New NASA image reveals the oceans' dead zones

New NASA image reveals the oceans' dead zones




Jeremy Hance
mongabay.com
July 22, 2010





A new image by NASA reveals the extent of the world's marine dead zones, which a study in 2008 found were doubling every decade. At that time 415 dead zones had been identified worldwide. Dead zones are regions of the ocean where dissolved oxygen has fallen to such low levels that most marine species can no longer survive. Such conditions are often seasonal.

The so-called dead zones are caused by agricultural runoff, especially nitrogen-rich fertilizers, as well as the burning of fossil fuels. Pollutants from these sources cause marine eutrophication, whereby the ecosystem receives too many nutrients, triggering massive algae blooms, which eventually die and are broken down bacteria. In breaking down the algae blooms, the bacteria consume excessive amounts of oxygen, essentially starving the marine system. Therefore the largest and most extreme dead zones occur near high populations and run-off areas for agriculture fertilizers.



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