Methane Chemistry in the Ice Covered Arctic Ocean from Winter to Summer Time

Methane is a powerful greenhouse gas. In the ocean, it originates from gas bearing sediments, can be produced by microorganisms in aerobic water column or released during sea ice formation in polar regions. Sea ice in the Arctic Ocean can act as a barrier for the oceanic methane to be released to the atmosphere. Thus, beneath the sea ice cover, methane can accumulate during winter time and emit in large volumes to the atmosphere when openings occur in the ice cover or when the ice starts melting. In this study we show unique data on dissolved methane concentrations in seawater and sea ice, collected during N-ICE2015 campaign that lasted from January to June 2015, with sampling from ice floes drifting in the Nansen basin, between 80 and 83°N. We found seawater methane concentrations generally 3 times higher than previously reported for the central Arctic Ocean. Elevated methane concentrations in bottom waters were only found in the area of the shallower Yermak plateau margin, where methane can potentially originate from sediments. Highest methane concentrations were found in surface waters in January north of 83° N beneath sea ice cover, showing that methane accumulates under sea ice cover in winter time.