Ocean dead zones a first, report says

SEATTLE – Dead zones off Oregon’s coast that have threatened sea life for the past six summers are unprecedented in the historical record, say scientists at Oregon State University.

The researchers combed through more than 50 years of ocean data to see if the extremely low oxygen levels measured recently also occurred in the past.

“The answer was no,” said OSU marine ecologist Francis Chan, lead author of a report published in Thursday’s issue of the journal Science. “It’s not normal to have oxygen levels this low and this close to shore.”

In 2006, the dead zone spread over 1,000 square miles. Oxygen levels dropped to zero in some places. Using a remotely operated submersible, the scientists took pictures and video that showed a wasteland littered with dead crabs.

When he revisited the areas the following year, some species had returned, but the diversity of invertebrates remained low.

“We used to see seven species of starfish on the reefs,” Chan said. “Now we saw one or two.”

While it’s impossible to link any one event to global climate change, the researchers say the dead zones are caused by wind shifts of the type expected as the planet’s temperature rises.

“In this part of the marine environment, we may have crossed a tipping point,” said OSU marine biologist Jane Lubchenco.

The dead zones form in the summer when coastal winds blow from north to south. The winds cause upwelling, which pulls nutrient-rich but oxygen-poor water from deep below the surface. Microscopic plants and animals feast on the influx of food, but when they die, their decomposition depletes the water of what little oxygen it has.

In 2006, northerly winds were twice as strong as usual, Chan said. “That was the smoking gun for why we were seeing those scenes of dead marine life,” he said.

It also shows marine ecosystem sensitivity to climate change.

“It’s remarkable to me that over 150 feet below the surface, what we’re seeing on the seafloor is really connected to what’s happening in the atmosphere,” Chan said.