Black Sea

Topic: World Physical Features and Natural Regions · NCERT: Beyond NCERT

Meaning

The Black Sea is an inland sea between Europe and Asia. Six countries border it: Turkey, Bulgaria, Romania, Ukraine, Russia and Georgia. It reaches the Mediterranean only through two narrow Turkish straits, the Bosphorus and the Dardanelles.

It matters for two reasons. First, it is the world's largest anoxic basin (a water body whose deep water has no oxygen), so it is a textbook example of how rivers and landforms control the salinity and oxygen of a sea. Second, it has been a war zone and a key grain-export route since the Russia–Ukraine war began.

Explanation

Shape and outlet: an almost closed sea

• Bordering countries (clockwise from the south): Turkey → Bulgaria → Romania → Ukraine → Russia → Georgia.
• The only way out to the ocean (north to south):

• Black Sea → Bosphorus (at Istanbul) → Sea of Marmara → Dardanelles → Aegean Sea → Mediterranean.

• Both straits belong to Turkey. Together they form the Bosphorus–Dardanelles chokepoint (a narrow strait that many ships must pass through; if it is blocked, trade slows down).

• Because the outlet is so narrow, the Black Sea behaves almost like a closed basin.

Why its salinity is low

• Cause: big rivers bring fresh water.

• The Danube, Dnieper and Dniester pour large amounts of fresh water into the sea.

• Cause: little sea water comes in.

• The sea is almost closed in.

• So only a little salty Mediterranean water mixes in through the narrow straits.

• Result: the surface water is less salty than the open ocean.

Why its deep water has no oxygen

• Step 1: the water forms layers.
• The fresher water is lighter, so it stays on top.

• The salty water is heavier, so it stays at the bottom.

• Step 2: the layers hardly mix.

• Oxygen from the air reaches only the top layer.

• It cannot get down to the deep water.

• Step 3: bacteria make hydrogen sulphide.

• Dead plants and animals sink to the bottom.

• Bacteria break them down without oxygen and release hydrogen sulphide (H₂S), a poisonous gas.

• Result: there is no oxygen below about 70–100 m in the centre of the sea and below about 100–150 m near its edges. Below this depth the water is full of hydrogen sulphide [3].

• This makes the Black Sea the largest anoxic basin in the world.

The Black Sea in the news: war and grain

• Russia–Ukraine war: the sea is a war zone. It is also a major route for grain exports from Ukraine.
• Black Sea Grain Initiative (July 2022 to July 2023): a deal that let ships carry grain safely out of Ukraine.
• A Joint Coordination Centre started work in Istanbul on 27 July 2022. Its members were Russia, Türkiye, Ukraine and the UN [2].
• It helped ships carry grain safely from three Ukrainian ports [2].
• By July 2023, about 32.8 million tonnes of grain and food had been exported under the deal [1].

Where it occurs

• Location: between Europe and Asia. Turkey lies to the south, Bulgaria and Romania to the west, Ukraine and Russia to the north, and Georgia to the east.
• Rivers feeding it:
• Danube: enters from the west, through Romania.

• Dnieper and Dniester: enter from the north, through Ukraine.

• Straits and linked seas:

• Bosphorus at Istanbul (Turkey).
• Sea of Marmara, a small sea between the two straits, inside Turkey.
• Dardanelles (Turkey), which opens into the Aegean Sea between Greece and Turkey.

• The Aegean opens into the Mediterranean Sea.

• Grain-deal centre: the Joint Coordination Centre was in Istanbul [2].

• Link to India: India has no direct coast here. However, the war in the Black Sea affects world grain and fertiliser supplies, and that affects import-dependent countries like India.

Don't confuse with

• Caspian Sea: a landlocked lake with no outlet to the ocean. The Black Sea does connect to the ocean, through the Bosphorus–Dardanelles route to the Mediterranean.
• Sea of Marmara: a small sea inside Turkey, lying between the Bosphorus and the Dardanelles. It is not the Black Sea, and it is not the Aegean.
• Red Sea: a young rift sea formed when the African and Arabian plates pulled apart. It joins the Mediterranean through the Suez Canal, not through the Turkish straits. The Black Sea's key feature is its layered, oxygen-free deep water, not rifting.
• Bosphorus vs Dardanelles: the Bosphorus (at Istanbul) touches the Black Sea. The Dardanelles touches the Aegean Sea. Both are Turkish.

Prelims Hooks

• Bordering countries (6): Turkey, Bulgaria, Romania, Ukraine, Russia, Georgia. Trap: Greece, Moldova and Azerbaijan do not border the Black Sea.
• Strait order going out: Black Sea → Bosphorus → Sea of Marmara → Dardanelles → Aegean → Mediterranean. Both straits belong to Turkey.
• Low salinity comes from the Danube, Dnieper and Dniester rivers and from the almost closed outlet.
• Anoxic deep water: no oxygen below about 70–100 m in the centre and 100–150 m near the edges, and full of hydrogen sulphide (H₂S) [3]. It is the world's largest anoxic basin.
• Black Sea Grain Initiative: July 2022 to July 2023. The Joint Coordination Centre was in Istanbul (Russia, Türkiye, Ukraine, UN) [2]. Grain was shipped from three Ukrainian ports [2], and about 32.8 million tonnes were exported [1].
• Chokepoint match: Bosphorus–Dardanelles joins the Black Sea to the Aegean/Mediterranean (Turkey). Bab-el-Mandeb joins the Red Sea to the Gulf of Aden. Hormuz joins the Persian Gulf to the Gulf of Oman.

Mains Points

• How physical geography shapes a sea (GS-I):
• The Black Sea is an almost closed basin that big rivers feed with fresh water.
• So its waters form layers that do not mix. The deep water loses its oxygen and fills with H₂S [3].

• Compare it with the shallow Persian Gulf, where high evaporation makes the water very salty. Together they show how relief, rivers and climate control salinity and oxygen in seas.

• Chokepoints and food security (GS-III):

• All Black Sea shipping must pass the Turkish straits, which gives Turkey a key role.
• The Russia–Ukraine war turned the sea into a war zone and disrupted grain exports.

• The Black Sea Grain Initiative used a Joint Coordination Centre in Istanbul to reopen exports from three Ukrainian ports [2], and about 32.8 million tonnes were shipped [1]. This shows how a regional conflict at sea can raise world food prices.

• Geopolitics of enclosed seas (GS-I/GS-II link):

• In small, closed seas like the Black Sea and the Baltic Sea, coastal powers compete closely. The Baltic is now almost ringed by NATO after Finland (2023) and Sweden (2024) joined.
• Control of narrow straits decides who can reach the open ocean. This links the physical shape of a sea to strategy and trade.

Related concepts

• Persian Gulf
• Red Sea
• Gulf of Aden
• Horn of Africa
• South China Sea
• Spratly and Paracel Islands
• Gulf of Guinea

Read more

• Seas and gulfs in the news