Terrestrial-originated submarine groundwater discharge through deep multilayered aquifer systems beneath the seafloor

Abstract

A large quantity of submarine groundwater discharge (SGD) of about 1000 m3 day−1 m−1 of the 600-km-long shoreline of South Atlantic Bight has been estimated by Moore (Global Biogeochemical Cycles, 2010b, 24, GB4005, doi:10.1029/2009GB003747). However, there is great uncertainty in estimating the percentage of net, land-originated groundwater recharge of SGD. Moreover, most previous studies considered the homogeneous case for the coastal superficial aquifers. Here, we investigated the terrestrial-originated SGD through a multilayered submarine aquifer system, which comprises two confined aquifers and two semi-permeable layers. The inland recharge includes a constant part representing the annual average and a periodical part representing its seasonal variation. An analytical solution was derived and used to analyse the distributions of the terrestrial-originated SGD from the multilayered aquifers along the Winyah Bay transect, South Atlantic Bight. It is found that the width of the zone of SGD from the upper aquifer ranges from ~0.8 to ~8.0 km depending on the leakance of the seabed semi-permeable layer. A head of the upper aquifer at a coastline 1.0 m higher than the mean sea level will cause a SGD of 1.82– 18.3 m3 day−1 m−1 from that aquifer as the seabed semi-permeable layer's leakance varies from 0.001 to 0.1 day−1, providing considerable possibility for considerable land-originated SGD. Seasonal terrestrial-originated SGD variations predicted by the analytical model provide consistent explanation of the seasonal variation of 226Ra observed by Moore (Journal of Geophysics, 2007, 112, C10013, doi:10.1029/2007JC004199). The contribution of the lower aquifer to SGD is only 1.2–12% of that of the upper aquifer. Copyright © 2014 John Wiley & Sons, Ltd.