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Effect of Diapycnal Mixing on Climatic Characteristics of the Laptev Sea in the Ice-Free Period
EFFECT OF DIAPYCNAL MIXING ON CLIMATIC CHARACTERISTICS OF THE LAPTEV SEA IN THE ICE-FREE PERIOD
Kagan Boris , Sofina Ekaterina
Purpose. The present study is aimed at evaluating the role of diapycnal mixing conditioned by the dissipation of baroclinic tide energy, in formation of climatic characteristics of the Laptev Sea in summer period. Methods and Results. The sea dynamics with and without tidal forcing is reproduced using the highresolution 3D finite element model. Spatial resolution of the unstructured grid varied from 1 to 18 km. The wind and thermohaline (seawater temperature and salinity restoring to the specified values on the sea surface) forcings, as well as the sea level at the domain open boundary, are set by the climatic affects corresponding to the summer (July, August) ice-free period in the Laptev Sea. The tidal forcing is set by an indirect method: the diapycnal diffusion coefficient defined, in accordance with the approximation of “weak interaction” of turbulence of various origins, by solving the problem on the baroclinic tide dynamics, is added to the vertical turbulent diffusion coefficient controlled by the wind and thermohaline forcings. Conclusions. The changes in seawater temperature and salinity induced by diapycnal mixing, having been compared to the climatic characteristics as such show that, as a rule, they (especially, their extremal values) are detectable well, and that their ignoring is not always acceptable. This is confirmed by the average (over the tidal cycle and over the area of the identified sea zone differing from the others by depth) vertical profiles of the uncorrected and corrected (due to the internal tidal wave effects) vertical turbulent mixing coefficients. The profiles differ from one another, if not in the entire sea, then at least within ~ 40% of its volume.
Features of the Stokes Drift in the Northeastern Coastal Zone of the Black Sea from Modelling Results
FEATURES OF THE STOKES DRIFT IN THE NORTHEASTERN COASTAL ZONE OF THE BLACK SEA FROM MODELLING RESULTS
Divinsky Boris , Kuklev Sergey , Ocherednik Vladimir , Kukleva Olga
The Stokes drift generated by surface waves affects many physical processes occurring in the coastal zone of the sea, including heat and salt transport, as well as transport of pollutants. Taking into account the parameters of sea currents caused by the Stokes drift is important for a more correct description of the general hydrodynamic structure of coastal waters. Moreover, sea currents generated by surface waves make a significant contribution to the processes of accumulation and redistribution of pollutants in the coastal zone of the sea. The article presents the results of the study of the Stokes drift on the northeastern shelf of the Black Sea near Gelendzhik for the period from 2003 to 2022. Seasonal and interannual features of variability of Stokes current velocities and directions have been identified. It has been shown that from December to April, excluding February, the Stokes transport has comparable repeatability in directions towards the coast, away from the coast, and towards the northwest. In February, the main flow tends to the open sea. In May and June, the repeatability of currents towards the coastline increases significantly, with the contribution of currents to the southeast increasing at the beginning of summer. In July, the currents directed to the southeast and away from the coast become almost identical in terms of repeatability. From August to November, the proportion of currents directed away from the coast increases with a gradual decrease in the repeatability of currents towards the southeast. In multi-year terms, the flow directed away from the coast to the open sea prevails (repeatability of 34.3%). The same flow has the highest mean velocity (0.053 m/s). Repeatability of the long-shore currents directed towards the southeast and northwest is almost the same, but the currents towards the northwest are much more intense.
Oxygen Dynamics during the Period of Dystrophic Processes in the Black Sea
OXYGEN DYNAMICS DURING THE PERIOD OF DYSTROPHIC PROCESSES IN THE BLACK SEA
Masevich Anna , Konovalov Sergey
Purpose. The paper is aimed at considering the peculiarities of the oxygen content and distribution in the Black Sea waters, and at analyzing the ratio of the observed changes in oxygen distribution, total primary production level and the changes in temperature mode, which is an indicator of intensity of the cold intermediate layer ventilation. Methods and Results. The expedition data (2015–2019) as well as the data array (1980–2013) from the Oceanographic Data Bank of Marine Hydrophysical Institute, RAS, were used to analyze the oxygen content. The data for the deep part of the Black Sea (exceeding the 200 m depth) were selected. To analyze the primary production values, the shipboard fluorometric measurements of the chlorophyll a concentrations (1980–2001), and also the surface chlorophyll a concentrations derived from the SeaWiFS and MODIS-Aqua color scanners remote sensing (1998–2019) were applied. Primary production was calculated using the regression equations of the form y = a + bx that bound up the primary production in the water column with the surface chlorophyll concentration. The calculated data show a signif icant increase in the annual primary production (to 400 g C/m2·year) in the first half of the 1980s, from 1985 to 1995 it declined on the average to ~140 g C/m2·year, and from 1998 up to present it is ~100 g C/m2·year. Such a course of the primary production value corresponds to the observed changes in the nitrates vertical distribution. Shown is a tendency towards increase in temperature of the cold intermediate layer core, which results in decrease of the oxygen concentration in the deep layers. Conclusions. Against the background of the trends to temperature increase in the upper layers of the water column, on the one hand, and to reduction of winter convective mixing intensity, on the other, a decrease in the oxygen supply in all the layers of the Black Sea aerobic zone is observed. This led to the fact that in 2010, the lowest oxygen content recorded in course of the whole period of observations had been revealed. At the same time, the dystrophic process has contributed to return of the Black Sea system to its natural state, when the oxygen content dynamics is conditioned mainly by variability of the waters’ physical ventilation intensity
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