Number of Ocean Dead Zones Up
The number of oxygen-starved "dead zones" in the world's seas and oceans has risen more than a third in the past two years because of fertilizer, sewage, animal waste and fossil-fuel burning, according to United Nations experts. Their number has jumped to about 200, according to new estimates.
Oxygen starvation robs the seas and oceans of many fish, oysters, sea grass beds and other marine life - and the number of such dead zones has grown every decade since the 1970s.
Not all of them persist year-round, as they do in the Gulf of Mexico, where the Mississippi River pours its fertilizers and other nutrients.
Some dead zones return each summer, depending on winds that generate upwelling, in which nutrient-rich water is brought to the surface from lower depths.
But all the dead zones pose a danger to global fish stocks, which many marine scientists say are increasingly hammered by overfishing and pollution.