Simulation of Vatnajokull ice cap dynamics -: art. no. F03009

We apply a coupled model of ice sheet dynamics and subglacial hydrology to investigate the dynamics and future evolution of the Vatnajokull ice cap, Iceland. In this paper we describe a new theoretical approach to introducing longitudinal stress coupling in the ice dynamics solution, and we analyze our ability to simulate the main features of Vatnajokull, with and without longitudinal stress effects. Equilibrium ice cap configurations exist for Vatnajokull but under a narrow range of climatic boundary conditions. Equilibrium reconstructions have an average ice thickness greater than what is observed at Vatnajokull, consistent with our inability to capture surge dynamics in Vatnajokull's outlet glaciers. Hydrological regulation of basal flow, longitudinal stress coupling, and a simple parameterization of the subglacial heat flux from Vatnajokull's geothermal cauldrons all help to reduce average ice thickness in the equilibrium reconstructions, but cases that reproduce the present-day ice volume have an ice cap area that is 5-10% less than the actual ice cap. Present-day reconstructions that adopt a realistic climate spin-up for the period 1600-1990 provide improved fits to the modern-day ice cap geometry. This indicates that climatic disequilibrium also plays a significant role in dictating Vatnajokull's morphology. Simulations for the period 1600-2300 illustrate that air temperature is the dominant control on Vatnajokull's volume and area. Longitudinal stress coupling and hydrological coupling both increase Vatnajokull's sensitivity to future warming.).