Spatial distribution and budget for submarine groundwater discharge in Eckernförde Bay (Western Baltic Sea)

Schlüter, Michael, Sauter, Eberhard J., Andersen, Claus E., Dahlgaard, Henning and Dando, Paul R. 2004 Spatial distribution and budget for submarine groundwater discharge in Eckernförde Bay (Western Baltic Sea). Limnology and Oceanography, 49 (1). 157-167.

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Submarine groundwater discharge (SGD) from subseafloor aquifers, through muddy sediments, was studied in Eckernförde Bay (western Baltic Sea). The fluid discharge was clearly traced by 222Rn enrichment in the water column and by the chloride profiles in pore water. At several sites, a considerable decrease in chloride, to levels less than 10% of bottom-water concentrations, was observed within the upper few centimeters of sediment. Studies at 196 sites revealed that >22% of the seafloor of the bay area was affected by freshwater admixture and active fluid venting. A maximal discharge rate of .9 L m−2 d−1 was computed by modeling pore water profiles. Based on pore water data, the freshwater flow from subseafloor aquifers to Eckernförde Bay was estimated to range from 4 x 106 to 57 × 106 m3 yr−1. Therefore, 0.3–4.1% of the water volume of the bay is replaced each year. Owing to negligible surface runoff by rivers, SGD is a significant pathway within the hydrological cycle of this coastal zone. High-resolution bathymetric data and side-scan sonar surveys of pockmarks, depressions up to 300 m long, were obtained by using an autonomous underwater vehicle. Steep edges, with depths increasing by more than 2 m within 8–10 m in lateral directions, equivalent to slopes with an angle of as much as 11°, were observed. The formation of pockmarks within muddy sediments is suggested to be caused by the interaction between sediment fluidization and bottom currents. Fluid discharge from glacial coastal sediments covered by mud deposits is probably a widespread, but easily overlooked, pathway affecting the cycle of methane and dissolved constituents to coastal waters of the Baltic Sea.

Item Type: Publication - Article
Subjects: Chemistry
Earth Sciences
Ecology and Environment
Marine Sciences
Divisions: Marine Biological Association of the UK > Other (MBA)
Depositing User: Professor Paul Dando
Date made live: 21 Dec 2021 10:30
Last Modified: 21 Dec 2021 10:30

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