Dynamics of groundwater recharge and seepage over the Canadian landscape during the Wisconsinian glaciation

Abstract

Pleistocene glaciations and their associated dramatic climatic conditions are suspected to ave had a large impact on the groundwater flow system over the entire North American continent. Because of the myriad of complex flow-related processes involved during a glaciation period, numerical models have become powerful tools for examining groundwater flow system evolution in this context. In this study, a series of key processes pertaining to coupled groundwater flow and glaciation modeling, such as density-dependent (i.e., brine) flow, hydromechanical loading, subglacial infiltration, isostasy, and permafrost development, are included in the numerical model HydroGeoSphere to simulate groundwater flow over the Canadian landscape during the Wisconsinian glaciation (∼ - 120 ka to present). The primary objective is to demonstrate the immense impact of glacial advances and retreats during the Wisconsinian glaciation on the dynamical evolution of groundwater flow systems over the Canadian landscape, including surface-subsurface water exchanges (i.e., recharge and discharge fluxes) in both the subglacial and the periglacial environments. It is shown that much of the infiltration of subglacial meltwater occurs during ice sheet progression and that during ice sheet regression, groundwater mainly exfiltrates on the surface, in both the subglacial and periglacial environments. The average infiltration/ exfiltration fluxes range between 0 and 12 mm/a. Using mixed, ice sheet thickness-dependent boundary conditions for the subglacial environment, it was estimated that 15-70% of the meltwater infiltrated into the subsurface as recharge, with an average of 43%. Considering the volume of meltwater that was generated subsequent to the last glacial maximum, these recharge rates, which are related to the bedrock type and elastic properties, are historically significant and therefore played an immense role in the evolution of groundwater flow system evolution over the Canadian landmass over the last 120 ka. Finally, it is shown that the permafrost extent plays a key role in the distribution of surface-subsurface interaction because the presence of permafrost acts as a barrier for groundwater flow. Copyright 2008 by the American Geophysical Union.