Jul
28
2006

"Dead zone" off Oregon beaches

Scientists are studying a 70-mile "dead zone" off the coast of Oregon.

First noticed in 2002, the dead zone is larger this year than in previous years.

What is a dead zone? It's an large area of water that's very low in oxygen and can't support life. (Scientists call this "hypoxia.") Dead zones are caused by the explosive growth of tiny aquatic plants called phytoplankton. When the phytoplankton die, they are decomposed by bacteria. Massive numbers of bacteria use up the oxygen in the water. Any animals that can swim out of the low-oxygen water--like many fish--do so. Others--some fish, many crabs, and others--suffocate because they can't get enough oxygen to live.

Dead crabs: Dead Dungeness crabs on beach, Oregon Coast (Photo by Jane Lubchenco)
Dead crabs: Dead Dungeness crabs on beach, Oregon Coast (Photo by Jane Lubchenco)

In this case, the phytoplankton blooms are caused when north winds cause upwelling in the water column. The cooler water is rich in nutrients, providing a feast for the phytoplankton. When the wind dies down, the upwelling stops, and many phytoplankton die a natural death. Their decomposition results in water that is deadly because it lacks oxygen needed for life.

This year, the upwelling started in April, stopped in May, and started up again in June. The off-and-on upwelling creates a thick mat of organic material that rots and uses up the oxygen in the water. Then, when a new upwelling occurs, the oxygen-depleted water moves toward shore, killing the plants and animals that can't get out of its way.

Measuring oxygen levels: Chris Holmes (left) and Dr. Francis Chan (right), PISCO researchers measuring oxygen levels off the Oregon coast from the OSU research vessel Elakha (Photo by Jane Lubchenco)
Measuring oxygen levels: Chris Holmes (left) and Dr. Francis Chan (right), PISCO researchers measuring oxygen levels off the Oregon coast from the OSU research vessel Elakha (Photo by Jane Lubchenco)

So, why the upwelling? Jane Lubchenco, professor of marine ecology at Oregon State University and a member of the Pew Oceans Commission, told the Associated Press:

"We are seeing wild swings from year to year in the timing and duration of the winds that are favorable for upwelling. ... This increased variability in the winds is consistent with what we would expect under climate change."

Global warming is also the suspect in dead zones off Namibia, South Africa, and Peru.

(The dead zone in the Gulf of Mexico at the mouth of the Mississippi River is caused by agricultural runoff containing fertilizers. The river carries all those nutrients into the Gulf, creating algal blooms that use up all the oxygen.)

Your Comments, Thoughts, Questions, Ideas

Bob13's picture
Bob13 says:

Is this the reason dead crabs are found by the dozens on other beaches? There are beaches inside the Puget Sound that are covered with dead crabs of every age, and several types.

posted on Tue, 07/10/2007 - 10:33am
Ka'ila See's picture
Ka'ila See says:

This is some very interesting stuff (:

posted on Sat, 03/20/2010 - 4:06am
milo triana's picture
milo triana says:

it looks like a crab zombie land

posted on Thu, 11/17/2011 - 11:08am

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