Seismic Reflection Methods in Offshore Groundwater Research

Bertoni, Claudia; Lofi, Johanna; Micallef, Aaron; Moe, Henning

doi:10.3390/geosciences10080299

Cited by 18 publications

(25 citation statements)

References 128 publications

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“…As highlighted in section 2.3.1, the present-day distribution and flow of groundwater in the offshore domain relates closely to the geological heterogeneity across a continental margin. Seismic reflection data analysis can provide indirect constraints on the main factors controlling this heterogeneity-from the lithology and permeability of the sediments, to the geometry of depositional units and faults (Bertoni et al, 2020)-as well as image bottom-simulating reflectors, which allow detection of hydrate and thus indicate if pore water freshening associated to hydrate dissociation is feasible (Berndt et al, 2004). Seismic and sequence stratigraphy (Mitchum et al, 1977;Vail et al, 1977) have traditionally been used to identify the type of depositional environment and provide insights into the changes in sea level in a basin through time and the palaeogeographic evolution of a sedimentary margin (Miller et al, 1998;Mitchum et al, 1977;Zecchin & Catuneanu, 2015).…”

Section: Reflection Seismic Methodsmentioning

confidence: 99%

“…Large-scale groundwater systems are slow to adapt to rapid sea level changes (Edmunds & Milne, 2001). As sea level rose after the Last Glacial Maximum, seawater overtopped OFG bodies because the landward migration of the freshwater-seawater interface was slower (<10 km per 10 ka) than the sea level rise Bertoni et al, 2020). Sequence stratigraphic surfaces, facies contacts, and systems tracts for a (a) siliciclastic shelf setting (modified from Zecchin & Catuneanu, 2013), overlying a deeper carbonate basement, and (b) carbonate margin (modified from Razin et al, 2010).…”

Section: Hydrological Factorsmentioning

confidence: 99%

“…Figure 3. Simplified diagram of facies distribution and sedimentary processes in siliciclastic and carbonate margins, with a focus on structures that have hydrogeological relevance (modified afterBertoni et al, 2020). Sequence stratigraphic surfaces, facies contacts, and systems tracts for a (a) siliciclastic shelf setting (modified fromZecchin & Catuneanu, 2013), overlying a deeper carbonate basement, and (b) carbonate margin (modified fromRazin et al, 2010).…”

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confidence: 99%

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Offshore Freshened Groundwater in Continental Margins

Micallef

Person

Berndt

et al. 2021

Reviews of Geophysics

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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. Plain Language Summary This review paper considers offshore freshened groundwater (OFG), which is water hosted in sediments and rocks below the seafloor, with a total dissolved solid concentration lower than seawater. We have compiled >300 records to demonstrate that freshened groundwater occurs offshore on most continents around the world and has a global volume of 1 × 10 6 km 3. The majority of OFG was deposited when sea level was lower than today and is hosted in sandy sub-seafloor layers that are located within 55 km of coasts in water depths less than 100 m. We present a range of geochemical, geophysical, and modeling approaches that have successfully been used to investigate OFG systems. We also propose approaches to address key scientific questions related to OFG, including whether it may be used as an unconventional source of potable water in coastal areas.

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Section: Reflection Seismic Methodsmentioning

confidence: 99%

Section: Hydrological Factorsmentioning

confidence: 99%

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confidence: 99%

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Offshore Freshened Groundwater in Continental Margins

Micallef

Person

Berndt

et al. 2021

Reviews of Geophysics

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“…Therefore, integrative analyses of CSEM with multi-channel seismic (MCS) reflection data (e.g. Bertoni et al 2020) have proven effective in differentiating lithological units from pore fluid salinity anomalies in siliciclastic margins (e.g. Gustafson et al, 2019).…”

Section: Introductionmentioning

confidence: 99%

Electrical Resistivity Anomalies Offshore a Carbonate Coastline: Evidence for Freshened Groundwater?

Haroon

Micallef

Jegen

et al. 2021

Geophysical Research Letters

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Carbonate lithologies host considerable quantities of the Earth's freshwater resources and partially supply a quarter of the global population with drinkable water. Carbonates constitute substantial amounts of the global coastlines, yet it is not known if and how they can sustain freshened groundwater offshore. Here, we use controlled source electromagnetic, seismic reflection, and core sample data to derive a lithological model for the eastern margin of the Maltese Islands and identify four distinct resistivity anomalies within the Upper Coralline Limestone, Globigerina Limestone, and Blue Clay formations. The anomalies hosted in the former are likely associated to low porosities, whereas the anomaly within the latter is indicative of pore fluid freshening. Hydrogeological modeling suggests that freshened pore fluids, emplaced during sea-level lowstands and preserved in low permeability units, are potentially still found within carbonate shelves. However, resource potential is low due to its relict nature and low permeability host environment.

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“…We compared our OFG estimates with several regional scale studies (Amir et al, 2013;Bakari et al, 2012;Bertoni et al, 2020;Engelen et al, 2019;Geldern et al, 2013;Gustafson et al, 2019;Haroon et al, 2018;Jiao et al, 2015;Knight et al, 2019;Larsen et al, 2017;Oteri, 1988;Paleologos et al, 2018;Pauw et al, 2014;Person et al, 2012Person et al, , 2003Thomas et al, 2019;Varma and Michael, 2011;Zhang et al, 2011) and a set of offshore observation wells (Micallef, 2020) limited to areas with unconsolidated sediments, see Figure 4-2. Unfortunately, the majority of these regional scale studies do not provide volume estimates.…”

Section: Resultsmentioning

confidence: 99%

Current and future state of groundwater in coastal unconsolidated sediment systems worldwide

Zamrsky¹

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Knowledge of aquifer thickness is crucial for setting up numerical groundwater flow models to support groundwater resource management and control. Fresh groundwater reserves in coastal aquifers are particularly under threat of salinization and depletion as a result of climate change, sea-level rise, and excessive groundwater withdrawal under urbanization. To correctly assess the possible impacts of these pressures we need better information about subsurface conditions in coastal zones. Here, we propose a method that combines available global datasets to estimate, along the global coastline, the aquifer thickness in areas formed by unconsolidated sediments. To validate our final estimation results, we collected both borehole and literature data. Additionally, we performed a numerical modelling study to evaluate the effects of varying aquifer thickness and geological complexity on simulated saltwater intrusion. The results show that our aquifer thickness estimates can indeed be used for regional-scale groundwater flow modelling but that for local assessments additional geological information should be included.

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Seismic Reflection Methods in Offshore Groundwater Research

Cited by 18 publications

References 128 publications

Offshore Freshened Groundwater in Continental Margins

Offshore Freshened Groundwater in Continental Margins

Electrical Resistivity Anomalies Offshore a Carbonate Coastline: Evidence for Freshened Groundwater?

Current and future state of groundwater in coastal unconsolidated sediment systems worldwide

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