EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Complex eyed pockmarks associated with submarine groundwater discharge in gaseous muddy sediments, Eckernförde Bay, SW Baltic Sea

Jasper Hoffmann1, Jens Schneider von Deimling2, Jan Schröder2, Mark Schmidt3, Philipp Held2, Jan Scholten2, Gareth Crutchley3, and Andrew Gorman1
Jasper Hoffmann et al.
  • 1University of Otago, Geology, Dunedin, New Zealand (
  • 2University of Kiel, Institute of Geosciences, Otto-Hahn-Platz 1, 24118 Kiel, Germany
  • 3GEOMAR – Helmholtz Centre for Ocean Research Kiel, Wischhofstraße 1-3, 24148 Kiel, Germany

Submarine groundwater discharge into coastal areas is a common global phenomenon and is rapidly gaining scientific interest due to its influence on marine biology and the coastal sedimentary environment, and it's potential as a future freshwater resource. We conducted an integrated study of hydroacoustic surveys combined with geochemical porewater and water column investigations at a well-known freshwater seep site in Eckernförde Bay (Germany).

The location and distribution of pockmarks in this area have been the focus of many studies since their discovery in 1966 including numerous investigations of their geochemical, geological and geophysical behavior. Despite several intense and extensive research campaigns (e.g. Sub-GATE/CBBL) their internal morphology and structure presented in this study were poorly constrained to date. With recent advances in shallow high-frequency multibeam echosounder methods combined with highly accurately positioned sediment cores, we can provide new insights on the influence of shallow gas and freshwater on the formation and internal morphology of the pockmarks. We show that high-frequency multibeam data can be used to detect free shallow gas in areas of enhanced freshwater advection in muddy sediments. Intra-pockmarks, forming due to ascending gas and freshwater, pose a new form of ‘eyed’ pockmarks revealed by their acoustic backscatter response. Our data suggest that in muddy sediments morphological lows combined with a strong multibeam backscatter signal can be indicative of free shallow gas and the subsequent advection of freshwater.

How to cite: Hoffmann, J., Schneider von Deimling, J., Schröder, J., Schmidt, M., Held, P., Scholten, J., Crutchley, G., and Gorman, A.: Complex eyed pockmarks associated with submarine groundwater discharge in gaseous muddy sediments, Eckernförde Bay, SW Baltic Sea, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12332,, 2020


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