Occurrence of active gas hydrate mounds in the southwestern slope of the Chukchi Plateau, Arctic Ocean

This study documents the discovery of mound morphologies containing gas hydrate and methane-derived authigenic carbonate (MDAC) in the southwestern slope of the Chukchi Plateau, during the IBRV Araon expeditions in 2016 and 2018. A multibeam bathymetric surveying was the basis for a new and detailed rendering around the mounds. Sub-bottom profiles and site-targeted gravity cores were also collected across these mounds which were located at water depths between 780 m and 580 m. Mounds are characterized by a circular plan shape of hundreds of meters in width and tens of meters in height. Below the mounds, gas accumulation in the sediment produces acoustic blanking in seismic data. MDACs are identified along the core collected from the top of a mound structure, indicating past methane oxidation processes. Gas hydrate has also been observed at the bottom of the core. Reverse geothermal gradients of the mound support the idea of active presentday seepage. We argue that the prolonged seepage activity of methane-rich fluid, possibly related to the formation of the rifted North Chukchi Basin, has led to the formation of the gas hydrate mounds, named hereafter the Araon Mounds, in the vicinity of the basin margin.