Oceanic "dead zones" are spreading

A sad and frankly scary report in Scientific American:

More bad news for the world's oceans: Dead zones—areas of bottom waters too oxygen depleted to support most ocean life—are spreading, dotting nearly the entire east and south coasts of the U.S. as well as several west coast river outlets.

According to a new study in Science, the rest of the world fares no better—there are now 405 identified dead zones worldwide, up from 49 in the 1960s—and the world's largest dead zone remains the Baltic Sea, whose bottom waters now lack oxygen year-round.

This is no small economic matter. A single low-oxygen event… off the coasts of New York State and New Jersey in 1976 covering a mere 385 square miles of seabed ended up costing commercial and recreational fisheries in the region more than $500 million. As it stands, roughly 83,000 tons of fish and other ocean life are lost to the Chesapeake Bay dead zone each year—enough to feed half the commercial crab catch for a year…

Only a few dead zones have ever recovered, such as the Black Sea, which rebounded quickly in the 1990s with the collapse of the Soviet Union and a massive reduction in fertilizer runoff from fields in Russia and Ukraine. Fertilizer contains large amounts of nitrogen, and it runs off of agricultural fields in water and into rivers, and eventually into oceans.

This fertilizer runoff, instead of contributing to more corn or wheat, feeds massive algae blooms in the coastal oceans. This algae, in turn, dies and sinks to the bottom where it is consumed by microbes, which consume oxygen in the process. More algae means more oxygen-burning, and thereby less oxygen in the water, resulting in a massive flight by those fish, crustaceans and other ocean-dwellers able to relocate as well as the mass death of immobile creatures, such as clams or other bottom-dwellers…

Much more at the link. Click image to enlarge.