Deep Hypersaline Anoxic Basins, Mediterranean Sea


Deep Hypersaline Anoxic Basins (DHABs) in the Mediterranean Sea are located south of Crete between Greece and the North African coast of Lybia (ranging from 34°17’N;20°0’E to 33°52’N;26°2’E from west to east) in a depth of 3000-4000 m. In the last few years a couple of basins were detected namely the L’Atalante, Urania, Discovery, Bannock, Tyro, Thetis, Medee and Kryos. They were formed in the Mediterranean Sea probably 5 Mio. years ago when, caused by tectonic plate movements, salt depots from the Miocene inside the sediment were released followed by a salt-enrichment of the bottom water. Typical for the DHABs is the high pressure (> 35 MPa), total darkness, anoxicity and extreme salt-conditions (the basins are basically “underwater extreme saline lakes” with >30% salinity; 10-times higher than normal seawater). Also high concentrations of ammonium, sulfide and manganese can be found in different basins. The high density of the salt layer, the brine, prevents it from mixing with the above laying oxic seawater. Therefore, permanent structured depth profiles (see below) with a chemocline or interface (suboxic) and a brine layer (anoxic) below were formed. We are interested in the DHABs because they probably comprise evolutionary long separated and maybe different evolved eukaryotic specialists. These had not to contend with many competitors for their ecological niches because of the extremity of the habitat. The global warming will cause an increase of hypersaline habitats e.g. the Aral Sea. Hence, hypersaline environments as habitats and their influence on ecological processes will also gain importance in the future.