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Offshore Freshened Groundwater in Continental Margins
Author(s) -
Micallef Aaron,
Person Mark,
Berndt Christian,
Bertoni Claudia,
Cohen Denis,
Dugan Brandon,
Evans Rob,
Haroon Amir,
Hensen Christian,
Jegen Marion,
Key Kerry,
Kooi Henk,
Liebetrau Volker,
Lofi Johanna,
Mailloux Brian J.,
MartinNagle Renée,
Michael Holly A.,
Müller Thomas,
Schmidt Mark,
Schwalenberg Katrin,
TrembathReichert Elizabeth,
Weymer Bradley,
Zhang Yipeng,
Thomas Ariel T.
Publication year - 2021
Publication title -
reviews of geophysics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 8.087
H-Index - 156
eISSN - 1944-9208
pISSN - 8755-1209
DOI - 10.1029/2020rg000706
Subject(s) - geology , groundwater , submarine pipeline , siliciclastic , aquifer , sea level , geophysics , paleontology , earth science , oceanography , structural basin , facies , geotechnical engineering
Abstract 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 × 10 6 km 3 ; 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.