Atmospheric Methane over the Arctic Ocean: Thermal IR Satellite and Ship- Based Observations Leonid Yurganov Joint Center for Earth Systems Technology, University of Maryland Baltimore County, 1000 Hilltop Cr., 21250, Baltimore, MD. E-mail: Yurganov@umbc.edu Ira Leifer Marine Science Institute, University of California, Santa Barbara, Santa Barbara, CA Xiaozhen Xiong NOAA Center for Satellite Applications and Research, College Park, MD Recent warming of the Arctic stimulated speculations about dissociation of methane hydrates in the Arctic seabed and a new climatic positive feedback. Here, for the first time, methane low tropospheric satellite retrievals over the Arctic from two instruments: AIRS (Atmospheric IR Sounder) and IASI (Infrared Atmospheric Sounding Interferometer) were analyzed. Analyzed are data for areas over open water with high values of the vertical thermal contrast (ThC, defined here as the temperature difference between the surface and altitude of 4 km); they have been found to be reliable. The seasonal cycles of the data well correlate with the cycles measured at the NOAA network on the surface. Long-term increase of methane over the Arctic has been detected by both instruments in accordance with surface data. Maximum anomaly of methane concentration measured by IASI has been found for Baffin Bay and northern parts of Barents and Kara Seas in November-December, 2013. Surface CH 4 data were collected on the Russian Research Vessel Akademik Fedorov from Norway to the Laptev Sea and back. Numerous CH 4 anomalies of 30 to 100 ppb were observed above the Barents and Laptev Seas, particularly for water depths 300-500 m, i.e., where methane hydrate is in stable state. 1. Introduction. Atmospheric methane (CH 4 ) is the second-most important anthropogenic greenhouse gas after carbon dioxide (Forster et al. 2007) on a century timescale; however, on a decadal time scale - comparable to its atmospheric lifetime, it is more important than carbon dioxide to the atmospheric radiative balance (Solomon et al. 2007). Despite likely increasing future natural emissions due to global warming feedbacks (Rigby et al. 2008) and anthropogenic activities (Wunch et al. 2009; Kirscheke et al. 2013), large uncertainties exist in current estimates from many sources, both marine and terrestrial, with greater uncertainty in future trends. Marine methane garners greater concern due to feedback from rapidly warming Arctic Oceans, which has higher heat capacity than similarly warming air. Also significant is the vast extent of submerged permafrost, primarily in the Russian Arctic, which covers 2.1 x 10 6 km 2 (Shakhova et al. 2010), many times larger than Siberian terrestrial wetlands. These permafrost were submerged under insulating layers of sediments by rising and particularly,