PLEISTOCENE RECHARGE MECHANISMS ON THE ATLANTIC CONTINENTAL SHELF

In many coastal settings around the world the distribution of freshwater within continental shelf sediments is far out of equilibrium with modern sea level conditions. One of the most remarkable examples of this can be found in New England, USA where groundwater within a shallow Miocene sand unit more than 100 km offshore Long Island is remarkably fresh ( ~ 3000 mg/l salinity). Pore fluids within Pleistocene to Upper Cretaceous sands beneath Nantucket Island were also found to be completely flushed of salt water down to 512 m. We hypothesize that the flushing of continental shelf aquifers may have been caused by either: (1) meteoric recharge during Pleistocene sea-level low-stands including; (2) sub-ice-sheet recharge during the last glacial maximum; or (3) recharge from proglacial lakes. We have developed new two- and three-dimensional paleo-hydrogeologic model that represent all of these proposed mechanisms along New England's continental shelf. The model solves coupled equations for variable-density groundwater flow, heat, and solute transport in response to sea level fluctuations and ice-sheet encroachment. In this talk, we present a suite of simulations which isolate the effects of these different end-member recharge mechanisms. We reconstructed paleo-ice sheet topography, temperature, permafrost, flexural adjustments to the lithosphere, and sea level elevation using isotopic records from the Greenland ice sheet. Our findings emphasize the important role of hydrologic windows through confining units along submarine canyons in providing locations of focused submarine discharge and facilitating sub-ice-sheet recharge.