Vertical distributions of dissolved methane concentration in sediments of background areas of Lake Baikal

Abstract

For the first time, vertical distributions of dissolved methane concentrations in bottom sediments from background (undisturbed sedimentation) areas of the Southern, Middle and Northern basins of Lake Baikal down to subbottom depths of ~3 m obtained and analyzed. Methane concentration profiles at all stations share common features, characterized by low concentrations in the near-surface layers (≤1–2 µM) and a steady increase of methane with subbottom depth. The highest sedimentary methane concentrations were observed in the Middle basin, somewhat lower values in the Southern, and an order of magnitude lower concentrations in the Northern basin. The exponential decrease in methane concentrations toward the bottom–water interface to equally low values, regardless of its content within the sediment, indicates its significant oxidation and, consequently, minimal influence on methane concentrations in near-bottom water. The obtained results fill a gap in knowledge concerning the vertical distribution of dissolved methane in Lake Baikal sediments and are important for assessing the stability and functioning of hydrocarbon systems in a cold, and deep freshwater reservoir.