Vol 58, No 4 (2018)

Transects near the estuarine area of the Lena River were studied on cruises 63 and 69 of the R/V Akademik Mstislav Keldysh, organized by the Institute of Oceanology, Russian Academy of Sciences, in 2015 and 2017, the program of which included hydrochemical studies. Based on the results, the components of the carbonate system were calculated, and their dynamics was studied in sea–river mixing zone. Despite the general similarity in the distribution of hydrochemical parameters, the patterns of variations in the content of dissolved inorganic carbon along the river–sea mixing line in 2015 and 2017 were significantly different. In 2015, the increase in the content of dissolved inorganic carbon along the river–sea mixing line was higher than can be provided by the oxidation of organic matter. In 2017, almost the entire influx of dissolved inorganic carbon into water could be controlled by the destruction of dissolved and/or particulate organic matter. The difference in the state of components of the carbonate equilibrium of waters and their dynamics may be the result of significantly higher runoff of particulate matter from the Lena River in 2015 than that in 2017.

Model and satellite data have been used to analyze interannual changes in the primary production (PP), ice-free area, and water temperature in the Kara Sea between 2002 and 2016. Significant positive trends for changes in the surface water temperature were recorded for all regions of the Kara Sea (R² = 0.37–0.61, p < 0.05). A reliable trend toward an increase in ice-free surface area was observed only for the Yenisei estuary. PP growth trends were significant in the northern Region of the sea and the Yenisei estuary. The decrease in ice cover area for the entire Kara Sea amounted to 1% per year. A PP minimum was recorded in 2003, and a maximum, in 2011. The average increase in Kara Sea PP during the study period was 2% per year. The most rapid increase in Kara Sea PP was observed during the spring season (April–May). The increase in annual PP was mostly due to the expansion of the ice-free area. The increase in the phytoplankton photosynthesis rate could not have resulted in the increase in PP, because the average photosynthesis rate for the entire sea decreased during the study period. Considerable region-specific variation in the patterns of interannual Changes in PP in the Kara Sea were observed.

Grazing impact of dominant zooplankton species on phytoplankton was estimated in the coastal areas of the White Sea in spring. The material was collected on expeditions of the R/V Ekolog in June 2012 and 2015 in Kandalaksha Gulf and Onega Bay of the White Sea. The data on the composition and biomass of zooplankton showed that depending on the intensity of the warming of the water column at the beginning of productive season, the zooplankton community was at the early-spring or late-spring stage of seasonal development. Zooplankton grazing impact varied from 1 to 90% of phytoplankton biomass and from 7 to 470% of primary production. The results are discussed in relation to the hydrothermal regime and the phase of coastal plankton community succession in different years.

Dispersed sedimentary matter was studied along the latitudinal transect 59°30′ N from Great Britain to Greenland on cruise 49 of the R/V Akademik Ioffe in June 2015. The concentrations of suspended particulate matter (SPM) along the transect were low, increasing from 0.24 to 1.07 mg/L in the surface layer (0–5 m), from 0.24 to 0.99 mg/L in the pycnocline (thermocline) zone, and appreciably decreasing toward the bottom layer, fluctuating from 0.10 to 0.56 mg/L. The isotopic composition of organic carbon in SPM was determined in 18 samples. The δ¹³C-C_org values vary from –17 to –24.6‰. Judging from the chlorophyll a content, the isotopic composition of water masses, and their remoteness from the coast, the carbon in SPM is mainly represented by autochthonous organic matter of phytoplanktonic origin. The presence of SPM with a heavy isotopic composition in the surface layer of the water column can serve as evidence for the current processes of phytoplankton bloom. In this case, differences in the intensity of these processes can be observed, creating a mosaic bloom pattern even within a distance of 150 NM.

In the Mezen River estuary, morpholithodynamic processes are regulated by tidal currents, river runoff, wind waves, and alongshore sediment flows. Due to the movement of a huge mass of sediments in the Mezen River estuary, intense deformations of silty sand banks occur, reforming the bottoms of channel grooves and displacing navigable waterways. On the whole, the Mezen River estuary is gradually being filled with river and marine sediments. Various sandy ridges form in the channel grooves of the estuary.

In the subpolar North Atlantic, four sediment cores were taken. All of them were suitable for reconstructing the dynamics of the meridional overturning circulation in the late Quaternary. Stratigraphy of the cores was performed by carbonate analyses, study of planktonic foraminifera, and oxygen isotopic composition in Neogloboquadrina pachyderma sin. Study of benthonic foraminifera assemblages has shown significant differences in the deep-water dynamics in the late Quaternary related to water exchange between the North Atlantic and Arctic seas. It has been established that at the end of the middle and most of the late Pleistocene, deep circulation in the subpolar North Atlantic was poor. Its strengthening took place in the time of deglaciations (Termination III and Termination II). During the optimum of the last interglacial (MIS 5e), water flow from the Norwegian Sea into the North Atlantic happened mainly in its western part. The modern deep water in the eastern part of the North Atlantic began to form at the end of the last glaciation.