The Three Scales of Submarine Groundwater Flow and Discharge across Passive Continental Margins

Abstract

A B S T R A C TIncreased study of submarine groundwater systems in recent years has provided a wealth of new data and techniques, but some ambiguity has been introduced by insufficient distinguishing of the relevant spatial scales of the phenomena studied. Submarine groundwater flow and discharge on passive continental margins can be most productively studied and discussed by distinct consideration of the following three spatial scales: (1) the nearshore scale, spanning approximately 0-10 m offshore and including the unconfined surficial aquifer; (2) the embayment scale, spanning approximately 10 m to as much as 10 km offshore and including the first confined submarine aquifer and its terminus; and (3) the shelf scale, spanning the width and thickness of the aquifers of the entire continental shelf, from the base of the first confined aquifer downward to the basement, and including influences of geothermal convection and glacioeustatic change in sea level.

The effect of meteoric phreatic diagenesis and spring sapping on the formation of submarine collapse structures in the Biak Basin, Eastern Indonesia

“…There are many examples of where spring sapping has resulted in the formation of submarine canyons worldwide (e.g. Johnson, 1939, Robb, 1984Paull and Neumann, 1987;Paull et al, 1990;Robb, 1990;Orange and Breen, 1992;Orange et al, 1994;Dugan and Flemings, 2000;2002;Green et al, 2007;Flemings et al, 2008;Bratton, 2010).…”

“…Lateral migration of meteoric water within marine basins is well documented (Wu and Chafetz, 2002;Bratton, 2010). Bratton (2010) defined three spatial scales of submarine groundwater discharge: 1) nearshore -0-10 m offshore, 2) embayment -10 m -10 km offshore, 3) shelf -width of the entire continental shelf.…”

“…Bratton (2010) defined three spatial scales of submarine groundwater discharge: 1) nearshore -0-10 m offshore, 2) embayment -10 m -10 km offshore, 3) shelf -width of the entire continental shelf. Fresh water has been reported in a well 100 km off shore Florida in the Gulf of Mexico, 10 km offshore of Saudi Arabia and offshore Bahrain in the Persian Gulf, and beneath the continental shelves of the North Atlantic (Kohout, 1966;Fetter, 1980;Chafetz et al, 1988;Chafetz and Rush, 1995;Edmonds, 2001;Wu and Chafetz, 2002;Person et al, 2003;Fleury et al, 2007).…”

“…The process of submarine spring sapping is interpreted to be driven by the freshwater lens responsible for the meteoric phreatic overprinting of samples collected onshore Biak and Supiori extending a considerable distance offshore ( Figure 8). The Biak and Supiori aquifer extending offshore into the Biak Basin represents the shelf scale of Bratton (2010). At the shelf scale the freshwater aquifer extends as far as the shallowest overlying confining unit, typically comprising fine-grained sediments (Bratton, 2010).…”

Submarine groundwater discharge revealed by radium isotopes (Ra-223 and Ra-224) near a paleochannel on the Southern Brazilian continental shelf

“…Bratton (2010) demonstrates that confined aquifers may stretch along the coast quite extensively and reach the continental shelf several kilometers offshore. In some cases, deep aquifers may have fractures in confined upper layers -such as ruptures triggered by the depressions found along the shelf -which makes an exchange of fluids across the sediment-water interface possible.…”