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'Dead zones' spread, thicken off
Oceanic wastelands may be becoming more severe, researchers say
July 27, 2006 The Oregonian
MICHAEL MILSTEIN A vast pool of oxygen-starved seawater is killing fish and crabs along the Oregon and Washington coasts, creating an offshore "dead zone" that is poised to spread its lethal fallout even wider.
The eerie phenomenon, which suffocates marine life that cannot move fast enough to escape, has emerged as an unsettling coastal presence in recent years. Dead zones also struck the Oregon coast with varying severity in 2002 and each year since, sometimes leaving fish scattered lifeless across the ocean floor.
Oregon State University researchers suspect the episodes have been more common and severe in the past few years, signaling increasingly unpredictable ocean behavior tied to winds and currents. That matches predictions that global warming trends may cause wilder swings in Earth's climate.
Researchers at OSU have installed new offshore sensors and are making regular research cruises to chart the extent of the low oxygen levels, as low or lower than during a severe dead zone documented in 2002.
They are also tracking reports from fishermen along the central Oregon coast who have pulled up traps full of dead Dungeness crabs in recent days. Dozens of bottom-dwelling fish such as ling cod and hundreds of crab have also washed up dead on beaches along the central Washington coast, said Liam Antrim of the Olympic Coast National Marine Sanctuary.
Waters turn deadly when oxygen levels fall below 1.4 mL per liter. Levels along the Oregon coast now hover at about one-third of that level -- as low as .46 mL per liter -- said Francis Chan, a marine ecologist at Oregon State and the Partnership for Interdisciplinary Studies of Coastal Oceans, a research alliance between OSU and other West Coast universities.
A reservoir of low-oxygen water stretches, ribbonlike, offshore of Oregon from about Florence north to Cascade Head, said Jack Barth, a professor of oceanography at OSU who checked the waters on a research cruise last week.
The reservoir, blanketing the ocean floor, also appears to extend north into Washington, he said. Monitoring by Olympic Coast sanctuary staff has verified low oxygen levels in spots off Washington, Antrim said.
Low-oxygen water is not always a bad thing. Oregon's coast owes its thriving marine life to deep ocean water low in oxygen but rich in nutrients. Summer winds usually draw that water up in a process called upwelling, nourishing tiny plants known as phytoplankton that in turn feed a chain of other sea life including salmon and sea birds.
Winds this summer have been more intermittent, too weak to keep flushing the deep water through. Instead, it seems to be collecting in a vast underwater pool resting on the ocean floor, Barth said.
"More upwelling is good for productivity," Chan said. "On the other hand, you can also have too much of a good thing."
The low-oxygen pool seems thicker this year and may reach farther north than scientists have documented before.
Meanwhile, small marine organisms near the surface die and rain down into the depths. Their decay then sucks even more oxygen out of the already-depleted water.
Dead zone nearing shore
Now that winds have begun to revive the upwelling, researchers say, the suffocating waters are spreading closer to shore.
"We're poised to see more die-offs," Barth said.
He said the upwelling historically was consistent but in recent years has become less predictable. He suspects it's connected to wobbles in the jet stream -- an important driver of Oregon winds -- coming in cycles of 20 to 40 days.
Researchers in Canada have also identified steadily declining oxygen levels in the Pacific Ocean, both off the British Columbia coast and in the Gulf of Alaska, in recent decades. That is typically a source of water that upwells along the West Coast.
It is not clear how often dead zones may have appeared off Oregon in the past, because monitoring equipment was not as plentiful as it is today. Fishermen have seen hints of past die offs, but it's hard to tell how severe or widespread they were, said Hal Weeks, marine habitat project leader at the Oregon Department of Fish and Wildlife.
The low-oxygen water, which scientists refer to as hypoxic, may be common off Washington, said Barbara Hickey, a professor of oceanography at the University of Washington. That's in part because the Washington coast appears to foster more plankton growth, which then saps the water of oxygen as it sinks and decays.
"I think it's a chronic thing," she said. "Now we have a lot more sensors on the water, a lot more people looking at it."
However, she was on a research cruise off the coast early this summer and said the episode this year was especially striking because oxygen concentrations fell so low, so soon.
"It was remarkable how much of an area this covered," she said.
Marine environments depend on delicate balances of weather, winds and currents, which scientists are only now deciphering in detail, she said. Changes in the climate brought about by global warming or other forces may rapidly upset those balances.
"The ecosystem is very sensitive to these perturbations in food, in oxygen and the timing," she said.
Oregon State researchers have examined records and have found the suffocating waters more severe, more common and extending into shallower waters than in the past. Researchers said marine species often live in such specialized environmental niches that even slight changes can have widespread impacts.
Michael Milstein: 503-294-7689; firstname.lastname@example.org
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