Methane Fluid Discharge Measurements by the Trap Method in Laspi Bay (Black Sea)

Abstract

Measurements of the methane fluid discharge from bottom sediments and daily monitoring of the main hydrophysical parameters near the site of the bubble gas discharge (seeps) in Laspi Bay have been carried out. Fluid flow values varied by an order of magnitude (1.4–74.3 mmol/(m${}^{2}$ day)) at points separated by a distance of no more than 10 m. It is assumed that denser carbonate deposits at the seepage site can localize gas flows, thus reducing the volume of fluid discharge. It is shown that the specific fluid discharge in Laspi Bay is comparable with the flow from point seeps; the maximum fluid flow is only 3.5 times lower compared to the minimum recorded seep flow. Changes in hydrological parameters above the gas release point are significantly influenced by waves. The maximum change in salinity during measurements was 0.08%o, which indicates that there is no high-rate freshwater submarine discharge, which often accompanies seeps. Episodes of an abrupt decrease in oxygen content with an amplitude of 0.5 mg/L at night, which are not related to changes in water temperature and meteorological conditions, may be caused by the seepage of hydrogen sulfide in the bubble and fluid gases.