Scientists in Oregon and Washington are noticing a disruptive ocean phenomenon is becoming more frequent and extreme. It involves a suffocating ribbon of low oxygen seawater over our continental shelf.
The technical term is hypoxia, sometimes called "dead zones," It's an unwelcome variation on normal upwelling of cold, nutrient rich water from the deep ocean. When the dissolved oxygen drops too low, it drives away fish and can suffocate bottom dwellers such as crabs and sea worms who can't scurry away fast enough.
It seemed to marine ecologist Francis Chan like this is happening most every summer lately. So the Oregon State University researcher looked back as far as coastal oxygen readings go—to about 1950—to see if it's always been this way.
"The ocean starting in 2000 really looked different from the ocean we had between the 1950s and 1990s,” Chan said.
Chan said climate change could affect oxygen levels via disrupted circulation and ocean warming. A September storm flushed away this year's low oxygen zone by churning Northwest coastal waters. But Chan described the severity of the low oxygen readings recorded this summer as among the worst ever observed locally.
"It's very much a patchy ribbon," he said from his post in Newport, Oregon. Marine surveys and fixed instruments recorded notably low oxygen values from south of Yachats up past Newport.
Ten oceanographic moorings deployed by the Olympic Coast National Marine Sanctuary also found very low (hypoxic) oxygen values between Cape Elizabeth and Cape Flattery, Washington, this summer.
"This is not a happy year for organisms out on the coast," said Jenny Waddell, the marine sanctuary's research coordinator.
Waddell added that at least one sensor dipped into anoxic conditions, "where there's literally no oxygen."
"We had indications of a relatively persistent hypoxia event along the Quinault Reservation coastline," wrote marine scientist Joe Schumacker of the Quinault Department of Fisheries in an email Friday. "Dead fish and shellfish at various locations and times beginning near the end of July and extending through most of August."
More frequent and severe near-shore hypoxia concerns fishermen and crabbers. Commercial harvesters face reduced catches and economic losses when crabs suffocate and fish and prawns flee the oxygen-starved waters.
One of the tip-offs to OSU researchers of the onset of low oxygen conditions this summer was when Oregon Department of Fish and Wildlife biologists monitoring crab populations noticed crabs dying from lack of oxygen in a research trap. Other observers noted crabs leaving the ocean to seek more oxygenated waters in coastal estuaries and bays.
Earlier this year, researchers and fishery advocates found a receptive ear at the Oregon Legislature when they presented their concerns about silent changes in the ocean. Legislators approved the creation of a new council to be co-chaired by the state Fish and Wildlife director and an OSU leader.
The council is tasked with recommending and coordinating a long-term strategy to address hypoxia as well as ocean acidification.