Submarine Groundwater Discharge: An Introduction

Controlling Forces

Terrestrial - Hydraulic gradient, climate
Marine - Tidal pumping, wave set-up, current-induced topographic flow, convection (salt fingering) and sea-level differences (across barrier islands)

Idealized hydrogeologic cross section showing submarine groundwater discharge.

Submarine groundwater discharge (SGD) is a ubiquitous coastal process that is driven by a composite of climatologic, hydrogeologic, and oceanographic processes. For example, terrestrial hydraulic gradients that reflect both short and long term climatic conditions almost always transport both surface and ground water toward the coast. In coastal waters, physical oceanographic processes such as wave set-up, tidal pumping, and density-driven circulation impact these hydraulic gradients and thus affect rates of submarine groundwater discharge. Although only fresh groundwater discharge has traditionally been accounted for in numerical simulations of coastal water budgets, the discharge of recirculated saline groundwater may be equally or even more important in terms of material transport (for example, nutrients, metals, organics) across land/sea margins. For the purposes of this site, we therefore define SGD to consist either of fresh ground water, re-circulated seawater, or a composite therefore, and will evaluate and present SGD in terms of a vector for nutrient delivery to coastal waters.

Until the mid-1990s, studies on SGD did not receive widespread attention, because it was generally thought that SGD rates were not large enough to be a direct influence on ocean water budgets. This omission may in part be due to the inherent difficulty in identifying sites and quantifying rates of SGD, because most SGD occurs as diffusive flow, rather than discrete spring flow. This is in sharp contrast to studies of river discharge or river chemistry, which are obviously more easily sampled and quantified. However, there is a growing recognition that the submarine discharge of fresh, brackish, and marine ground water into coastal oceans is just as important as river discharge in some areas of the coastal ocean. This site will thus review the progress made in SGD science (with particular emphasis on new applications of geochemical tracers and novel geophysical tools), provide links to many SGD projects and study sites, and present an inclusive list of relevant publications. The eventual goal of our SGD science is to develop some forecasting or predictive capability based on being able to de-couple climatic and seasonal signatures from SGD rates.

"U/Th series radionuclides as tracers of coastal groundwater," Chemical Reviews, volume 107 issue 2, pages 663-674, doi:10.1021/cr0503761

Submarine Groundwater Discharge: An Introduction

Controlling Forces

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