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Scientists Probe Ocean's Dead Zone Mystery

Scientists just back from a research cruise are reporting "a wave of death" in the Pacific Ocean off America's Northwest Coast. Underwater sea life is literally suffocating from lack of dissolved oxygen. Beachcombers in the region also reported several unusual fish kills in July. Scientists are not sure what to make of the phenomenon.

They could scarcely believe the most recent oxygen readings they recorded in waters off the central Oregon Coast. They were near zero a short distance off shore. Oregon State University marine ecologist Francis Chan, who was on board, says the researchers deployed an underwater camera to look with their own eyes.

"It was really quite shocking, to be honest. We were all huddled in the cabin of the research vessel staring at multiple video monitors." Chan recalls the evidence of a 'silent killer.' "Shapes started coming into focus and we were seeing what looked to be dead worms -- fairly good sized worms. Then we started coming upon piles and piles of dead Dungeness crabs. We didn't see one living fish all day long."

This is the fifth year in a row that a so-called "dead zone" has appeared off the Oregon Coast. But Chan says this one appears to be more severe and more extensive than any before.

At the end of July, crabbers off the Washington coast started pulling up pots of dead crabs. Then thousands of dead fish washed ashore at the Quinault Indian reservation, even farther north. "I grew up in this village and community and I don't ever recall seeing this sort of thing on the beach," says Quinault Nation president Fawn Sharp. "It was very disturbing to see that much on our coastline."

She says tribal crabbers and beachcombers noticed two waves of fish kills. But now the ocean off the coastal reservation seems back to normal. "We were hoping that is was just a short-term, not a long-term problem or phenomenon that's killing our seafood. But now it's gone. So hopefully, the good Lord willing, it's run its course."

Obviously, scientists have a major mystery to unravel.

Marine biologist Mary Sue Brancato, who monitors coastal beaches for the Olympic Coast National Marine Sanctuary, is one of those working to unravel it. "Part of the picture we're missing," she says, "is how long has this been going on, how often does it happen, and how much of the population does it affect. It might be that it's been occurring over time and the populations do fine with this periodic occurrence."

Seasonal winds drive some coastal currents. When the wind slackens or changes direction, it can disrupt the water circulation. Then you have the potential for an underwater 'dead zone.' Oregon State's researchers suspect that the disrupted ocean currents could be a sign of global warming. But for now, Brancato of the Marine Sanctuary remains cautious, adding "I think that would be fascinating to understand better and I think over the long-term that is exactly what we want to do."

Oregon marine ecologist Francis Chan notes the "dead zones" vary in size and severity. He says nothing can be done about the phenomenon except to study it. "This is really an immense event. It's sort of like a heat wave. There's very little you can do but ride it out."

Mostly it's scientists riding this wave in the Pacific Northwest, as fisheries there have not been affected. Elsewhere, though, the ripples have touched more people, more broadly. For example, dead zones occur off Namibia in the South Atlantic, off Peru in the Pacific and west of India in the Arabian Sea. In those areas, fishermen face reduced catches - and economic losses - when fish and prawns flee the oxygen-starved waters. Then the impact extends far beyond the water line.