Seasonal Variations in the Dynamics of the Number and Biomass of the Black Sea Macrozooplankton Populations

The abundance and biomass dynamics of the jellyfish Aurelia aurita and ctenophores-invadors Mnemiopsis leidyi and Beroe ovata in 2019 on the northeastern shelf of the Black Sea were studied. Data on the maxima of reproduction of each species of gelatinous macrozooplankton were obtained, as well as conclusions on the dynamics of individuals growth in populations and average life expectancy were drawn.

PHYTOPLANKTON OF THE OPEN NORTH-EASTERN PART OF THE BLACK SEA IN THE WINTER PERIOD 2017

The seasonal dynamics of phytoplankton development in winter is less studied than in other seasons, therefore it is of certain interest. The article presents the results of the study of taxonomic structure and the level of quantitative development of phytoplankton in the open area of the Black Sea northeastern shelf in December 2017. 34 Species belonging to 5 divisions of Bacillariophyta, Dinophyta, Chrysophyta, Cryptophyta and Chlorophyta were found in phytoplankton. The maximum species diversity was recorded among Dinophyta (21 species) and Bacillariophyta (8 species), other divisions were represented by 1–2 species. Previous studies have shown that the taxonomic composition of phytoplankton in the open area of the Black Sea northeastern part includes a large number of dinophytic species, while the diversity of diatoms is significantly inferior to them. The abundance and biomass of planktonic algae were extremely low during the study period (on average, 2706 cells / liter 11.49 mg / m3 ). The maximum abundance of species (26) and the highest values of quantitative development (5399 cells / l and 32.27 mg / m3 ) were observed in the area of the Taman Peninsula. These values were 2–4 times higher than the values of abundance and biomass found in the rest of the study area. The abundant development of planktonic algae was probably facilitated due to the ingress of waters of the Azov Sea, richer in nutrients, into the Kerch region of the Black Sea. Bacillariophyta (Pseudo-nitzschia pseudodelicatissima, P. seriata, Thalassionema nitzschioides, Pseudosolenia calcar-avis, Ditylum brightwellii), and Dinophyta (Prorocentrum cordatum, Prorocentrum micans and Ceratium species) formed the basis of the abundance (55 and 23 %, respectively) and biomass (24 and 68 %) of phytoplankton. Cryptophyta (Plagioselmis prolonga and P. punctata) accounted for 16 % of the phytoplankton population during the study period. Among the Chrysophyta and Chlorophyta, the species Octactis octonaria and Pterosperma undulatum, common for the open part of the Black Sea, were observed in small quantities. The favorable ecological situation in this region of the sea is proved by the complete absence of Cyanophyta and Euglenophyta, which are indicative of polluted and desalinated sea areas.

SEASONAL VARIABILITY OF OCEANOLOGICAL CONDITIONS ON THE NORTHEASTERN SAKHALIN SHELF BASED ON THE SURVEYS ON STANDARD SECTIONS

The long-term mean temperature and salinity distributions on 5 standard oceanological sections on the northeast shelf of Sakhalin were analyzed for 4 months of the navigation period (July-October) including a radical restructuring of hydrological conditions in the transition from summer to autumn. The data of soundings performed during the pollock ichthyoplankton surveys were used to study oceanological conditions in June. The low salinity water formed by the Amur River runoff are shown to appear on the northeastern shelf in the first half of June after the heavy ice breaking in the southern Sakhalin Bay. Low salinity water and ice are pushed off toward the deep sea under the influence of the southern winds typical for a warm season, and an oceanological front is formed near the 52°N. This front prevents the low-salinity water from flowing southward until the second half of September, when changes into a winter monsoon with the prevailing northerly winds take place. This promotes destruction of hydrological front and deepening of the cold intermediate water layer. The waters with the 4–6°C temperature and salinity of about 31 psu occur at the shelf edge along the northeastern Sakhalin coast. A powerful stream with the relatively warm low salinity water is being formed along the shore that reaches the southeastern part of Sakhalin and northern coasts of Hokkaido Island.

Sediments of northeastern shelf of the sea of Okhotsk in the area of South Kirin hydrocarbon deposits: microstructure, mineral, chemical and trace element composition

The study results of the microstructure, mineral, chemical and trace element composition of the northeastern shelf sediments in the area of the South Kirin hydrocarbon deposits of the Sea of Okhotsk in the Sakhalin region are considered. Sediment samples were taken during well drilling from the «Trias» special vessel at the depth of 25—30 m from the bottom surface (by the sea depth of 200—220 m). Interval coring (every one meter) was carried out by the pressing-in method. Analytical studies were performed for 30 air-dry samples (firmly cemented cylinders with a diameter of 4 cm, a height of 3 cm, and a weight of 50—70 g) of well No. 49 (30 m). According to lithological characteristics, three intervals are distinguished in the section which are represented by clay sands (0,0—4,0 m), sandy, silty clays (4,0—21,0) and clays (21,0—30,0). REM images of the sediment microstructure were obtained using a scanning microscope JEOL JIB-Z4500 (xlOOO-6000) for each interval. The scientific imaging was performed for ten thin undisturbed plates from the top part of air-dry sample-cylinder. Fauna residues and micropores were found. The content of aggregates, primary (free) particles and the volume of real clay content were determined by the «Microstructure» method. On the basis of these data, grouping of samples was carried out using the Q-type cluster analysis program which confirmed the picked intervals in the studied section. Changes in the mineral composition were determined by powder diffraction in the sediment thickness. The quartz content decreases with depth, and the clay phase increases in which hydromica dominates, and the almost complete absence of kaolinite is noted. The content of rock-forming oxides (method of silicate analysis) and statistical data processing showed a homogeneous distribution of silicon, aluminum and potassium oxides in the section, the coefficient of variation (V, %) was only 1—3 %. Augmentation of variability was found for БегОз (P12). Values of geochemical coefficients and statistical data processing revealed their insignificant variability in the section (V3—8). Noticeable changes are characteristic for the ratio of calcium and magnesium oxides (V16). A lesser degree of chemical transformations of sediments was established. The content of 23 trace elements was determined by the X-ray fluorescence method using an S8 TIGER spectrometer. The sediment thickness has the critical level of pollution by values of the pollution index (Zc) calculated for a group of toxic elements (V, Cr, Co, Ni, Cu, Zn, Pb, As). Based on the obtained information, the conclusions were drawn about the zonal structure of the sediment thickness, the features of their microstructure, mineral and chemical composition, as well as the degree of contamination by toxic trace elements.