Origin and Extent of Fresh Paleowaters on the Atlantic Continental Shelf, USA

Abstract

While the existence of relatively fresh groundwater sequestered within permeable, porous sediments beneath the Atlantic continental shelf of North and South America has been known for some time, these waters have never been assessed as a potential resource. This fresh water was likely emplaced during Pleistocene sea-level low stands when the shelf was exposed to meteoric recharge and by elevated recharge in areas overrun by the Laurentide ice sheet at high latitudes. To test this hypothesis, we present results from a high-resolution paleohydrologic model of groundwater flow, heat and solute transport, ice sheet loading, and sea level fluctuations for the continental shelf from New Jersey to Maine over the last 2 million years. Our analysis suggests that the presence of fresh to brackish water within shallow Miocene sands more than 100 km offshore of New Jersey was facilitated by discharge of submarine springs along Baltimore and Hudson Canyons where these shallow aquifers crop out. Recharge rates four times modern levels were computed for portions of New England's continental shelf that were overrun by the Laurentide ice sheet during the last glacial maximum. We estimate the volume of emplaced Pleistocene continental shelf fresh water (less than 1 ppt) to be 1300 km(3) in New England. We also present estimates of continental shelf fresh water resources for the U.S. Atlantic eastern seaboard (10(4) km(3)) and passive margins globally (3 x 10(5) km(3)). The simulation results support the hypothesis that offshore fresh water is a potentially valuable, albeit nonrenewable resource for coastal megacities faced with growing water shortages.

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

“…On the New England continental shelf, fine-grained sediments range in permeability from 10 À10 to 10 À18 m 2 [Cohen et al, 2010], whereas clayey silts have an average permeability of 10 À16.5 m 2 [Person et al, 2003]. Glacigenic sediments such as till can have permeability of 10 À16 m 2 or lower [Keller et al, 1989].…”

“…The continental margin off Massachusetts was repeatedly glaciated throughout the late Pleistocene [Oldale and O'Hara, 1984;Uchupi et al, 2001;Siegel et al, 2012]. Two-and three-dimensional paleohydrologic models simulate how these glacial cycles, in combination with sea level fluctuations, had a strong influence on the offshore hydrogeologic system [Person et al, 2003;Marksamer et al, 2007;Cohen et al, 2010]. In particular, the models show that these glaciation cycles may have emplaced large volumes of subsurface freshwater tens of kilometers beyond the edge of the ice sheets [Person et al, 2003;Marksamer et al, 2007;Cohen et al, 2010].…”

“…Two-and three-dimensional paleohydrologic models simulate how these glacial cycles, in combination with sea level fluctuations, had a strong influence on the offshore hydrogeologic system [Person et al, 2003;Marksamer et al, 2007;Cohen et al, 2010]. In particular, the models show that these glaciation cycles may have emplaced large volumes of subsurface freshwater tens of kilometers beyond the edge of the ice sheets [Person et al, 2003;Marksamer et al, 2007;Cohen et al, 2010]. A glacial influence on this hydrogeologic system may also explain lowsalinity groundwater observed on Nantucket Island [Folger et al, 1978].…”

Modelling water flow under glaciers and ice sheets

“…Early three-dimensional treatments were rare [156], as most model applications were confined to two-dimensional transects or paleo flowlines [157,158]. Recent work has seen increased use of three-dimensional models [151,152], though compromises are still necessary at the largest scales. In their investigation of groundwater flow beneath the North American ice sheets, Lemieux et al [160,165] use a coarse classification of bedrock geology as one of four types (oceanic crust, orogenic belt, Canadian shield or sedimentary rocks) in order to implement their continentalscale model in HydroGeoSphere.…”

“…The motivation for such studies is varied, ranging from understanding basal effective pressure, till deformation and landform development [148,149] to assessing the influence of glaciation and permafrost on groundwater recharge, circulation and geochemistry [150][151][152][153]. The first theoretical models were hatched with the Pleistocene ice sheets in mind [144] ( figure 3); geographically referenced model applications followed, first to the paleo ice sheets of Europe [154][155][156][157] and then North America [151,[158][159][160][161].…”