Vol 59, No 1 (2019)

A model of an advective thermocline is proposed for the case of continuously stratified Sverdrup circulation with a ventilated layer caused by the divergence of flows in the Ekman layer: an immiscible layer with homogenized vorticity and a layer of abyssal liquid, which applies to anticyclonic gyre waters. The results of calculations for the Atlantic Ocean (region 15–52° N, 0–63° E) carried out with this model are presented. With an abyssal density of 28.0, the values of the surface density and density of the unventilated layer increase to the north from 24.2 to 27.0 and from 27.8 to 27.9, respectively, with an almost zonal distribution; i.e., ventilation zones have latitudinal circles. From calculations of the depths of wind circulation, it follows that the ventilated layer is as deep as 900 m in the northwestern region and rises to 250 m in the southern and eastern parts of the basin. The same tendency is traced for the depth of the gyre, but here there is an increase in depth from 500 to 1500 m. The active dynamics in the ventilating layer and the shadow area on the eastern border are noted. The structure of the thermocline is demonstrated with a typical zonal section, characterizing a much larger isopycnic increment for ventilated layers than in nonventilated layers.

Based on the archival oceanographic databank of the Institute of Natural and Technical Systems, the annual and interannual variability was analyzed for the dissolved oxygen content and temperatures in the upper deep-water layer and northwestern parts of the Black Sea from 1923 to 2013. The seasonal variations in the dissolved oxygen content and temperatures are in antiphase. On average, over the considered time frame, the dissolved oxygen content was maximum in winter in the northwestern area of the sea and minimum in the open parts in summer. The amplitude of seasonal variations was over 50 µM/L. In general, this is in agreement with earlier publications. However, the seasonal trend changes considerably within certain 20- to 30-year time intervals, which is related to quasiperiodic variability of the oxygen content on a typical time scale of several decades, exhibited differently in different seasons and sea areas.

The study analyzes data of ship-based observations on 45 stations performed aboard the R/V Akademik M.A. Lavrentyev on cruise 33 May 7–18, 2004, in the northwestern part of the Sea of Japan (35–44° N, 130–137° E). The following in situ data were used: CTD-data, assimilation number, concentrations of nutrients (nitrogen, phosphorus, and silicon compounds) and chlorophyll a (Сhl a). Satellite data on Сhl a concentration, diffuse attenuation coefficient at a wavelength of 490 nm, primary production (PP), and Photosynthetically Active Radiation (PAR) available from the Climate Change Initiative Ocean Colour (CCI-OC) and Ocean Productivity databases were also used for the same stations. The Chl a concentration in the first optical layer estimated from the results of ship-based measurements, was on average 0.55 ± 0.58 mg/m³, but the satellite-derived estimates were almost twice as high (0.95 ± 0.36 mg/m³). Ship assessments of PP were 1870 ± 900 mgC m^–2 day^–1; the value obtained using satellite data was 1.5 times smaller: 1226 ± 432 mgC m^–2 day^–1. Vertical Chl a profiles showed that the largest amount of Chl a was concentrated in the 20–45 m layer. Measurements of the assimilation number showed that most production occurs within the 0–55 m layer in the south of the study area and within the 0–30 m layer in the north. The weak correlation between ship- and satellite-derived Chl a and PP values can be explained by low accuracy of satellite-derived estimates.

Specific features of the structure and distribution of autumn zooplankton in the southeastern Baltic Sea (SEB) in October 2015 have been found taking into account the hydrological and hydrochemical data. No changes have been detected in the taxonomic composition of phyto- and zooplankton, including the increase in the number of stenothermic and stenohaline species as well as significant differences in the hydrological parameters compared to the long-term similar data. This indicates the absence of the impact of the winter Major Baltic Inflow in December 2014 on SEB plankton the following autumn. The level of phytoplankton vegetation in the upper homogeneous layer (125 000 ± 39 000 cells/L, 664 ± 143 mg/m³) is higher compared to the long-term data. The abundance and biomass of zooplankton (5100–16 800 ind./m³ and 49–143 mg/m³) are within the typical values for autumn in the SEB area. The features of the spatial zooplankton distribution are determined by trophic resources and the thermohaline structure of the water column.

Using a landscape approach, the paper presents for the first time the results of a comparative analysis of spatiotemporal changes in the macrophytobenthos, performed in the Laspi Bay for the period from 1983 to 2008 with landscape maps of Laspi Bay compiled by the authors. In addition, it describes the distribution of the bottom natural complexes with key Black Sea phytocoenoses. It was found that over a span of 25 years, the plant components of bottom natural complexes in Laspi Bay underwent significant restructuring and degradation due to natural factors and anthropogenic activity in the coastal zone.

A comparative analysis of two large Arctic sedimentary basins was performed: the Sverdrup and East Barents, with emphasis on the quantitative parameters of sedimentation in the Mesozoic, determined by A.B. Ronov’s volumetric method. The similarities and differences of both basins are revealed, in particular, in sediment accumulation areas, in masses of sedimentary material per time unit, and in gross sand ratio. It was concluded that at the end of the Paleozoic and in the Mesozoic, both basins were close to each other but did not merge into one structure. In the Cenozoic, the distance between the basins increased due to spreading of the Eurasian Basin.

Based on benthic foraminifera from three sediment cores, the deep-water circulation near the Hunter Channel (Southwest Atlantic) in the Late Pleistocene and Holocene has been reconstructed (marine isotope stages (MIS) 4–1). Today, the North Atlantic Deep Water (NADW) moves through the Hunter Channel from north to south. At MIS 2 and 4, lower NADW flowed in the same direction. At MIS 3, NADW, Antarctic Bottom Water (AABW), and Lower Circumpolar Deep Water (LCDW) periodically appeared in the Hunter Channel. On the approach to the Hunter Channel from the Argentine Basin, there are no AABW signatures in the Late Pleistocene or Holocene. In the Holocene, carbonates dissolved in the deeper eastern part of the Hunter channel. During glaciations, dissolution processes intensified and also reached the western part of the channel. Dissolution proceeded and continues to proceed not because of AABW but NADW, which becomes aggressive here toward calcium carbonate.

For the first time, vertical and lateral distribution patterns of mercury in White Sea bottom sediments have been determined. An abrupt change in the nature of mercury concentrations has been revealed, with a general tendency to decrease with depth. Natural variations in mercury concentrations within 0.01–0.03 µg/g dry weight (dw) have been established. An upper value of 0.03 µg/g dw is taken for the natural background content of the element. The distribution of mercury concentrations in the sequence of bottom sediments is influenced by both anthropogenic and natural factors and processes. With distance from the marine–estuary boundary of the Northern Dvina River, the river’s role in supplying mercury to the White Sea is reduced, and global and regional atmospheric mass transfer take over. The mercury content is used as an indicator of landslide processes in Kandalaksha Gulf of the White Sea. The accumulation chronology of mercury in White Sea sediments is studied, and the proportion of anthropogenic mercury is calculated.