Oxygen-poor ocean zones are growing

Oxygen-starved waters are expanding in the Pacific and Atlantic as ocean temperatures increase with global warming, threatening fisheries and other marine life, a study published today concludes.

Most of these zones remain hundreds of feet below the surface, but they are beginning to spill onto the relatively shallow continental shelf off the coast of California and are nearing the surface off Peru, driving away fish from commercially important fishing grounds, researchers have found.

The low-oxygen, or hypoxic, zones may also be connected to the Pacific coast invasion of the Humboldt, or jumbo, squid. These voracious predators, which can grow 6 feet long, appear to be taking advantage of their tolerance for oxygen-poor waters to escape predators and devour local fish, another team of scientists theorizes.

Researchers believe these phenomena are linked to subsurface layers of hypoxic water in the tropical Pacific and Atlantic oceans that have been thickening over the last 50 years, according to the analysis published today in the journal Science.

The study, led by Lothar Stramma at the University of Kiel in Germany, warns that the spread of hypoxic waters that suffocate marine life is consistent with climate models forecasting what would happen as greenhouse gases accumulate in the atmosphere.

The trend, the study points out, eerily echoes a scenario that unfolded about 250 million years ago, when 95% of life on Earth went extinct after heat-trapping carbon dioxide spewing from volcanoes warmed the planet and the oceans became stripped of oxygen.

"If you warm waters, they hold much less oxygen," said coauthor Gregory C. Johnson, an oceanographer with the federal Pacific Marine Environmental Laboratory in Seattle. "That's the same as a bottle of soda water. If you open it warm, it'll fizz all over the place. If you open it cold, it will slowly fizz out as it warms."

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