[R-G] Ocean warming threatens Antarctic wildlife

[Tim Murphy]

Wednesday October 19, 2005
The Guardian
www.guardian.co.uk


Ocean warming threatens Antarctic wildlife

· Sea ice melts and glaciers shrink at accelerating rate
· Decline in stocks of krill hits entire food chain

by

David Adam, environment correspondent


Scientists working in Antarctica have discovered an alarming rise in sea
temperature that threatens to disrupt populations of penguins, whales, seals
and a host of smaller creatures within a few decades.

The new study shows the ocean west of the Antarctic Peninsula(1) has warmed
by more than a degree since the 1960s - confounding computer models(2) and
experts who believed that a combination of ice, winds and currents would
keep the water cool and shield fragile marine creatures from the effects of
climate change. This is the first evidence that the key Southern Ocean is
getting warmer: a finding with potentially severe implications for wildlife.

Lloyd Peck, a marine biologist with the British Antarctic Survey, said: "The
sea temperature is going up in a way that wasn't predicted and this makes me
more worried for the marine animals. The evidence we've got and the models
we've been looking at said sea temperature was not likely to change much in
the Antarctic. A one degree increase puts us into the region where the
animals are pushed to one end of their biological, physiological and
ecological capabilities."

Animals that live on the seabed around the Antarctic Peninsula, where
summertime water temperatures currently peak at about 0.5C, are sensitive to
small shifts in temperature. In water just two degrees warmer, molluscs
become unable to bury themselves in seabed sediment, limpets cannot turn
over and scallops lose the ability to swim. These changes would make them
more susceptible to predators, disrupting the food chain and quickly
endangering larger animals and birds.

"If the warming goes on at the same rate for 50 years or 100 years then lots
of populations of animals I work on, and maybe entire species, would be at
risk," Professor Peck said.

The climate of the Antarctic Peninsula, which reaches north from the frozen
continent towards South America, is the most rapidly changing in the
southern hemisphere. Air temperatures there have risen nearly 3C since 1951
and sea ice cover around it has dropped 20% since 1979. Now, polar experts
Michael Meredith and John King, also with the British Antarctic Survey, have
shown that sea temperatures are on the rise.

There are few long term analyses of conditions in the Southern Ocean, making
temperature trends difficult to monitor. Instead, Dr Meredith and Dr King
combined several sets of satellite data, historical records and measurements
taken from ships to reconstruct the temperature in the upper layer of the
sea over the past few decades. They found the average sea temperature off
the peninsula during the summer rose by 1.2C during the period 1955 to 1994.

The amount of salt in the top layer of water has also increased: a crucial
discovery as dissolved salt lowers the freezing point of water and helps to
make it more difficult for the insulating cover of sea ice to form in
winter. Dr Meredith said less ice would form on warmer seas in winter, which
in turn would increase the warming effect because sea ice reflects sunlight
and protects the water from the warmer air.

"Both the temperature and salinity trends are in a direction that will act
to reduce future sea ice production. Since a reduction in ice cover was
important in the instigation of these trends, they constitute positive
feedbacks,"(3) the scientists write in the journal Geophysical Research
Letters.

The rising sea temperature will also speed up the melting of glaciers. "The
melt rates of glaciers depend critically on the temperature of the ocean
they are in contact with. Our findings of strong surface warming and
positive ocean feedbacks have significant implications for the future of the
ice sheet in this region," they say.

Rising temperatures and greater losses of sea ice could also spell big
problems for krill(4). A study published last year showed krill numbers had
fallen by 80% since the 1970s. Experts linked its collapse to shrinking sea
ice.

Prof Peck said increased loss of sea ice would also hit species which rely
on it to reproduce.

Antarctic creatures are particularly vulnerable to rising temperatures
because the roughly circular Antarctic continent stops them moving south(5)
to escape warmer conditions. "Our animals appear to be very sensitive to
temperature change. They don't appear to have the physiological make-up to
cope," Prof Peck said.

Footnotes:

1. Antarctic Peninsula
Home to the British research bases in Antarctica, the peninsula has the
mildest climate on the continent and a string of mountains believed to be a
continuation of the South American Andes

2. Computer models
These souped up weather forecasts help scientists predict climate. A
shortage of data for the computer modelling, combined with complicated
winds, currents and icy conditions mean they perform poorly in Antarctica

3. Positive feedbacks
Climate change can get locked into cycles where the warming generates
effects that speed up warming. Loss of sea ice is a classic example because
exposed water absorbs more of the sun's heat

4. Krill
Shrimp like crustaceans that grow up to 6cm (2.4 inches) long. They are a
staple food for everything from fish to whales and their decline could have
dramatic consequences for the food chain

5. Moving south
The easiest way for species that like cold conditions to cope with global
warming is to move closer to the poles. Marine creatures around Antarctica
cannot do this - the circular solid continent blocks them

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