Seepage in Isfjorden and its tributary fjords, West Spitsbergen

Abstract

This study analyses pockmark morphology and their spatial distribution in Isfjorden relative to seabed morphology, bedrock geology, fault systems, glacial landforms and processes using multibeam bathymetric data. It provides insight into the possible mechanisms of pockmark formation, high density pockmark field evolution, and fluid migration pathways. A total of 1304 pockmarks occur in the Isfjorden at water depths of 40 to 320 m, varying from circular to elongate in plan-view. Their diameter ranges from 14 to 265 m and their depths from 1 to 11 m. Elongate pockmarks are dominant in the Isfjordbanken and outer Isfjorden where the seafloor is influenced by the West Spitsbergen Current. The West Spitsbergen fold-and-thrust belt and other fault systems subcropping at the Isfjorden seafloor correlate spatially with the high density pockmark zones. The pockmarks are preferentially located on the marine sediments draping the bedrock of Isfjorden fjord system. They are most abundant in the areas underlain by Jurassic-Cretaceous and the Triassic-Lower Jurassic bedrock. Pockmarks found ahead of submarine slope failures may have formed due to dewatering of soft sediments as a result of rapid increase of overpressure caused by deposition of glacigenic debris lobes. Fault conduits, potential source rock and thin postglacial sediment layers are found to be crucial for the formation of pockmarks. Modeling results of the near-shore subsea permafrost and potential gas hydrate stability zone imply thawing permafrost and gas hydrate dissociation as additional possible mechanisms for pockmark formation in Isfjorden.

Postglacial response of Arctic Ocean gas hydrates to climatic amelioration

“…Furthermore, across the East Greenland shelf, δ 13 C records in benthic and planktonic foraminifera indicate at least three methane release episodes since deglaciation related to dissociating hydrates (53). It is also likely that many GHPs that reside outside of the present-day GHSZ have collapsed, forming large depressions, a phenomenon that has been widely reported in previously glaciated trough systems in the Arctic (13,14,54).…”

Geological Controls on Fluid Flow and Gas Hydrate Pingo Development on the Barents Sea Margin

“…The conjunction of geologically controlled methane flow, stable gas hydrates, and deformable superficial sediments is a rare combination across the Barents Sea shelf, which allows for formation of gas hydrate pingos. Other known seep sites at similar physiographic position typically occur within glacial tills (Roy et al, ), or lithified rocks (Andreassen et al, ) less prone to seabed heaving.…”

Ice-sheet-driven methane storage and release in the Arctic

“…We collate over 1,000 pockmarks and active gas flares across the shallow West Spitsbergen shelf and fjord environments ( Fig. 3 ) 14 23 38 . Gas from deeper hydrocarbon sources is likely to migrate along the tectonic lineaments.…”

“…Alternatively, release from thawing relic permafrost also should be considered 8 . However, 546 of 1,304 individual pockmarks studied in Isfjorden are confined to thrust faults, indicating focused fluid flow migration 38 . The present-day gas discharge across the shelf west of PKF is coincident with the exposure point of subglacial GHSZ modelled here ( Figs 1 and 2 ).…”