At what depth does oxygen disappear in the Black Sea?

In the Black Sea, oxygen is present only in the upper water levels, which supports marine life. The depth at which oxygen disappears varies depending on the location within the sea:

• At the sea's centre: Oxygen is absent below a depth of approximately 230 to 330 feet (70 to 100 metres).12
• Near the sea's edge: Oxygen is absent below a depth of approximately 330 to 500 feet (100 to 150 metres).12

Below these depths, the water is contaminated by hydrogen sulfide, creating a "dead" zone that is largely devoid of life, save for specific bacteria adapted to these conditions. This lack of oxygen is caused by the weak ventilation of the sea's deep layers rather than by pollution.12