Ocean dead zones multiplying.

• Author: Chafe, Zoe
• Position: Environmental Intelligence

The number of oxygen-starved areas in oceans and bays around the world has doubled to 146 since 1990, according to Global Environmental Outlook Yearbook 2003, newly released by the United Nations Environment Programme (UNEP). Such areas have increased every decade since the 1970s.

These ocean areas, often called "dead zones" because they are so inhospitable to most forms of life, occur when high concentrations of nitrogen build up in marine waters. Several types of pollution--including excess chemical fertilizers, human waste, airborne industrial waste, and traffic fumes--can cause nitrogen concentrations to reach damaging levels. The excess nitrogen sparks rapid growth of microscopic plants called phytoplankton. The growth and decomposition of the phytoplankton can use up much of the oxygen in the water and drive out other marine life. Dead zones range up to 70,000 square kilometers in size, an area larger than Latvia.

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Scientists believe that global warming will only exacerbate the problem, via rising seawater temperatures and increased flooding. After the severe Mississippi River flood of 1993, the U.S. National Ocean Service reported that the oxygen-starved area in the Gulf of Mexico more than doubled...