Black Sea

The Black Sea is a large inland sea between south-eastern Europe and western Asia. Six countries border it: Ukraine, Russia, Georgia, Türkiye, Bulgaria and Romania. It connects to the open ocean only through a narrow chain of Turkish waterways, the Bosporus and the Dardanelles. Because of this, it is a key route for grain, oil and warships, and a frontline of the Russia-Ukraine war.

Where exactly is it?

Picture a large oval-shaped sea. To the north lies Ukraine, with the Crimean Peninsula sticking out into the sea. To the north-east is Russia, and to the east is Georgia. Türkiye forms the whole southern shore. Bulgaria and Romania lie on the west.

• In the north-east, the narrow Kerch Strait (about 35 km long) connects the Black Sea to the small, shallow Sea of Azov. Russia opened the Crimean Bridge across it in 2018.
• In the south-west, the Bosporus (about 30 km long and at its narrowest about 750 m wide) runs through the city of Istanbul. It connects the Black Sea to the Sea of Marmara.
• The Dardanelles (about 61 km long) then connects the Sea of Marmara to the Aegean Sea, which opens into the Mediterranean Sea.
• Together, the Bosporus, the Sea of Marmara and the Dardanelles are called the Turkish Straits. A ship leaving Odesa for India must pass through all of them, then the Mediterranean, the Suez Canal and the Red Sea.

Its physical features

• Size: about 4,36,400 sq km in area, with a maximum depth of about 2,212 m.
• Rivers: many large European rivers flow into it, including the Danube, Dnieper, Dniester and Southern Bug. The Don flows into the Sea of Azov. This large inflow of fresh water makes the surface water less salty than the open ocean.
• A "dead" deep layer: Below roughly 150 to 200 m, the water has almost no dissolved oxygen and is full of hydrogen sulphide (a poisonous gas). The lighter, less salty surface water floats on top of heavier, saltier deep water, and the two layers barely mix. This makes the Black Sea the largest anoxic (oxygen-free) water body in the world. Only the top layer supports most marine life. Old shipwrecks in the deep layer are preserved remarkably well because there is little oxygen to decay them.

Why does it matter so much?

1. World food supply: Ukraine and Russia are among the world's biggest exporters of wheat, maize (corn), barley and sunflower oil. Ukraine is the world's largest exporter of sunflower oil (about a third of the global market as of 2026). Most of this leaves through Black Sea ports like Odesa, Chornomorsk and Pivdennyi (Yuzhny) in Ukraine and Novorossiysk in Russia. Countries in Africa and West Asia, like Egypt, depend heavily on this grain.
2. Energy: Oil and gas from Russia and the Caspian region move across or along the Black Sea through tankers and pipelines.
3. Military power: Russia's Black Sea Fleet has its main base at Sevastopol in Crimea. Control of the sea gives naval reach into the Mediterranean.
4. NATO's southern edge: Three Black Sea states, Türkiye, Romania and Bulgaria, are members of NATO (the North Atlantic Treaty Organization, a Western military alliance).

A history of conflict

• Crimean War (1853-1856): Russia fought the Ottoman Empire, Britain and France, largely over influence around the Black Sea and the straits.
• 2014: Russia annexed Crimea from Ukraine. Most countries do not recognise this.
• 2022 onwards: After Russia's full-scale invasion of Ukraine in February 2022, Ukraine's sea ports were blocked, cutting off its grain exports and pushing up world food prices. This led to the UN-brokered Black Sea Grain Initiative (July 2022 to July 2023). After it ended, Ukraine opened its own humanitarian shipping corridor along its coast in August 2023.
• March 2025: After talks in Riyadh, Saudi Arabia, the United States announced that Russia and Ukraine had agreed in principle to ensure safe navigation in the Black Sea. The two sides disagreed on the details, and it did not hold as a lasting arrangement.

What does international law say? The Montreux Convention (1936)

Passage through the Turkish Straits is governed by the Montreux Convention Regarding the Regime of the Straits, signed in 1936 in Montreux, Switzerland. It gives Türkiye control over the straits. Its main rules:

• Merchant ships (cargo ships, tankers) of all countries have freedom of passage in peacetime.
• Warships face limits. Countries that do not border the Black Sea can keep warships there only up to a total tonnage limit (a base of 30,000 tons, which can rise to a maximum of 45,000 tons), and each warship can stay for no more than 21 days. Advance notice must be given to Türkiye.
• In wartime, if Türkiye is not at war, it can close the straits to the warships of the countries that are at war (Article 19), except those returning to their home bases in the Black Sea.

Türkiye used this power in February 2022, closing the straits to warships of the warring parties. This is why the Black Sea war has been fought largely by the navies already inside it.

Regional cooperation

The Organization of the Black Sea Economic Cooperation (BSEC) was founded on 25 June 1992 in Istanbul by 11 countries. It now has 13 members, with its secretariat in Istanbul. India is not a member.

India's position and interests

• Food and fertiliser prices: India imports sunflower oil largely from Ukraine and Russia. When Black Sea trade stops, cooking oil and fertiliser prices rise in India.
• Indian sailors: Many merchant ships in the region have Indian crew. Attacks on shipping put Indian seafarers at risk.
• Global South voice: India has said the war's effect on food, fuel and fertiliser hurts developing countries most, and it supports freedom of navigation under international law.
• Balanced diplomacy: India keeps ties with both Russia and Ukraine, which gives it room to suggest practical steps like a maritime truce.

Commonly confused concepts

• Bosporus vs Dardanelles: The Bosporus links the Black Sea and the Sea of Marmara and runs through Istanbul. The Dardanelles links the Sea of Marmara and the Aegean Sea. Remember the order from north to south: Black Sea, Bosporus, Marmara, Dardanelles, Aegean.
• Black Sea vs Caspian Sea: The Black Sea is connected to the ocean through the Turkish Straits. The Caspian Sea is completely landlocked; it is the world's largest inland body of water.
• Sea of Azov vs Sea of Marmara: Azov is in the north-east, joined by the Kerch Strait. Marmara is in the south-west, between the Bosporus and the Dardanelles, fully inside Türkiye.
• Montreux Convention vs UNCLOS: UNCLOS (1982) is the general global law of the sea, including "transit passage" through international straits. The Turkish Straits are governed by the older Montreux Convention (1936), a special treaty that UNCLOS leaves in place.
• Montreux Convention vs Montreux Record: The Montreux Record is a list of threatened wetlands under the Ramsar Convention. It has nothing to do with the Black Sea straits.

Issues, criticism and the way forward

• Shipping security: Mines, drones and missile strikes on ports have made the sea dangerous for merchant ships and pushed up insurance costs.
• Food security: Any blockade hits import-dependent countries in Africa and West Asia hardest.
• Montreux debates: Some argue the Convention limits outside navies too strictly; others, including Türkiye, see it as a source of stability that keeps the Black Sea from becoming a zone of big-power naval rivalry.
• Environmental stress: Pollution from rivers, overfishing, oil spills and war damage threaten an already fragile sea with a thin layer of oxygen-rich water.
• Way forward: limited, verifiable truces on shipping and energy, a return to safe corridors for grain, mine clearance, and support for freedom of navigation, as the step-by-step proposals now under discussion try to do.

Concepts to Know

• Strait: A narrow strip of water connecting two larger bodies of water.
• Anoxic: Without oxygen. Anoxic water cannot support most fish and animals.
• Hydrogen sulphide: A poisonous gas with a rotten-egg smell, produced when bacteria break down dead matter without oxygen.
• Annexation: When one country takes over another country's territory and declares it its own.
• Tonnage: The size or weight of ships, used here to cap how much naval power outside countries can bring into the Black Sea.
• Freedom of navigation: The principle that ships of all countries may sail through international waters and straits without interference.