Vol 59, No 3 (2019)

The paper examines the temperature dependence of the specific growth rate and ratio of variable to maximum fluorescence (F_V/F_M) in a number of marine planktonic algae from collections of cultures. It determines the optimum growth temperatures (T_opt), upper and lower limits of the tolerance zone, and in some cases, changes in the dynamics of these parameters outside the tolerance zone. Temperature characteristics of the species corresponded to the growth conditions of these species in a natural environment. Prolonged stress exposure to a low positive temperature (4–6°C) was reversible; recovery of the growth rate and F_V/F_M was observed immediately after the temperature increased. In diatoms, temperatures 2–3°C above the T_opt for diatoms induced gradual degradation of the culture, which, depending on the duration of exposure, could lead to the death of algae. Springtime dinoflagellates exhibited higher temperature resistance and remained viable at temperatures 5–8°C above T_opt with lower specific growth rates. The increasing portion of temperature dependence of the specific growth rate approximated a linear dependence; the regression coefficient is 0.08–0.13 for diatoms and 0.03–0.11 for dinoflagellates. The normalized values for this parameter (the relative value of change in the specific growth rate, %) was 5.3 ± 0.4 for diatoms and 6.4 ± 0.5 for dinoflagellates for 1°C of temperature change. Dinoflagellates exhibited larger values for the Q₁₀ parameter. F_V/F_M for most species had high values in the entire range of temperatures at which the algae maintained a steady-state growth. A drop in this parameter outside the limits of the tolerance zone was associated with the temperature-induced inhibition of growth processes.

We studied vertical distribution of bacteria and viruses in different layers of the Arctic sea ice drilled at the North Pole. The sampled multi-year ice was characterized by uneven vertical distribution of bacterial abundance. This characteristic varied within the range of 8 ± 1.2 × 10³ to 95 ± 2.6 × 10³ cells mL^–1. The layers with the maximal bacterial abundance were located in the intermediate and lower layers of the ice cores. Bacterial biomass varied from 0.5 to 5 mg C m^–3 with the mean value 1.57 ± 0.2 mg C m^–3. The ratio of viral to bacterial abundance varied from 0.6 to 28, with the mean value 12.5. The average total number of phages attached to bacteria was 6.2 × 10³ viral particles mL^–1. The number of viral particles located within the bacterial cells varied from 2 to 21 particles per a bacterial cell. The frequency of visibly infected bacterial cells (FVIC) calculated for the upper, intermediate and lower layers of the ice was 0.92, 1.23 and 0.8% of the total bacterial abundance, respectively. The overall frequency of infected cells (FIC) calculated for the same layers was 6.3, 8.4 and 0.8% of bacteria numbers, respectively, while the viral-mediated mortality of bacteria (VMB) was 7.1, 9.8 and 6.1%, respectively. Our data show that during the study period the rate of viral infection of bacterial cells and the viral-mediated mortality of bacterial cells in the multy-year ice of the North Pole were relatively low.

Impact of salinity changes on the composition of the Sea of Azov ichthyofauna is considered. To date, not only the quantitative, but also the qualitative composition of ichthyofauna and commercial catches has changed. The Black Sea sprat Clupeonella cultriventris, European anchovy Engraulis encrasicolus, gobiids of the family Gobiidae, as well such alien species as so-iuy mullet Planiliza haematocheila and Prussian carp Carassius gibelio, began to dominate in commercial catches. In the eastern part of Taganrog Bay, the golden gray mullet Chelon aurata, the flathead gray mullet Mugil cephalus, and Black Sea turbot Scophthalmus maeoticus have been recorded for the first time. The number of resident semianadromous species has decreased many times due to the deterioration of environmental and spawning conditions. Recommendations are presented for the rationalization of fisheries under conditions of salinization of the Sea of Azov.

Fauna of the circumpolar Arctic and Antarctic regions was compared based on the example of cold-water Scleractinia corals. In similar subzero temperatures of surrounding waters, not only the distribution of corals, but also the number of species and their morphological characteristics differ radically between the Arctic and Antarctic (17 coral species occur in the Subantarctic region, including six endemic species, whereas the Arctic and high latitudes are inhabited by two species). We believe that the difference between these two faunas is due to the difference in geological history of these regions. In the southern hemisphere, the formation of Antarctic circumpolar currents ended before the Neogene. Stable conditions that existed for several million years in the Subantarctic region led to the formation of well-developed scleractinian fauna and species endemic to this area. In the Northern Hemisphere, stable hydrological conditions at high latitudes and in the Arctic have existed since the beginning of the Holocene for approximately 11–12 ka, when colonization by corals species with a wide distribution began. Indirect evidence on the vertical thickness of the Circumantarctic current ring is presented.

Aquatic palynomorph assemblages in sediment cores obtained from the western Laptev Sea shelf make it possible to reconstruct the major phases of environmental changes related to the last postglacial global sea level rise for the time since 17.5 ka cal BP. In the time interval of 17.5–13.0 ka cal BP, in the western part of the studied sea, there was a very cold-water basin with a permanent sea ice cover; in 12.3–11.2 ka cal BP, the outer shelf was characterized by higher sedimentation from river runoff in the estuarial environment of the Anabar and Khatanga rivers; and the period of 11.2–7.0 ka cal BP was marked by the enhanced influence of Atlantic water at the continental margin of the Laptev Sea. The conditions close to present day were established in this part of the sea approximately 7.0 ka cal BP.

New data are presented on sedimentary matter fluxes and its main components along a meridional transect (59°30′ N) in the North Atlantic under the effect of multidirectional transport of water masses. The material for the study was collected July 2015 to July 2017 using sediment traps installed as parts of four automatic deep-water sedimentary observatories. In the subsurface layer, the annual variation in fluxes and composition of sinking material are determined by primary production. Bottom sedimentary material fluxes on the slopes of the Reykjanes Ridge are formed under conditions of transport of water masses and, accordingly, suspended particulate matter to the southwest along the ridge from the Iceland–Faroe and Greenland–Iceland rises. There is back transfer of material at the foot of the European continental slope. Sinking material is dominated by the biogenic component, the proportion of which decreases with depth due to dissolution and to less biological activity in the upper layer in winter. The role of lithogenic material is maximum in the bottom layer, where material is additionally supplied from the bottom.

Multielement chemical analysis and oxygen isotopic data has been employed for the first time to study the distribution of certain geochemical indicators in a sediment core recovered on the western slope of the Snorry contourite drift (station AI-3378, North Atlantic) during cruise 49 of the R/V Akademik Ioffe in 2015. Down the core, an asynchronous change in terrigenous (IRD, Al, Si, Ti, Zr, Cr) and biogenic indicators (CaCO₃, C_org) was recorded. The multielement geochemical data have revealed a rhythmic distribution of terrigenous and biogenic sedimentary material in the core. Sedimentary material entered the study area as result of ice and iceberg unloading, as well as bottom currents. The intensity and direction of the bottom contour currents apparently changed dramatically with alternating warming and cooling periods during stages MIS 1–6 (the last 190 ka).

The article is devoted to research of warm-water planktonic foraminifera species in the Arctic. The fauna of planktonic and benthic foraminifera in the surface and subsurface layer of Kara Sea sediments were studied. It was found that benthic foraminifera complexes were characteristic of this region. In planktonic foraminifera complexes obtained near Novaya Zemlya, a significant amount of warm-water species from equatorial, tropical, and subtropical regions not native to this region were present. We suggested that these species were brought to the Arctic by waters from low latitudes. The results were compared with published data, demonstrating the presence of warm-water planktonic foraminifera species in sediments around Novaya Zemlya and the Arctic. It was shown that living warm-water planktonic foraminifera were noted in the water column of the Laptev Sea and their tests were observed in modern sediments of its marginal part.