Pockmarks in the Witch Ground Basin, central North Sea

Böttner, Christoph, Berndt, Christian, Reinardy, Benedict T.I., Geersen, Jacob, Karstens, Jens, Bull, Jonathan M., Callow, Ben J., Lichtschlag, Anna, Schmidt, Mark, Elger, Judith, Schramm, Bettina and Haeckel, Matthias (2019) Pockmarks in the Witch Ground Basin, central North Sea Geochemistry, Geophysics, Geosystems . DOI 10.1029/2018GC008068.

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Marine sediments host large amounts of methane (CH4), which is a potent greenhouse gas. Quantitative estimates for methane release from marine sediments are scarce, and a poorly constrained temporal variability leads to large uncertainties in methane emission scenarios. Here, we use 2D and 3D seismic reflection, multibeam bathymetric, geochemical and sedimentological data to (I) map and describe pockmarks in the Witch Ground Basin (central North Sea), (II) characterize associated sedimentological and fluid migration structures, and (III) analyze the related methane release. More than 1500 pockmarks of two distinct morphological classes spread over an area of 225 km2. The two classes form independently from another and are corresponding to at least two different sources of fluids. Class 1 pockmarks are large in size (> 6 m deep, > 250 m long, and > 75 m wide), show active venting, and are located above vertical fluid conduits that hydraulically connect the seafloor with deep methane sources. Class 2 pockmarks, which comprise 99.5 % of all pockmarks, are smaller (0.9‐3.1 m deep, 26‐140 m long, and 14‐57 m wide) and are limited to the soft, fine‐grained sediments of the Witch Ground Formation and possibly sourced by compaction‐related dewatering. Buried pockmarks within the Witch Ground Formation document distinct phases of pockmark formation, likely triggered by external forces related to environmental changes after deglaciation. Thus, greenhouse gas emissions from pockmark fields cannot be based on pockmark numbers and present‐day fluxes but require an analysis of the pockmark forming processes through geological time.

Document Type: Article
Keywords: Hydrocarbon, Seepage, Fluid flow, Glaciology, Quaternary Geology, Sedimentology
Research affiliation: NOC
OceanRep > GEOMAR > FB2 Marine Biogeochemistry > FB2-MG Marine Geosystems
OceanRep > GEOMAR > FB4 Dynamics of the Ocean Floor > FB4-GDY Marine Geodynamics
Refereed: Yes
DOI etc.: 10.1029/2018GC008068
ISSN: 1525-2027
Projects: STEMM-CCS
Date Deposited: 29 Mar 2019 13:23
Last Modified: 02 Apr 2019 15:47
URI: http://eprints.uni-kiel.de/id/eprint/46244

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