Restoration of the Baltic Proper by decadal oxygenation of the deepwater

Abstract

Sediment core data from the Baltic Proper show that deepwater sediments during the present brackish state have alternated between anoxic and oxygenated episodes, implying that anoxic episodes were shut off by a natural restoration mechanism. This mechanism is identified as sustained oxygenation of the deep bottoms which shuts off the internal phosphorus (P) source from anoxic sediments. When this happens, P sink processes rapidly reduce the winter surface concentration c 1 of P. A P budget model shows that the presently eutrophic Baltic Proper can be restored in about 10 years by man-made (or natural) sustained oxygenation of the deepwater. This will reduce the total P supply and c 1 to about 25 % of present day values and the oxygen demand in the deepwater will be reduced proportionally, meaning that the natural water exchange again should be able to oxygenate the Baltic Proper and the restoration equipment can be removed.