"Dead Zone" off Oregon Coast Is Growing, Study Says
for National Geographic News
|August 4, 2006|
A "dead zone" of low-oxygen water has been appearing along the Oregon coast each summer since 2002, suffocating crabs and other creatures that can't swim or scuttle away.
This year the zone is stretching longer and thicker than it ever has before, possibly reaching into the waters off Washington State.
"This is the first year we've seen the dead zone expand," said Jane Lubchenco, a marine biologist at Oregon State University in Corvallis.
This year's zone blankets approximately 70 miles (113 kilometers) of the central Oregon coast and may extend another 170 miles (274 kilometers) into Washington waters (map of Oregon).
In some spots the zone is 98 feet (30 meters) thick, swallowing nearly half of the water column.
In both states people have reported dead rockfish and other bottom fish on beaches. Fishers have found their crab pots packed with dead crabs.
"These are the biological indicators that we've had that something [unusual] is going on down below, out of sight," said Liam Antrim, a resource protection specialist at the Olympic Coast National Marine Sanctuary in Washington.
Change in the Winds
Development of the dead zone is related to ocean upwellinga natural process driven by winds.
Along the Oregon coast, upwelling occurs when spring winds consistently push warmer surface water offshore.
Colder, nutrient-laden water rises from the ocean floor to replace the lost mass, and the surge of nutrients provides food for microscopic plants called phytoplankton that live at the surface.
"It's one of the reasons we have such rich fisheries," Lubchenco said. Plankton form the base of the ocean food chain.
But during the last few years the winds off the Oregon coast have become much more unpredictable.
Some experts think the shifting winds are changing the timing of the upwelling, and in turn, the size of the dead zone.
This year the winds slowed after upwelling brought a pulse of nutrients to the surface, and blooming plankton began to die.
Without a flushing of this dead matter provided by upwelling, the remains of the phytoplankton settled to the bottom.
Bacteria then started decomposing the plankton, gobbling up oxygen in the process and creating a buildup of low-oxygen water below the surface.
When the winds started again, upwelling brought this oxygen-poor water close to shore, where it has been stifling marine life.
Tracking the dead zone has been difficult, because rough seas make it hard for scientists to reach the instruments that record ocean conditions such as oxygen levels.
This year the team started trying out new instruments that use cell-phone technology to send near-real-time data back to the lab.
The scientists have also deployed remote underwater vehicles that phone home via satellite once they surface.
"What you want to do is to be able to see how this changes day to day, season to season, and year to year," said Jack Barth, an oceanographer at Oregon State who is part of the research team.
Based on their data, the researchers found that oxygen in the water in July had dipped as low as 0.46 milliliter per liter.
Anything less than 1.4 milliliters of oxygen per liter of water can be fatal to sea life.
Oregon's oxygen-poor area is one of nearly 150 dead zones that pop up around the world.
The zones often appear in places where human activitiesincluding agricultural and urban runoff and wastewater treatmentfunnel nutrients such as nitrogen and phosphorous seaward.
These nutrients feed algal blooms that die, sink, and decompose, using up the water's oxygen.
Whether upwelling or human activity starts the process, the results are similar.
"You have the same oxygen-demand issues, which results in a loss of habitat for fish," said David Whitall, a coastal ecologist with the National Oceanic and Atmospheric Administration.
Whitall has been studying the Gulf of Mexico's dead zone, which is primarily created by agricultural runoff (read "Gulf of Mexico 'Dead Zone' Is Size of New Jersey").
It may be possible to manage pollution-induced dead zones by mitigating human activity, he says.
But dead zones fuelled by upwelling, such as the ones off Chile, Namibia, and the Oregon coast, may be more difficult to address.
The jury's still out on whether rising global temperatures are triggering a change in the winds that create dead zones, Oregon State's Barth says.
But highly variable winds are part of the predictions in many climate change models, he says.
Andrew Bakun, an oceanographer at the University of Miami in Florida, says that upwelling may grow stronger with climate change.
"If that's the case," Bakun said, "these upwelling-related dead zone phenomena would tend to increase as greenhouse gases are added to the atmosphere."
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