Cause unknown for `dead zone'

Scientists puzzled by oxygen-low area emerging in waters off coast of Oregon


For the fifth year in a row, unusual wind patterns off the coast of Oregon have produced a large "dead zone," an area so low in oxygen that fish and crabs suffocate.

This dead zone is unlike those in the Gulf of Mexico and elsewhere, which result from fertilizer, sewage or runoff from hog or poultry operations carried by rivers. The Oregon zone appears when the wind generates strong currents carrying nutrient-rich but oxygen-poor water from the deep sea to the surface near shore, a process called upwelling.

The nutrients encourage the growth of plankton, which eventually die and fall to the ocean floor. Bacteria there consume the plankton, using up oxygen.

Jane Lubchenco, a marine biologist at Oregon State University, said the phenomenon did not appear to be linked to recurring El Nino or La Nina currents or to long-term cycles of ocean movements. That made Lubchenco wonder whether climate change might be a factor, she said, adding, "There is no other cause, as far as we can determine."

The dead zone, which appears in late spring and lasts for weeks, has quadrupled in size since it first appeared in 2002. This year it covers about 1,235 square miles, an area about as large as Rhode Island, Lubchenco said.

The zone dissipates when winds shift.

It is not clear what effect the dead zone may have on fish or crab catches, Lubchenco said. So far, she said, the dead zone has not formed until the Dungeness crab season has been nearly over.

Hal Weeks, a marine ecologist who leads the Marine Habitat Project for the Oregon Department of Fish and Wildlife, said the formation of the low-oxygen, or hypoxic, areas had so far caused "localized disruptions" in fishing but no overall decline in catches and no interference with recreational fishing.

Weeks said these areas might have occurred in the past and gone undetected. But he added that when he convened a meeting of scientists and fishermen about 18 months ago to discuss the issue, the fishermen said they did not recall problems occurring so regularly.

"Based on people's memories," Weeks said, "they did not have a pattern or periodicity to it."

He and Lubchenco said scientists would take a research vessel out to sea Tuesday and lower a robot vehicle to photograph the sea bottom to check fish and crab mortality.

"You don't normally haul up a pot and find any dead crabs in it," Lubchenco said. "And the crabbers that we have talked to have all reported dead crabs."

Weeks said he hoped the research cruise would help explain what was going on. "I am expected to give the best possible technical advice to my managers," he said, "and I am afraid right now I don't have answers for them."

In 2002 when the dead zone first appeared, Lubchenco said, she and other researchers dismissed it as an interesting anomaly. "But now, five years in a row, we are beginning to think there has been some sort of fundamental change in ocean conditions off the West Coast," she said.

Baltimore Sun Articles
Please note the green-lined linked article text has been applied commercially without any involvement from our newsroom editors, reporters or any other editorial staff.