Circum-Arctic Patterns of Proxy-Derived Methane Release from Shelf Sediments

Enhanced methane cycling has been observed in various regions of the Arctic Ocean. Particularly, hotspots of high seawater methane concentrations in the surface waters of the Laptev and East Siberian seas highlight the risk of this methane to serve as an atmospheric source and further exacerbate climate warming. While seawater methane observations display the general distribution patterns within this region, the measurements are often compromised by the timing of expeditions and the frequent storm ventilation of the water column in these remote and shallow regions. Consequently, there is a need for an assessment of “long-term” methane cycling to better assess the geospatial patterns of methane cycling in the Arctic Ocean. Complementary tools such as compound-specific isotope analysis (CSIA) of hopanoid biomarkers has been suggested as a proxy to trace such regions of enhanced methane cycling. To investigate the long-term methane cycling over recent years in these areas, we quantified tracers of aerobic methane oxidation (C₃₀ hopanoids; n=154) in surface sediments and, in a subset, their stable isotope compositions across the circum-Arctic shelf seas. The highest hopanoid concentrations were observed in the Laptev, East Siberian Seas and the Kara Sea together with methane indicating isotope compositions. Additionally, high hopanoid concentrations were widely accompanied by elevated concentrations of methane in the overlying seawater. However, local hotspots of elevated methane concentrations were also present in the Herald Canyon, Beaufort Sea, and in south-western Svalbard, yet C₃₀ hopanoids in these regions did not corroborate the abundance of long-term enhanced methane cycling. Taken together, we display the first circum-Arctic assessment of seawater methane cycling through time-integrated measurements, highlighting regions and hotspots of enhanced methane cycling.