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This page is about the oceanic phenomenon; see The Dead Zone for the novel by Stephen King.
 Sediment from the Mississippi River carries fertilizer to the Gulf of Mexico Dead zones are hypoxic (low-oxygen) areas in the world's oceans, the observed incidence of which have been on the increase since environmentalists began noting them in the 1970s. In March 2004, when the recently-established UN Environment Programme published its first Global Environment Outlook Year Book (GEO Year Book 2003) it reported 146 "dead zones" where depleted oxygen levels were unable to support life. Some of them were as small as a square kilometer, but the largest dead zone covered 70,000 square kilometers.
Causes of Dead Zones
 Nitrogen cycle that causes dead zones These marine dead zones are caused by the process of eutrophication, triggered by an excess of nitrogen and phosphates from untreated sewage and combustion emissions from vehicles, power generators and factories. In a cascade of effects, the nutrients trigger a bloom of marine algae and other photosynthesizers. They are at the bottom of the marine food chain and cause surface plankton to proliferate. As phytoplankton and zooplankton die and sink below the photic zone where photosynthesis can occur, a bloom of natural bacterial degradation exhausts the water's supplies of dissolved oxygen.
It might be expected that fish would flee this suffocation, but they are often rendered unconscious and are doomed. Slow moving bottom-dwelling creatures like clams, lobsters and oysters are unable to escape. All colonial animals are extinguished. The normal mineralization and recycling that occurs among benthic life-forms is stifled.
Humankind is engaged in a gigantic, global experiment as a result of the inefficient and often overuse of fertilizers, the discharge of untreated sewage and rising emissions from vehicles and factories, the executive director of the UN program, Klaus Toepfer, wrote in a statement introducing the 2004 report.
Locations of Dead Zones
 Dead Zones around the World In the 1970s, marine dead zones were first noted in areas where intensive economic use stimulated "first-world" scientific scrutiny: in the U.S. East Coast's Chesapeake Bay, in Scandinavia's strait called the Kattegat, which is the mouth of the Baltic Sea and in other important Baltic Sea fishing grounds, in the Black Sea, (which may have been anoxic in its deepest levels for millennia, however) and in the northern Adriatic.
Currently the most notorious dead zone is a 20,000 square kilometer region in the Gulf of Mexico, where the Mississippi River dumps fertilizer runoff from its vast drainage basin, which includes the heart of U.S. agribusiness, the Midwest, affecting important shrimp fishing grounds.
Other marine dead zones have appeared in coastal waters of South America, China, Japan, southeast Australia and even in the waters of New Zealand, which have a reputation for being some of the planet's most pristine near-coastal marine environments.
Reversal of Dead Zones
Dead zones are not irreversible. The Black Sea dead zone, previously the largest dead zone 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 force 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 cleanup by reducing larger industrial emissions. From 1985-2000, 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.
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