From 14 to 28 December 2017, in the central part of the Black Sea, within the exclusive economic zone of the Russian Federation, a joint interdepartmental comprehensive oceanological expedition was carried out on board the R/V «Professor Vodyanitsky». The main goal of the expedition was to study the characteristics of the hydrological, hydrochemical, hydro-optical and hydrobiological structure of the Black Sea waters during the winter, as well as to collect material for studying the sedimentation system of the sea, which allows assessing the particle fluxes in the water column, the rate of its sedimentation to the bottom and biogeochemical processes occurring in water and bottom sediments.
In 2016-2017, for the first time, nearly year-long measurements of the current velocities were carried out below the thermocline at a depth of 100 m and at a depth of 1700 m that was about 100 m above the seabed by using the mooring station in the deep central part of the Black Sea. Analysis of the new data set allowed us to uncover the followings. In the near-bottom layer, the significant flow velocities were recorded, reaching a peak magnitude of 0.13 m/s. Near the frequency of 110-6 Hz, in the transition region of the energy spectrum, the spectral energy of the deep current was close to that observed in the same range in the subthermocline layer of the sea. In the range of balanced geostrophic motions, the energy spectrum had a slope of -2,8 that should be compared to a spectrum slope of -1,8 obtained for current below the thermocline. The regular strong horizontal currents were observed near the local inertial frequency fI. There was a blue shift of the inertial maximum up to 5% with respect to fI in the energy spectrum.
The first results of the multidisciplinary expedition aboard the RV «Akademik Mstislav Keldysh» to the North Atlantic in July 2017 are given. Continuation of deep convection in the Irminger Sea to a depth of 1500 m, which began in 2015, is discovered. New information is provided on the structure of the main jets of the North Atlantic Current in the Iceland basin and in the Irminger Sea (Irminger Current), as well as the East Greenland Current. New samples of atmospheric aerosols, suspended particulate matter and bottom sediments are collected. New data on the particle fluxes have been obtained using sediment traps.
Six day temperature records carried out at the three mooring levels revealed isotherm fluctuations in the Denmark Strait sill in July 2018 caused by internal waves. In addition to the field measurements, fluctuations of isopycnals were estimated on the basis of a numerical model. It was shown that the vertical displacements of water particles caused by semidiurnal internal tides are approximately 50 m in the region of the sill crossing the strait. The displacements decrease to 30 m over a distance of 100 km from the sill. The internal waves in the northern part of the strait are more intense than in the southern part because the wave propagates in the opposite direction to the mean current. In the southern part the waves and the current propagate to the south, which increases the wavelength and decreases their amplitudes.
New data on the particle fluxes of sedimentary matter and its main components at the meridional section along 59°30' N in the North Atlantic under the influence of multidirectional transfer of water masses are given. The material for the study was collected for two years from July 2015 to July 2017 using sediment traps installed as part of four automatic deep-water sedimentary observatories. In the subsurface layer, the annual variation of the fluxes and the change in the composition of the sinking matter are determined by the primary production. Near-bottom fluxes of sedimentary matter on the slopes of the Reykjanes ridge are formed under conditions of water masses and, respectively, suspended particulate matter transfer in a south-westerly direction along the ridge from the Iceland-Faeroe and Greenland-Iceland rises. There is a reverse directional transfer of matter at the foot of the European continental slope. The composition of the sinking matter is dominated by the biogenic component, the proportion of which decreases with depth due to dissolution, and in winter due to the weakening of the biological activity of the upper active layer. The role of lithogenic matter is maximal in the bottom layer, including due to the supply of material from the bottom.
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