Long‐term pockmark maintenance by fluid seepage and subsurface sediment mobilization – sedimentological investigations in Lake Neuchâtel

Loher, Markus; Reusch, Anna; Strasser, Michael

doi:10.1111/sed.12255

“…The absence of significantly elevated rims around the pockmarks (Fig. 5d) further supports the efficient lateral sediment transport and precludes significant subsurface sediment mobilization and transport of particles to the seafloor (Loher et al, 2016). 137 Cs activity contents in the organic-rich surface mud layer in the pockmark E are at the post-Chernobyl level (Fig.…”

Section: Submarine Groundwater Dischargementioning

confidence: 62%

Submarine groundwater discharge site in the First Salpausselkä ice-marginal formation, south Finland

Virtasalo

¹

,

Schröder

²

,

Luoma

³

et al. 2018

Preprint

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Abstract. Submarine groundwater discharge (SGD) has been implicated as a significant source of nutrients and other potentially harmful substances to coastal sea. Although the number of reported SGD sites has increased recently, their stratigraphical architecture and aquifer geometry are rarely investigated in detail. This study analyses a multifaceted dataset of offshore seismic sub-bottom profiles, multibeam and sidescan sonar images of the seafloor, radon measurements of seawater and groundwater, and onshore ground-penetrating radar and refraction seismic profiles in order to reconstruct the detailed stratigraphical architecture of a high-latitude SGD site, which is connected to the Late-Pleistocene First Salpausselkä ice-marginal formation on the Hanko Peninsula in Finland. The studied location is characterized by a sandy beach, a sandy shore platform that extends 100–250 m seaward sloping gently to ca. 4 m water depth, and a steep slope to ca. 17 m water depth within ca. 50 m distance. The onshore radar and offshore seismic profiles are correlated based on unconformities, following the allostratigraphical approach. The aquifer is hosted in the distal sand-dominated part of an ice-contact subaqueous fan foreset. It is interpreted that gravel and coarse sand interbeds and lenses in the distal foreset, and, potentially, coarse couplet layers in the overlying glaciolacustrine rhythmite, provide conduits for localized groundwater flow. The SGD takes place predominantly through pockmarks on the seafloor, which are documented on the shore platform slope by multibeam and sidescan sonar images. Elevated radon-222 activity concentrations measured 1 m above seafloor confirm SGD from two pockmarks with fine sand surface sediment, whereas there was no discharge from a third pockmark that was covered with a thin organic-rich mud layer. The thorough understanding of the local stratigraphy and the geometry and composition of the aquifer that have been acquired in this study are crucial for successful hydrogeological modeling and flux studies at the SGD site.

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“…The absence of significantly elevated rims around the pockmarks (Fig. 5d) further supports the efficient lateral sediment transport and precludes significant subsurface sediment mobilization and transport of particles to the seafloor (Loher et al, 2016).…”

Section: Submarine Groundwater Dischargementioning

confidence: 61%

Submarine groundwater discharge site in the First Salpausselkä ice-marginal formation, south Finland

Virtasalo¹,

Schröder²,

Luoma³

et al. 2018

Preprint

View full text Add to dashboard Cite

Abstract. Submarine groundwater discharge (SGD) has been implicated as a significant source of nutrients and other potentially harmful substances to coastal sea. Although the number of reported SGD sites has increased recently, their stratigraphical architecture and aquifer geometry are rarely investigated in detail. This study analyses a multifaceted dataset of offshore seismic sub-bottom profiles, multibeam and sidescan sonar images of the seafloor, radon measurements of seawater and groundwater, and onshore ground-penetrating radar and refraction seismic profiles in order to reconstruct the detailed stratigraphical architecture of a high-latitude SGD site, which is connected to the Late-Pleistocene First Salpausselkä ice-marginal formation on the Hanko Peninsula in Finland. The studied location is characterized by a sandy beach, a sandy shore platform that extends 100–250 m seaward sloping gently to ca. 4 m water depth, and a steep slope to ca. 17 m water depth within ca. 50 m distance. The onshore radar and offshore seismic profiles are correlated based on unconformities, following the allostratigraphical approach. The aquifer is hosted in the distal sand-dominated part of an ice-contact subaqueous fan foreset. It is interpreted that gravel and coarse sand interbeds and lenses in the distal foreset, and, potentially, coarse couplet layers in the overlying glaciolacustrine rhythmite, provide conduits for localized groundwater flow. The SGD takes place predominantly through pockmarks on the seafloor, which are documented on the shore platform slope by multibeam and sidescan sonar images. Elevated radon-222 activity concentrations measured 1 m above seafloor confirm SGD from two pockmarks with fine sand surface sediment, whereas there was no discharge from a third pockmark that was covered with a thin organic-rich mud layer. The thorough understanding of the local stratigraphy and the geometry and composition of the aquifer that have been acquired in this study are crucial for successful hydrogeological modeling and flux studies at the SGD site.

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“…Schlüter et al, 2004), and by threedimensional groundwater flow modelling (e.g. Luoma and Okkonen, 2014).…”

Section: Submarine Groundwater Dischargementioning

confidence: 99%

“…Groundwater abstraction for the needs of coastal cities further increases the vulnerability of low-lying aquifers to high sea levels (Ferguson and Gleeson, 2012). Recent groundwater modelling and hydrogeochemical studies show that the water quality of a glacigenic coastal aquifer in the Hanko Peninsula, south Finland, may be compromised due to groundwater pumping and the predicted sealevel rise and increase in precipitation (Luoma and Okkonen, 2014;Luoma et al, 2015).…”

Section: Introductionmentioning

confidence: 99%

Submarine groundwater discharge site in the First Salpausselkä ice-marginal formation, south Finland

Virtasalo

¹

,

Schröder

²

,

Luoma

³

et al. 2019

View full text Add to dashboard Cite

Abstract. Submarine groundwater discharge (SGD) has been implicated as a significant source of nutrients and potentially harmful substances to the coastal sea. Although the number of reported SGD sites has increased recently, their stratigraphical architecture and aquifer geometry are rarely investigated in detail. This study analyses a multifaceted dataset of offshore seismic sub-bottom profiles, multibeam and side-scan sonar images of the seafloor, radon measurements of seawater and groundwater, and onshore ground-penetrating radar and refraction seismic profiles in order to establish the detailed stratigraphical architecture of a high-latitude SGD site, which is connected to the Late-Pleistocene First Salpausselkä ice-marginal formation on the Hanko Peninsula in Finland. The studied location is characterized by a sandy beach, a sandy shore platform that extends 100–250 m seaward sloping gently to ca. 4 m water depth, and a steep slope to ca. 17 m water depth within ca. 50 m distance. The onshore radar and offshore seismic profiles are correlated based on unconformities, following the allostratigraphical approach. The aquifer is hosted in the distal sand-dominated part of a subaqueous ice-contact fan. It is interpreted that coarse sand interbeds and lenses in the distal fan deposits, and, potentially, sandy couplet layers in the overlying glaciolacustrine rhythmite, provide conduits for localized groundwater flow. The SGD takes place predominantly through pockmarks on the seafloor, which are documented on the shore platform slope by multibeam and side-scan sonar images. Elevated radon-222 activity concentrations measured 1 m above seafloor confirm SGD from two pockmarks in fine sand sediments, whereas there was no discharge from a third pockmark that was covered with a thin organic-rich mud layer. The thorough understanding of the local stratigraphy and the geometry and composition of the aquifer that have been acquired in this study are crucial for successful hydrogeological modelling and flux studies at the SGD site.

show abstract

Long‐term pockmark maintenance by fluid seepage and subsurface sediment mobilization – sedimentological investigations in Lake Neuchâtel

Cited by 10 publications

References 59 publications

Submarine groundwater discharge site in the First Salpausselkä ice-marginal formation, south Finland

Submarine groundwater discharge site in the First Salpausselkä ice-marginal formation, south Finland

Submarine groundwater discharge site in the First Salpausselkä ice-marginal formation, south Finland

Submarine groundwater discharge site in the First Salpausselkä ice-marginal formation, south Finland

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