Passive acoustic monitoring for seabed bubble flows: Case of shallow methane seeps at Laspi Bay (Black Sea).

This article focuses on quantifying the seasonal and daily variability of methane gas release from a natural shallow thermocatalytic methane seep in Laspi Bay, Black Sea. Using an adaptive single bubble identification technique applied to passive acoustic data, the study determined that gas is emitted predominantly as clusters of single bubbles with an average radius of 0.4 cm, consistent with underwater video observations and Minnaert's equation. The estimated bubble gas flow rate ranged from 26 to 37 liters per day, with emission periodicities showing similarity across daily and interseasonal scales. Hydrostatic pressure fluctuations caused by sea swell influenced gas flow variability, while continuous hydrological measurements indicated no significant environmental impacts such as hypoxia or freshwater inflow at the seep site. The research highlights the suitability of passive acoustic monitoring for shallow seeps producing discrete bubbles and underscores the importance of shallow methane seeps as potential contributors to atmospheric methane emissions.