Scientists Say Warming Triggers Dead Zone

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Scientists Say Warming Triggers Dead Zone

 

August 07, 2006 — By Jeff Barnard, Associated Press

GRANTS PASS, Ore. — Bottom fish and crabs washing up dead on Oregon beaches

are being killed by a recurring " dead zone " of low-oxygen water that is larger

than in previous years and may be triggered by global warming, scientists said.

 

There are signs it is spreading north to Washington's Olympic Peninsula.

 

Scientists studying the 70-mile-long zone of oxygen-depleted water, along the

Continental Shelf between Florence and Lincoln City, conclude that it is being

caused by explosive blooms of tiny plants known as phytoplankton, which die and

sink to the bottom, then are eaten by bacteria which use up the oxygen in the

water.

 

The recurring phytoplankton blooms are triggered by northerly wind, which

generates a process known as upwelling in which nutrient-rich water is brought

to the surface from lower depths.

 

" We are seeing wild swings from year to year in the timing and duration of the

winds that are favorable for upwelling, " Jane Lubchenco, professor of marine

ecology at Oregon State and a member of the Pew Oceans Commission, said from

Corvallis. " This increased variability in the winds is consistent with what we

would expect under climate change. "

 

Scientists first noticed a dead zone off Newport in 2002. That one was traced

back to a rare influx of cold water rich in nutrients and low in oxygen that had

migrated from the Arctic, said Jack Barth, professor of oceanography at Oregon

State and with Lubchenco a principal investigator for the Partnership for

Interdisciplinary Studies of Coastal Oceans.

 

Dead zones have returned each summer since then, but these have been marked by

intense bursts of upwelling that were followed by calm periods, when the water

contains lower nutrient levels, Barth added.

 

This year, the upwelling started strongly in April, stalled in May and picked up

again in late June. Following the upwellings, scientists found the oxygen levels

lower.

 

" We know it's not pollution. It's not a toxic algal bloom. The simple fact is

there's not enough oxygen, " said Francis Chan, a research professor of zoology

at Oregon State who has been measuring ocean oxygen levels.

 

Oxygen levels are generally lower in deeper water, said Lubchenco, but what is

unusual about this condition is that it is moving into relatively shallow water,

about 50 feet deep, and moving toward shore, where the richest marine ecosystems

are.

 

Deep water fish, such as ling cod, wolf eels and rockfish, are showing up in

Oregon tide pools, apparently driven toward shore by the advancing dead zone,

said Lubchenco.

 

Although the dead zone has been documented along 70 miles of coast, dead crabs

and fish also have been showing up along Washington's Olympic Peninsula, Barth

said.

 

" If we continue like we are now, we could see some ecological shifts, " Barth

said. " It all depends on what happens with the warming and the greenhouse

gases. "

 

Dead zones in other places around the country, such as Hood Canal in Washington

and the Mississippi River Delta off Louisiana are caused by agricultural runoff

fueling blooms of algae that rot and deplete oxygen levels, said Lubchenco. But

dead zones like the one off Oregon also occur off Namibia and South Africa in

the Atlantic and off Peru in the Pacific.

 

" We're not really sure what is down the road. If it's just for a short period of

time, it will not be as devastating as if it starts lasting a significant

fraction of summer, " she said.

 

Source: Associated Press

 

 

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