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

Michael, Holly A.; Scott, Kaileigh C.; Koneshloo, Mohammad; Yu, Xuan; Khan, Mmr; Li, Katie

doi:10.1002/2016gl070863

Cited by 121 publications

(132 citation statements)

References 54 publications

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“…Freshened groundwater has been detected tens to hundreds of kilometers offshore of coastlines worldwide (Post et al, ), and simulations indicate that this could be common across a range of geologic systems (Michael et al, ). Offshore groundwater resources can potentially be exploited for uses such as drinking, agriculture, and oil recovery (Bakken et al, ; Jiao et al, ; Kwong et al, ; Person et al, ; Ziegler et al, ).…”

Section: Introductionmentioning

confidence: 99%

“…Onshore and offshore groundwater systems connect through the subsurface, and the extent to which one influences the other depends on the geologic structure. Preferential flow paths can enhance connectivity relative to homogeneous aquifers in systems with karst conduits (Evans & Lizarralde, ; Xu et al, ), palaeochannels (Mulligan et al, ), natural faults (Varma & Michael, ), and a range of other heterogeneous geologic settings (Houben et al, ; X. Li et al, ; Michael et al, ). Knight et al () analyzed 27 coastal sites globally and found that widespread losses of offshore freshwater are associated with onshore pumping due to connections between offshore and onshore fresh groundwater reserves.…”

Section: Introductionmentioning

confidence: 99%

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Offshore Pumping Impacts Onshore Groundwater Resources and Land Subsidence

Michael

2019

Geophysical Research Letters

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Freshened groundwater exists offshore along many coastlines worldwide. Pumping of these offshore resources has been proposed for more efficient oil production as well as drinking and agriculture. Although pumping can occur tens to hundreds of kilometers offshore, these activities may threaten connected onshore aquifer systems. We conducted numerical simulations of variable‐density groundwater flow and salt transport in coastal aquifers with different geologic structure subject to offshore pumping to assess potential impacts. Results show that offshore pumping can diminish both onshore groundwater availability and submarine groundwater discharge and can cause widespread land subsidence. Heterogeneity increases water resource vulnerability relative to equivalent homogeneous and layered systems and exacerbates the magnitude of land subsidence. More continuous geologic structure causes propagation of maximum subsidence farther landward. This work suggests that coastal aquifers may be vulnerable to offshore pumping activities and that these effects should be considered in feasibility assessments for offshore drilling.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Offshore Pumping Impacts Onshore Groundwater Resources and Land Subsidence

Michael

2019

Geophysical Research Letters

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“…Terrestrial groundwater discharge, density‐driven flow, tides, and waves are major driving forces affecting SGD and SWI in coastal aquifers (Figure ) [ Burnett et al ., ; Heiss and Michael , ; Li et al ., ; Michael et al ., ; Moore et al ., ; Taniguchi et al ., ; Xin et al ., ]. In early work, it was assumed that SGD could be estimated based on a summation of fluxes driven by these forces independently [ Burnett et al ., ; Li et al ., ; Taniguchi et al ., ], i.e.,

SGD = Q_{f} + Q_{c} = Q_{f} + Q_{d} + Q_{t} + Q_{w}

where

Q_{f}

and

Q_{c}

are the inland freshwater input and total circulating seawater flux, respectively; and

Q_{c}

is given by a linear combination of the density‐driven flow (

Q_{d}

), tidally driven flow (

Q_{t}

), and wave‐induced flow (

Q_{w}

).…”

Section: Introductionmentioning

confidence: 99%

“…Terrestrial groundwater discharge, density-driven flow, tides, and waves are major driving forces affecting SGD and SWI in coastal aquifers (Figure 1) [Burnett et al, 2006;Heiss and Michael, 2014;Li et al, 1999;Michael et al, 2016;Moore et al, 2008;Taniguchi et al, 2002;Xin et al, 2010]. In early work, it was assumed that SGD could be estimated based on a summation of fluxes driven by these forces independently [Burnett et al, 2006;Li et al, 1999;Taniguchi et al, 2002], i.e., above the denser seawater associated with the saltwater wedge (SW).…”

Section: Introductionmentioning

confidence: 99%

Effects of episodic rainfall on a subterranean estuary

Xin

et al. 2017

Water Resources Research

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Numerical simulations were conducted to examine the effect of episodic rainfall on nearshore groundwater dynamics in a tidally influenced unconfined coastal aquifer, with a focus on both long‐term (yearly) and short‐term (daily) behavior of submarine groundwater discharge (SGD) and seawater intrusion (SWI). The results showed nonlinear interactions among the processes driven by rainfall, tides, and density gradients. Rainfall‐induced infiltration increased the yearly averaged fresh groundwater discharge to the ocean but reduced the extents of the saltwater wedge and upper saline plume as well as the total rate of seawater circulation through both zones. Overall, the net effect of the interactions led to an increase of the SGD. The nearshore groundwater responded to individual rainfall events in a delayed and cumulative fashion, as evident in the variations of daily averaged SGD and salt stored in the saltwater wedge (quantifying the extent of SWI). A generalized linear model (GLM) along with a Gamma distribution function was developed to describe the delayed and prolonged effect of rainfall events on short‐term groundwater behavior. This model validated with results of daily averaged SGD and SWI from the simulations of groundwater and solute transport using independent rainfall data sets, performed well in predicting the behavior of the nearshore groundwater system under the combined influence of episodic rainfall, tides, and density gradients. The findings and developed GLM form a basis for evaluating and predicting SGD, SWI, and associated mass fluxes from unconfined coastal aquifers under natural conditions, including episodic rainfall.

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“…SGD is a path for groundwater outflow that may have a substantial effect on water budget of coastal aquifers (e.g., Moore, ), as well as coastal water quality (e.g., Johannes, ; Moore, ) and seafloor morphology (e.g., Orange et al, ). Because of its importance, SGD has been a subject of extensive studies either by direct observations (Burnett et al, , ; Cable et al, ; Lambert & Burnett, ; Moore, ; Swarzenski et al, ) and/or modeling (Bokuniewicz, ; Croucher & O'Sullivan, ; Glover, ; McBride & Pfannkuch, ; Michael et al, ; A. J. Smith, ; L. Smith & Zawadzki, ; Wilson, ). The vast majority of these studies focused on shallow, near‐shore SGD, but SGD can occur also in deeper water along the continental shelf (Bratton, ).…”

Section: Introductionmentioning

confidence: 99%

Deep Submarine Groundwater Discharge—Evidence From Achziv Submarine Canyon at the Exposure of the Judea Group Confined Aquifer, Eastern Mediterranean

et al. 2020

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Deep submarine groundwater discharge (DSGD) of fresh-brackish water was suggested to occur globally, yet its driving mechanism is not well constrained. Specifically, it is unclear whether the phenomenon may represent a steady-state condition of a hydrological system, in which the terrestrial recharge area is hydraulically connected with the submarine discharge area (by a confined aquifer, for example). Recently, our hydrogeological modeling suggested that such a system exists in northern Israel. The model predicted the location of a brackish water seepage within the Achziv Submarine Canyon,~10 km offshore, where the Cretaceous Judea Group confined aquifer is carved by the canyon. The present work is a field study that attempts to identify these brackish seeps in the water column of the canyon at the aquifer exposure. The field observations include salinity and temperature profiling of the water column along the canyon during three cruises and 224 Ra measurements of water samples from the canyon. The results point to a significant near-bottom low-salinity and low-temperature anomaly right where the aquifer submarine outcrop is mapped that coincide with a high 224 Ra activity anomaly. Such near-bottom anomalies are absent in an adjacent submarine canyon, in which the confined aquifer is not exposed. The anomalies in the water column of the Achziv Submarine Canyon corroborate the results of the hydrogeological modeling that predicted brackish DSGD from the sea bottom at the aquifer outcrop. The possibility of DSGD in specific geo-hydrological settings is relevant for various biological, geochemical, hydrological, and geotechnical studies of the marginal ocean.

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

Cited by 121 publications

References 54 publications

Offshore Pumping Impacts Onshore Groundwater Resources and Land Subsidence

Offshore Pumping Impacts Onshore Groundwater Resources and Land Subsidence

Effects of episodic rainfall on a subterranean estuary

Deep Submarine Groundwater Discharge—Evidence From Achziv Submarine Canyon at the Exposure of the Judea Group Confined Aquifer, Eastern Mediterranean

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