Ocean Dead Zone Off Oregon Dissipating
GRANTS PASS, Ore. -- An ocean dead zone off Oregon that killed fish, crabs and sea worms in an area bigger than Rhode Island last summer lasted nearly three times longer than any of its predecessors before dissipating with autumn's change in the weather, scientists said Monday.
This year's dead zone off Oregon ran for 17 weeks, compared to the previous high of six weeks in 2004, and saw oxygen readings near zero that left the ocean bottom littered with dead crabs, sea stars and sea anemones. This is the fifth straight year the dead zone returned. It covered 70 miles of the central Oregon Coast and there are indications a dead zone also formed off southern Washington.
Southerly winds in recent weeks have flushed out the oxygen-depleted waters that were stuck along the Continental Shelf off the central Oregon Coast, and put an end to the condition known as ocean upwelling that triggered the dead zone, Jack Barth, professor of physical oceanography at Oregon State University, said from Corvallis.
"The fact that we've seen five in five years now, and this one in 2006 was the most devastating does not bode well for the future," Jane Lubchenco, a professor of marine biology at OSU who served on the Pew Oceans Commission, said from Corvallis. "We're seeing a system that is acting very sporadically. It's changing in ways we haven't seen before, or at least we haven't documented before. We can trace all those changes to changes in the winds."
A recent United Nations report listed 200 dead zones around the world, including one off the mouth of the Mississippi River in the Gulf of Mexico. Almost all of them are caused by fertilizer and pollution running down rivers to feed huge algae blooms, which die and decompose on the bottom, depleting the water of oxygen.
The Oregon dead zone is different. Strong northerly winds drive a phenomenon known as upwelling, which turns over the waters on the Continental Shelf, bringing nutrients from the bottom to the top, and feeding an explosion of tiny organisms at the bottom of the food web known as phytoplankton.
When the phytoplankton die, they sink to the bottom, where they are consumed by bacteria, using up all the oxygen.
Similar dead zones have been documented off Africa off the coasts of Namibia and South Africa, and off South American off the coasts of Peru and Chile.
The northerly winds that produce strong upwelling were twice as prevalent this summer as normal _ a condition consistent with global warming, said Barth. The idea is that as the land warms, it creates low pressure that draws more air off the ocean. That also meant fewer of the southerly winds last summer that would normally flush out the dead zone.
The condition was intensely documented within a 1,200-square-mile study area by instrument readings taken from research buoys, research ships, and a kind of torpedo called an autonomous underwater vehicle. The study area runs 70 miles from Cascade Head near Lincoln City to Strawberry Hill near Florence. The dead zone extended 15 to 30 miles offshore to a depth of about 100 feet.
"It's pretty obvious from video images we saw on the 21st of August that most life there was dead if it hadn't been able to escape," said Lubchenco. "And the bottom was being taken over by mats of bacteria _ white fuzzy growths all over the place. We suspect that is a bacterium that thrives in anoxic _ no oxygen _ conditions."
Francis Chan, an Oregon State ecologist, is leading an effort to monitor the area over the winter and spring to see how well marine life can re-establish itself before the expected return of a new dead zone next summer. Researchers are applying for grants from the National Oceanic and Atmospheric Administration
While sampling for juvenile coho salmon last September, Bill Peterson, a NOAA oceanographer based in Newport, found extremely low oxygen levels in continental shelf waters stretching from the Columbia River to LaPush, Wash.
"We frankly don't know what is down the road, but we are concerned," said Lubchenco. "But we don't understand enough about how the global or local climate systems to have any confidence in making precise predictions."
Source: Associated Press