Death Bloom of Plankton A Warning on Warming

Published on
by
The San Francisco Chronicle

Death Bloom of Plankton A Warning on Warming

by
David Perlman

Vanishing Arctic sea ice brought on by
climate change is causing the crucially important microscopic marine
plants called phytoplankton to bloom explosively and die away as never
before, a phenomenon that is likely to create havoc among migratory
creatures that rely on the ocean for food, Stanford scientists have
found.

A few organisms may benefit from this disruption of the Arctic's
fragile ecology, but a variety of animals, from gray whales to
seabirds, will suffer, said Stanford biological oceanographer Kevin R.
Arrigo.

"It's all a question of timing." Arrigo said. "If migratory animals
reach the Arctic and find the phytoplankton's gone, they'll have missed
the boat."

Phytoplankton throughout the world's oceans is the crucial nutrient
at the base of the food web on which all marine life depends; when it's
plentiful, life thrives and when it's gone, marine life is impossible.

Arrigo and his colleagues gathered 10 years of observations from six
NASA satellites to study changes in the evidence of chlorophyll - a key
to measuring the annual abundance and disappearance of phytoplankton
blooms - at the surface of the oceans. The satellite network has also
recorded the yearly appearance and disappearance of vast expanses of
sea ice and the increasing areas of open ocean all around the Arctic,
an indication of how climate change is taking hold in the northern
reaches of the globe.

A report of their findings is to appear in the current issue of the journal Geophysical Research Letters.

Unwelcome changes

The annual deep freeze that has covered much of the northern seas
with ice around the polar regions was once a regular event, but what
has been normal for millennia in the High Arctic is no longer the case.
As global climate change has warmed the world's oceans, warmer water
has moved into the frigid Arctic, causing changes in the once-regular
appearance and disappearance of sea ice over vast areas.

The result is a shift in when explosive blooms of phytoplankton appear and disappear, Arrigo's team has found.

"It's a complex system," Arrigo said in an interview, "but as the
changes in ice cover throw the timing of phytoplankton abundance off,
then the birds and animals whose brains have long been programmed to
migrate north at specific times of the year will have missed the boat
if there's no nourishment for them when they get there."

Every spring and summer, phytoplankton in the Arctic blooms richly
in explosive pulses, nourished by nitrogen and phosphorous in the
seawater, and when those chemicals are consumed, the blooms end, Arrigo
said.

Lower sea ice

The summer of 2007 experienced "by far the lowest sea ice cover ever
recorded," Arrigo and his colleagues said. The ice cover was an
unprecedented 23 percent lower than the previous low recorded only two
years earlier, according to a recent report from the National Snow and
Ice Data Center at the University of Colorado in Boulder.

As a result of all that open water, "primary production" of
phytoplankton in the open ocean of the Arctic reached a peak of more
than 10 million tons last year, compared with only 700,000 tons in
2006, Arrigo found.

Most of the explosive increase in plant production was due to the
longer growing season made possible by the increasing extent of
ice-free open ocean - particularly in the shallower waters of the
continental shelves that surround the entire north polar region.

But plankton is short-lived, and when its chemical nutrients run out
and the plants disappear, the marine life that depends on it is
threatened.

"Continued reductions in Arctic sea ice and the associated increase
in primary production (of phytoplankton) are almost certain to impact
marine ecosystems ... and could precipitate profound ecological
shifts," Arrigo wrote in his team's report.

Some fish and other creatures in the far north that serve as prey
for animals higher in the food chain may benefit from increases in
phytoplankton, but many migratory animals like gray whales and all the
seabirds that shuttle to the Arctic at fixed times are bound to lose
out if the timing of the phytoplankton cycle changes, Arrigo said.

His colleagues in this report are Gert van Dijken, the project's
technical expert, and Sudeshna Pabi, a geophysics graduate student at
Stanford.

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