Virginia Gewin
Nature News
August 17, 2010

  • A d v e r t i s e m e n t
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The dead fish were one of the first signs. In July 2002, scientists with the Oregon Department of Fish and Wildlife found unusual numbers of bottom-feeding sculpin lying lifeless on the ocean floor, which would normally be teeming with life. Crabs were also dying, and they washed up onto some beaches in large numbers.

Officials at the government agency asked Francis Chan, a biogeochemist at Oregon State University in Corvallis, for help in discovering the cause of the disturbance as quickly as possible. Chan was about to set off on a scheduled research cruise along the Oregon coast, so he grabbed all the extra equipment he could think of, including a brand-new oxygen sensor.

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Ocean surface waters normally contain 5–8 millilitres of oxygen per litre of water, a number that declines rapidly with depth. But on his first day out, Chan found that at a depth of 50 metres the inner coastal waters off Oregon were hypoxic — oxygen levels there were lower than 1.43 millilitres per litre, so low that fish can’t survive.

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