Maximum depth of the Black Sea

The Black Sea is quite deep compared with other seas around Ukraine. Next to the Sea of Azov (average depth only about 7 m) or even the Mediterranean, the difference is striking: here you find a true basin more than two kilometres deep, filled with water that barely mixes with the surface.

Key figures

Modern bathymetric data (EMECS, EMODnet, RV Atlantis II, 1969) give:

surface area (excluding the Sea of Azov): about 436,400 km²;
water volume: about 547,000 km³;
average depth: about 1250 m (older references sometimes cite 1197 m);
maximum depth: 2212 m (the Encyclopedia of Ukraine lists 2245 m);
length (east-west): about 1175 km.

Where is the deepest point?

The deepest spot lies on the Euxine abyssal plain in the central basin, just south of Yalta on the Crimean Peninsula, where echo-sounding recorded 2212 m.

The plain covers about 12% of the sea. A wide continental shelf runs from the north-west (up to 190 km wide, depths mostly 100-160 m, locally over 200 m), then drops sharply along the continental slope. Off Turkey and Georgia the shelf is narrow (often under 20 km) and steep, with submarine canyons.

Comparison with other seas

Black Sea: average ~1250 m, maximum 2212 m.
Mediterranean Sea: average ~1540 m, maximum 5267 m.
Sea of Azov: average ~7 m, maximum ~14 m.
Baltic Sea: average ~55 m, maximum ~459 m.
Caspian Sea: average ~211 m, maximum ~1025 m.
Sea of Marmara: average ~494 m, maximum ~1370 m.

The Black Sea is deeper than the Caspian and the Sea of Marmara but shallower on average than the Mediterranean. It is unique as the world's largest meromictic basin: deep water hardly mixes with the surface layer.

Water layers and the "dead zone"

Below roughly 150 m the water is nearly oxygen-free. The sulfidic "dead zone" (from ~90-150 m to the seabed) holds hydrogen sulfide (H₂S) and accounts for more than 90% of the sea's volume. Below 1750 m, H₂S stays stable at about 383 ± 2 µmol/l (2017-2019 expeditions).

The only external "breath" of oxygen comes from salty Mediterranean inflow through the Bosporus, but it barely reaches below 100-150 m.

Life at different depths

0-150 m: about 168 fish species, thousands of invertebrates, 4 marine mammals.
150-300 m: thiotrophic bacterial mats (Beggiatoa) on the Crimean margin.
200-300 m: active ciliates, nematodes and foraminifera in sulfidic sediments (Sergeeva et al., 2014).
Below 1700 m: mainly microbial life; the basin is studied as a model of ancient ocean "dead zones".

Basin history and legends

For much of the Quaternary the Black Sea was a large freshwater lake (Neoeuxinian), drawn down 100-140 m below today's level. About 7500 years ago Mediterranean water broke through the Bosporus sill. Ryan and Pitman (1997) linked the event to flood myths (Noah, Utnapishtim), though most geologists now favour a gradual fill (Aksu et al., 2002; Yanko-Hombach et al., 2006). Sediments still record a sharp shift from freshwater to marine shells.

Ancient Greeks called it Euxine Pontos, the "hospitable sea". The name Euxine abyssal plain survives from that tradition.

What is changing today

The upper oxygenated layer is shrinking. The anoxic boundary rose from ~140 m (1955) to ~100 m (2005) and ~90 m (2015), roughly 0.9 m per year (Capet et al., 2016; TÜBA, 2021), driven by river eutrophication.

Practical notes

Swimmers: shallow near many beaches (5-15 m), then a steep drop beyond the shelf. Divers: recreational limits to 40 m; below 100-150 m requires special gear because of anoxic water. Sailors: waves up to 12 m, no tides; shoals on the north-west shelf are the main hazard, not the central abyss.

In brief

Deepest point: 2212 m, south of Yalta.
Average depth about 1250 m; more than half the seabed lies below 1000 m.
Over 90% of the volume is anoxic, sulfidic water.
Former freshwater lake turned marine ~7500 years ago.
The H₂S boundary is rising by about 1 m per year.