GRANTS PASS (A P) — Scientists studying the ocean dead zone along the Oregon coast in recent years have searched records back to 1950 and found nothing like it , increasing the likelihood that it is the new normal as the climate gets warmer.
“I wouldn’t be surprised if we have another low oxygen or hypoxic event next year,” Jack Barth, professor of physical oceanography at Oregon State University and one of the authors of the study, said from his office in Corvallis.
Their findings appear in today's edition of the journal Science.
The zone of oxygen depleted water close to shore showed up off the Central Oregon Coast in 2002 and has returned every summer since.
2006 worst year
In the worst year, 2006, oxygen levels dropped to zero. Dead crabs and other sea life littered the bottom and washed up on shore. Last year, a ribbon of low oxygen levels stretched from Oregon north along the Washington Coast.
“ When we were out at sea we looked at the ( low oxygen) numbers and looked at the footage (of dead sea life), and it always struck us there was something extraordinary happening,” Francis Chan, a research assistant professor at OSU and lead author of the study, said in a telephone interview. “But we didn’t have a way of quantifying what the norm really is.
“I think the data is in now.”
Chan examined records of ocean surveys back to 1950 and found only one reading out of 10,000 showing as low as 0.5 milliliters of dissolved oxygen per liter of water at shallow depths.
Since 2002, low readings — even readings of zero dissolved oxygen — have became common, particularly in 2006.
“ The concern is that the kinds of conditions that set (the dead zone) up every summer — we are in a period of time where those sets of conditions are aligning themselves on a much more regular basis,” Chan said.
Unlike the dead zones in the Gulf of Mexico and Chesapeake Bay, which are caused by fertilizer washing down rivers, the Oregon Coast dead zone is triggered by northerly winds, which create an ocean-mixing condition called upwelling.
This brings low- oxygen water from deep in the ocean close to shore, and spreads nitrogen and other nutrients through the water column, kicking off a population boom of plankton, the tiny plants and animals at the foundation of the ocean food web. When huge amounts of plankton die , they fall to the bottom of the ocean, where they decompose, depleting the water of 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 closer to shore.
Barth noted that upwelling areas account for only 1 percent of the ocean, but 20 percent of global fish production.