Oxygen-Deprived Dead Zones Increasing in World’s Oceans

Last week the U.N. Environment Program announced that the number of oxygen-deprived “dead zones” in the world’s oceans has been increasing since the 1970s and has nearly reached 150, threatening fisheries as well as humans who depend on fish.

These “dead zones” are caused by dumped sewage, emissions from vehicles and factories, and an excess of nitrogen from farm fertilizers. In what experts call a “nitrogen cascade,” the chemical flows untreated into oceans and triggers the proliferation of plankton, which in turn depletes oxygen in the water.

While fish might flee this suffocation, slow moving, bottom-dwelling creatures like clams, lobsters and oysters are less able to escape.

UNEP program executive director Klaus Toepfer noted that 146 dead zones—most in Europe and the U.S. East Coast—range from under a square mile to up to 45,000 square miles. “Unless urgent action is taken to tackle the sources of the problem,” he said, “it is likely to escalate rapidly.”

The program noted that some of the earliest recorded dead zones were in Chesapeake Bay, the Baltic Sea, Scandinavia’s Kattegat Strait, the Black Sea and the northern Adriatic Sea. The most infamous zone is in the Gulf of Mexico, where the Mississippi River dumps fertilizer runoff from the Midwest.