Studying Diurnal Dynamics of Vertical Methane Distribution in the Black Sea Aerobic Zone Combined with Acoustic Research of the Sound-Scattering Layers

Purpose. The purpose of the study is to assess the diurnal dynamics of CH4 vertical distribution in the aerobic zone of the Black Sea at the stations of different depths joint with surveying the sound scattering layers (SSL).Methods and Results. The surveys were performed in the 113th cruise of the R/V Professor Vodyanitsky (June, 2020) in the upper 100-m layer at the deep-water station (1570 m) in the northeastern Black Sea, and at the shallow-water station (39 m) in the Yalta Bay. The differences in vertical distribution of the CH4 concentration in the seawater in these areas were found. Diurnal range of the CH4 concentrations in the surface water layer (0-1 m) was 0.8-16 nmol/l and 0.2-7 nmol/l for the shallow and deep-water areas, respectively. Shown was the fluxes' high variability at the water - atmosphere boundary in course of a day, namely, from the atmospheric CH4 inflow to the seawater up to the CH4 emission (up to 3 mu mol/m(2)day) to the atmosphere.Conclusions. The maximum CH4 fluxes to the atmosphere recorded at both stations were observed at night. It was shown that the atmospheric CH4 emission to seawater was not a significant factor in the CH4 redistribution in a water column since the calculated values of the atmosphere - seawater specific daily CH4 flux constituted the fractions of a percent of its store in the water column. Diurnal dynamics of the vertical CH4 distribution and SSL in the aerobic layer of the deep-water station was revealed to be of a similar pattern. Against high variability of the data for the individual time ranges, obtained were significant determination coefficients between the CH4 concentration and the sound-scattering coefficient of layer ml' as a characteristic of the biomass amount.