for National Geographic News
A "dead zone" of low-oxygen water has been appearing along the Oregon coast each summer since 2002, suffocating crabs and other creatures that can't swim or scuttle away.
This year the zone is stretching longer and thicker than it ever has before, possibly reaching into the waters off Washington State.
"This is the first year we've seen the dead zone expand," said Jane Lubchenco, a marine biologist at Oregon State University in Corvallis.
This year's zone blankets approximately 70 miles (113 kilometers) of the central Oregon coast and may extend another 170 miles (274 kilometers) into Washington waters (map of Oregon).
In some spots the zone is 98 feet (30 meters) thick, swallowing nearly half of the water column.
In both states people have reported dead rockfish and other bottom fish on beaches. Fishers have found their crab pots packed with dead crabs.
"These are the biological indicators that we've had that something [unusual] is going on down below, out of sight," said Liam Antrim, a resource protection specialist at the Olympic Coast National Marine Sanctuary in Washington.
Change in the Winds
Development of the dead zone is related to ocean upwellinga natural process driven by winds.
Along the Oregon coast, upwelling occurs when spring winds consistently push warmer surface water offshore.
Colder, nutrient-laden water rises from the ocean floor to replace the lost mass, and the surge of nutrients provides food for microscopic plants called phytoplankton that live at the surface.
"It's one of the reasons we have such rich fisheries," Lubchenco said. Plankton form the base of the ocean food chain.
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