Ocean “dead zones” are caused by low levels of dissolved oxygen, and one of the largest is in the Gulf of Mexico.
That desolate undersea area is clearly caused by agricultural runoff and other pollution coming down the Mississippi.
But scientists have detected large, growing dead zones off Southern California and the Northwest coast … and while they need more time to be sure, they say that the changes fit current climate-change models.
Changes in the wind and ocean circulation over the past eight years have disrupted the exchange of deep, oxygen-poor waters for shallow, oxygen-rich waters, trapping low-oxygen zones near the coasts of Washington and Oregon.
(See the illustration at the end of this article for a depiction of how the deadening process works.)
The lack of oxygen has killed millions of Dungeness crabs and sea stars, crippled sea anemones and produced hordes of noxious bacteria.
Although areas of low oxygen in the deep ocean have always existed in the Pacific, Atlantic and Indian oceans they appear to be spreading, advancing toward the surface and even invading the continental shelf within sight of the Pacific Northwest coastline.
As Gregory Johnson, a U.S. government oceanographer told the McClatchy-Tribune Information Services, “The depletion of oxygen levels in all three oceans is striking.”
Oxygen levels off the Southern California coast have dropped by about one-fifth over the past 25 years and by one-third in other places.
The same article quoted Oregon State University oceanographer Jack Barth on the trend: “The real surprise is how this has become the new norm. We are seeing it year after year.”
In the coming weeks, we'll publish our exclusive interview with Sven Huseby, who appears in the prize-winning film, "A Sea Change", about the adverse, acidifying effects of rising atmospheric carbon on the ocean food chain.
Source
Blumenthal L. Growing low-oxygen zones in oceans worry scientists. Sunday, March 7. McClatchy Washington Bureau. Accessed at http://dailyme.com/story/2010030700000544/growing-low-oxygen-zones-oceans-worry-scientists.html
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