Dead Zone Off Oregon Needs Storms to Break
GRANTS PASS, Ore. The dead zone of oxygen-depleted water that has been killing crabs and fish along the central Oregon Coast is showing the first signs of breaking up, but will likely remain in place until fall storms move in next month.
"I think the recovery is still a ways off," Jack Barth, professor of oceanography at Oregon State University in Corvallis, said Wednesday. "If you want to talk about improvement up towards more normal numbers, yeah, we're seeing that. But there's still a pool out there that has very low (oxygen) values. It's still of substantial size."
Since a stretch of rainy weather earlier this month, scientific instruments have been measuring slightly higher oxygen levels around Cape Perpetua, but they remain far below normal, Barth said.
It will likely take a stronger series of storms that normally arrive in mid-October to break up the northerly winds creating the dead zone, Barth said.
The full size of the dead zone is not known, but monitoring this year has found an area of oxygen-depleted water extending 70 miles along the Continental Shelf between Florence and Lincoln City.
Scientists first noticed a dead zone off Newport in 2002 and traced it to a rare influx of cold water rich in nutrients and low in oxygen that had migrated from the Arctic.
Each year since then, they have returned in the summer, but these have been caused by unusually intense bursts of northerly winds that cause the ocean water to turn over, bringing nutrients up from the bottom and feeding an explosion of tiny organisms known as phytoplankton.
During calm periods, the phytoplankton die for lack of food and fall to the ocean bottom, where they are consumed by bacteria, which use up the oxygen.
The wind patterns responsible for the dead zones are consistent with what is expected with global warming: warmer temperatures on land strengthen a low pressure area that draws more air in from the cooler ocean, creating the winds that set up the upwelling, and driving the dead zone close to shore.
A kind of torpedo loaded with scientific instruments, known as an autonomous underwater vehicle, has been running back and forth through the area collecting thousands of measurements of oxygen, salinity, temperature, and chlorophyl and periodically transmitting them by satellite telephone to scientists.
Barth said it will likely be spring before an underwater video camera can be brought in to see whether sea worms, crabs and fish are moving back in.
Source: Associated Press