The Black Sea and the Sea of Azov belong to the Atlantic Ocean basin. Waters of the Black Sea wash the shores of Ukraine, Russia, Georgia, Turkey, Bulgaria, and Rumania, and the Azov Sea waters – those of Ukraine and Russia. The seas are connected by the shallow Kerch Strait. They border along the line Cape Takyl – Cape Panagia. The Black Sea is connected with the Sea of Marmara by the Bosphorus Channel (the border is denoted by the line Cape Rumeli – Cape Anadolu) and farther through the Dardanelles – with the Mediterranean. The maximum length of the Black Sea (along 42°29'S) is 1 148 km, its maximum width (between the town of Ochakiv and Cape Eregli) is 611 km, and its minimum width lies along the meridian of the southern point of the Crimea (Cape Sarych) and amounts 258 km. The maximum length of the Sea of Azov (between the Arabat Spit and the Don estuary) is 360 km and its maximum width is 176 km. The average depth of the Black Sea is 1 300 m and maximum one is 2 245 m. The Sea of Azov is shallow: its average depth is 7 m and maximum one is 15 m.
The Black Sea coastline is slightly indented, only the low-lying shores of its northwestern part are cut by bays, inlets and estuaries. The northwestern coast of the Black Sea is low. To the east off the Sevastopol Bay the coast noticeably rises. The Kerch Peninsula shores are precipitous almost along the whole length. The northeastern coast of the Black Sea is mainly high except for the region where it is approached by the vast Colchis lowland. The southern coast of the sea is high and precipitous almost everywhere. The coast west off the Bosphorus Strait is rather low. The capes in this part drop steeply towards the sea. From Cape Kaliakra to the Danube delta the coast gradually descends.
The shores of the Sea of Azov in the west, north and east are mainly low, whereas in the south they are steep. A characteristic feature of the Sea of Azov shores is sand spits separating a number of shallow bays and estuaries. The largest of them, the Arabat Spit, separates the shallow Syvash Bay.
The Black Sea bottom structure includes the regions with continental, subcontinental and subocean crust. In its topography shelf, continental slope and abyssal depression are distinctly observed. The shelf occupies about 25% of the sea bottom area. The shelf maximum width (200–250 km) is in the northwest; near the Southern Coast of the Crimea, the Caucasian and the Anatolian shores its width is several kilometers. The continental slope constitutes almost 40% of the bottom and is bounded by the isobaths of 100 and 2 000 m. The depression bottom (below the isobath of 2 000 m) makes almost 35% of the bottom area and represents an accumulation plain slightly inclined southward. The predominantly flat bottom of the Sea of Azov descends gradually to the depression center.
Climatic conditions of the Black Sea and the Sea of Azov are determined by their geographical position and general atmospheric circulation. The northern part of the Black Sea and the Sea of Azov are located in the southern part of the moderate climate zone, and the southern part of the Black Sea – in the northern part of the subtropical climatic belt. In January mean air temperature above the central part of the Black Sea is 8°C, in the northwestern part it decreases to 0–3°C with the absolute minimum -30°C. Mean air temperature in July is 22–24°C with its maximum 35°C. In the Sea of Azov cold winters (up to -33°C) can be followed by dry and sultry summers (up to 40°C). The annual amount of precipitations over the Sea of Azov and the west and northwest of the Black Sea is 300–500 mm, on the south of the Black Sea – 700–800 mm, and on the east – 1 800–2 500 mm. Above the greater part of the Black Sea northerly and northeasterly winds prevail, whereas southerly and southeasterly ones are typical of its southeastern part. Average monthly wind speed is maximal in January–February (7–8 m/s) and minimal – in June–July (4–6 m/s). Constant maximum wind speed is observed in the western Black Sea, and the minimum one – in its southeast part.
Ice is formed on the Sea of Azov every year. In severe winters it covers a considerable part and sometimes even the entire surface of the sea. In mild winters, ice is found in estuaries, bays, and along the coast. In the Black Sea ice that can hamper navigation is found only in the northwestern part. Fast ice is formed annually only in the bays and estuaries. Complete freezing of the open areas in the northwestern part of the sea is possible only in very cold winters.
A great number of rivers flow into the Black Sea. Their total runoff amounts up to 350 km3/year. About 80% of the river runoff (Danube, Dnipro, Dnister, and Southern Buh) flows into the northwestern part of the sea. Total river runoff (Don and Kuban are the largest ones) into the Sea of Azov averages 35 km3/year.
In the coastal zone of the northern part of the Black Sea water temperature varies from the values of water freezing (-0.97°C at the salinity 18‰ and -0.54°C at the salinity 10‰) to 28–29°C under maximum warming-through. Mean water temperature in the Black Sea is about 9°C. The thermal structure of the Black Sea is characterized by presence of cold intermediate layer, i.e. subsurface (40–80 m) layer of minimum temperature which is traditionally distinguished by the isotherm 8°C. Below 75–100 m temperature monotonically increases with depth up to 9.1°C on the bottom. Mean water temperature in the Sea of Azov is 11.5°C. In winter on the sea surface in the regions of high salinity it decreases up to -1°C (Syvash Bay), and in the low salinity regions – to -0.1°C. In July and August water temperature in the major part of the sea is 24–25°C (near the coast – up to 32°C).
Salinity of the Black Sea surface layer (18‰) is almost half as much as that of the ocean surface water, salinity in the Sea of Azov is even lower (10–12‰). Average salinity in the Black Sea increases monotonically from the surface (17.6‰ in May and 18.1‰ in February) to the bottom (22.33‰). The abyssal part of the sea receives highly saline water of the Sea of Marmara with the Lower Bosphorus current. The vertical haline structure is characterized by presence of two haloclines (the layers of salinity sudden change): the seasonal one – in the 0–30 m layer and the constant one – in the 50–200 m layer.
The peculiarities of the thermohaline structure of the Black Sea water consist in a sudden change of density (conventional density reaches 16.15 – 16.25) called a main pycnocline. It results in a considerable restriction of the vertical water exchange.
The water masses and the structure of the Black Sea water are formed as a result of interaction of the Sea of Marmara water mass brought by the Lower Bosphorus current and fresh water from rivers and precipitations. Five types of the Black Sea water masses are distinguished. They differ in their thermohaline characteristics: the coastal Black Sea water mass, the upper Black Sea water mass, the cold intermediate layer, the intermediate Black Sea water mass and the abyssal Black Sea water mass. The water mass of the Sea of Azov is formed by the water exchange with the Black Sea and by the fresh water inflow.
In the Black Sea the cyclonic water motion prevails. It breaks up into two cyclonic circulations in the western and eastern parts of the sea in June – December. In the same period under the decreased intensity of the general circulation of the sea, the anticyclonic eddies are developed localizing in the zone of the continental slope. The Sea of Azov currents are mainly caused by wind being of cyclonic character. The current structure in the Kerch Strait where the water flows can be directed from the Black Sea to the Sea of Azov and vice versa depending on the wind direction is the most complex. Under the prolonged winds the compensation currents directed against the wind occur in the strait.
A characteristic feature of the Black Sea is presence of a rather thin surface layer of aerobic water and a thick abyssal hydrosulphuric layer. To a greater extent it is associated with a change of the water density that results in considerable restriction of the vertical oxygen flow. The hydrochemical structure of the water layer above the major pycnocline and the processes of its formation are similar to those observed in the oxygenated water in the greater part of the World ocean. Oxygen is generated in the upper 30–40 m photic layer of the sea or comes to this layer from the atmosphere and then is transported to the deeper water layers by the physical processes of water exchange. The hydrochemical structure of the major pycnocline layer is transitional from the aerobic conditions to the anaerobic ones. Below the major pycnocline the content of hydrogen sulphide increases and reaches its maximum values in the bottom water layer.
The process of formation of contemporary flora and fauna of the Black Sea has been going on for the last 5–8 thousand years after its recurrent joining with the World ocean. At present, according to their genesis, four main groups of hydrobionts are distinguished: Mediterranean immigrants, the most numerous in species and quantitative composition; Pontian autochthonous relicts; freshwater species; and the introduced species.
According to the present notions, within the Ukrainian economic zone about 150 species of animal plankton have been discovered, among which there are several invading ones. At the same time some indigenous species have become extinct, including important foodstuff for fish larvae. According to the estimations of the 90ies, the content of ‘fodder’ zooplankton in the upper populated layer (150–200 m depth) varied from 1 to 25 g/m2. Sharp decrease of quantity and biomass of the ‘fodder’ zooplankton in the 90ies coincided with the invasion of the comb jellyfish (Mnemiopsis leidyi).
Macrovegetation in the Ukrainian part of the Black Sea shelf numbers more than 270 species, including 4 species of seagrass and 2 species of flowers. In the algaflora red algae (almost 140 species) dominate, the amounts of brown and green algae are similar and half as much, respectively.
Plant associations are common on the depth 0–20 m, but the largest thickets of macrophytes are concentrated within 1–5 m. During the last decades essential changes took place in composition and structure of Cystoseira and Phyllophora phytocenoses. They are most evident in the northwestern part of the Black Sea and in some places near the Crimean coast.
Species composition, the amount of spawn and larvae, and larvae survival under different conditions are major indicators of the state of ichthyoplankton associations. In the early 90ies the amount of ichthyoplankton became by 1–2 orders of magnitude less in comparison with that in the 50ies–60ies, and the part of dead spawn increased from 40% to 80% and more. In 2000–2003 a part of dead spawn decreased approximately to 70%.
The ichthyofauna of the Black Sea numbers almost 200 species and subspecies including stray fresh- and salt-water fishes known by single finds. Seawater fishes (about 140 species and subspecies) make up the major part of ichthyofauna and, in their turn, are classified into two groups: Mediterranean immigrants and boreal-Atlantic relicts. Mediterranean species inhabit mainly the upper warmed-through layer. More than 60 species of them have naturalized completely, even to the formation of endemic subspecies, and all the stages of their life cycle are connected with the Black Sea. Other species regularly migrate to feed from the other seas of the Mediterranean in the warm period of the year. The boreal-Atlantic subgroup is represented by 13 species which during the warm period of the year live mainly in the cold subsurface layer and get into the surface layer in winter. The group of brackish-water fishes numbers 22 endemic or common with the Caspian Sea species and subspecies which are the autochthonous relicts of the brackish-water Lower Pliocene Pontian lake-sea. Anadromous and semi-migratory fishes are represented by 25 species that originated 1.5–2 mln years ago. The Far East mullet has been artificially acclimatized in the Azov-Black Sea basin.
The Black Sea and the Sea of Azov are of great economic importance as a promising region of extraction of hydrocarbon resources, fishery zone, significant shipping lane, fishery zone, and possess a great recreation potential.
The Ukrainian sectors of the Black Sea and the Sea of Azov water areas are an important hydrocarbon resource base. About 30% of total resources of hydrocarbons in Ukraine are concentrated here. Within the northwestern shelf of the Black Sea 8 gas and gas-condensate deposits have been discovered: Holitsyns’ke, Yuzhne-Holitsyns’ke, Shtormove, Arkhanhel’s’ke, Shmidtivs’ke, Kryms’ke, Odes’ke, and Bezymenne. In the Sea of Azov, 6 gas deposits have been found: Strilkove, Mors’ke, Pivnichnokerchens’ke, Pivnichnokazantyps’ke, Skhidnokazantyps’ke, and Pivnichnobulhanats’ke.
Until recently, the Black Sea and the Sea of Azov were the most productive in the Mediterranean basin. However, the excessive level of anthropogenic impact in the last quarter of the 20th century resulted in a critical state of their ecosystems and a considerable decrease in fish capacity. In recent decades sprat and anchovy was the main food fish in the Azov-Black Sea basin. The Black Sea share in the total catch of these species in Ukraine exceeds 98%. In the Sea of Azov fishery is based on common kilka, anchovy, mullet, and zander, and now recovery of bullhead resources is observed. The present state of the resources of the most valuable species of the Azov-Black Sea basin – sturgeon, Black Sea salmon and turbot – causes anxiety.
Izmail, Illichivs’k, Odesa, Yuzhne, Mykolaiv, Kherson, Sevastopol’, Feodosia, and Kerch are the largest Ukrainian ports on the Black Sea, and Berdians’k and Mariupol – on the Sea of Azov. Odesa, Illichivs’k, and Yuzhne are of special importance not only in the transportation system of Ukraine but also in the structure of international transportation corridors that are being developed actively.
Favorable natural and climatic conditions open up vast opportunities for the development of resorts and tourism in the coastal zone of the both seas. The length of the seacoast in Ukraine is about 2 500 km and 1 160 of them are valuable beaches. There are two major regions of natural recreation resources – the Crimean and the Azov-Black Sea ones. The Southern Coast of the Crimea is the largest climatic health resort. Sea curative mud deposits are a valuable element of the Ukrainian recreation potential.
During recent decades, the ecosystems of the Black Sea and the Sea of Azov were subjected to heavy anthropogenic load. Among the crucial factors forming the major ecological problems are the influence of river runoff 80% of which inflow to the most ecologically vulnerable shallow northwestern part of the Black Sea, wastewater inflow from the point (especially dangerous for the Sea of Azov) and diffuse coastal sources, and pollutions from sea vessels. Eutrophication that affects the ecosystems of the Black Sea and the Sea of Azov is the most negative anthropogenic factor. The eutrophication level and the volume of entering pollutants exceeded the assimilation capacity of marine environment by early 80ies and over and over increased by middle 90ies. In 2 000ies the ecological state rather improved: a stable tendency to restoration of bio-diversity and quantitative characteristics of numerous hydrobiont species including productive ones is observed; the degree of the basin eutrophication decreased but it did not reach the ecologically safe level.
