DISTRIBUTION OF METHANE FLUXES AT WATER–ATMOSPHERE BOUNDARY WITHIN THE PETER THE GREAT GULF AND ADJACENT SLOPE IN AUTUMN SEASON

We present the research results based on experimental data obtained during the expedition of the R/V Akademik Oparin to the Peter the Great Gulf (cruise No. 54, October 2017). Methane fluxes at the water–atmosphere boundary have been calculated for each sampling point using the measured concentrations of dissolved methane in the seawater surface layer and methane in the near-surface atmosphere, temperature, salinity, and wind speed. In all cases, the concentrations of dissolved methane in the seawater surface layer exceed the values in equilibrium with the atmosphere. Methane fluxes from the sea surface vary from 1 to 981 mol/km2·day with an average value of 7.1 ± 4.5 mol/km2·day. The most intense emission has been observed near the mouth of the Tumen River. Gas-saturated sediments with inclusions of subaqueous authigenic minerals have been discovered on the continental slope. The analysis of geological and hydrochemical information has revealed areas of methane influx from bottom sediments. The application of models of current fields and advective impurity transport during the expedition provides the opportunity to determine the prospective zones with increased concentrations of dissolved methane and also to identify for the first time an underwater source of groundwater discharge (presumably the element of the Tumen paleochannel), which affects the distribution of dissolved methane concentrations and salinity in the subsurface waters of the gulf. Comparison of calculated and experimental data on methane transport has shown their spatial coincidence. The calculations have established that tidal currents determine not only the local maxima of methane concentrations and fluxes from the sea surface in certain areas of the gulf but also its transport to the pelagic waters in the western part of the Central Basin of the Sea of Japan.