Dissolved Methane in Coastal Waters of the Northeastern Black Sea

Abstract

As the largest methane reservoir in the world, the Black Sea is characterized by significant variability in its dissolved methane distribution patterns. Aerobic waters in the coastal regions are influenced by various factors governing the biogeochemical processes in the water column; however, their impact on the distribution pattern of dissolved methane is not always well studied, especially in the shallow areas of the northeastern Black Sea, which have hitherto not been thoroughly covered by observations. Here, we consider the measurements of methane content in several regions of the northeastern Black Sea carried out from 2013–2017 with large and detailed spatial coverage in order to identify the key factors determining the dissolved methane pattern in each region of the study area. The CH4 pattern in the region of Sochi is dominated by the impact of river flow. The increased methane saturation in surface waters of the southeastern Crimean shelf (up to 40 nM) is caused by the influence of the Azov Sea outflow. The waters of the Feodosia Bay and to the south of it are mainly characterized by an increase in methane content towards the bottom (up to 100 nM), which is associated with water–sediment interactions and gas emission from the bottom.