The runoff of Yenisei and Ob has a significant impact on the Kara Sea freshening. The paper analyzes longterm satellite data on the sea surface salinity in the Kara Sea during the ice-free period for 2015–2021 in order to identify the position and dynamics of the river plumes and the region of the freshwater influence. It was found that the area of the freshwater influence limited by the isohaline of 26 psu, is determined by the total Yenisei and Ob inflow into the Kara Sea. The interannual variability of the freshwater area in August is determined by the runoff of the Ob and Yenisei accumulated for June–August and the wind regime. Analysis of the sea surface salinity identified three types of freshwater distribution based on the analysis of salinity at the sea surface. The different types of large-scale atmospheric circulation over the Kara Sea, determined by the Arctic Oscillation index, has also been shown to affect the formation of freshwater regions. It was found that during the negative phase of the Arctic Oscillation, when the anticyclonic pressure area is over the Arctic, most part of the Kara Sea is occupied by freshwater and the position of the 26 psu isohaline is northern of 77°N. This type of freshwater propagation was observed in August 2015 and 2019. Other types of freshwater propagation are characteristic of the positive phase of the Arctic Oscillation, when a cyclonic pressure area is located on the Arctic Ocean.
The maximum rivers inflow into the northwestern part of the Black Sea is on May-June. The plume occupies the largest area during this period. The alongshore current of desalinated waters, directed to the south, is formed, its transport increases. The mixing of water and its transport affect the spatiotemporal distribution of chlorophyll-"a" concentrations and, in general, the ecological state of the shelf waters. The six typical wind field distributions are obtained as a result of synoptic situations analysis by self-organizing Kohonen map method. It’s can be grouped by the predominance of the northward and southward winds. Estimates of the frequency of occurrence of synoptic situations for a decade have been obtained and their interannual variability has been analyzed in comparison with climatic indices characterizing large-scale atmospheric circulation.
The spatiotemporal variability of chlorophyll concentrations on the North-Western Shelf of the Black Sea was studied. The monthly average chlorophyll data of the CMEMS for 2007-2017 are analyzed with a spatial resolution of 1 km. As a result, a breakdown scheme for 4 regions is proposed and the cross-correlation coefficients are estimated for each pair of neighboring regions by the moving correlation method. The wind field repeatability was analyzed using the six-hour ERA-Interim reanalysis surface wind data for the periods which were identified by the maximum values of the correlation coefficients. The duration and frequency of transport of chlorophyll between regions has significant interannual variability due to the variability of the wind field on the same time-scale. The results are discussed and compared with recent achievements about the spatial variability and cross-frontal exchange of chlorophyll on the North-Western Shelf of the Black Sea.
It is studied the plume response, formed by the Danube River in the North-Western part of the Black Sea, to the wind forcing. Two cases are considered: the wind of the N-NE and S-SW directions. The plume evolution, alongshore flow formation and suspended matter transfer are analyzed on the base of satellite data at a wavelength of 551 nm for these two wind forcing scenarios. The coastal current dynamics and formation of Danube plume and salinity front are studied on the basis of 3D numerical model which was adapted to the conditions of the North-Western shelf. The obtained results from the satellite data analysis are compared with results of numerical simulation of plume formation under the action of wind in order to estimate the model sensitivity to variations of the wind direction and of the wind speed magnitude.
The purpose of this study is to investigate the interannual variability of the Black Sea suspended matter concentrations based on satellite data. The spatial and temporal variability of the bio-optical parameters are investigated by satellite data analysis. To analyze the interannual variability of suspended matter concentration on the northwestern shelf of the Black Sea, the combined monthly fields of the backscatter factor (BBP) for the period 1998-2010, obtained from the data of the SeaWiFS scanners, MODIS, MERIS are presented in a uniform spatial resolution grid of 4.6 km. empiric orthogonal function (EOF) analysis is applied to these data arrays with the aim to classify the spatial variability of BBP signal. As a result, the characteristics of the interannual spatial-temporal variability of the suspended matter concentration are given by four Empiric orthogonal function maps. They describe around 52% of summary suspended matter variance on the northwestern shelf of the Black Sea and thus its define the main regions (sources) of matter input. The influence of the Danube water inflow and suspended matters transport on the northwestern part of the Black Sea are discussed. The relationship between interannual variability of the suspended matter concentrations and large-scale atmospheric circulation processes was compared via North Atlantic Oscillation index.
The main objective of this research is to study the interannual variability of the Black Sea chlorophyll-a concentrations related to the forcing of physical factors (SST, wind, sea circulation) and/or influence of climate variability. The Self-Organization Map (SOM) analysis was applied to identify typical (recurrent) spatial patterns of chlorophyll-a concentrations and physical forcing data. The results of SOM analysis are compared with temporal variability of the climatic indices (NAO, EAWR). The propagation of desalinated water through Danube delta along the Western Black Sea coast and the hydrological structure of shelf water are studied. The dynamics, the coastal current, and formation of Danube plume and salinity front are studied on the basis of numerical modeling which was adapted to the conditions of the North-Western shelf. The results of numerical modeling of effects of plume and buoyancy current evolution, shelf water stratification and wind forcing for summer period conditions are discussed. As a result, the model gives qualitatively correct position of salinity front related with Danube discharge, plume and alongshore current evolution.
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