The western basin of the Gotland deep is the deepest basin in the Baltic Sea (459 m), while the eastern basin is the second deepest (250 m). The Gotland deep is located between 57 degrees and 58 degrees North and 20 degrees East, between the Swedish Island Gotland and the westcoast of Lativa. The water column is chracterized by a chemical stratification (halocline) with saline bottom water. The water exchange in the central Baltic Sea is only minimal due to a narrow channel (Skagerrak) that connects the brackish eastern Baltic to the marine waters of the North Sea  and another narrow and shallow channel (Darßer Schwelle) connecting the eastern and the central Baltic. Only occasionally a major inflow of salt water occurs caused by specific (and very rare) meteorologic and hydrographic conditions. Thus, below a depth of ca. 100-110 m the Gotland Sea is anoxic to the bottom.