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Dieren en planten

Water en land

Mens en Milieu

Ecological processes   Oxygen cycle   

Oxygen cycle

Oxygen in seawater has two sources: the atmosphere and plants, which live in the sea. There is enough oxygen found on or near the sea surface. It is too dark for green plants to grow at greater depths, deeper than 200 meters. There is no oxygen produced there. In most seas, the oxygen-rich surface water mixes with water at great depths by currents in the water. If that doesn't happen, then the sea will be depleted of oxygen and therefore depleted of life. That is the situation in the Black Sea.