Scientists Fear 'Tipping Point' in Pacific Ocean
Coast Has Seen Deadly Drop-off in Oxygen Levels for Sea Life
ROBERT MCCLURE / Seattle Post-Intelligencer 15feb2008
Where scientists previously found a sea bottom abounding with life, two years ago they discovered the rotting carcasses of crabs, starfish and sea worms, swooshing from side to side in the current. Most fish had fled — and those that didn't or couldn't joined the deathfest on the sea floor.
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Extraordinarily low oxygen levels were to blame — swept up from the deep ocean into normally productive waters just off the Pacific Northwest coast by uncharacteristically strong winds.
On Thursday scientists announced they had documented that low oxygen levels that killed the sea life in 2006 were the lowest in a half-century — and that for the first time, parts of the ocean off our coast were measured with zero oxygen in the water; 2007 looked only a bit better.
Strong winds and low oxygen levels have persisted for eight summers now, leading scientists to conclude that the ocean may be "poised for significant reorganization"— their way of saying an ecosystem gone awry.
It looks like the Pacific has reached a "tipping point," a threshold where low-oxygen levels are becoming the rule, researchers said. And while scientists can't prove it's caused by a changing climate, that's consistent with what is predicted by computer projections built to anticipate global warming.
"The real thing in the back of our minds is: Is this the first signs of what global warming might be like?" said Bill Peterson, a federal scientist and co-author of the research published in the journal Science. But because it's not conclusive proof, he said, "We tried not to go there too much."
Whatever the cause, it's worrisome, researchers said, because shallow, productive ocean areas like those off the Northwest coast occupy just 1 percent of the globe's oceans — yet produce 20 percent of the fish we eat.
"People keep asking us, 'Is this situation really all that different or not?' " said Jane Lubchenco, a co-author and prominent ocean researcher, in a news release about the research.
"Now we have the answer to that question, and it's an unequivocal 'yes.' The low oxygen levels we've measured in the last six years are abnormally low for our system. We haven't seen conditions like this in many, many decades."
Only once during the past seven years did the strong northerly winds of spring and summer go away — and that time, in spring and early summer of 2005, the pendulum swung wildly the other way, with little wind at all until partway through summer.
That set off a chain of events that scientists concluded were responsible for a startlingly widespread wave of seabird deaths — from the Farallon Islands off San Francisco to Vancouver Island.
After that, researchers from Oregon State University, the National Oceanic and Atmospheric Administration and the Oregon Department of Fish and Wildlife looked intensely at waters off the Oregon coast for the research announced Thursday. And the same thing is happening off Washington's coast.
Mary Sue Brancato and her colleagues first noticed it on a visit to the coast in 2000 or 2001.
"We were out there for another (research) project and we were like, 'What is it with these thousands of dead crabs?' " said Brancato, a marine biologist who works at the Olympic Coast National Marine Sanctuary.
Those were Dungeness crabs. Later other species were affected, Brancato said, leading scientists to surmise it was some widespread cause. By 2004 they were taking measurements to document low levels of dissolved oxygen, the kind of oxygen sea creatures can use.
By the time the biggest oxygen drop-off happened in 2006, it lasted for two weeks and researchers noted species of rockfish, eels and crabs normally found in deep water were along the coast instead, she said.
"It could be climate change, but we don't have definitive proof of that," Brancato said
She said the findings mirror a Canadian study that has been going on for 50 years that also detected declining dissolved oxygen levels.
Brancato was not on the team of researchers whose work is being published this week.
Those researchers had realized for years that they were seeing "really low" oxygen levels, said lead author Francis Chan.
"But the key is, what is the norm?" Chan said.
To ascertain that, Chan conducted a painstaking search for recordings of oxygen off the Northwest coast. He was able to find reliable records extending back into the 1950s.
"Now we know exactly what the norm looks like and we see that the kinds of values we've gotten (in 2000-2006) are really unprecedented for our system," Chan said.
Oxygen levels in the spring and summer of 2007 also were depressed, but not as much as 2006.
The way the strong spring and summer winds reduce oxygen levels is complex. When these winds blow from the north as the Earth is turning toward the east, the water in the shallows along the coast is forced farther out to sea.
This allows water from deeper in the ocean — colder water with little oxygen but lots of nutrients — to seep up near the coast. It's filled with nutrients because it contains dead plankton, fish excrement and more.
Once in the shallow water, these nutrients feed an explosion of one-celled plants. They die, falling to the bottom — only to fuel a massive buildup in bacteria that gobble up the oxygen while they eat the dead microscopic plants.
It's possible that such low-oxygen periods occurred before reliable measurements were made starting in the '50s, Chan said. But 50 years is enough time to have covered many oscillations between the El Niño and La Niña phases of ocean activity.
"If this was because of El Niño or La Niña cycles, we should have seen it in the past," Chan said.
Even the changes known to last decades in the Pacific have switched back and forth several times in the past half-century.
Researchers would like to find out now how much oxygen levels have varied over the course of tens of thousands of years around here. But already, Chan said, "if we look at the deeper past, it gives us an idea that changes in climate do lead to changes in the intensity of low-oxygen zones.
"Oxygen is such a basic, critical (need) for the ecological processes for marine life that changing that number in a rapid and dramatic way, is likely to have some big ecological consequences," Chan said.
source: 19feb2008
Dead Zones off Oregon and Washington
Likely Tied to Global Warming, study says
Low-oxygen areas that show scant signs of sea life have
expanded.
'We seem to have crossed a tipping point,' a scientist says.
KENNETH R WEISS / Los Angeles 15feb2008
NEWPORT, ORE. — Peering into the murky depths, Jane Lubchenco searched for sea life, but all she saw were signs of death.
Video images scanned from the seafloor revealed a boneyard of crab skeletons, dead fish and other marine life smothered under a white mat of bacteria. At times, the camera's unblinking eye revealed nothing at all — a barren undersea desert in waters renowned for their bounty of Dungeness crabs and fat rockfish.
"We couldn't believe our eyes," Lubchenco said, recalling her initial impression of the carnage brought about by oxygen-starved waters. "It was so overwhelming and depressing. It appeared that everything that couldn't swim or scuttle away had died."
Upon further study, Lubchenco and other marine ecologists at Oregon State University concluded that that the undersea plague appears to be a symptom of global warming. In a study released today in the journal Science, the researchers note how these low-oxygen waters have expanded north into Washington and crept south as far as the California state line. And, they appear to be as regular as the tides, a lethal cycle that has repeated itself every summer and fall since 2002.
"We seem to have crossed a tipping point," Lubchenco said. "Low-oxygen zones off the Northwest coast appear to be the new normal."
Although scientists continue to amass data and tease out the details, all signs in the search for a cause point to stronger winds associated with a warming planet.
If this theory holds up, it means that global warming and the build-up of heat-trapping gases are bringing about oceanic changes beyond those previously documented: a rise in sea level, more acidic ocean water and the bleaching of coral reefs.
Low-oxygen dead zones, which have doubled in number every decade and exist around the world, have a variety of causes.
A massive dead zone off Louisiana is created each spring by a slurry of nutrient-rich farm runoff and sewage that flows out the Mississippi River, causing algae to bloom riotously, die and drift to the bottom to decompose. Bacteria then take over. In the process of breaking down the plant matter, they suck the oxygen out of the seawater, making it unable to support most forms of sea life.
Off Oregon, the dead zone appears to form because of changes in atmospheric conditions that create the oceanic river of nutrient-rich waters known as the California Current.
The California Current along the West Coast and the similar Humboldt Current off Peru and Benguela Current off South Africa are rarities. These powerful currents account for only about 1% of the world's oceans but produce 20% of the world's fisheries.
Their productivity comes from wind-driven upwelling of nutrient-rich waters from the deep. When those waters reach the surface and hit sunlight, tiny ocean plants known as phytoplankton bloom, creating food for small fish and shellfish that in turn feed larger marine animals up the food chain.
What's happening off Oregon, scientists believe, is that as land heats up, winds grow stronger and more persistent. Because the winds don't go slack as they used to do, the upwelling is prolonged, producing a surplus of phytoplankton that isn't consumed and ultimately dies, drifts down to the seafloor and rots.
"It fits a pattern that we're seeing in the Benguela Current," said Andrew Bakun, a professor at the University of Miami's Pew Institute for Ocean Science who wasn't part of the Oregon study. "It's reasonable to think these hypoxic and anoxic zones will increase as more greenhouse gases build up in the atmosphere."
The Benguela Current has seen sporadic dead zones. There, rotting clumps of algae have also released clouds of hydrogen sulfide gas that smell like rotten eggs and poison sea life. Residents along the coast of South Africa and Namibia have witnessed waves of rock lobsters crawl onto shore to escape the noxious gases.
Bakun considers the Benguela, the world's most powerful current, to be a harbinger of changes in other currents. His theory is that warm, rising air over the land makes upwelling more frequent and more intense. The phenomenon, he said, is complicated by decades of heavy fishing that has reduced schools of sardines to a tiny fraction of their former abundance.
Not enough fish remain to consume phytoplankton before it dies and settles on the bottom, creating an anoxic dead zone.
Crab fisherman were the first to take note of Oregon's dead zone. Al Pazar recalls his alarm in 2002 when he pulled up his traps and found something seriously amiss.
"It was a good amount of crabs," Pazar said. "But they were dead, or dying or very, very weak. Those that we managed to keep alive didn't survive for long."
The fishermen called Oregon State, which dispatched a boat of researchers to investigate.
"It was a big mystery," Lubchenco said. "We didn't know what was killing them."
Fishermen found other oddities. As they pulled up their crab traps, they found baby octopuses, about the size of silver dollars, inching their way up the lines toward the buoys floating on the surface.
"I'd tell my crewmen, be careful with these cute little things," said Dennis Krulich, a longtime fishermen in Newport. "Peel them off the rope, and we'll put them back."
Only later did he realize that these babies were coming up from oxygen-depleted waters that hover near the seafloor, climbing to save their lives. "In 30 years of crabbing, I'd never seen anything like it before, Krulich said. "It's spooky, this dead-zone thing."
The size of the zone has fluctuated over the years. In 2006, it was the largest ever measured, covering an expanse slightly larger than Rhode Island.
Last year, it was smaller but detected over a longer stretch of coastline.
To make sure the phenomenon was actually new, Oregon State marine ecologist Francis Chan reconstructed data from water sampling at 3,100 stations dating to 1950.
He found that low-oxygen areas have long existed in deeper waters, but there was virtually no evidence until recently of hypoxic waters in prime fishing waters, which extend down to 165 feet.
"It's pretty clear this is unprecedented," Chan said. "It's never been detected since we began to measure oxygen levels."
So far, the seasonal dead zones, which begin as early as June and wrap up in September, have not hurt the crab fishery, which mostly operates in the winter. Many crabs and fish manage to flee the low-oxygen area. And fishermen have learned to set their traps in the wasteland of the previous year's dead zones, to catch crabs that return to feed on the detritus of all the suffocated animals.
Scientists say seafood caught in low-oxygen zones is not harmful to eat.
source: 19feb2008
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