Thermal Characterization of Pockmarks Across Vestnesa and Svyatogor Ridges, Offshore Svalbard

The Svalbard margin represents one of the northernmost gas hydrate provinces worldwide. Vestnesa Ridge (VR) and Svyatogor Ridge (SR) west of Svalbard are two prominent sediment drifts showing abundant pockmarks and sites of seismic chimney structures. Some of these sites at VR are associated with active gas venting and were the focus of drilling and coring with the seafloor‐deployed MARUM‐MeBo70 rig. Understanding the nature of fluid migration and gas hydrate distribution requires (among other parameters) knowledge of the thermal regime and in situ gas and pore fluid composition. In situ temperature data were obtained downhole at a reference site at VR defining a geothermal gradient of ~78 mK m−1 (heat flow ~95 mW m−2). Additional heat probe data were obtained to describe the thermal regime of the pockmarks. The highest heat flow values were systematically seen within pockmark depressions and were uncorrelated to gas venting occurrences. Heat flow within pockmarks is typically ~20 mW m−2 higher than outside pockmarks. Using the downhole temperature data and gas compositions from drilling we model the regional base of the gas hydrate stability zone (BGHSZ). Thermal modeling including topographic effects suggest a BGHSZ up to 40 m deeper than estimated from seismic data. Uncertainties in sediment properties (velocity and thermal conductivity) are only partially explaining the mismatch. Capillary effects due to small sediment grain sizes may shift the free gas occurrence above the equilibrium BGHSZ. Changes in gas composition or pore fluid salinity at greater depth may also explain the discrepancy in observed and modeled BGHSZ

Pliocene-Quaternary mass wasting along the Ionian Calabrian margin, offshore southern Italy

The Ionian Calabrian margin, offshore southern Italy, is a tectonically active area, located above a subduction zone dominated by the rollback of the African plate. A variety of mass wasting features are known to occur along the inner continental slope, based on seafloor mapping during the Italian project MaGIC (Marine Geohazards Along the Italian Coasts). New high-resolution geophysical data are available from a wider area following two surveys, in 2014 of the German RV Meteor, which acquired multibeam bathymetry (50 m DTM) and Parasound sub-bottom profiles, and in 2015 of the Italian RV OGS Explora, which acquired Chirp sub-bottom and multichannel seismic reflection profiles. Here we integrate these data with existing geophysical datasets and published exploration wells to map submarine slope failures and mass wasting deposits within the Pliocene-Quaternary succession. The results show that features of mass failures are widespread along the steep (higher than 10\ub0) slopes of the Ionian margin south of Calabria and within the intra-slope basins of the margin east of Calabria. Seafloor features range from small-scale features (hundreds of meters in extent), mainly located on the canyon headwalls and sidewalls, to larger slides ( up to 10 km in extent) on open slopes. Subsurface profiles across open slopes and intra-slope basins provide evidence of repeated failures, particularly in the upper Quaternary. The stratigraphic distribution of failures suggests that widespread mass wasting features occur above an unconformity tentatively dated to the Middle Pleistocene (<1 Ma). This unconformity also provides a lower bound for the onset of canyon formation. We infer that the onset of both mass wasting and canyon formation could be a response to the rapid km-scale differential uplift of Calabria over last 1 Ma, which has driven a seaward tilting of the Ionian Calabrian margin

Quantifying in-situ gas hydrates at active seep sites in the eastern

www.biogeosciences.net/8/3555/2011

Methanhydrate in arktischen Sedimenten – Einfluss auf Klima und Stabilität der Kontinentalränder

Methane hydrates in marine sediments – Impact on climate and stability of continental slopes: The Arctic Ocean increasingly gets into the focus of methane hydrate research with respect to Global Warming. In the cold Arctic Ocean, hydrates are stable at relatively shallow water depths, and due to rapidly increasing water temperatures this region is considered to become a major source of atmospheric methane in the near future. But many factors, which are essential to make solid predictions about the fate and consequences of hydrate-related methane in the Arctic, still remain unclear. Uncertainties range from the size of the Arctic methane hydrate inventory to the efficiency of microbes to consume methane that is liberated in sediments and migrating through the water column. A potential collateral impact of massive gas hydrate destabilization could be failures of Arctic continental slopes with resulting mass wasting and tsunami formation. Although the correlation between hydrates and mass wasting are still a matter of debate, historic events have been identified and their causes are part of ongoing research. This book chapter will provide an overview of most recent research and discussions about Arctic gas hydrates and its fate in the light of Global Warming