Natural Science Forum / Earth Science / Oceanography / March 2007

source: http://tinyurl.com/2wnjtv
February 18, 2007

Unprecedented changes to ocean currents are having a devastating
effect on finely balanced marine ecosystems, scientists meeting in the
US have warned.

Off the west coast of the United States, the disruption has led to the
death of huge numbers of sea animals including crabs, salmon and tens
of thousands of birds.

Similar ecosystem upheaval has been recorded in other parts of the
world, particularly South America and Africa.

Early evidence suggests that global warming is driving the changes by
throwing previously predictable seasonal winds out of kilter.

The effects appear to be consistent with what has been predicted by
climate change models, say scientists.

Experts at the annual meeting of the American Association for the
Advancement of Science in San Francisco described two extraordinary
linked events in 2005 and 2006.

The first occurred when 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 phytoplankton, the microscopic plant organisms
that form the vital base of the ocean ecosystem and upon which larger
animals depend for food.

Salmon, which normally take to the sea at this time, starved. The
effects rippled up through the food web as predators, including many
sea birds, went hungry and died.

The following year the west coast current came back with a vengeance,
producing an upwelling of nutrient-rich water twice as strong as the
average recorded for several previous years.

Phytoplankton bloomed to levels not seen before, turning the sea to
green-brown soup. They then died and sank, causing oxygen levels in
the water to plummet virtually to zero.

The result was a "dead zone" in which nothing could survive.
Scientists conducting a submarine survey found dead crabs and marine
worms scattered across the ocean floor, and no sign of any fish.

The knock-on effects were once again disastrous for sea birds which
relied on the sea creatures for food. Huge numbers of dead birds were
washed up on the shores.

The 2006 dead zone, which remained for nearly 17 weeks, was three
times bigger than any seen in the region before, said Dr Francis Chan,
from Oregon State University in Corvallis.

He said: "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 to months on end.

"It went from a low oxygen system to a no oxygen system. This had a
dramatic effect on marine life."

Dr Julia Parrish, from the University of Washington in Seattle, said
there were "many spikes" in sea bird mortality during 2005 and 2006.

"Beaches were literally littered with the bodies of dead sea birds,"
she told the meeting. "Tens of thousands of additional birds were
washing up on the shore."

Many of the starving birds had also been unable to breed, she said.

Seasonal winds blowing across the sea affect ocean currents by pushing
away surface water, which is then replaced by colder water from below.

Warmer land temperatures resulted in higher pressures and stronger
winds, which in turn had an impact on currents, said the scientists.

Normally these effects were predictable, but recently the system had
become unstable and volatile - a pattern that mirrored climate change
models.

Professor Jane Lubchenco, from Oregon State University, said: "Wild
fluctuations in the intensity of ocean upwellings are wreaking havoc
with the ecosystems of the west coast.

"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 had shown that the events were
"unprecedented in this ecosystem", she said.

She pointed out that similar ocean current disruption had been seen in
other regions of the world, particularly Peru, Chile and parts of
Africa.

"The ultimate causes of the changes are unknown," Professor Lubchenco
added. "We finger the winds as the important culprit, but we do not
know definitively why these winds are changing. We do know that the
changes are what would be expected under climate change scenarios, and
climate change is a viable hypothesis... We should expect more
surprises."

Findings related to the 2005 event were reported in the online version
of the journal Proceedings of the National Academy of Sciences.