Oceanology

It is generally accepted that changes in the heat content of the North Atlantic can be a source of some surprises in the present-day climate evolution, especially in Europe. The RAPID program, which monitors this heat content, is used to investigate this problem. However, the results of such monitoring are too short-term for any conclusion. Therefore, we use wavelets to analyze variations in the mean sea surface temperature in the North Atlantic as an indirect characteristic of the heat content. These variations have already been observed for quite a long time period (from the mid-20th century). Three scales, which define the temporal variability of this characteristic, have been found: 2–4, 7–10, and ~22 years. It is assumed that the sources of variations of the first two scales above are wobbles in the Earth’s rotation axis, and the source of variations of the third scale is Hale’s heliomagnetic activity cycle.

One of the key problems of physical oceanology is the search for effective global mechanisms that can result in formation and sustainability of the oceanic thermohalocline, which accumulates huge amounts of heat in the middle latitudes. The study revealed a genetic relationship between this element of macroscale stratification and the intensity of vertical mixing of waters caused by double diffusion in the form of salt fingers. It has been established that the more orderly work in the ocean water column of such a small-scale process as convection of salt fingers transforms the structure of the thermohaline, due to which the transition from warm and saline surface waters to underlying waters occurs not abruptly, but rather gradually, through a stationary transition layer: the oceanic thermohalocline. The results support our viewpoint on the salt finger convection as a climate-generating factor.

Three-year monitoring (2014–2016) of isotope parameters (δD and δ¹⁸О) of water in Sedov and Tsivolky bays (Novaya Zemlya Archipelago) freshened by water of different origin (continental river runoff, atmospheric precipitation, and water supplied from the archipelago) showed that the degrees of freshening and sources of fresh water components were different for water located at different depths. The variability of the δD and δ¹⁸О values was characteristic only of surface layer water containing up to 30% freshwater component. In 2015, surface water of Sedov Bay contained Ob River water, whereas water supplied from Novaya Zemlya predominated in Tsivolky Bay. The deep water of both bays showed evidence of freshening by high-latitude atmospheric precipitation. This water might have been transported via the St. Anna and Voronin troughs. The difference in freshening mechanisms of water in Sedov and Tsivolky bays was determined by the different seafloor morphologies and degrees of free exchange with Kara Sea water.

Intra-annual variability in methane fluxes at the water–atmosphere boundary was shown for the first time in the water area of the Sea of Okhotsk east of Sakhalin Island. The variability in methane fluxes is determined by the presence and activity of submarine methane sources and is related to seasonal changes in the hydrological and hydrochemical parameters of seawater and current structure in this region. In spring and autumn, the average fluxes are higher than in those in summer. The methane flux from the sea surface decreases during summer water modification and the increase in stratification. In autumn, methane accumulated in transitional waters is emitted into the atmosphere due to seasonal water convection and high average wind speed.

The spatial distribution of picophytoplankton abundance, biomass, chlorophyll a and the contribution of picoalgae to the total chlorophyll a was studied in the outer Ob River estuary with the adjacent shelf and in the western part of the Kara Sea. In August–September, the picophytoplankton abundance and biomass varied from 0.1 to 17.3 × 10⁶ cell/L and from 0.06 to 9.20 mg С/m³, respectively. Photosynthetic picoeukaryotes dominated in the plankton picofraction; the contribution of cyanobacteria to the total picophytoplankton biomass did not exceed 11%. The highest contribution of picophytoplankton to the total phytoplankton abundance was observed at a lower (<11 mg/m²) euphotic zone integrated chlorophyll a. The spatial heterogeneity of picoforms contribution was determined by the silicon concentration.

The species composition, abundance, biomass, and distribution of zooplankton were studied on the shelf and slope of the northwestern Laptev Sea and the shelf of the East Siberian Sea in summer 2015. The trophic status of common zooplankton and fish species, as well as their position in the food webs of these two seas, has been determined based on stable carbon and nitrogen isotope analyses (δ¹³C and δ¹⁵N). Data of both stomach content and stable isotope analyses show significant age-related variations in the trophic status of the Arctic cod Boreogadus saida, which is the dominant fish species.

Naturalization of the invasive copepod Oithona davisae is examined based on long-term (2003–2014) routine observations of zooplankton in Sevastopol Bay (the Black Sea). The study analyzes inter-annual and seasonal variability of the species and their impact on the native copepod community. The invasion of O. davisae and their undoubted dominance in terms of abundance have been shown to alter the community structure, while not causing a decline in abundance of native species, except the earlier Black Sea invader Acartia tonsa. A significant decline in A. tonsa numbers over the phases of establishment and naturalization of O. davisae indicates competition between the species. It has been demonstrated that O. davisae have gained a competitive advantage over A. tonsa, which ensured the rapid spread of the former across the Black Sea, acclimatization to the new habitat, and successful competition over native species.

The benthic fauna of Oga Bay (Kara Sea, Novaya Zemlya archipelago) was studied in 2015–2016 during the R/V Akademik Mstislav Keldysh expeditions. Five grab stations at depths of 70–140 m were sampled (three grabs per station). Three macrobenthic communities consecutively replacing each other from the inner near-glacier part of the bay toward the outer slope were revealed. Concentration of suspended matter in the water column and in the near-bottom layer, caused by powerful sedimentation from the Goluboi (Oga) glacier was the main factor determining the macrobenthic communities distribution. An overall decrease in abundance, biomass and diversity of macrofauna was found in the area of glacier discharge. The community dominated by bivalve Portlandia arctica inhabits the main part of the bay. The peculiarities of the benthic communities of the Arctic glacial bays and fjords are discussed.

The article discusses the preliminary results of plume and bottom sediment studies of the Trollveggen hydrothermal vent field based on data from cruise 68 of the R/V Akademik Mstislav Keldysh. The hydrothermal vent field is located east of the axial zone of the slow-spreading Mohn Ridge near the Jan Mayen hotspot at a depth of about 550 m (71°18′ N, Norwegian–Greenland Basin). The hydrothermal vent field plume was characterized by a weak distribution in the water column; temperature, density, and salinity anomalies; a moderate methane concentration; and a low concentration of suspended particulate matter near the bottom. The enrichment of bottom sediments in barium, strontium, and some sulfide-forming elements (zinc, lead, copper, and molybdenum) was shown. Two mineral assemblages of hydrothermally modified bottom sediments were revealed: pyrite and barite–marcasite. The temperature of hydrothermal fluids was established by thermal and cryometric studies of gas–liquid fluid inclusions in barite (128–260°С); the FeS–ZnS equilibrium diagram of sulfide minerals was also used (130–290°С). Our data were close to direct fluid temperature measurement data [28]. We compared the hydrothermal mineralization of the Trollveggen vent field and earlier studied fields of the Mid-Atlantic Ridge located near the Azores hotspot. As a result, we confirmed the influence of ocean depth and PT conditions on the formation of hydrothermal deposits.

The article presents the results of geophysical and geomorphological works on the western shelf of the Crimean Peninsula (Yevpatoriya–Balaklava). The sedimentary sequence structure, seafloor topography, and paleogeographic reconstructions of the formation conditions of the western shelf in the Late Pleistocene–Holocene are considered. Geoacoustic profile analysis aided in identifying the main shelf morphostructures; a brief description is presented. The abrasion–accumulative complex is identified, which consists of the abrasion platform and associated accumulative clinoform, the formation of which is related to the coastline of Late Pleistocene Black Sea regression to depths of about 90 m, traced from Yevpatoriya to Yalta. On the shelf of Kalamita Bay, fragments of a drowned river network and coastal accumulative landforms such as bars were studied.

The research program of the dynamics and ecosystem of the Drake Passage and Scotia Sea is scientifically substantiated. Measurements will be carried out by the interdepartmental expedition of the Russian Academy of Sciences with the participation of nine institutes aboard the the R/V Akademik Mstislav Keldysh. The research will be based on study of the functioning of the Antarctic marine ecosystem and measurements in the Antarctic Circumpolar Current.

During cruise 73 of the R/V Professor Gagarinskiy and cruise 53 of the R/V Akademik Oparin, oceanographic studies of the Sea of Japan and Sea of Okhotsk and the Northwest Pacific were carried out. New data were obtained on the seafloor structure, water structure, and slope convection features in the Sea of Japan.