Dead zones are ocean expanses that lose most of their marine life during the summer due to a lack of oxygen, called hypoxia. The Pacific Northwest dead zones, which have appeared every summer since 2002, are located in one of the nation's most important fisheries.
Jack Barth, a professor of oceanography at OSU, says, "I wouldn't be surprised if coastal dead zones appear every summer from now on because oceanic and atmospheric conditions are now primed for their regular, repeated formation."
Connections between climate change and the recent formation of dead zones in Pacific Northwest coastal waters are being studied by a research team that is funded by the National Science Foundation and co-led by Barth and Francis Chan of Oregon State University. Jane Lubchenco, now on leave from the university while serving as administrator of the National Oceanic and Atmospheric Administration, NOAA, previously co-led the team.
"We did experience hypoxic conditions for the eighth consecutive year, but unlike 2006 when strong, steady winds led to near zero-oxygen, or anoxic, conditions, we got a break," said Barth. "A series of wind reversals late in the summer helped dissipate the low oxygen, in essence allowing the system to flush itself."
The OSU scientists conduct research off Newport, Oregon using undersea gliders equipped with oxygen sensors, and similar instruments on four moorings. They also had sensors aboard a NOAA hake survey cruise that sampled waters from northern California to the Strait of Juan de Fuca this summer.
The team will soon deploy a new network of undersea gliders and cabled moorings off the coast as part of the national Ocean Observatories Initiative, a $386.4 million effort funded by the National Science Foundation to gauge the effects of climate change on the world’s oceans.
Hal Weeks, a researcher with the Oregon Department of Fish and Wildlife, deploys a remote operated underwater vehicle as part of the OSU effort document the Oregon dead zone. Summer 2006. (Photo courtesy OSU)
The Earth now has more than 400 dead zones with the count doubling every 10 years.
Barth and his colleagues suspect that dead zones off the Oregon and Washington coasts may be caused by climate change, unlike most of the others.
Most dead zones form where microscopic marine plants called phytoplankton are exposed to excess nutrients, such as fertilizers and sewage, that flow down rivers and streams to the ocean.
These tiny plants bloom, then die and decompose, robbing the ocean of life-sustaining oxygen. Animals that fail to escape dead zones either suffocate or suffer severe stress.
But nutrient runoff is not the only way that phytoplankton blooms form.
On a teleconference with reporters today, Barth said he believes that climate change is driving down the oxygen content of deep subsurface offshore waters and altering coastal winds.
He said the wind-driven mixing of cold, nutrient-rich deep water with surface waters, called "seasonal upwelling" is triggering the formation of low-oxygen dead zones off the Oregon coast.
This fertilization of the upper water column generates large phytoplankton blooms, and as the plant material dies, it sinks to the bottom and decomposes, lowering the oxygen level of the water just off the seafloor.
This seasonal upwelling is normal, the scientists say, yet dead zones were not observed in near-shore waters before 2002. What changed, Barth said, was the pattern of northwest winds and decreasing oxygen levels in the deep, offshore waters that are upwelled toward the coast.
"Historically, winds would blow at the coast for a week or so, then settle down for several days," he pointed out. "As the winds eased, so did upwelling, and low-oxygen water was washed away – likely off the continental shelf. But in some years, those traditional wind patterns have shifted and now may last 20 to 30 days instead of a week. The system doesn’t have time to cleanse itself."
Barth says the change in wind patterns and decrease in the oxygen levels in deep offshore waters are consistent with impacts suggested by many climate change models.
Oregon coast hypoxia is most severe in late summer, he said, then dissipate when winter storms blow through and reoxygenate the waters.
Barth says there are three dead zones caused by climate change - one off the coast of Chile and Peru, and two others off the east and west coasts of Africa.
He suspects the Pacific Northwest dead zones are part of a continuum with those off Peru and Chile, thousands of miles to the south.
Barth says that for him the real questions now are, "How big will the dead zones be? How long will they last? And how often will oxygen levels plunge low enough to cause marine die-offs?"
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