Modeling subglacial groundwater along a flow line of the Scandinavian Ice Sheet using MODFLOW

Moeller, Carolyn A., Mickelson, David M., Anderson, Mary P., Winguth, Cornelia, Univeristy of Wisconsin-Madison, Department of Geology and Geophysics, 1215 W. Dayton, Madison, WI 53706

Basal water pressure and flow patterns are significant factors in controlling the behavior of an ice sheet, because they influence ice sheet thickness, stability, and extent. Water, if produced by basal melting, travels toward the ice margin through the groundwater system, and if present in sufficient quantities, as sheet or channelized flow. The flow of subglacial groundwater along a flow line of the Scandinavian Ice Sheet is examined using a two-dimensional MODFLOW-based profile model, assuming that groundwater flow is parallel to the ice flow line. The amount of basal meltwater being added to the system is derived from a two-dimensional, time dependent, thermomechanically coupled ice flow model along the same flow line. The meltwater component from the ice-flow model is used as recharge input for the groundwater model, and evolving ice-sheet topography is used to compare resulting porewater pressures to the ice overburden pressures. The groundwater model allows us to test the flow capacity of the aquifer along this flow line, the importance of a drainage system, and the effects of changing ice margin positions on subglacial hydrology. Results show that the sediment layer underlying the ice would not have been capable of transmitting all of the meltwater out of the fjord during times of advance, as well as at the maximum position at the edge of the continental shelf. The model simulations for glacial retreat indicate that the sediments could have easily handled all of the basal meltwater, but once an addition of surface melt is included in the simulation, groundwater flow through the sediment layer is no longer a sufficient means of meltwater evacuation. This suggests that other forms of basal drainage must have been present during these stages of glaciation. Episodes of high basal water pressure may explain non-climatically driven margin readvances during the overall retreat phase.