Sea of Azov

The Sea of Azov is an inland shelf sea in Eastern Europe connected to the Black Sea by the narrow Strait of Kerch, and sometimes regarded as a northern extension of the Black Sea. The sea is bounded by Russia on the east, and by Ukraine on the northwest and southwest. It is an important access route for Central Asia, from the Caspian Sea via the Volga–Don Canal.
The sea is largely affected by the inflow of the Don, Kuban, and other rivers, which bring sand, silt, and shells, which in turn form numerous bays, limans, and narrow spits. Because of these deposits, the sea bottom is relatively smooth and flat, with the depth gradually increasing toward the middle. Because of the river inflow, water in the sea has low salinity and a high amount of biomass that affects the water colour. Abundant plankton result in unusually high fish productivity. The sea shores and spits are low; they are rich in vegetation and bird colonies. The Sea of Azov is the shallowest sea in the world, with the depth varying between. There is a constant outflow of water from the Sea of Azov to the Black Sea.

Names

The name is likely to derive from the settlement of an area around Azov, whose name comes from the Kipchak Turkish asak or azaq 'lowlands'. A Russian pseudo-etymology, however, instead derives it from an eponymous Cuman prince named "Azum" or "Asuf", said to have been killed defending his town in 1067. A formerly common spelling of the name in English was the.
In antiquity, the sea was known as the Maeotis Swamp, from the marshlands to its northeast. It remains unclear whether it was named for the nearby Maeotians or viceversa if that name was an exonym, broadly applied to various peoples who happened to live beside it. Other names included or Maeotius ; the Maeotian or ; the Cimmerian or ; and the Cimmerian or . The Maeotians themselves were said by Pliny to call the sea Temarunda, meaning "Mother of Waters".
The medieval Russians knew it as the after the adjacent city now known as Sudak. It was known in Ottoman Turkish as the Balük-Denis from its high productivity.

History

Prehistory

There are traces of Neolithic settlement in the area now covered by the sea.
In 1997, William Ryan and Walter Pitman of Columbia University published a theory that a massive flood through the Bosporus occurred in ancient times. They claim that the Black and Caspian Seas were vast freshwater lakes, but in about the Mediterranean spilled over a rocky sill at the Bosporus, creating the current link between the Black and Mediterranean Seas. Subsequent work has been done both to support and to discredit this theory, and archaeologists still debate it. This has led some to associate this catastrophe with prehistoric flood myths.

Antiquity

The Maeotian marshes around the mouth of the Tanais River were famous in antiquity, as they served as an important check on the migration of nomadic people from the Eurasian steppelands. The Maeotians themselves lived by fishing and farming, but were avid warriors able to defend themselves against invaders. Misled by its strong currents, ancient geographers had only a vague idea of the extent of the sea, whose fresh water caused them to typically label it a "swamp" or a "lake". Herodotus judged it as large as the Black Sea, while the Pseudo-Scylax thought it about half as large.
It was long believed to provide direct communication with the Arctic Ocean. Polybius confidently expected that the strait to the Sea of Azov would close in the near future, due to ongoing deposition of sediments from rivers. In the 1st century, Strabo reckoned the distance from the Cimmerian Bosporus to the mouth of the Tanais at, a roughly correct figure, but did not know that its width continuously narrows.
Milesian colonization began in the 7th century BC. The Bosporan Kingdom was named for the Cimmerian Bosporus rather than for the more famous Bosporus at the other end of the Black Sea. Briefly annexed by Pontus from the late 2nd century BC, it stretched along both southern shores of the Sea of Azov from the time of Greek colonization to the end of the Roman Empire, serving as a client kingdom which exported wheat, fish, and slaves in exchange for Greek and Roman manufactures and luxuries. Its later history is uncertain but probably the Huns, after defeating the Alans people who had settled in the region from central Asia, overran it in the late 4th century.

Azov campaigns of 1695–96 and 1736–37

The Sea of Azov was frequently the scene of military conflicts between Russia, pursuing naval expansion to the south, and the major power in the region, Turkey. During the Russo-Turkish War, there were two campaigns in 1695–96 to capture the then Turkish fortress of Azov defended by a garrison of 7,000. The campaigns were headed by Peter I and aimed to gain Russian access to the Sea of Azov and Black Sea. The first campaign began in the spring of 1695. The Russian army consisted of 31 thousand men and 170 cannons and included selected trained regiments and Cossacks. It reached Azov on 27–28 June and besieged it by land by 5 July. After two unsuccessful assaults on 5 August and 25 September, the siege was lifted.
The second campaign involved both ground forces and the Azov fleet, which was built in Moscow Oblast, Voronezh, Bryansk and other regions between winter 1695 and spring 1696. In April 1696, the army of 75,000 headed by Aleksei Shein moved to Azov by land and by ship via the Don River to Taganrog. In early May, they were joined by another fleet led by Peter I. On 27 May, the Russian fleet blocked Azov by sea. On 14 June, the Turkish fleet tried to break the blockade but, after losing two ships, retreated to the sea. After intensive bombardment of the fortress from land and sea, on 17 July the Russian army broke the defense lines and occupied parts of the wall. After heavy fighting, the garrison surrendered on 17 July. After the war, the Russian fleet base was moved to Taganrog and Azov, and 215 ships were built there between 1696 and 1711. In 1711, as a result of the Russo-Turkish War and the Treaty of the Pruth, Azov was returned to Turkey and the Russian Azov fleet was destroyed. The city was recaptured by Russia in 1737 during the Russo-Austrian-Turkish War. However, as a result of the consequent Treaty of Niš, Russia was not allowed to keep the fortress and military fleet.

Crimean War 1853–1856

Another major military campaign on the Sea of Azov took place during the Crimean War of 1853–56. A naval and ground campaign pitting the allied navies of Britain and France against Russia took place between May and November 1855. The British and French forces besieged Taganrog, aiming to disrupt Russian supplies to Crimea. Capturing Taganrog would also result in an attack on Rostov, which was a strategic city for Russian support of their Caucasian operations. On 12 May 1855, the allied forces easily captured Kerch and gained access to the Sea of Azov, and on 22 May they attacked Taganrog. The attack failed and was followed by a siege. Despite the vast superiority of the allied forces, the city withstood all attempts to capture it, which ended around August 1855 with the retreat of the allied army. Individual coastal attacks continued without success and ceased in October 1855.

21st century

In December 2003, Ukraine and the Russian Federation agreed in a treaty to treat the sea and the Kerch Strait as shared internal waters.
In September 2018, Ukraine announced the intention to add navy ships and further ground forces along the coast of the Sea of Azov, with the ships based at Berdiansk. The military posturing was exacerbated following the construction of the Crimean Bridge, which is too low to allow passage of Panamax ships into Ukraine's port. Late that September, two Ukrainian vessels departed from the Black Sea port Odesa, passed under the Crimean Bridge, and arrived in Mariupol. Tensions increased further after the Kerch Strait incident in November 2018, when Russia seized three Ukrainian Navy vessels attempting to enter the Sea of Azov.
Control of the western shore of the Sea is vital to the economy of Ukraine but it is also of immense strategic importance to Russia, as a land route to Crimea as well as it is for passage by Russian marine traffic.
On December 10, 2021, the Ukrainian Navy announced that Russia had blocked off nearly 70 percent of the Sea of Azov, issuing navigation warnings, ostensibly to conduct artillery fire exercises on the sea..."near Mariupol, Berdyansk and Henichesk." It raised apprehension regarding a potential Russian invasion since it had begun amassing tens of thousands of troops near the southeast Ukraine border and had begun a propaganda war against the Kyiv government. The Russians seized three Ukrainian military vessel as the boats were trying to cross the strait, and captured 24 sailors who were finally released after months of negotiations.
On February 24, 2022, Russian forces began shelling Mariupol at the start of the 2022 Russian invasion of Ukraine. By May, with the end of the siege of Mariupol, Russia fully captured the city and blocked off Ukraine's access to the sea by controlling the entire north Pryazovia.

Geology and bathymetry

The International Hydrographic Organization defines the limit of the Sea of Azov in the Kertch Strait as "The limit of the Black Sea", which is itself defined as "A line joining Cape Takil and Cape Panaghia ".
The sea is considered an internal sea of Russia and Ukraine, and its use is governed by an agreement between these countries ratified in 2003.
The sea is long and wide and has an area of ; it is the smallest sea within the countries of the former Soviet Union. The main rivers flowing into it are the Don and Kuban; they ensure that the waters of the sea have comparatively low salinity and are almost fresh in places, and also bring in huge volumes of silt and sand. Accumulation of sand and shells results in a smooth and low coastline, as well as in numerous spits and sandbanks.
The Sea of Azov is the shallowest sea in the world with an average depth of and maximum depth of ; in the bays, where silt has built up, the average depth is about. The sea bottom is also relatively flat with the depth gradually increasing from the coast to the centre. The Sea of Azov is an internal sea with passage to the Atlantic Ocean going through the Black, Marmara, Aegean and Mediterranean seas. It is connected to the Black Sea by the Strait of Kerch, which at its narrowest has a width of and a maximum depth of. The narrowness of the Kerch Strait limits the water exchange with the Black Sea. As a result, the salinity of the Sea of Azov is low; in the open sea it is 10–12 on the Practical Salinity Scale, about one third of the salinity of the oceans; it is even lower in the Taganrog Bay at the northeast end of the Sea. The long-term variations of salinity on the PSS are low, and are mostly caused by changes in humidity and precipitation.
Although more than 20 rivers flow into the sea, mostly from the north, two of them, the Don and Kuban rivers, account for more than 90% of water inflow. The contribution of the Don is about twice that of the Kuban. The Kuban delta is located at the southeast, on the east side of the Kerch Strait. It is over 100 km long and covers a vast flooded area with numerous channels. Because of the spread, the delta has low contrast in satellite images, and is hardly visible in the map. The Don flows from the north into the large Taganrog Bay. The depth there varies between 2 and 9 metres, while the maximum depth is observed in the middle of the sea.
Typical values of the annual inflow and outflow of water to the sea, averaged over the period from 1923 to 1985, are as follows: river inflow 38.6 km³, precipitation 15.5 km³, evaporation 34.6 km³, inflow from the Black Sea 36–38 km³, outflow 53–55 km³. Thus, about 17 km³ of fresh water is outflowing from the Azov Sea to the Black Sea. The depth of Azov Sea is decreasing, mostly due to the river-induced deposits. Whereas the past hydrological expeditions recorded depths of up to 16 metres, more recent ones could not find places deeper than 13.5–14 metres. This might explain the variation in the maximum depths among different sources. The water level fluctuates by some 20 cm over the year due to the snow melts in spring.
The Taman Peninsula has about 25 mud volcanoes, most of which are active. Their eruptions are usually quiet, spilling out mud, and such gases as methane, carbon dioxide and hydrogen sulfide, but are sometimes violent and resemble regular volcanic eruptions. Some of those volcanoes are under water, near the shores of the peninsula. A major eruption on 6 September 1799, near Golubitskaya stanitsa, lasted about 2 hours and formed a mud island 100 metres in diameter and 2 metres in height; the island was then washed away by the sea. There were similar eruptions in 1862, 1906, 1924, 1950 and 1952.
The current vertical profile of the Sea of Azov exhibits oxygenated surface waters and anoxic bottom waters, with the anoxic waters forming in a layer in thickness. The occurrence of the anoxic layer is attributed to seasonal eutrophication events associated with increased sedimentary input from the Don and Kuban Rivers. This sedimentary input stimulates biotic activity in the surface layers, in which organisms photosynthesise under aerobic conditions. Once the organisms expire, the dead organic matter sinks to the bottom of the sea where bacteria and microorganisms, using all available oxygen, consume the organic matter, leading to anoxic conditions. Studies have shown that in the Sea of Azov, the exact vertical structure is dependent on wind strength and sea surface temperature, but typically a 'stagnation zone' lies between the oxic and anoxic layers.