Glaciation and regional groundwater flow in the Fennoscandian shield

Abstract

AbstractRegional‐scale groundwater flow modeling of the Fennoscandian shield suggests that groundwater flow can be strongly affected by future climate change and glaciation. We considered variable‐density groundwater flow in a 1500‐km‐long and approximately 10‐km‐deep cross‐section through southern Sweden. Groundwater flow and shield brine transport in the cross‐sectional model were analyzed under projected surface conditions for the next 140 ka. Simulations suggest that blockage of recharge and discharge by low‐permeability permafrost or cold‐based ice causes sinking of brine and consequent freshening of near‐surface water in areas of natural discharge. Although recharge of basal meltwater is limited by the requirement that water pressure at the base of the ice sheet not exceed the pressure exerted by the weight of the ice, warm‐based ice with basal melting creates a potential for groundwater recharge rates much larger than those of present, ice‐free conditions. In the simulations, regional‐scale redistribution of recharged water by subsurface flow is minor over the duration of a glacial advance (approximately 10 ka). During glacial retreat, significant upward flow of groundwater may occur below the ice sheet owing to pressure release. If the mechanical loading efficiency of the rocks is high, both subsurface penetration of meltwater during glacial advance and up‐flow during glacial retreat are reduced because of loading‐induced pressure changes. The maximum rate of groundwater discharge in the simulations occurs at the receding ice margin, and some discharge occurs below incursive postglacial seas. Recharge of basal meltwater could decrease the concentration of dissolved solids significantly below present‐day levels at depths of up to several kilometers and may bring oxygenated conditions to an otherwise reducing chemical environment for periods exceeding 10 ka.