Chemical signals from submarine fluid advection onto the continental shelf

Moore, Willard S.; Shaw, Timothy J.

doi:10.1029/98jc02232

Cited by 92 publications

(77 citation statements)

References 25 publications

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“…3, 4). 226 Ra does not appear to be an indicator of submarine groundwater discharge in Eckernförde Bay, in contrast to other coastal regions (Moore 1996;Burnett et al 2001). Compared to that of 222 Rn (t 1/2 ϭ 3.8 d), the longer half-life of 226 Ra (t 1/2 ϭ 1,600 yr) exceeds the residence time of the water in Eckernförde Bay, which is on a scale of a few weeks.…”

Section: Discussionmentioning

confidence: 99%

“…Budget of fluid discharge based on 222 Rn inventories-226 Ra and 222 Rn activities can be used to derive budgets for the release of fluids from the seafloor (e.g., Moore 1996;Cable et al 1997;Corbett et al 2000). Groundwater sampled from the subseafloor aquifer, located Ͼ5 m below seafloor, had a 222 Rn activity of 5,000 to 10,000 mBq L Ϫ1 , approximately three orders of magnitude larger than the average seawater level.…”

Section: Discussionmentioning

confidence: 99%

“…222 Radon and 226 Radium analysis-Fluid discharge from the seafloor can be estimated on the basis of the distribution of 222 Radon (half-life 3.8 d) and 226 Radium (half-life 1,600 yr) in the water column (Moore 1996;Cable et al 1997;Moore and Shaw 1998). 222 Rn is the product of 226 Ra decay in sediments and seawater.…”

Section: Methodsmentioning

confidence: 99%

“…Techniques used to localize discharge sites and to determine flow rates include: visual observation by towed camera systems, direct measurements by different types of seep meters, pore water investigations and modeling, measurements of sediment temperature, as well as water column studies of trace elements and naturally occurring radionuclides such as 222 Rn and 226 Ra (Moore 1996;Albert et al 1998;Burnett et al 2001;Taniguchi et al 2002). Nevertheless, in most cases, the origin and subseafloor pathways of fluids and their impact on pore water composition is not well understood.…”

Section: Acknowledgmentsmentioning

confidence: 99%

“…Since then a few studies have considered the importance of fluid discharge from sediments for nutrient budgets of coastal environments, formation of offshore plankton blooms, hydrological cycles, or the release of trace elements and gases such as radon from the seafloor (Johannes 1980;Valiela et al 1990;Moore 1996;Cable et al 1997;Laroche et al 1997). For the South Atlantic Bight, on the eastern coast of the United States, Moore (1996) deduced that the quantity of submarine groundwater discharge (SGD; here taken as fresh plus salt water) represented 40% of the river input into the study area. Although these figures probably overestimate the contribution of submarine seepage 1 Corresponding author (mschlueter@awi-bremerhaven.de).…”

mentioning

confidence: 99%

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Spatial distribution and budget for submarine groundwater discharge in Eckernförde Bay (Western Baltic Sea)

Schlüter

Sauter

Andersen

et al. 2004

Limnology & Oceanography

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Submarine groundwater discharge (SGD) from subseafloor aquifers, through muddy sediments, was studied in Eckernförde Bay (western Baltic Sea). The fluid discharge was clearly traced by 222 Rn enrichment in the water column and by the chloride profiles in pore water. At several sites, a considerable decrease in chloride, to levels less than 10% of bottom-water concentrations, was observed within the upper few centimeters of sediment. Studies at 196 sites revealed that Ͼ22% of the seafloor of the bay area was affected by freshwater admixture and active fluid venting. A maximal discharge rate of Ͼ9 L m Ϫ2 d Ϫ1 was computed by modeling pore water profiles. Based on pore water data, the freshwater flow from subseafloor aquifers to Eckernförde Bay was estimated to range from 4 ϫ 10 6 to 57 ϫ 10 6 m 3 yr Ϫ1 . Therefore, 0.3-4.1% of the water volume of the bay is replaced each year. Owing to negligible surface runoff by rivers, SGD is a significant pathway within the hydrological cycle of this coastal zone. High-resolution bathymetric data and side-scan sonar surveys of pockmarks, depressions up to 300 m long, were obtained by using an autonomous underwater vehicle. Steep edges, with depths increasing by more than 2 m within 8-10 m in lateral directions, equivalent to slopes with an angle of as much as 11Њ, were observed. The formation of pockmarks within muddy sediments is suggested to be caused by the interaction between sediment fluidization and bottom currents. Fluid discharge from glacial coastal sediments covered by mud deposits is probably a widespread, but easily overlooked, pathway affecting the cycle of methane and dissolved constituents to coastal waters of the Baltic Sea.For coastal areas, Sonrel (1868) reported the discharge of freshwater from submarine springs and speculated on their use and risks for sailors. Since then a few studies have considered the importance of fluid discharge from sediments for nutrient budgets of coastal environments, formation of offshore plankton blooms, hydrological cycles, or the release of trace elements and gases such as radon from the seafloor (Johannes 1980;Valiela et al. 1990;Moore 1996;Cable et al. 1997;Laroche et al. 1997). For the South Atlantic Bight, on the eastern coast of the United States, Moore (1996) deduced that the quantity of submarine groundwater discharge (SGD; here taken as fresh plus salt water) represented 40% of the river input into the study area. Although these figures probably overestimate the contribution of submarine seepage 1 Corresponding author (mschlueter@awi-bremerhaven.de). AcknowledgmentsWe thank the captains and crews of RVs Littorina, A. v. Humbold, and Alkor for their support during several cruises. We are grateful to W. Lemke and J. Harff from the Institute of Baltic Research (IOW, Warnemünde) for providing the vibro corer system. Jayne Wolf-Welling is gratefully acknowledged for improving the English text. We thank DeBeers Marines/Maridan for conducting the AUV dives. Application of GIS was supported by Dr. A. Schäf-er. The pap...

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Acknowledgmentsmentioning

confidence: 99%

mentioning

confidence: 99%

See 3 more Smart Citations

Spatial distribution and budget for submarine groundwater discharge in Eckernförde Bay (Western Baltic Sea)

Schlüter

Sauter

Andersen

et al. 2004

Limnology & Oceanography

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Geologic influence on groundwater salinity drives large seawater circulation through the continental shelf

Michael

Scott

Koneshloo

et al. 2016

Geophysical Research Letters

121

104

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Observations of offshore freshened groundwater and saline groundwater discharge along continental shelves have important implications for water resources, ecosystem function, and the composition of the ocean, but they cannot be explained by basic theory. We show that these independent observations are linked and result from processes that drive variable‐density groundwater flow through the spatial heterogeneity that is ubiquitous in geologic formations. We use lithologic data to develop geostatistical models that mimic the architecture of coastal aquifers. Simulation of groundwater flow and salt transport through these random realizations shows that heterogeneity produces spatially complex subsurface salinity distributions that extend tens of kilometers offshore, even at steady state. The associated density gradients drive high saline groundwater circulation rates that cannot be predicted by equivalent homogeneous models. Results suggest that these phenomena may be common along continental shelves, potentially altering estimates of ocean chemical budgets and impacting coastal water management for future generations.

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Seawater‐groundwater mixing in and fluxes from coastal sediment overlying discrete fresh seepage zones: A modeling study

et al. 2017

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Submarine fresh groundwater discharging from discrete zones such as conduits overlain by thick sediment remains poorly documented and understood despite common anecdotal accounts of it. We analyzed this phenomenon by a suite of variable‐density, variably saturated groundwater flow simulations guided by field studies. The field observations included point flux and salinity measurements using seepage meters spread across the intertidal and the subtidal zones. The discretely measured seepage fluxes in the subtidal region were as high and the salinity was as fresh as those from the intertidal zone. Both fluxes and salinities varied with tides. Two‐dimensional simulations of the idealized beach‐ocean vertical section with discrete freshwater springs at the base showed the development of seawater recirculation cells along the edge of freshwater discharge plumes emanating from the outlets, causing mixing. Brackish water discharges at the sediment‐water interface above where the plume mixes with the recirculating seawater. Sensitivity analyses showed that stronger terrestrial fresh groundwater flow increases the freshwater plume size but does not affect the mixing zone width. Tidal oscillations and a dynamic fresh groundwater flow widened the mixing zones and increased pore water flux across the sediment‐water interface. Sediment thickness had a minor effect on the width of both the freshwater plume and its surrounding mixing zone. The subtidal freshwater plume and mixing zone likely represent a unique but potentially ubiquitous setting which hosts dramatic ecological and chemical gradients. Their local biogeochemical niche and coastal scale ecosystem impacts will need to be considered in investigations of coastlines.

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Chemical signals from submarine fluid advection onto the continental shelf

Cited by 92 publications

References 25 publications

Spatial distribution and budget for submarine groundwater discharge in Eckernförde Bay (Western Baltic Sea)

Spatial distribution and budget for submarine groundwater discharge in Eckernförde Bay (Western Baltic Sea)

Geologic influence on groundwater salinity drives large seawater circulation through the continental shelf

Seawater‐groundwater mixing in and fluxes from coastal sediment overlying discrete fresh seepage zones: A modeling study

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