Seismic evidence for shallow gas-escape features associated with a retreating gas hydrate zone offshore west Svalbard
Sarkar, Sudipta, Berndt, Christian, Minshull, Timothy A., Westbrook, Graham K., Klaeschen, Dirk, Masson, Douglas G., Chabert, Anne and Thatcher, Kate E. (2012) Seismic evidence for shallow gas-escape features associated with a retreating gas hydrate zone offshore west Svalbard. Journal of Geophysical Research, 117, (B09102), 1-18. (doi:10.1029/2011JB009126).
Active gas venting occurs on the uppermost continental slope off west Svalbard, close to and upslope from the present-day intersection of the base of methane hydrate stability (BMHS) with the seabed in about 400 m water depth in the inter-fan region between the Kongsfjorden and Isfjorden cross-shelf troughs. From an integrated analysis of high-resolution, two-dimensional, pre-stack migrated seismic reflection profiles and multibeam bathymetric data, we map out a bottom simulating reflector (BSR) in the inter-fan region and analyze the subsurface gas migration and accumulation. Gas seeps mostly occur in the zone from which the BMHS at the seabed has retreated over the recent past (1975–2008) as a consequence of a bottom water temperature rise of 1°C. The overall margin-parallel alignment of the gas seeps is not related to fault-controlled gas migration, as seismic evidence of faults is absent. There is no evidence for a BSR close to the gas flare region in the upper slope but numerous gas pockets exist directly below the predicted BMHS. While the contour following trend of the gas seeps could be a consequence of retreat of the landward limit of the BMHS and gas hydrate dissociation, the scattered distribution of seeps within the probable hydrate dissociation corridor and the occurrence of a cluster of seeps outside the predicted BMHS limit and near the shelf break indicate the role of lithological heterogeneity in focusing gas migration.
|Digital Object Identifier (DOI):||doi:10.1029/2011JB009126|
|Keywords:||bottom-water warming, bright spots, gas hydrates, gas seeps, glacimarine strata|
|Subjects:||G Geography. Anthropology. Recreation > GC Oceanography
Q Science > QE Geology
|Divisions:||Faculty of Natural and Environmental Sciences > Ocean and Earth Science > Geology & Geophysics
National Oceanography Centre (NERC) > Marine Geoscience
|Date Deposited:||06 Nov 2012 10:54|
|Last Modified:||31 Mar 2016 14:36|
Dynamics of gas hydrates in polar marine environments.
Funded by: NERC (NE/D005728/2)
Led by: Timothy Minshull
1 April 2008 to 31 January 2011
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