TY - JOUR
T1 - Offshore Freshened Groundwater in Continental Margins
AU - Micallef, Aaron
AU - Person, Mark
AU - Berndt, Christian
AU - Bertoni, Claudia
AU - Cohen, Denis
AU - Dugan, Brandon
AU - Evans, Rob
AU - Haroon, Amir
AU - Hensen, Christian
AU - Jegen, Marion
AU - Key, Kerry
AU - Kooi, Henk
AU - Liebetrau, Volker
AU - Lofi, Johanna
AU - Mailloux, Brian J.
AU - Martin-Nagle, Renée
AU - Michael, Holly A.
AU - Müller, Thomas
AU - Schmidt, Mark
AU - Schwalenberg, Katrin
AU - Trembath-Reichert, Elizabeth
AU - Weymer, Bradley
AU - Zhang, Yipeng
AU - Thomas, Ariel T.
N1 - Publisher Copyright:
© 2020. The Authors.
PY - 2021/3
Y1 - 2021/3
N2 - First reported in the 1960s, offshore freshened groundwater (OFG) has now been documented in most continental margins around the world. In this review we compile a database documenting OFG occurrences and analyze it to establish the general characteristics and controlling factors. We also assess methods used to map and characterize OFG, identify major knowledge gaps, and propose strategies to address them. OFG has a global volume of 1 × 106 km3; it predominantly occurs within 55 km of the coast and down to a water depth of 100 m. OFG is mainly hosted within siliciclastic aquifers on passive margins and recharged by meteoric water during Pleistocene sea level lowstands. Key factors influencing OFG distribution are topography-driven flow, salinization via haline convection, permeability contrasts, and the continuity/connectivity of permeable and confining strata. Geochemical and stable isotope measurements of pore waters from boreholes have provided insights into OFG emplacement mechanisms, while recent advances in seismic reflection profiling, electromagnetic surveying, and numerical models have improved our understanding of OFG geometry and controls. Key knowledge gaps, such as the extent and function of OFG, and the timing of their emplacement, can be addressed by the application of isotopic age tracers, joint inversion of electromagnetic and seismic reflection data, and development of three-dimensional hydrological models. We show that such advances, combined with site-specific modeling, are necessary to assess the potential use of OFG as an unconventional source of water and its role in sub-seafloor geomicrobiology.
AB - First reported in the 1960s, offshore freshened groundwater (OFG) has now been documented in most continental margins around the world. In this review we compile a database documenting OFG occurrences and analyze it to establish the general characteristics and controlling factors. We also assess methods used to map and characterize OFG, identify major knowledge gaps, and propose strategies to address them. OFG has a global volume of 1 × 106 km3; it predominantly occurs within 55 km of the coast and down to a water depth of 100 m. OFG is mainly hosted within siliciclastic aquifers on passive margins and recharged by meteoric water during Pleistocene sea level lowstands. Key factors influencing OFG distribution are topography-driven flow, salinization via haline convection, permeability contrasts, and the continuity/connectivity of permeable and confining strata. Geochemical and stable isotope measurements of pore waters from boreholes have provided insights into OFG emplacement mechanisms, while recent advances in seismic reflection profiling, electromagnetic surveying, and numerical models have improved our understanding of OFG geometry and controls. Key knowledge gaps, such as the extent and function of OFG, and the timing of their emplacement, can be addressed by the application of isotopic age tracers, joint inversion of electromagnetic and seismic reflection data, and development of three-dimensional hydrological models. We show that such advances, combined with site-specific modeling, are necessary to assess the potential use of OFG as an unconventional source of water and its role in sub-seafloor geomicrobiology.
KW - continental margin
KW - geochemistry
KW - geophysics
KW - marine hydrogeology
KW - modeling
KW - offshore freshened groundwater
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U2 - 10.1029/2020RG000706
DO - 10.1029/2020RG000706
M3 - Review article
AN - SCOPUS:85103205082
SN - 8755-1209
VL - 59
JO - Reviews of Geophysics
JF - Reviews of Geophysics
IS - 1
M1 - e2020RG000706
ER -