Geological features of methane vents in the East Siberian Sea, the Arctic Ocean

The Eastern Siberian Sea is known for the presence of subsurface permafrost and for emitting significant amounts of methane close to the coastline. The thawing of permafrost accelerates the release of methane and carbon dioxide, contributing to increased greenhouse gas concentrations in the atmosphere. In 2021 and 2023, a multidisciplinary survey aboard the Korean icebreaker Araon was conducted on the continental shelf of the East Siberian Sea. The survey area lies more than 500 km away from the nearest coastline and falls within international waters. During the survey, areas with high methane concentration were identified on the shallow continental shelf, at depths ranging from 50 to 70 meters, utilizing underway CH4 measurements. These zones extend in a northwest-southeast direction. Multiple surveys were conducted to pinpoint gas seepage zones and delineate subsurface structures. The EK80 scientific echosounder proved instrumental in locating the gas vents, as it displayed methane gas eruptions clearly, resembling pillars in the imaging. The shallow sedimentrary structure of the lower part of the gas vent, observed  by the SBP survey, revealed high-amplitude reflections at a shallow depth (~5 m) below the seafloor. At the gas expulsion sites, seismic profiles show numerous vertical faults within the shallow sedimentary layers and scatterings in the water column caused by the methane emission from the seafloor. Backscattered images from the side-scan sonar clearly depict gases emitting from the vents and moving upward in the water column. These gas vents were found to have about 10 meters in diameter.