Offshore Freshened Groundwater in Continental Margins

Aaron Micallef, Mark Person, Christian Berndt, Claudia Bertoni, Denis Cohen, Brandon Dugan, Rob Evans, Amir Haroon, Christian Hensen, Marion Jegen, Kerry Key, Henk Kooi, Volker Liebetrau, Johanna Lofi, Brian J. Mailloux, Renée Martin-Nagle, Holly A. Michael, Thomas Müller, Mark Schmidt, Katrin SchwalenbergElizabeth Trembath-Reichert, Bradley Weymer, Yipeng Zhang, Ariel T. Thomas

Research output: Contribution to journalReview articlepeer-review

1 Scopus citations

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 × 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.

Original languageEnglish (US)
Article numbere2020RG000706
JournalReviews of Geophysics
Volume59
Issue number1
DOIs
StatePublished - Mar 2021

Keywords

  • continental margin
  • geochemistry
  • geophysics
  • marine hydrogeology
  • modeling
  • offshore freshened groundwater

ASJC Scopus subject areas

  • Geophysics

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