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Pockmarks in the inner Oslofjord, Norway

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Abstract

Multibeam bathymetric surveys of the Inner Oslofjord, Norway have revealed a high density of pockmarks in the 179-km2 inner fjord area, which contains over 500 pockmarks of varying size, typically 20–50 m in diameter and 2–10 m deep. These pockmarks have been investigated with a variety of techniques, including acoustic subbottom profiling, sedimentological and geochemical analyses of cores, remotely operated vehicle observation, and morphometry. Both the distribution and shapes of the pockmarks suggest that they are related to structures in the bedrock underlying relatively thin (<50 m) unconsolidated glacial and postglacial sediments. The data provide no direct indication of a particular mode of pockmark formation, but release of large amounts of biogenic, shallow methane seems unlikely. Several lines of evidence point to a continuous process of pockmark formation followed by inactivity, with some pockmarks recently active whereas others have been inactive for a considerable time. Some pockmarks are characterised by coarse sediment in their centres. The density, variety and easy access make this pockmark field an ideal model area for pockmark research.

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Authors and Affiliations

  1. Physics of Geological Processes, University of Oslo, P.O. Box 1048, Blindern, 0316, Oslo, Norway

    Karen E. Webb & Øyvind Hammer

  2. Norwegian Geological Survey, 7491, Trondheim, Norway

    Aivo Lepland

  3. Institute of Biology, University of Oslo, Oslo, Norway

    John S. Gray

Authors
  1. Karen E. Webb
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  2. Øyvind Hammer
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  3. Aivo Lepland
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  4. John S. Gray
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Correspondence to Karen E. Webb.

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John S. Gray is deceased.

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Webb, K.E., Hammer, Ø., Lepland, A. et al. Pockmarks in the inner Oslofjord, Norway. Geo-Mar Lett 29, 111–124 (2009). https://doi.org/10.1007/s00367-008-0127-1

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  • DOI: https://doi.org/10.1007/s00367-008-0127-1

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