Description: Recent results include the publication of drilling results from the central Laptev Sea, carried out by a consortium of partners from t. Petersburg (Arctic and Antarctic Research Institute), Yakutsk (Mel’nikov Permafrost Institute), the Universities of Hamburg and Potsdam, and two Potsdam research institutes (Alfred Wegener Institute, Geoforschungszentrum). We were able to measure methane concentrations within thawing but still frozen submarine permafrost. Based on approximate duration of inundation, it was possible to estimate rates of methane release (Overduin et al. 2015). Surprisingly, however, methane from permafrost did not migrate to the sea bed, but was oxidized by bacteria within the unfrozen sediment on top of the frozen permafrost (see Nature Climate Change comment on our work: Thornton and Crill, 2015). In further work, results of the innovative passive seismic method for detection of frozen submarine permafrost were published, detailing the method and first results. Modelling demonstrated that the observed signals correlate with the depth of unfrozen sediment overlying the ice-bonded permafrost (Overduin et al. 2015). This method is promising, since it has no impact on the seabed or biota, and can be operated without disturbing marine mammals. The next steps are to develop the instruments for operation over larger regions and for a wider range of permafrost depths. Real time operation (as opposed to deployment with autonomous logging) promises to speed up measurement, an important consideration for the large area of the Siberian shelf. Part of 2015 was occupied with proposal-writing to obtain support for this instrument development and testing in Siberia; the review process is on-going. Modelling efforts continue, together with a new partner, Climate Analytics GmbH in Berlin. A functioning model of submarine permafrost has been developed and is currently being tested. The goal is to develop a circum-arctic understanding of permafrost development over glacial-interglacial cycles. The first stage of modelling is expected to be completed by the end of the year, with results to be publicized at next year’s 11th International Conference on Permafrost in Potsdam, Germany. References Overduin, P. P., C. Haberland, T. Ryberg, F. Kneier, T. Jacobi, M. N. Grigoriev, and M. Ohrnberger (2015), Submarine permafrost depth from ambient seismic noise, Geophys. Res. Lett., 42, doi:10.1002/2015GL065409. Overduin, P. P., Liebner, S. , Knoblauch, C. , Günther, F. , Wetterich, S. , Schirrmeister, L. , Hubberten, H. W. and Grigoriev, M. N. (2015), Methane oxidation following submarine permafrost degradation: Measurements from a central Laptev Sea shelf borehole, Journal of Geophysical Research: Biogeosciences, 120 (5), pp. 965-978, doi:10.1002/2014JG002862. Thornton, B. F., and Crill, P. (2015), Arctic Permafrost: Microbial lid on subsea methane, Nature Climate Change, 5: 723-724.

Description: Ice-rich permafrost coasts in the Arctic are susceptible to a variety of changing environmental factors, all of which currently point to increasing coastal erosion rates and mass fluxes of sediment and carbon to the shallow arctic shelf seas. Coastal erosion and flooding inundate terrestrial permafrost with seawater and create submarine permafrost. Permafrost begins to warm under marine conditions, which can destabilize the sea floor and may release greenhouse gases. The rate and spatial distribution of subsea permafrost degradation in the Laptev, East Siberian and Chukchi seas, which together comprise more than half of the Arctic Ocean continental shelf, remain poorly explored. We report on the transition of terrestrial to subsea permafrost at four coastal sites in the Laptev Sea: Cape Mamontov Klyk in the western Laptev Sea, and Buor Khaya Peninsula, Muostakh Island and the Bykovsky Peninsula in the central Laptev Sea. We use coastal erosion rates from about the last 70 years to estimate the period of inundation at these sites. Combined with direct (drilling and temperature) and indirect (geophysical) observations of thaw depths of ice-bonded permafrost, we estimate recent degradation rates of permafrost over the past centuries. Based on these observations, the unfrozen sediment layer overlying ice-bonded permafrost increased from less than a meter at the shoreline to over 30 m below seabed with increasing distance from the shoreline at our study sites, with high spatial variability between and within sites. Observed temperatures of the sediment ranged from -5 °C to positive temperatures. In coastal sediments, it is difficult to establish an age-depth model, making corroboration of estimated degradation rates a challenge. Nonetheless, as the thickness of the unfrozen sediment layer increases over time, the vertical thermal and salt concentration gradients decrease, slowing the downward heat and mass fluxes responsible for degradation. High sedimentation rates and ice contents probably stabilize subsea permafrost. We suggest that permafrost degradation relevant to gas flow is likely to have occurred where permafrost warmed prior to inundation.

Description: Thawing submarine permafrost is a source of methane to the subsurface biosphere. Methane oxidation in submarine permafrost sediments has been proposed, but the responsible microorganisms remain uncharacterized. We analyzed archaeal communities and identified distinct anaerobic methanotrophic assemblages of marine and terrestrial origin (ANME-2a/b, ANME-2d) both in frozen and completely thawed submarine permafrost sediments. Besides archaea potentially involved in anaerobic oxidation of methane (AOM) we found a large diversity of archaea mainly belonging to Bathyarchaeota, Thaumarchaeota, and Euryarchaeota. Methane concentrations and δ13C-methane signatures distinguish horizons of potential AOM coupled either to sulfate reduction in a sulfate-methane transition zone (SMTZ) or to the reduction of other electron acceptors, such as iron, manganese or nitrate. Analysis of functional marker genes (mcrA) and fluorescence in situ hybridization (FISH) corroborate potential activity of AOM communities in submarine permafrost sediments at low temperatures. Modeled potential AOM consumes 72–100% of submarine permafrost methane and up to 1.2 Tg of carbon per year for the total expected area of submarine permafrost. This is comparable with AOM habitats such as cold seeps. We thus propose that AOM is active where submarine permafrost thaws, which should be included in global methane budgets.