Marine Desert: Baltic Sea Dead Zones
Marine Deserts - or Marine dead zones- are characterized by low oxygen levels and a lack of marine life. They are typically located in areas where there is high nutrient runoff from human activities such as agricultural practices or industrial waste. The dead zones in the Baltic Sea have been increasing in size and number over the past few decades.
"The Baltic Sea is an almost completely enclosed inland sea with a particular topography comprising narrow straits as well as a highly structured sea floor with submarine sills and deep basins. Limited water exchange with the much saltier Worlds Ocean via the North Sea and high freshwater runoff from the large catchment area with its many tributaries causes both horizontal and vertical water column stratification, i.e., a salinity decreasing from south to north as well as saline bottom and less saline surface waters. In contrast to the well mixed and oxygenated surface waters, the denser bottoms are less ventilated. Bacteria and other microorganisms use up the available oxygen in those deeper waters by degrading algae-derived organic matter sinking down from the surface, thus creating oxygen-poor or completely oxygen free conditions. If toxic hydrogen sulfide develops through further bacterial processes, only highly specialized microorganisms can survive in these underwater deserts, called ‘dead zones’." Dr. Olaf Dellwig, Leibniz Institute for Baltic Sea Research Warnemünde (IOW)