Melting Ice May Slow Global Warming

Scientists discover that minerals found in collapsing ice sheets could
feed plankton and cut C02 emissions

David Adam, environment correspondent

The Observer, Sunday December 7 2008

Collapsing antarctic ice sheets, which have become potent symbols of
global warming, may actually turn out to help in the battle against
climate change and soaring carbon emissions.

Professor Rob Raiswell, a geologist at the University of Leeds, says
that as the sheets break off the ice covering the continent, floating
icebergs are produced that gouge minerals from the bedrock as they
make their way to the sea. Raiswell believes that the accumulated
frozen mud could breathe life into the icy waters around Antarctica,
triggering a large, natural removal of carbon dioxide from the
atmosphere.

And as rising temperatures cause the ice sheets to break up faster,
creating more icebergs, the amount of carbon dioxide removed will also
rise. Raiswell says: ‘ It won’t solve the problem, but it might buy us
some time.’

As the icebergs drift northwards, they sprinkle the minerals through
the ocean. Among these minerals, Raiswell’s research shows, are iron
compounds that can fertilise large-scale growth of photosynthetic
plankton, which take in carbon dioxide from the air as they flourish.

According to his calculations, melting Antarctic icebergs already
deposit up to 120,000 tonnes of this ‘bioavailable’ iron into the
Southern Ocean each year, enough to grow sufficient plankton to remove
some 2.6 billion tonnes of carbon dioxide, equivalent to the annual
carbon pollution of India and Japan. A 1 per cent increase in the
number of icebergs in the Southern Ocean could remove an extra 26
million tonnes of CO2, equivalent to the annual emissions of Croatia.

Raiswell, a Leverhulme Emeritus Fellow, said: ‘We see the rapid ice
loss in Antarctica as one obvious sign of climate warming, but could
it be the Earth’s attempt to save us from global warming?’ He added
that the effect had not been discovered before because scientists
assumed that the iron in the iceberg sediment was inert and could not
be used by plankton.

In a paper published in the journal Geochemical Transactions, Raiswell
and colleagues at the University of Bristol and the University of
California describe how they chipped samples off four Antarctic
icebergs blown ashore on Seymour island by a storm in the Weddell Sea.

They found that they contained grains of ferrihydrite and
schwertmannite, two iron minerals that could boost plankton growth.
‘These are the first measurements of potentially bioavailable iron on
Antarctic ice-hosted sediments,’ they write. ‘Identifying icebergs as
a significant source of bioavailable iron may shed new light on how
the oceans respond to atmospheric warming.’

No rivers flow into the Southern Ocean and the only previously
identified major source of iron for its anaemic waters is dust blown
from South America. The team says that icebergs could deliver at least
as much iron as the dust.

A key question is how much of the carbon soaked up by the growing
plankton is returned to the atmosphere. ‘We simply don’t know the
answer to that,’ Raiswell said. Seeding the oceans with iron will only
benefit the climate if the plankton sink to the bottom when they die,
taking the carbon with them.

David Vaughan, a glaciologist with the British Antarctic Survey, said:
‘It’s a very interesting new line of research and one that should be
looked at in more detail.’

He said the number of icebergs in the Antarctic was expected to rise
by about 20 per cent by the end of the century, which could remove an
extra 500 million tonnes of carbon dioxide each year, if they all
seeded plankton growth.

guardian.co.uk © Guardian News and Media Limited 2008

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