Something strange is happening off the coast of Oregon
Jane Lubchenco recalls when the trouble started. Fishermen were bringing up pots of dead crabs. Schools of bottom-feeding fish washed up on beaches. As a marine biologist then with Oregon State University, Lubchenco was among those who found that waters off the Oregon coast had been depleted of oxygen – that ocean life was suffocating. “We thought it was a one-time event,” she says.
That was in 2002. The next year, things were back to normal. But the dead zone, as marine biologists call it, returned in 2004, 2005, and 2006, growing larger. It blanketed 70 miles of the Oregon coast and extended 170 miles along Washington’s. It seemed to have been caused by a combination of higher temperatures, unusual winds, and upwellings. The effect upon fisheries was devastating. In October 2006, the winds changed, the upwellings ceased, and levels began returning to normal. Officials announced that “the longest, largest hypoxic event” ever recorded in those waters had concluded.
Soon it was back, and it may be here to stay.
This year’s dead zone, though not quite as large, confirms a fact of life for the Northwest fisheries. The ocean’s patterns have changed. From 1950-2000, researchers took four thousand samples, and never saw oxygen levels as low as they have become. “It’s hard for us to believe what we’re seeing,” says Lubchenco.
All over the world, for a variety of reasons, dead zones have appeared in oceans. Some, like a patch in the Gulf of Mexico roughly the size of New Jersey, seem to have been caused by agricultural runoff. The dead zone off Oregon is trickier. It has come about by a Rube Goldberg mechanism that would ordinarily make for abundant sea life.
In normal times, spring winds push warm, shallow water farther away from shore, and deep water full of nutrients rises to the surface. This creates a bloom of plankton – just what fishermen hope for. But when the winds temporarily stop, plankton starve and fall to the ocean floor, where they decompose and rob the water of oxygen. Then the winds blow again, and that oxygen-depleted water makes its way to surface, killing larger fish. It stays like that until the winds change.
So how can the dead zone return year after year? It sounds like nothing more than a stroke of rare bad luck. Jane Lubchenco can identify some possible causes. As land grows warmer, winds grow stronger, creating larger plankton blooms (and die-offs).
“One of the things we’ve observed is how wind patterns have changed and greatly affected upwelling,” says Jack Barth, also of Oregon State University. “Two decades ago, the winds would last for three or four days, and then subside. Now they persist for 20 to 40 days before settling down.
“What you want to do is to be able to see how this changes day to day, season to season, and year to year,” he says.
Most aquatic life can’t survive when oxygen levels fall below 1.4 milliliters per liter. The team has recorded surface levels a third of that minimum. Farther down, the number drops to zero. Some species can migrate to safer waters, but crabs and other shellfish have been decimated.
“Some of the worst conditions are now approaching what we call anoxia, or the absence of oxygen,” says Francis Chan of OSU. “This can lead to a whole different set of chemical reactions, things like the production of hydrogen sulfide, a toxic gas. It’s hard to tell just how much mortality, year after year, these systems are going to be able to take.”
Fishermen insist that the seasonal dead zone hasn’t diminished their yearly catches. Nick Furman of the Oregon Dungeness Crab Commission says, “Crabbing has been fine. Our historical average is 10.3 million pounds. The last few years, we’ve been on an upswing – we’ve been averaging 13 million. In fact, we’ve taken 23 million this year. Biologists are scratching their heads. It seems to be a combination of six or seven things. We’ve had good ocean conditions, upwellings, good temperatures. Some of the predator species were fished out.”
What about the dead zones? “Anecdotally we don’t think it had a big impact on the crab fishery,” he says. “Crabs are fairly mobile. As soon as situation isn’t comfortable, they move, even 150 miles up the coast. Now, crabs that were captive in pots did die during dead zones. But others could walk away. Those dead zones occur in spring and summer, when crabbing is done and most of our product is on the beach. We’ve all heard reports of crab carcasses littering the ocean floor, but those may have been empty shells that had just been molted.” Apparently what the ocean takes away with one hand, it gives back with another.
Whether or not the dead zone is evidence of climate change, it will receive more federal attention now that Jane Lubchenko heads the National Oceanic and Atmospheric Administration. “The vastness of our oceans may have engendered a sense of complacency about potential impacts from global climate change,” she says. “The world’s oceans are undergoing profound physical, chemical and biological changes whose impacts are just beginning to be felt.”
