Аннотация:From 2019 to 2021, integrated studies of new shallow-water methane bubble gas seeps were carried out in thecoastal zone near Cape Fiolent (Southwest Coast of Crimea). The studies included determination of thehydrocarbon and isotope composition of bubble gas, measurement of the methane and nutrient concentra-tion in the water in the areas of gas seeps, estimation of the value of bubble f lows, and measurement of thehydrophysical parameters over the seep sites compared to background areas. A seasonal type of Cape Fiolentmethane seps was noted, and the durations of its active gas emission phases differed in different years. Theincreased pore water silica concentration at the seep sites and their localization in the vicinity of freshwaterslope springs may indicate its association with submarine freshwater discharge in the area. However, no sig-nificant desalination of either pore water or the bottom water layer above the siphons was recorded. Dissolvedmethane concentrations in pore water at seep sites were two orders of magnitude higher compared to thebackground areas, reaching 448 μmol/L. High values were also obtained for surface water directly above thebubble gas emission points (maximum 353 nmol/L). Multihour monitoring of the hydrophysical parametersabove the active seeps showed a decrease in dissolved oxygen compared to the background sites. The maxi-mum difference in O2 concentrations was 3 mg/L. The carbon isotope composition of bubble gas methaneδ13C-CH4 (–62.84 to –38.27‰) and carbon dioxide δ13C-CO2 (–16.83 to –10.17‰) corresponded to a mix-ture of isotopically heavy gas and near-surface isotopically light gas of microbial origin. The question remainsopen: what are the reasons for the change in the summer active and cold season passive gas emission phases?
