Vol 64, No 4 (2024)

Material was obtained during cruise 92 of R/V “Akademik Mstislav Keldish” in the area with latitudilal extent 72°32.0' to 73°14.5' N including Ob river estuary and adjacent shallow shelf on October 12–13 in a period preceding seasonal ice formation. Estuarine front was well pronounced in salinity (gradients 0.6 PSU/km) and temperature and had quasimeridional direction. Sharp borders in distribution of nutrients typical for earlier seasons were not observed. Numbers and biomass of phytoplankton varied in a range of 22×10³ to 75×10³ cell/l and 7.3 to 19.0 mg/m³, correspondingly, which were two to three orders of magnitude lower than in July and September observations. The basis of phytoplankton numbers (30–78%) and biomass (28–80%) across the whole area was formed by diatoms among which Fragilariopsis cylindrus dominated. Abundance of freshwater diatoms Aulacoseira was low and the species was presented only by dead cells. The scheme is presented which reflects borders between phytoplankton communities of different composition and quantitative characteristics as well as specificity of conditions in the eastern area of the wide external part of Ob river estuary.

The present paper describes the results of studies of two main components of meiobenthos – nematodes and harpacticoid copepods – conducted in 2013 and 2020 in Blagopoluchiya Bay (Novaya Zemlya, Kara Sea). A mosaic distribution of the two taxonomic groups was observed due to high species diversity and low occurrence of most species. Nevertheless, we identified patterns in the changes in the species structure of both groups related to the effect of two main environmental gradients (spatial gradient, related to the distance from the mouth of the bay to the sea, and depth-related gradient) as well as to the mosaic distribution of sediments. Changes among 2013 and 2020 were analyzed. In the seven years between the two surveys in Blagopoluchiya Bay, the abundance of nematodes increased tenfold, the copepod abundance also increased, but to a much lesser extent. Taxonomic changes in the two groups were observed at both species and family levels, with no differences in the functional structure of the taxa. The observed changes may be related both to changes in abiotic factors, and to general changes in the trophic system of the bay due to the introduction of the snow crab Chionoecetes opilio.

The results of meiobenthic survey on Con Dao Archipelago (Vietnam) is present. Samples were collected in five locations in mangroves and on the adjacent reef-flat. Quantitative date form meiobenthos is given along with taxonomic composition of two most abundant groups^ nematodes and harpacticoids. High species diversity occurs in two main groups – harpacticoid copepods and free-living nematodes. High level of species diversity together with a large number of singleton species prevents direct comparison on the species level and makes it non-informative. The general characters (composition of families and the spectra of live-forms) are more informative. The taxonomic composition of each of the studied bays were shown, inter-biotopic differences make a smaller contribution to the overall diversity, i. e. each bay has its own set of species, from which the population of each of the biotopes is formed with no respect to the distance.

The paper deals with a comparative analysis of the Barents Sea red king crab fecundity, size composition and sizes of 50%-mature individuals. The analysis was carried out with the focus on the period of the expansion and acclimatization of the species before commercial exploitation and on the present when crab is actively taken. Based on the literature data, the difference was reviewed between the above-mentioned parameters and that in the red king crab native habitat. According to the recent research data (2019–2022), the Barents Sea red king crab show a decreasing trend of its reproductive capacity compared to that in the period of active acclimatization before commercial exploitation (1995–2003). The maximum carapace width (CW) of berried females decreased on the average from 197 mm to 175 mm whereas the average CW size of 50%-mature individuals increased from 116 mm to 121 mm in these periods. There was a significant decrease found in the weight of eggs in a clutch (39%) and individual absolute fecundity (30%) of same-sized females. The weight of an egg also decreased by 12% on the average. In addition to that, there is a statistically significant decrease in fecundity per CW that may be attributed to the fact that there is a decrease in number of large males that are engaged in the reproduction and contribute to effective fertilization of more eggs laid by a female. Changes of the reproductive features of the Barents Sea red king crab population over the last few years make it more similar to native populations in the Pacific.

Vivianite, an authigenic mineral from the phosphate class, was discovered in the bottom sediments of the Kara Sea for the first time. Similar finds of vivianite were previously known only for the outer shelf of the Laptev Sea, the northern part of the Barents Sea and the eastern part of the White Sea. Its presence in the subsurface sedimentary strata indicates desalinization of the surface layer of the sea. Corer 7444, sampled in the tectonic depression of the southern part of the Kara Sea during the first stage of the 89th cruise of the R/V Akademik Mstislav Keldysh (2022), uncovered the Holocene sedimentary strata up to 6.19 m thick. Vivianite formations of coarse aleurite and sandy grain sizes are found throughout the entire thickness, starting from 0.11 m. Vivianite was investigated by a complex of methods: optical microscopy, X-ray diffraction, scanning electron microscopy with energy dispersive spectroscopy. The morphology, microstructures and chemical composition of vivianite formations were studied. Three morphological types of these formations were identified: microconcretions and their aggregates, crystalline aggregates and their aggregates, and tubiform aggregates.

The phenomenon of rhythmic patterns of the coastal-zone morphology (beach cusps, alongshore sand waves, spits and nearshore bars) is considered as the result of self-organization of the relief when establishing a positive feedback between sediment transport and morphology. It is shown that the dynamics of the contour and profile of the coast can be described in terms of the diffusion equation, which allows for both attenuation and growth of relief disturbances. The conditions under which the self-organization mechanism is activated and the resulting disturbances grow over time are determined. Rhythmic structures of the coastal contour are traditionally associated with waves propagating at a large angle relative to the coastal normal. However, it has been shown that the self-organization of beach cusps and megacusps is also realized in normal shore waves due to the development of circulation cells in the surf zone. The conclusion is substantiated that the formation of nearshore bars under certain conditions is also determined by the self-organization mechanism. The results obtained help to interpret the available observational data regarding the evolution of multiple bar systems.

Experimental results of geological and geomorphological observations in some marine areas with active gas emission from bottom sediments are presented and analyzed. The work was carried out using an instrumental complex of geophysical sonar equipment, which included a subbottom profiler and a side scan bathymetric sonar using an interferometric method for measuring depths in the field of view. The results obtained confirm the possibility of using the complex to classify the morphology of the seabed and control the processes of gas emission. The use of sonar equipment for remote mapping of the bottom under satellite observations can be used to interpret the results of satellite remote sensing of the atmosphere.

The paper describes complex research of the Krasnaya and Varkutsyakha Rivers of the Vaigach Island in a 2023 summer low water period completed by the Shirshov Institute of Oceanology North-Western Branch. This research is aimed to studying mixing zones formation specifics for lagoon estuaries of arctic islands. Suspended particulate matter concentrations maximum was found near the mixing zone upper bound. The maximum metal accumulation areas were observed in the river's mouth frontal area and in its upper part for manganese and arsenic.

Multidisciplinary studies of “sediments–water column–atmospheric layer near sea surface” system in the Barents and Pechora seas and the Baidaratskaya Bay of the Kara Sea were carried out in the expedition of “European Arctic–2023: Geological Record of Environmental and Climate Change” during the season of polar night and active development of autumn-winter thermal convection. Fundamentally new data on a number of areas of oceanology were obtained in the cruise.