Fine-grained marine sediments along continental slopes and rises are saturated with gas rich fluids. The mechanisms of gas transport from the source toward the seafloor influence the sediment geomechanical properties as well as gas hydrate accumulations and seepage dynamics (e.g.,

Seafloor hydrocarbon seepage is a natural fluid release process that occurs worldwide on continental shelves, slopes, and in deep oceanic basins. The Vestnesa sedimentary ridge in the eastern Fram Strait hosts a deep-water gas hydrate system that became charged with hydrocarbons ∼2.7 Ma and has experienced episodic seepage along the entire ridge until a few thousand years ago, when seepage activity apparently ceased in the west but persisted in the east. Although it has been documented that faults and fractures play a key role in feeding the seeps with thermogenic gases, the mechanisms controlling seepage periodicity remain poorly understood. Here we integrate high-resolution P-cable 3D seismic and Chirp data to investigate the spatial and temporal evolution of high-resolution fractures and fluid flow features in the west of the Vestnesa Ridge. We characterize sediment deformation using a fracture density seismic attribute workflow revealing two highly deformed stratigraphic intervals and associated small-scale pockmarks (<20 m diameter). Chronostratigraphic constraints from the region show that these two highly deformed intervals are influenced by at least three major climatic and oceanic events during the last 1.2 million years: the Mid-Pleistocene Transition (∼1.25–0.7 Ma), the penultimate deglaciation (∼130 ka) and the last deglaciation (Heinrich Stadial 1: ∼16 ka). These periods of deformation appear associated with seismic anomalies potentially correlated with buried methane-derived authigenic carbonate and have been sensitive to shifts in the boundary of the free gas-gas hydrate interface. Our results show shifts (up to ∼30 m) in the depth of the base of the gas hydrate stability zone (GHSZ) associated with major changes in ocean bottom water temperatures. This ocean-driven effect on the base of the GHSZ since the Last Glacial Maximum coincides with the already highly deformed Mid-Pleistocene Transition sedimentary interval and likely enhanced deformation and gas leakage along the ridge. Our results have implications for understanding how glacial cycles impact fracture formation and associated seepage activity.

<p>The continent–ocean transition along the passive margin off western Svalbard is, in places, only a few kilometers away from the formerly glaciated continental shelf. Strong bottom currents in the Fram Strait have led to the deposition of several kilometers thick sedimentary ridges that extend from continental to oceanic crust all the way onto the flanks of the oblique-spreading Molloy and Knipovich mid-ocean ridges. The sedimentary ridges represent large contourite drifts and are characterized by faults that extend to the present-day seafloor. Generally, it is argued that gravitational forcing or flexure due to fast sedimentation and/or erosion is the main force leading to deformation of Quaternary sediments, and that horizontal forcing is negligible. However,  high resolution 2D and 3D seismic data along the western Svalbard margin reveal that sedimentary faults commonly propagate from the termination of rift-related faults in the oceanic crust, and are not always favorably oriented to accommodate gravitational collapse. We suggest that coupling between the slow-spreading oceanic crust and the sedimentary cover results in a transfer of stress and strain that influences near-surface sedimentary deformation. Deep crustal fluids are also transferred into the Quaternary succession utilizing faults as migration pathways. Such faults sustain shallow gas accumulations, wide-spread gas hydrate formation and cold seeps. Simultaneously, glacial isostatic rebound leads to additional lithospheric deformation and also exerts a control on fault kinematics and gas seepage. We discuss seismic examples of deep marine seepage systems and the potential implications of coupling between lithospheric deformation and sedimentation on the spatiotemporal evolution of seafloor seepage at Arctic margins.</p>