Ocean Dead Zones

Dead zones are hypoxic (low-oxygen) areas in the world’s oceans and large lakes, caused by excessive nutrient pollution from human activities coupled with other factors that deplete the oxygen required to support most marine life in bottom and near-bottom water. In the 1970s oceanographers began noting increased instances of dead zones. These occur near inhabited coastlines, where aquatic life is most concentrated. The vast middle portions of the oceans, which naturally have little life, are not considered dead zones. Scientists are expecting a very large dead zone in the Gulf of Mexico and a smaller than average hypoxic level in the Chesapeake Bay this year, based on several NOAA-supported forecast models.

Dead zones are reversible. The Black Sea dead zone, previously the largest in the world, largely disappeared between 1991 and 2001 after fertilizers became too costly to use following the collapse of the Soviet Union and the demise of centrally planned economies in Eastern and Central Europe. Fishing has again become a major economic activity in the region.

While the Black Sea cleanup was largely unintentional and involved a drop in hard-to-control fertilizer usage, the U.N. has advocated other cleanups by reducing large industrial emissions. From 1985 to 2000, the North Sea dead zone had nitrogen reduced by 37% when policy efforts by countries on the Rhine River reduced sewage and industrial emissions of nitrogen into the water. Other cleanups have taken place along the Hudson River and San Francisco Bay.

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