Basal Melt Under the Interior of the Greenland Ice Sheet: Comparison of Models, Deep Ice Cores, and Radar Observations

Abstract:

Basal ice temperature is a critical boundary condition for ice sheet models. It modulates the basal melt rate and sliding conditions, and also affects the ice hardness which alters the deformational velocity. Therefore, in order to obtain reliable estimates on the future mass loss of the ice sheets using numerical models, basal ice temperature is of paramount importance. In this study, the basal temperature and basal melt rate under the Greenland Ice Sheet are estimated using the Robin temperature solution. The analytical Robin solution is obtained by solving the heat conservation equation for steady state conditions, assuming that advection and diffusion are significant only in the vertical direction. In this study, the sensitivity of the basal temperature obtained from the Robin solution to changes in input parameters, including changes in atmospheric conditions, ice thickness, and geothermal heat flux is tested.

Although the Robin solution is frequently used in glaciology, there has been no quantitative study to estimate the effect of neglecting the horizontal advection on basal temperatures in regions of higher velocity. Here, a two-dimensional model is applied to quantify the effect of horizontal heat advection on basal temperatures. Overall, horizontal heat advection lowers the basal temperature except in regions where surface mass balance gradients are negative along the flow. Comparing the results from the 2D temperature model to the Robin solution along multiple flowlines of the Greenland Ice Sheet suggest that the horizontal heat advection alters the basal temperatures by less than 3°C up to 30-45% of the flow distance away from the ice divide; at greater distances this difference increases rapidly. All simulations using the Robin solution predict substantial basal melting under the northeast drainage basin of the ice sheet. Our 2D model results also show that because of the negative surface mass balance gradient, horizontal heat advection increases the basal temperatures in the northeast basin. Our obtained map of basal melting area matches well with the radar detected basal water under the north and northeast drainage basins. However, low basal temperatures estimated at the Camp Century ice core location in the northwest of the ice sheet is in contrast with the radar observations.