Black Sea

The Black Sea is a nearly landlocked body of water formerly linked to its eastern neighbor, the Caspian Sea. Geological changes separated it from the Caspian and created two narrow waterways, the Bosphorus and the Dardanelles, that connect it with the Mediterranean Sea. Just to the north is the much smaller Sea of Azov, connected by the Kerch Strait. Some of the Black Sea's most interesting physical features make it unique among the world’s small to medium-sized seas.

General Features

The Black Sea, with a surface area of more than 400,000 square kilometers (more than 160,000 square miles) of brackish water, is located on the southern margin of the Eurasian landmass. Its shores include territories in several countries. From the southern and southwestern coast of the Türkiye, the shoreline proceeds clockwise through Bulgaria, Romania, Ukraine, Russia, and Georgia.

The name "Black Sea" is a literal translation of the Turkish Karadeniz. This name, suggesting a somewhat ominous image (particularly in comparison to the Turkish name White Sea, or Akdeniz, referring to the Mediterranean), dates from the Turkish occupation of the southern shores of the Black Sea between the thirteenth and the fifteenth centuries. The sense of blackness refers not to any impression of the color of its waters but rather to a presumed inhospitable environment. When the Turks captured the Greek-named Pontus Euxinus (meaning “hospitable sea”) from the Byzantine Greeks, they adopted a much earlier Greek denomination for the same body of water, namely Pontus Axeinus (or “inhospitable sea”).

The major ports of the Black Sea littoral states are Trabzon, Samsun, Sinop, and Zonguldak (Türkiye); Burgas and Varna (Bulgaria); Odessa (Ukraine); Sevastopol (Crimea); and Batumi (Georgia).

Geological Origins

Geologically, the Black Sea appears to be a basin left behind by the retreating ancient Tethys Sea, which took place over about 200 million years. This long geological evolution reached a significant stage about 50 million years ago as the upward thrust of the Anatolian landmass (Türkiye) and Western Iran split the Caspian Sea basin off from the Black Sea. Further mountain-forming activity, including the upheavals that created the Pontic, Caucasus, Carpathian, and Crimean landmasses, also affected the basin that eventually held the waters of the Black Sea. Finally, the geology associated with the Turkish Straits, which connect the Black Sea to the Mediterranean via the straits of the Bosphorus and the Dardanelles, with the Sea of Marmara in between, appears to have been the most recent stage contributing to the current configuration of the Black Sea, occurring less than 10,000 years ago.

The total area of the Black Sea is about 422,000 square kilometers, although some sources put it at over 436,000. At its widest, the sea extends more than 1,175 kilometers from west to east. Its narrowest north-to-south point, running from the tip of the Crimean Peninsula to the Turkish coast at the Kerempe Burmi Cape, is about 260 kilometers.

Several important freshwater rivers feed the sea. The most famous of these, the Danube, enters the sea along the coast of Romania. The Dniester, which flows parallel to the northern fringes of the Carpathian Mountain range, ends at the delta that feeds the farthest northwest area of the Black Sea. The Dniester Delta forms part of the major port complex of Odessa in Ukraine. To the east of the Dniester is the Dnieper, the last major river to enter the north coast of the Black Sea proper before its coastline is broken by the Crimean landmass and the waters and rivers associated with the Sea of Azov.

The depth of the sea varies; the deepest area, in the southern part of the basin, about midway from east to west, measures more than 2,120 meters deep. The fact that the deeper zones of the Black Sea receive very low levels of ventilation (circulation of oxygen) means that these areas do not support any significant plant growth or fish populations. In deep waters, a high hydrogen sulfide concentration causes whatever oxygen exists to ionize. These conditions mean that only certain species of bacteria can survive at lower depths. The beginnings of low oxygen levels, with consequential decreases in marine life, occur at depths of around 150 meters. Where waters are sufficiently ventilated, there are substantial numbers of fish, although only a few species are sought by commercial fisheries.

The most outstanding irregularity at surface level along the coast is the Crimean Peninsula, which juts southward into the Black Sea from the mainland just east of the Dnieper River Delta. The Crimean Peninsula is the site not only of the traditional seaside vacation town of Yalta (where the Western allies met with the Soviet Union’s Joseph Stalin near the end of World War II) but also of the strategic port of Sevastopol, founded by Russian czars as a strategic maritime outpost for Russian access to the Mediterranean. Part of Russia since the eighteenth century, the Crimea, as the peninsula is also known, was made part of Ukraine in the 1950s but annexed again by Russia in 2014. In 2024, the Crimean pensinsula is recognized as part of Ukraine, though annexed by the Russian Federation.

There are no major islands in the Black Sea. Most geographical accounts overlook the few smaller islands, mentioning only Zmiyini, located east of the Danube River delta, and Berezan, near the mouth of the Dniester.

The Kerch Strait, located east of the Crimean Peninsula, where a city by that name stands, connects the Black Sea to the Sea of Azov. The latter, part of the same residual basin complex left behind by the receding Tethys Sea, encompasses approximately 39,000 square kilometers. The Sea of Azov receives the waters of two major rivers, the Don and the Kuban.

With the one major exception of the Crimean Peninsula, the coastline of the Black Sea is quite regular, reflecting its geological origins as a residual basin. The shallow coastal shelf is seldom deeper than 90 meters. It can be very wide but generally extends out from the shore about 11 kilometers. If one takes the average of 11 kilometers and adds areas where the shelf is considerably wider, these shallow waters make up almost one-fourth of the total surface of the Black Sea.

Tidal Phenomena and Currents

There is little regularly predictable tidal movement in the Black Sea. When moderate tidal movements occur, their levels can be affected by a sudden rise or fall of atmospheric pressures in different regions, either over the sea or on the surrounding landmasses. Such tides rarely cause dangers for boats or pier structures along the shorelines.

Currents are strongest near the shores of the sea, where the water is not very deep. Such currents run an average of between 40 and 50 centimeters per second. In areas of deeper water, very slow currents are difficult to measure but generally do not run faster than 2.5 to 5 centimeters per second. A particular phenomenon of currents exists in the Bosphorus Straits zone leading from the Black Sea to the Sea of Marmara. Here, a current near the surface carries water from the Black Sea past the city of Istanbul into the Sea of Marmara and eventually into the Mediterranean. At deeper levels, the current moves in the opposite direction, carrying water with higher saline content that originates in the Mediterranean into the Black Sea.

The salinity level of the Black Sea is roughly one-half that of the world’s major oceans. Salinity counts (relative proportions of salt to water) near the surface are between seventeen and eighteen parts of salt per thousand parts of water. In the cold band beneath the first layer of Black Sea surface water, the salinity count increases rapidly, reading twenty-one parts per thousand. The proportion of salt to water increases as one descends to deeper zones. However, the rate of increase is much more gradual than the sudden increase that occurs in the intermediate-level cold band. The highest salinity count in the deep water is about thirty parts salt to one thousand parts water. Measurements are higher in the Bosphorus Straits, but this phenomenon is linked to transferring Mediterranean water into the Black Sea via subsurface currents.

The surface temperature of the Black Sea varies considerably from season to season. Winter temperatures in the northern zones hover just below 0 degrees Celsius. Where freshwater inflow from major rivers is substantial, some freezing can occur near the coast. However, most zones' saline content is sufficiently high to prevent widespread freezing of Black Sea waters. Winter temperatures are more moderate in the southern half of the sea, reaching about 10 degrees Celsius in the southeast corner near the Turkish border with Georgia. Summer brings surface temperatures up to nearly 21 degrees Celsius. The warming effect, however, is limited to depths down to about 45 meters. Below this level, down to about 90 meters, there is a more or less constant cold band, where temperatures remain at about 7 degrees Celsius throughout the year. Deeper waters may even be a bit warmer than the cold band, but this phenomenon stems from an insulating effect and is not tied to rising temperatures at the surface.

Natural Resources and Economic Potentials

Until the late twentieth century, perhaps the best-known natural resource exploited on an industrial scale in the Black Sea region was coal, shipped in large quantities from the Turkish port of Zonguldak. Caspian Sea petroleum transit shipments from the Black Sea port of Batumi were always a factor in the economic history of the Black Sea during the period of the Soviet Union. However, their importance grew rapidly in the last decade of the twentieth century, as newly opened free international markets for Caspian Sea oil provided incentives for expanded construction of pipelines and port facilities in the southeast coastal region of the Black Sea.

Fishing is the most traditional form of economic activity in the Black Sea. It appears to have a limited capacity for expansion beyond levels reached by the middle of the twentieth century. The most common species of fish in the Black Sea are Mediterranean varieties, some of which move into and out of the Black Sea via the Sea of Marmara from season to season. Specialists have noted nearly two hundred different species of fish, but only about forty varieties are exploited commercially. The most important locally processed fish include horse mackerel and anchovies.

Significance

The study of the Black Sea region can be beneficial for comparison with small to moderately large inland seas worldwide. The scale of ecological considerations in such circumstances drastically differs from what would apply to studying large oceans. In this case, two comparable bodies of water, the Black Sea and the Caspian Sea, are located much in the same region but demonstrate quite different characteristics. On the one hand, for example, the Black Sea has not been seriously affected by large-scale petroleum development, which has had significant effects on the ecology of the Caspian Sea. On the other hand, the Black Sea has considerably more large urban port cities around its coasts. Examination of pollution levels and marine biology in the Black Sea can lead to a better understanding of its environmental prospects and similar bodies of water in other areas. The Black Sea was strategically important in the war between Russia and Ukraine in 2022 and 2023. Leaders in Kyiv, the capital of Ukraine, called on the North Atlantic Treaty Organization (NATO) to help secure Ukraine’s Black Sea coastline in defense of Russian forces. Ukraine argued that doing so was integral for peace not just in Ukraine but throughout Europe.

For the entirety of the twenty-first century, the Black Sea has suffered environmentally and has been one of Europe’s most polluted bodies of water. This pollution has affected all aspects of the sea, including marine life, biodiversity, and human health. Its polluted state has interfered with tourism, fisheries, and shipping and, therefore, had dire economic effects. Attempts were made to address the pollution of the Black Sea through the Blueing the Black Sea Program, as well as other initiatives in the mid-2020s. However, exacerbating the situation, in June 2023, Russia destroyed Ukraine's Nova Kakhovka hydroelectric power plant. This released a surge of polluted water into the Black Sea. The Black Sea remained a highly contentious area of the Russia-Ukraine war as the conflict stretched into the mid-2020s. 

Principal Terms

Bosphorus and Dardanelles Straits: straits leading to and from the Sea of Marmara; they are the only sea lanes linking the countries with shores on the Black Sea to the Mediterranean

Crimean Peninsula: a large peninsula located on the north-central shore of the Black Sea; it is the most significant irregularity on the otherwise regular coastline

Danube River: probably the most famous river that enters the Black Sea; the river is a vital means for international maritime access via the Black Sea for several European countries

Istanbul: a major international city located in Türkiye just at the entry point of the Bosphorus into the Sea of Marmara

Kerch Straits: the strategic narrows that join the Black Sea to the Sea of Azov, located northeast of the Crimean Peninsula and sharing a similar ecology

Odessa: the major Black Sea city of Ukraine; its port, Ilichyovsk, is possibly the busiest maritime center on the Black Sea

Tethys Sea: the much larger geological predecessor of both the Black Sea and the Caspian Sea to its east; named after the Titan and wife of the Greek god of the great outer sea, Oceanus

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