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

Virtasalo, Joonas J.; Schröder, Jan; Luoma, Samrit; Majaniemi, Juha; Mursu, Juha; Scholten, Jan

doi:10.5194/se-10-405-2019

Cited by 31 publications

(29 citation statements)

References 66 publications

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“…Dead corals with algae were identified by Johan et al (2017) within and around the area of the crater. SGD seems to affect the morphology of the seafloor in many places around the globe (Buongiorno Nardelli et al 2017;Swarzenski et al 2017;Virtasalo et al 2019) which may be used in more depth as a tool in future SGD studies. Active submarine springs could, for example, be identified based on bathymetry measurements.…”

Section: Discussionmentioning

confidence: 99%

Nutrient dynamics in submarine groundwater discharge through a coral reef (western Lombok, Indonesia)

Oehler

Bakti

Lubis

et al. 2019

Limnology & Oceanography

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Submarine groundwater discharge (SGD) from tropical volcanic islands locally transports significant amounts of terrestrial nutrients into the coastal ocean, which can affect sensitive coastal ecosystems such as coral reefs. In northwestern Lombok, terrestrial submarine groundwater discharges through several submarine springs at the seafloor into a coral reef. In order to understand the transport mechanisms of nutrients from land into the reef, we investigated nutrient fluxes via SGD within the area using a combination of different methods, including recharge estimates in the coastal catchment area, echosounder profiling of the seafloor, discharge measurements, and hydrochemical analyses (stable isotopes of water, radon, and nutrients). Different types of springs can be distinguished based on their morphology. One spring showed a “crater”‐shaped structure while other springs consisted of fissures. Recharge rates in the coastal catchment amounted to 5 L s−1, while discharge rates from the largest spring were 5 L s−1 for total SGD and 2.5 L s−1 for fresh SGD, which is similar to discharge rates from smaller onshore springs at the slopes of a volcano. SGD was in general a source of nutrients such as dissolved silicon (~ 226 mol d−1), phosphate (0.61 mol d−1), or total dissolved nitrogen (13.4 mol d−1). Nitrate concentrations varied among the different springs, probably due to different sources in the hinterland, transformations (e.g., denitrification), or biological uptake during transport from land into the ocean. As nitrate can considerably affect coral reef health, our findings suggest that especially nitrate should be monitored around submarine springs in Indonesia.

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Section: Discussionmentioning

confidence: 99%

Nutrient dynamics in submarine groundwater discharge through a coral reef (western Lombok, Indonesia)

Oehler

Bakti

Lubis

et al. 2019

Limnology & Oceanography

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“…The GPR profiles were interpreted following Neal (2004) and were calibrated with the groundwater levels from four observation boreholes measured at the same period, and the drill logs of 12 groundwater observation wells. Details of acquisition, processing and interpretation of GPR and offshore seismic survey data are presented in Virtasalo et al (2019). Data from previous studies consist of the gravimetric survey during 2004 obtained from the Geological Survey of Finland (GTK 2020) and courtesy of the city of Hanko (Sito 2018); information on groundwater observation boreholes (e.g.…”

Section: Methodsmentioning

confidence: 99%

“…For many locations along the Hanko Peninsula, groundwater flow models imply fresh groundwater discharge from the SSI to the coastal Baltic Sea (Luoma and Okkonen 2014). Indeed, Virtasalo et al (2019) recently discovered the first SGD site in Finland, which is connected to the SSI. The groundwater discharge is associated with pockmarks on the seafloor at seawater depths between 4 and 17 m, with estimated SGD rates from 222 Rn measurements of approximately 0.4-1.2 cm day −1 .…”

Section: Introductionmentioning

confidence: 99%

Geological and groundwater flow model of a submarine groundwater discharge site at Hanko (Finland), northern Baltic Sea

et al. 2021

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Three-dimensional geological and groundwater flow models of a submarine groundwater discharge (SGD) site at Hanko (Finland), in the northern Baltic Sea, have been developed to provide a geological framework and a tool for the estimation of SGD rates into the coastal sea. The dataset used consists of gravimetric, ground-penetrating radar and shallow seismic surveys, drill logs, groundwater level monitoring data, field observations, and a LiDAR digital elevation model. The geological model is constrained by the local geometry of late Pleistocene and Holocene deposits, including till, glacial coarse-grained and fine-grained sediments, post-glacial mud, and coarse-grained littoral and aeolian deposits. The coarse-grained aquifer sediments form a shallow shore platform that extends approximately 100–250 m offshore, where the unit slopes steeply seawards and becomes covered by glacial and post-glacial muds. Groundwater flow preferentially takes place in channel-fill outwash coarse-grained sediments and sand and gravel interbeds that provide conduits of higher hydraulic conductivity, and have led to the formation of pockmarks on the seafloor in areas of thin or absent mud cover. The groundwater flow model estimated the average SGD rate per square meter of the seafloor at 0.22 cm day−1 in autumn 2017. The average SGD rate increased to 0.28 cm day−1 as a response to an approximately 30% increase in recharge in spring 2020. Sensitivity analysis shows that recharge has a larger influence on SGD rate compared with aquifer hydraulic conductivity and the seafloor conductance. An increase in recharge in this region will cause more SGD into the Baltic Sea.

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“…Other examples of sea floor morphological expressions related to groundwater are depressions formed around submarine fresh and/or brackish springs in the Mediterranean, where extensive nearshore carbonate formations caused the development of submarine karstic aquifers (Rousakis et al, 2014). Depressions, which are similar in appearance to pockmarks formed by gas seeps, have also been found where freshwater escapes through the sea floor (Whiticar and Werner, 1981;Khandriche and Werner, 1995;Virtasalo et al, 2019). Groundwater discharge into the ocean is recognized as a widely occurring process and is commonly referred to as submarine groundwater discharge (SGD) (Moore, 2010).…”

Section: Introductionmentioning

confidence: 99%

Potential links between Baltic Sea submarine terraces and groundwater seeping

et al. 2020

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Abstract. Submarine groundwater discharge (SGD) influences ocean chemistry, circulation, and the spreading of nutrients and pollutants; it also shapes sea floor morphology. In the Baltic Sea, SGD was linked to the development of terraces and semicircular depressions mapped in an area of the southern Stockholm archipelago, Sweden, in the 1990s. We mapped additional parts of the Stockholm archipelago, areas in Blekinge, southern Sweden, and southern Finland using high-resolution multibeam sonars and sub-bottom profilers to investigate if the sea floor morphological features discovered in the 1990s are widespread and to further address the hypothesis linking their formation to SGD. Sediment coring and sea floor photography conducted with a remotely operated vehicle (ROV) and divers add additional information to the geophysical mapping results. We find that terraces, with general bathymetric expressions of about 1 m and lateral extents of sometimes >100 m, are widespread in the surveyed areas of the Baltic Sea and are consistently formed in glacial clay. Semicircular depressions, however, are only found in a limited part of a surveyed area east of the island of Askö, southern Stockholm archipelago. While submarine terraces can be produced by several processes, we interpret our results to be in support of the basic hypothesis of terrace formation initially proposed in the 1990s; i.e. groundwater flows through siltier, more permeable layers in glacial clay to discharge at the sea floor, leading to the formation of a sharp terrace when the clay layers above seepage zones are undermined enough to collapse. By linking the terraces to a specific geologic setting, our study further refines the formation hypothesis and thereby forms the foundation for a future assessment of SGD in the Baltic Sea that may use marine geological mapping as a starting point. We propose that SGD through the submarine sea floor terraces is plausible and could be intermittent and linked to periods of higher groundwater levels, implying that to quantify the contribution of freshwater to the Baltic Sea through this potential mechanism, more complex hydrogeological studies are required.

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

Cited by 31 publications

References 66 publications

Nutrient dynamics in submarine groundwater discharge through a coral reef (western Lombok, Indonesia)

Nutrient dynamics in submarine groundwater discharge through a coral reef (western Lombok, Indonesia)

Geological and groundwater flow model of a submarine groundwater discharge site at Hanko (Finland), northern Baltic Sea

Potential links between Baltic Sea submarine terraces and groundwater seeping

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