[Mike]

http://www.guardian.co.uk/climatechange/story/0,12374,1580628,00.html

Acidic oceans threaten marine food chain

Ian Sample, science correspondent
Thursday September 29, 2005
The Guardian

Rising carbon dioxide in the atmosphere is threatening to make oceans
too corrosive for marine organisms to grow protective shells,
according to researchers.

If emissions continue unabated, the entire Southern Ocean, which
stretches north from the Antarctic coastline, and subarctic regions
of the Pacific Ocean will soon become so acidic that the shells of
marine creatures will soften and dissolve making them easy targets
for predators. Others will not be able to grow sufficient shells to
survive.

The loss of shelled creatures at the lower end of the food chain
could have disastrous consequences for larger marine animals. North
pacific salmon, mackerel, herring, cod and baleen whales all feed on
pteropods or sea butterflies, one of the species under imminent
threat.

“These are extremely important in the food chain and what happens if
they start to disappear is a great unknown,” said Jim Orr, lead
scientist on the study at the Laboratory for Science of the Climate
and Environment in Gif-sur-Yvette, near Paris.

Previous studies have suggested it would take centuries for emissions
to acidify the oceans to such an extent, but the latest report,
published today in the journal Nature, claims entire ecosystems will
be threatened much sooner. “Within decades, there may be serious
trouble brewing in these polar oceans,” said Dr Orr. “Unlike climate
predictions, the uncertainties here are small.”

Carbon dioxide is churned out by the burning of fossil fuels and
other industrial processes. Each day, the average person burns enough
fuel to emit 11kg (about 24lbs) of carbon dioxide, 4kg of which is
absorbed by the oceans. When carbon dioxide is taken up by oceans, it
strips out carbonate ions dissolved in surface waters, so there is
less available for marine organisms to build calcium carbonate shells
and exoskeletons from.

Dr Orr and an international team from Britain, the US, Japan and
Australia combined recent measurements from oceans with computer
models to work out how CO2 levels are likely to change the acidity of
oceans in coming decades if emissions continue as expected.

They found that by 2100, the amount of carbonate available for marine
organisms would drop by 60%. By 2050, there could be too little
carbonate in surface waters for organisms to form shells.

In a follow-up experiment, Victoria Fabry at California State
University San Marcos investigated how marine organisms reacted to
the predicted changes by immersing live pteropods in sea water as
acidic as the models predicted for 2100. She found the shells began
to dissolve rapidly, with pits forming on their surfaces and external
layers peeling away.

Life in the polar oceans will be first to feel the brunt of rising
carbon dioxide levels. Atmospheric carbon dioxide has increased from
pre-industrial levels of around 280 parts per million to 380ppm today.