Yes, the Black Sea has oxygen, but only in its upper layers.
The Black Sea is characterized by a unique feature: it's meromictic. This means its water layers don't mix completely. Oxygen is present and supports diverse marine life in the top layers of the sea. However, below a certain depth, the water becomes anoxic, meaning it lacks oxygen.
Oxygen Levels in the Black Sea
- Oxygen-Rich Upper Layer: The upper 70 to 100 meters (approximately 230 to 330 feet) in the central part of the sea, and up to 100 to 150 meters (approximately 330 to 500 feet) near the edges, contains dissolved oxygen. This is where most of the sea's marine life exists.
- Anoxic Lower Layer: Below these depths, the water is anoxic and contains high concentrations of hydrogen sulfide ($H_2S$). This layer is largely devoid of oxygen-dependent life forms.
Reason for Anoxia
The lack of mixing between the upper and lower layers of the Black Sea is the primary reason for the anoxia. The deep waters are denser due to higher salinity and colder temperatures, preventing them from mixing with the oxygen-rich surface waters. Decomposition of organic matter in the deep layers further consumes any available oxygen, leading to the production of hydrogen sulfide.
In summary, while the Black Sea does contain oxygen, it's limited to the upper layers, making the deeper waters uninhabitable for most oxygen-breathing organisms.
