A. G. Zatsepin

Circulation in the southwestern part of the Kara Sea in September 2007

During cruise 54 of the R/V Akademik Mstislav Keldysh to the southwestern Kara Sea (September 6 to October 7, 2007), a large amount of hydrophysical data with unique spatial resolution was obtained on the basis of measurements using different instruments. The analysis of the data gave us the possibility to study the dynamics and hydrological structure of the southwestern Kara Sea basin. The main elements of the general circulation are the following: the Yamal Current, the Eastern Novaya Zemlya Current, and the St. Anna Trough Current. All these currents are topographically controlled; they flow over the bottom slopes along the isobaths. The Yamal Current begins at the Kara Gates Strait and turns to the east as part of the cyclonic circulation. Then, it turns to the north and propagates along the Yamal coast over the 100-m isobath. The Eastern Novaya Zemlya Current (its core is located over the eastern slope of the Novaya Zemlya Trough) flows to the northeast. Near the northern edge of Novaya Zemlya, it encounters the St. Anna Trough Current, separates from the coast, and flows practically to the east merging with the continuation of the Yamal Current. A strong frontal zone is formed in the region where the two currents merge above the threshold that separates the St. Anna Trough from the Novaya Zemlya Trough and divides the warm and saline Arctic waters from the cooler and fresher waters of the southwestern part of the Kara Sea. This threshold, whose depth does not exceed 100–150 m, is a barrier that prevents the spreading of the Barents Sea and Arctic waters to the southwestern part of the Kara Sea basin through the St. Anna Trough.

The upper desalinated layer in the Kara Sea

An area of about 40000 km2 of desalinated upper layer waters with a salinity of less than 25 psu was found during cruise 54 of the R/V Akademik Mstislav Keldysh in the southwestern part of the Kara Sea (September 2007). Close to the boundary of this region located near the eastern coast of Novaya Zemlya, the salinity was less than 16 psu. The thickness of the desalinated layer was about 10 m. The results of the chemical analysis revealed that the observed desalination of the sea water was produced, first of all, by the Yenisei River, while the contribution of the Ob River’s waters was secondary. However, the most desalinated region near the eastern coast of Novaya Zemlya was separated from the Ob-Yenisei estuary and corresponded to a quasi-isolated lens. It is likely that the formation of this lens, as well as the major part of the desalinated upper layer waters, occurred in June when the flood of the Yenisei was maximal, while the further drift of the desalinated waters to the west of the Ob-Yenisei estuary was forced by the prevailing northern wind. The additional desalination (by 2–3 psu and even more) of the upper layer waters near the eastern coast of Novaya Zemlya might be related to the melting of the Novozemelskiy ice massif. The regularities of the temporal evolution of the upper desalinated layer, as well as the influence of this layer on the hydrological structure and dynamics of the southwestern Kara Sea, are discussed.

Impact of the winter cooling on the variability of the thermohaline characteristics of the active layer in the Black Sea

The influence of the winter atmospheric forcing on the interannual variability of the Black Sea’s active layer’s thermohaline structure during 1982–2008 is investigated. The results are based on the combined analysis of the hydrological measurements from a ship, satellite measurements of the sea’s surface temperature (SST), and the NCEP/NCAR reanalysis data for the surface air temperature (SAT). A high correlation between the variability of the winter mean SST/SAT and the thermohaline characteristics of the active layer during the following warm season was found. It is shown that the winter atmospheric forcing significantly affects the variability of the temperature, salinity, and density down to the 150–200 m depth, and this has to be considered in the analysis of the interannual and long-term variability of the Black Sea’s active layer.

Laboratory investigation of the mechanism of the periodic eddy formation behind capes in a coastal sea

The observations carried out in the Caucasian sector of the Black Sea have shown that, under certain conditions, the Rim Current detaches from the coast behind Cape Idocopas. In these cases, an anticyclonic eddy is formed between the detached Rim Current and the coast. Sometimes, the eddy grows in size until it is captured by the flow and goes downstream. After that, a next eddy is formed nearly at the same place, etc. The conditions of the periodic eddy formation behind a cape are revealed by means of laboratory modeling. The laboratory results are compared with the data of field observations in the Black Sea.

Propagation and transformation of waters of the surface desalinated layer in the Kara Sea

A new method for the calculating propagation of brackish waters from the Ob-Yenisei estuary in the Kara Sea is proposed. This method is based on satellite altimetry measurements and meteorological data. Surface currents in the upper layer are estimated as the sum of geostrophic and parameterized wind-driven transport. Geostrophic velocities are calculated using altimetry-derived sea-level anomalies and mean dynamic topography. The method has been used previously to calculate surface currents in the Black Sea [7, 12]. In this paper it has been successfully verified on the basis of comparisons with field observations of surface salinity and satellite images of sea-surface chlorophyll in the Kara Sea.

Variability of currents in the coastal zone of the Black Sea from long-term measurements with a bottom mounted ADCP

The results of long-term measurements (16 months) of the current’s velocity in the Black Sea coastal zone near Golubaya Bukhta (Blue Bay) by a bottom mounted acoustic Doppler current profiler (ADCP) are presented and discussed. It was found that the alongshore component of the current dominates and its absolute value is an order of magnitude larger than the absolute value of the normal to the shore component. The annual average value of the alongshore current’s velocity is close to zero. A well pronounced oscillatory mode of the alongshore current’s velocity is revealed. This mode is characterized by quasi-periodic changes in the direction of the alongshore current. The maximal amplitudes of the unidirectional alongshore current’s velocity are observed with a time scale from several hours to several days.

Observations of a cycle of intense coastal upwelling and downwelling at the research site of the Shirshov Institute of Oceanology in the Black Sea

The paper presents the results of joint analysis of the response of vertical temperature and current velocity profile distributions in the coastal zone of the Gelendzhik region of the Black Sea to strong wind forcing in the third ten-day period of September 2013. This forcing was caused by the propagation of an atmospheric cyclone, which first initiated coastal upwelling that was later replaced by downwelling. We formulate a criterion for the development of full coastal upwelling and demonstrate its efficiency. We assume that frequent events of incomplete coastal upwelling and downwelling are associated with changes in the water dynamics (variations in the intensity and direction of the alongshore current) generally not related to local wind forcing.

Hydrophysical features of deep water troughs in the western Kara Sea

In the 59th cruise of the RV Akademik Mstislav Keldysh (September–October, 2011) a large amount of hydrophysical data was obtained with the help of various measuring systems. The data allowed us to study the dynamics and hydrological structure of deep-sea troughs of the western part of the Kara Sea at a high spatial resolution. In particular, the analysis of this material showed that a cyclonic jet exists in the central spur of the St. Anna Trough at depths of 150–300 m and penetrates down to the bottom. The jet is able to play a role of a dynamic barrier that prevents the penetration of water from the southwestern part of the Kara Sea to higher latitudes. In the eastern spur of the St. Anna Trough, the jet weakens, becomes less barotropic, and can no longer inhibit the northward spreading of the shelf waters of the Kara Sea. The weakest and least coherent currents were recorded in the Novaya Zemlya trough, in the southern part of which we traced waters of a Barents Sea origin.

Mesoscale Water Dynamics

An analysis of the results of hydrographic surveys and satellite measurements performed during in roughly the last two decades is presented in order to demonstrate the diversity of manifestations of the mesoscale water dynamics in the coastal zone and in the deep-water part of the Black Sea and the role of mesoscale structures (eddies and jets) in the horizontal (including that between the coastal zone and the open sea) and vertical water exchange. The characteristic routes of movement of coastal and deep-sea anticyclonic eddies are considered, together with the mechanisms of their formation, spatio-temporal and kinematic parameters, the features of manifestation in the surface temperature field, and their influence on the formation of large meanders and branching of the Rim Current. The factors providing the transformation of coastal anticyclonic eddies into deep-sea ones and the long-term (to about eight months) existence of the latter in the eastern deep-water basin are discussed. An asymmetry in the intensity of vortical activity in the eastern and western Black Sea is noted. Based on the results of recent laboratory modeling, the differences in the local values of the continental slope width are regarded as the possible reason for this asymmetry.

Marine environmental monitoring in the shelf zone of the Black Sea: Assessment of the current state of the pelagic ecosystem

The state of the shelf pelagic ecosystem has been assessed based on multidisciplinary monitoring performed in the northeastern Black Sea in 2005–2014. Seasonal and interannual variations in sea surface temperature (SST) and chlorophyll a (Chl-a) concentration have been analyzed along with the concentration of nutrients (silicate, nitrogen, and phosphate), biomass, and taxonomic compositions of phytoplankton, zooplankton, and gelatinous macroplankton. The linear trend shows an increase in the annual average SST by 0.9°C over the last decade. An increase in the winter SST is accompanied by a decrease in the concentration of silicates in spring (p < 0.05) and an increase in summer SST, by a decrease in Chl-a concentration and biomass of diatoms in the period of summer to fall (p < 0.05). A decrease in the phosphate concentration also has a negative effect on the development of diatoms (p < 0.01). The decrease in diatom biomass caused a decrease in herbivorous zooplankton biomass in the second half of the year (p = 0.05). Correlation analysis shows no significant dependence between the biomass of gelatinous top predators and mesozooplankton biomass. The assessed current state of the shelf pelagic ecosystem is regarded as stable; however, trends of a decrease in biomass and a change in the taxonomic composition of phytoplankton and zooplankton are observed during the last 2 years; the latter is likely to result from both direct and indirect effects of temperature increase in the upper sea layer.