Ocean 'dead zones' spell disaster as wind patterns change
Pastor Dale Morgan
Ocean 'dead zones' spell disaster as wind patterns change*
Robin McKie, science editor
The Observer
A few months ago, the clear blue Pacific Ocean waters off the coast of
Oregon suddenly turned a thick greenish brown. A swell of nutrients
produced a bizarre blooming of plankton that reached levels never seen
before by scientists. Then the plankton died and sank, causing oxygen
levels in the water to plummet to zero.
The living ocean was transformed into a dead zone. Scientists conducted
a submarine survey and found only the bodies of crabs and marine worms
scattered across the ocean floor. There were no signs of any fish.
Nothing had survived the cataclysm.
Nor has this been the only such disaster to strike a marine ecosystem in
recent years. As scientists reported at the annual meeting of the
American Association for the Advancement of Science in San Francisco
yesterday, unprecedented changes to ocean currents are having a
devastating effect on finely balanced marine ecosystems all over the
globe. Similar upheavals have been recorded in other parts of the world,
particularly off South America and Africa.
Marine researchers are convinced the evidence points to one culprit:
global warming. Man-made changes to the climate are throwing previously
predictable seasonal winds out of kilter. 'We finger the winds as the
important culprit, but we do not know definitively why these winds are
changing,' said Professor Jane Lubchenco from Oregon State University.
'However, we know the changes are what would be expected under climate
change scenarios, and climate change is a viable hypothesis. We should
expect more surprises.'
Seasonal winds blowing across the sea affect ocean currents by pushing
away surface water, which is then replaced by colder water from below.
But warmer land temperatures result in higher pressures and stronger
winds, which in turn have an impact on currents, said the scientists.
Normally these effects were predictable, but recently the system had
become unstable and volatile - a pattern that mirrors climate change
models. 'Wild fluctuations in the intensity of ocean upwellings are
wreaking havoc with ecosystems,' added Lubchenco. 'We're seeing extreme
distortions on both sides of the norm. This is a system that is out of
kilter. It's fluctuating rapidly.'
Up to five decades of data have shown that these events were
unprecedented, she said, pointing out that similar ocean current
disruption had been seen in other regions, particularly off Peru, Chile
and parts of Africa.
Last year's ecosystem collapse on the Oregon coast was the second to
strike there in as many years. In 2005, a nutrient-rich ocean current
that normally appears off northern California and Oregon in spring was
delayed by a month. This led to a loss of plankton, the microscopic
plant organisms upon which larger animals depend for food. Salmon, which
normally take to the sea at this time, starved. The effects rippled
through the food web as predators, including sea birds, went hungry and
died. Huge numbers of dead birds washed up on the shores.
'Beaches were littered with the bodies of dead sea birds,' said Dr Julia
Parrish, from the University of Washington in Seattle. Many of the
starving survivors have been unable to breed since then, she added.
Then, a year later, in 2006, the dead zone appeared and remained for
nearly 17 weeks. 'It grew to an area the size of the state of Ohio and
lasted much longer than we thought would be possible, from something
that we tracked day to day for months on end,' said Dr Francis Chan,
from Oregon State University in Corvallis. 'It went from a low-oxygen
system to a no-oxygen system. This had a dramatic effect on marine life.'