The seafloor of the Eastern Siberian Arctic Ocean holds significant, but as yet virtually unsurveyed, methane deposits. As part of an international collaborative effort to better understand the climate, cryosphere and carbon system of the Arctic (SWERUS-C3), we have been invited to use newly developed acoustic water-column imaging techniques to map the distribution (and to help quantify the flux) of methane gas seeps from the seafloor. Specifically, we hope to use the multibeam sonar onboard the Swedish Icebreaker ODEN to locate and characterize gas seeps in the water column and then apply a newly developed wideband transceiver to the split-beam echosounder onboard the ODEN to constrain the size and fate of gas bubbles rising to the surface. Together, these acoustic observations will help the SWERUS-C3 team understand the flux of methane from the seafloor into the water column and potentially into the atmosphere. If successful, these techniques will allow the mapping of the gas flux in the Arctic over scales never before possible. This proposal requests support for the participation of the UNH team on this expedition and for post-cruise work-up of the data. Among problems to be addressed by the SWERUS-C3 program are: (1) Quantification of methane release from subsea permafrost and the deep sea; (2) The fate of carbon in the shelf sea released from thawing coastal permafrost; (3) The magnitude of air/sea methane exchange; (4) The recent/post-glacial/paleoclimate sediment record of permafrost carbon releases, and; and (5) The longer-term history of Arctic sea ice and its impact on carbon fluxes. The UNH contribution will provide a means (using underway acoustic systems) to broadly map the location and character of gas seeping from the seafloor into the water column.