Transfer of free methane by gas bubble streams from anaerobic to aerobic waters of the Black Sea

“Breath of earth” in the form of methane gas bubble streams from a seabed (methane seeps, bubble emanations) is a planetary phenomenon that was noticed only at the end of the XX century. The study of this phenomenon, being an important link in processes of lithosphere, hydrosphere, atmosphere, and biosphere interaction, is relevant to date. In this work, methane fluxes were determined in the known area of intense methane occurrences of biogenic nature, geographically tied to Dnieper River paleochannel in the northwest of the Black Sea. Bubbling (free) methane flux from anaerobic to aerobic waters in the active methane seeps area of Dnieper River paleochannel in the depth range of 140–725 m is estimated averagely as 1.2·10³ m³·km−2·year−1 (STP), or 2.8 % of bubbling methane emitted from a seabed. The value of the investigated flux was 4.2 % of the specific flux of bubbling methane to a water column on shelf depths (less than 140 m) in the same area. Methane flux estimate, obtained in this work, seems to be a significant environmental factor in conditions of strong stratification of Black Sea waters, where methane transfer by gas bubble streams is the main mechanism for introducing deep-water methane into biogeochemical cycles and carbon transformation processes of Black Sea aerobic zone.