Scientists Say Warming Triggers 'Dead Zone'
July 27, 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 appears to be triggered by global warming, scientists say.
The area is larger and more deadly 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
"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 are generally lower in deeper water, where fish evolve
to deal with it, said Lubchenco. 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
Monitoring of oxygen levels in the ocean has documented the dead zone
in varying intensities along 70 miles of coast from Florence to
Lincoln City, but the ribbon of dead phytoplankton on the ocean
bottom that creates it could extend to Washington's Olympic
Peninsula, where dead crabs and fish have been showing up, Barth
"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 the oxygen, 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.
Crab fishermen in Oregon and Washington are finding dead crabs in
their pots, and deeper water fish, such as ling cod, wolf eels and
rockfish, are showing up in Oregon tide pools, apparently chased to
shore by the dead zone advancing across the Continental Shelf, said
In Washington, dead fish and crabs are also being spotted on the
beach along the Olympic Coast National Marine Sanctuary and the
Quinault Indian Reservation, Liam Antrim, resource protection
specialist for the marine reserve, said from Port Angeles, Wash.
"Last year we did some routine monitoring along six transects every
other week. We never documented low oxygen conditions low enough to
kill things," Antrim said. "This year we have."
Source: Associated Press