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Fluid chemistry and shallow gas hydrate dynamics at active pockmarks of the Vestnesa Ridge, west Svalbard margin
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  • Wei-Li Hong,
  • Thomas Pape,
  • Christopher Schmidt,
  • Haoyi Yao,
  • Klaus Wallmann,
  • Andreia Plaza Faverola,
  • James William Buchanan Rae,
  • Aivo Lepland,
  • Stefan Bünz,
  • Gerhard Bohrmann
Wei-Li Hong
Geological Survey of Norway

Corresponding Author:wei-li.hong@geo.su.se

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Thomas Pape
MARUM - Center for Marine Environmental Sciences and Department of Geosciences, University of Bremen
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Christopher Schmidt
GEOMAR Helmholtz-Zentrum für Ozeanforschung Kiel
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Haoyi Yao
CAGE - Centre for Arctic Gas Hydrate, Environment and Climate, Department of Geosciences, UiT - The Arctic University of Norway
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Klaus Wallmann
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Andreia Plaza Faverola
UiT The Arctic University of Norway
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James William Buchanan Rae
University of St Andrews
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Aivo Lepland
Geological Survey of Norway
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Stefan Bünz
UiT Arctic University of Norway
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Gerhard Bohrmann
MARUM at University of Bremen
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Gas hydrate dynamics and the fluid flow systems from two active pockmarks along Vestnesa Ridge (offshore west Svalbard) were investigated through the pore fluid geochemistry obtained during the 2016 MARUM-MeBo 70 drilling cruise. Based on the pore water chloride concentration profiles from Lunde and Lomvi pockmarks, we estimated up to 47% pore space occupied by gas hydrate in the sediments shallower than 11.5 mbsf. These gas hydrates were formed during periods of gaseous methane seepage, but are now in a state of dynamic equilibrium sustained by a relatively low methane supply at present. We detect a saline formation pore fluid around nine meters below seafloor from one of the seepage sites in Lunde pockmark. This formation pore fluid has elevated dissolved chloride concentrations and B/Cl ratios, higher δO and δD isotopic signatures of water and lower δB signatures, which collectively hint to a high temperature modification of this fluid at great depths. By integrating our findings with the previous work from Vestnesa Ridge, we show that the variable fluid phases (gaseous vs. aqueous fluid) and migration pathways are controlled by the sediment properties, such as buried carbonate crusts, and the state of fluid reservoirs.