shows that Barnes reached a quasi-equilibrium state about 1000 years ago and has been relatively stable since. The flat and low-elevation bedrock topography under Barnes implies that the accumulation area owes its existence to the ice cap itself. As a “self-sustaining” ice mass, Barnes is expected to be sensitive to climate and/or dynamical changes given the surface-elevation / mass-balance feedback. In this study, we combine historical observations (1960-1980) with new satellite and air-borne data (1995-2010) to drive a mass-balance model coupled to a transient full-Stokes thermo-mechanical model with an adaptive mesh geometry. The model is used to characterize the current state of the ice cap and to investigate its stability as a function of climate and internal ice dynamics. Thermo-mechanically coupled simulations show zones of locally enhanced ice flow that imprint themselves on the shape of the ice-cap. These simulations suggest that an additional heat source, such as refreezing of water at the base of the ice cap, is required to maintain temperate conditions where sliding is known to occur. Modelled dynamics highlight the influence of contrasting viscosities between Pleistocene and Holocene ice that affect the form and flow of the ice cap. On millennial timescales, the internal dynamics of the ice cap may lead to divergent evolution pathways even for a constant climate. Sensitivity experiments reveal that Barnes was in a delicate equilibrium with pre-industrial climate. An increase in air temperature of less than 0.2K or a decrease precipitation of less than 15%, relative to this climate, is enough to push the ice cap into an unstable regime. Based on recent observations of the equilibrium line altitude, Barnes is expected to disappear even with no additional warming.