Inter-Comparison of the Spatial Distribution of Methane in the Water Column From Seafloor Emissions at Two Sites in the Western Black Sea Using a Multi-Technique Approach

Understanding the dynamics and fate of methane (CH 4 ) release from oceanic seepages on margins shelves into water column, quantifying budget its total discharge at different spatial temporal scales, currently represents a major scientific undertaking. Previous works escaping seafloor underlined challenge in both, estimating concentration distribution identifying gradients. In April 2019, Envri Methane Cruise has been conducted onboard R/V Mare Nigrum Western Black Sea to investigate two shallow seep sites ∼120 m ∼55 depth. Dissolved CH measurements were with continuous in-situ sensors: membrane inlet laser spectrometer (MILS) commercial sensor (METS) Franatech GmbH. Additionally, discrete samples collected CTD-Rosette deployment standard laboratory analysis was performed by gas chromatography coupled either purge-and-trap or headspace techniques. The resulting vertical profiles (from both situ sample measurements) dissolved follow an expected exponential dissolution function sites. At deeper site, high concentrations are detected up ∼45 seabed, while sea surface equilibrium atmospheric concentration. shallower four times higher than value. Our results seem support that may be transferred atmosphere, depending local depths. accordance previous studies, water, more likely is sea-to-atmosphere transport methane. High resolution data also this hypothesis. Well localized enriched waters found near sites, but their locations appear decoupled ones seepages. This highlights need better understanding processes responsible for transformation especially stratified masses like Sea.