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On the basis of theoretic-probability analogies, a quantitative characteristic of diversity of the river delta, the variance, is proposed. The series of computer experiments with a hydrological model demonstrate that an increase in the variance of the delta structure reduces the intraannual amplitude of fluctuations in salinity of the closing reservoir. The simulations for the Don River and Taganrog Bay (the Sea of Azov) used as the closing reservoir show that modern climatic change and anthropogenic factors reduce the proper functioning of the River Don arms. Therefore, there is a prospect of decrease in the variance of river runoff and, hence, destabilization and increase in the variability of salinity in the closing reservoir.

This work reports on the cyclicity of the climate in the Sea of Azov Region studied on the basis of paleogeographic methods. The results of drilling on Dolgaya Spit of the Sea of Azov are presented. The diatoms and palynological analyses, as well as the soil column dating, indicate the cyclical pattern of climatic variability and accelerated silting of the Don delta under regulated runoff. The rate of sedimentation in the Sea of Azov during the Ancient Azov and New Azov stages varied from 0.2 to 2.0 mm/year. In the current period, under conditions of water scarcity and lack of floods, the sedimentation rate of clayey silts was 10–30 mm/year at the avandelta. Based on the analysis of hydrometeorological information, the period of time from 1884 to 2020 can be divided into three periods: I, cold; II, transitional; and III, warm. The study of the indicated specific features of the development of natural processes gives grounds to expect the next transitional period with dramatical interannual fluctuations of temperatures and alternation of warm and severe winters in the coming decade.

Integrated mathematical model of the Barents and White seas LME is proposed as a tool for assessing natural risks and rational use of biological resources. The model includes the following main blocks (modules): a) oceanographic conditions and biological productivity; b) trophodynamics and fishery management; c) environmental and biota pollution; d) socio-economic development; e) assessment of environmental risks from marine activities. Integrated model was used for assessing: the hydrological variability, long-term dynamics of ecosystem productivity and fishing load on the most important commercial species of the Barents Sea. A new zoning of the Barents Sea taking into account the geomorphological and hydrological factors was performed under the guidance of academician G.G. Matishov. Maps of the simulated gross primary production in the Barents Sea for the second half of the 20th and first decade of the 21st centuries are presented. The energy balance in the Barents Sea ecosystem at the end of the 20th and the beginning of the 21st century was calculated by trophodynamic model. It is concluded that determination of the fishing load on populations should base on using ecosystem mathematical models instead of single-species models. To estimate the fishing mortality, it is necessary to take into account not only the spatial effects associated with the characteristics of the fishes' life cycle and the distribution of fishing load, but also the influence of climatic factors and inner-ecosystem interactions. The use of modern information technologies, both in the field of primary data analysis, and in the area of their generalization to diagnose past changes, makes it possible to better understand the consequences for the Barents and White seas LME of existing natural resource use plans, taking into account the experience (sometimes negative) of past years and the expected climatic changes.

An integrated mathematical model of the Barents Sea and White Sea Large Marine Ecosystem proposed as a tool for assessing natural risks and efficient use of the biological resources is considered. The model includes the following main blocks (modules) of (а) oceanographic variation and biological productivity; (b) trophodynamics and fishery management; (c) environmental and biota pollution; (d) social and economic development; and (e) assessment of ecological risks from marine activities. The results of using the integrated model for assessing hydrological variability, long-term dynamics of ecosystem productivity, and assessment of fishing pressure on the most important fishery species of the Barents Sea are presented. A new scheme of zoning of the Barents Sea area performed under the supervision of Academician G.G. Matishov with respect to geomorphological and hydrological factors is proposed. A comparative scheme of distribution of the estimated gross primary production in the Barents Sea area in the second half of the twentieth century and in the 2010s is presented. The energy balance of the Barents Sea ecosystem in the late 1900s and early 2000s is calculated by the model of trophodynamics. The necessity of using mathematical models of the ecosystem instead of single-species models during the calculation of fishing pressure on the populations is suggested. To estimate fishing mortality, it is necessary to take into account not only spatial effects related to the features of a fish life cycle and distribution of fishing pressure, but also the impact of climate factors and ecosystem interactions. The use of recent information technologies both in the field of accumulation and analysis of the primary data and in the area of their subsequent generalization for the diagnosis of past changes makes it possible to understand better the possible consequences of the existing plans for developing and use of available natural resources for the Barents Sea and White Sea LME based on the experience (sometimes negative) of recent years and expected climate changes.

The chlorophyll a concentration (Cchl a) in the Sea of Azov is estimated by the two-band NIR-red algorithm [34] from MERIS images for 2002–2012. The sea-truth spectrophotometric measurements and MERIS remote estimates of Cchl a are compared. The monthly average Cchl a values are mapped from MERIS data for its lifetime for the first time. The features of the spatiotemporal distribution of Cchl a are ascertained. Differences between the seasonal dynamics of Cchl a in the Sea of Azov according to the literature data and the dynamics derived from MERIS data are found, namely: the summer–autumn phytoplankton growth period is longer than the spring period and is characterized by higher Cchl a values throughout the water area.

The paper presents approach used for the development of the forecasting system of extreme hydro-meteorological events in the region of the Sea of Azov. Due to numerous dangerous extreme events that occurred in the beginning of XXI century the issue of creation such system has become very relevant and important. The forecasting system, named EX-MARE, was started developing in 2014 as a complex of mathematical models. For each type of hydro-meteorological events, the modeling component was designed. The EX-MARE system is based on a scenario approach implied the consideration a variety of possible futures taking into account the existing uncertainty. Accurate extreme events estimation requires automated monitoring systems and longterm database application. In the paper, the detail description of the system components and the data sources is examined. Three case studies about the sea surges, flash flood and ice conditions researches demonstrate the application of the EX-MARE system and the benefits of its using. Further development of the EX-MARE system assumes adding data on exposure and vulnerability to perform the risk assessment, as well as focusing on multi-hazards exploring methodology.

Base long-term modern scenarios of hydrochemical and temperature regimes of the Sea of Azov were considered. New schemes of modeling mechanisms of algal adaptation to changes in the hydrochemical regime and temperature were proposed. In comparison to the traditional ecological-evolutionary schemes, these models have a relatively small dimension, high speed and allow carrying out various calculations on long-term perspective (evolutionally significant times). Based on the ecology-evolutionary model of the lower trophic levels the impact of these environmental factors on the dynamics and microevolution of algae in the Sea of Azov was estimated. In each scenario, the calculations were made for 100 years, with the final values of the variables and parameters not depending on the choice of the initial values. In the process of such asymptotic computer analysis, it was found that as a result of climate warming and temperature adaptation of organisms, the average annual biomass of thermophilic algae (Pyrrophyta and Cyanophyta) naturally increases. However, for a number of diatom algae (Bacillariophyta), even with their temperature adaptation, the average annual biomass may unexpectedly decrease. Probably, this phenomenon is associated with a toughening of competition between species with close temperature parameters of existence. The influence of the variation in the chemical composition of the Don Rivers flow on the dynamics of nutrients and algae of the Sea of Azov was also investigated. It turned out that the ratio of organic forms of nitrogen and phosphorus in sea waters varies little. This stabilization phenomenon will take place for all high-productive reservoirs with low flow, due to autochthonous origin of larger part of organic matter in water bodies of this type.

A brief review of studies of the hydrological regime of the Sea of Azov and approaches to assessing the average salinity—a key indicator of the state of its ecosystem is given. A database of salinity measurements at 47409 oceanographic stations over hundred years (from 1913 to 2014) were used to evaluate the sea-averaged mean annual salinity. The obtained values of the average salinity were found to differ from those published before because of the different approaches used to its calculation and different volumes of data involved. The difference was most significant for Taganrog Bay because of the high variability of its hydrological regime. Anomalies of the average salinity over period 1922–2014 were constructed, and the start of one more period of salinity increase in the Sea of Azov was recognized.