Methane anomalies, its flux on the sea–atmosphere interface and their relations to the geological structure of the South-Tatar sedimentary basin (Tatar Strait, the Sea of Japan)

The paper presents the effects of gasgeochemical survey in the upper layer and water column, as well as in bottom sediments in the Tatar Strait (the North of the Sea of Japan) in 2012, 2014, 2015 and 2017. The features of methane, hydrogen, and helium distribution in the water column and sediments of the Tatar Strait were identified. The elevated methane, hydrogen, and helium concentrations in the sediments and water column on the southwest shelf and slope of Sakhalin are possibly associated with seismo-tectonic activity, gas hydrates, the presence of centers and migration channels of these gases. Methane emission, concentrations of which exceeds the equilibrium with the atmospheric value in the surface layer (C* = 2.2–3.6 nmol/L), occurs within the whole water area of the South-Tatar Strait. The difference between the measured and equilibrium methane values (ΔC) was 1.1–112 nmol/L. The most intense methane fluxes on the water-atmosphere boundary reach up to 482 mol/(km2 × day) and are observed on the gas-containing southwest shelf and gas hydrate-containing slope of Sakhalin. The calculation model of the current fields and impurity transfer for the water area under study has shown that formation of increased methane emissions from the sea surface is located in areas with its possible vertical migration from lithospheric sources. The role of hydrodynamics in the formation of zones of increased methane emissions from the surface of water area is subordinate to geological factors. The prospects for prediction of hydrocarbon accumulations according to the data on methane flux from the surface of the shallow sea are described.