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Ian Cloke
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Scientists: Global warming triggering fish-killing "dead zone"
By Jeff Barnard
The 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 appears to be triggered by global warming, scientists say.
The area is larger and more intense than in past years, and there are signs it is spreading north to Washington's Olympic Peninsula.
Scientists studying a 70-mile-long zone of oxygen-depleted water along the Continental Shelf between Florence and Lincoln City have concluded it is being caused by explosive blooms of tiny plants known as phytoplankton, which die and sink to the bottom.
The phytoplankton are eaten by bacteria, which use up the oxygen in the water. The recurring phytoplankton blooms are triggered by north winds generating a rollover of the water column in a process known as upwelling.
"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.
Each year since then, dead zones have returned in the summer. But these have been caused by intense bursts of upwelling followed by calm periods. During the calm periods, when the water contains fewer nutrients, phytoplankton die for lack of food and fall to the ocean bottom, 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.
The off-and-on action of the upwelling builds up a thick layer of organic material that robs the water of oxygen as it rots. When a new upwelling occurs, it draws the deadly water toward shore, killing fish and crabs that cannot get out of its way, Barth said.
"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 the oxygen levels.
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By Jeff Barnard
The 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 appears to be triggered by global warming, scientists say.
The area is larger and more intense than in past years, and there are signs it is spreading north to Washington's Olympic Peninsula.
Scientists studying a 70-mile-long zone of oxygen-depleted water along the Continental Shelf between Florence and Lincoln City have concluded it is being caused by explosive blooms of tiny plants known as phytoplankton, which die and sink to the bottom.
The phytoplankton are eaten by bacteria, which use up the oxygen in the water. The recurring phytoplankton blooms are triggered by north winds generating a rollover of the water column in a process known as upwelling.
"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.
Each year since then, dead zones have returned in the summer. But these have been caused by intense bursts of upwelling followed by calm periods. During the calm periods, when the water contains fewer nutrients, phytoplankton die for lack of food and fall to the ocean bottom, 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.
The off-and-on action of the upwelling builds up a thick layer of organic material that robs the water of oxygen as it rots. When a new upwelling occurs, it draws the deadly water toward shore, killing fish and crabs that cannot get out of its way, Barth said.
"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 the oxygen levels.
continues.........