| The Black Sea is a classic anoxic ocean basin resembling the earth's ancient oceanic conditions. Its present structure has evolved during the last 2.5 billion years, and is characterized by a well-defined sub-oxic zone at the interface between the oxic and sulfidic layers where many important bacterially-mediated redox reactions occur. The sub-oxic zone involves extremely low oxygen and sulfide concentrations with no perceptible vertical gradients. This is due to very strong density stratification along the sub-oxic and anoxic layers, which markedly restricts the downward flux of oxygen and upward flux of chemical properties and therefore maintains a stable structure with some inter-annual variations. The upper layer biogeochemical structure above the deep... |
