The ocean dead zone that formed this summer off Oregon was less severe than in years past, but it looks like the phenomenon apparently linked to global warming is here to stay.
Oregon State University scientists said Thursday that winds that are a factor in the severity of the phenomenon abated in July, allowing the low-oxygen waters to dissipate before they got too deadly to marine life.
"It really feels like this is the new normal," said OSU research scientist Francis Chan. "We have shifted into a set of conditions where the likelihood of seeing this is high every year."
While most dead zones around the world are formed by pollutants washing down rivers, the one off Oregon appears to be linked to global warming. It has shown up for eight straight years.
The worst year was 2006, when dead crab, fish and other marine life washed up on beaches, unable to escape the sudden appearance of waters practically devoid of dissolved oxygen.
OSU oceanographer Jack Barth said there is increasing evidence that warmer ocean temperatures at the surface are making it more difficult for deep cold ocean waters to draw oxygen from the atmosphere, because the warm layer on top won't mix with the cold layer below.
They are still working to understand how climate change may affect the coastal winds that are also a factor, he said.
Huge amounts of new data gathered by underwater gliders that run grid patterns through the ocean are increasing their understanding, Barth said.
It occurs when cold deep waters low in oxygen from the northern Pacific migrate to the Oregon Coast in spring, Barth said.
Conditions are made worse when coastal winds cause the water to turn over, drawing nutrients from the ocean floor up through the water column in what is called upwelling.
The process feeds an explosion of plankton. When they die, they fall to the ocean floor and rot, using up the little oxygen that is there.