Pleistocene hydrology of North America: The role of ice sheets in reorganizing groundwater flow systems

Abstract

[1] While the geomorphic consequences of Pleistocene megafloods have been known for some time, it has been only in the past 2 decades that hydrogeologists and glaciologists alike have begun to appreciate the important impact that ice sheet -aquifer interactions have had in controlling subsurface flow patterns, recharge rates, and the distribution of fresh water in confined aquifer systems across North America. In this paper, we document the numerous lines of geochemical, isotopic, and geomechanical evidence of ice sheet hydrogeology across North America. We also review the mechanical, thermal, and hydrologic processes that control subsurface fluid migration beneath ice sheets. Finite element models of subsurface fluid flow, permafrost formation, and ice sheet loading are presented to investigate the coupled nature of transport processes during glaciation/ deglaciation. These indicate that recharge rates as high as 10 times modern values occurred as the Laurentide Ice Sheet overran the margins of sedimentary basins. The effects of ice sheet loading and permafrost formation result in complex transient flow patterns within aquifers and confining units alike. Using geochemical and environmental isotopic data, we estimate that the volume of glacial meltwater emplaced at the margins of sedimentary basins overrun by the Laurentide Ice Sheet totals about 3.7 Â 10 4 km 3 , which is about 0.2% of the volume of the Laurentide Ice Sheet. Subglacial infiltration estimates based on continental-scale hydrologic models are even higher (5 -10% of meltwater generated). These studies in sum call into question the widely held notion that groundwater flow patterns within confined aquifer systems are controlled primarily by the water table configuration during the Pleistocene. Rather, groundwater flow patterns were likely much more complex and transient in nature than has previously been thought. Because Pleistocene recharge rates are believed to be highly variable, these studies have profound implications for water resource managers charged with determining sustainable pumping rates from confined aquifers that host ice sheet meltwater.

Integrating geophysical, hydrochemical, and hydrologic data to understand the freshwater resources on Nantucket Island, Massachusetts

“…Equation 2 is capable of representing groundwater flow induced by water table gradients, spatial variations in subsurface fluid density as well as sediment and ice-sheet loading [Person et al, 2007].…”

“…To date most studies that have developed quantitative models of groundwater flow beneath ice sheets have utilized static representations of ice-sheet geometry and neglected the effects of hydromechanical loading Piotrowski, 1997;Person et al, 2003]; however, if the ice sheet overrides low-permeability sediments, or if rapid sedimentation occurs following glaciation, then hydromechanical effects need to be simulated to account for the effect of loading on groundwater flow [Lerche et al, 1997;Bekele et al, 2003;Lemieux et al, 2006;Person et al, 2007]. Here we use variabledensity, cross-sectional models of fluid flow, solute transport, and sediment loading to predict fluid pressures and solute distribution.…”

Subglacial methanogenesis: A potential climatic amplifier?

“…While at the pressure melting point and underlain by soil or till, the subglacial hydrology of the Laurentide and European ice sheets would comprise water flow through porous sediments [Walder and Fowler, 1994]. In sedimentary basins, recharge by glacial meltwaters would have also stimulated the development of deeper and continental-scale groundwater reservoirs [Boulton et al, 1995;Breemer et al, 2002;Person et al, 2007]. Thus microbes would be free to move and grow and there would be exchange of nutrients and organic carbon between different components of the subice sheet hydrological system.…”

Glacially generated overpressure on the New England continental shelf: Integration of full‐waveform inversion and overpressure modeling

“…We solve a 1-D equation for groundwater flow similar to ones solved by Person et al [2007] and Marksamer et al [2007] that incorporates ice sheet loading, erosion, and sedimentation,…”