| Australian scientists, looking for ways to reduce the amount of carbon
dioxide in the atmosphere, have dumped 10 tonnes of iron in the ocean off
Antarctica.
The iron caused giant blooms of marine algae, which over 13 days absorbed
2000 tonnes of carbon dioxide.
Ten years ago it was proposed that fertilising the oceans with iron might
create algal blooms capable of soaking up much of the excess carbon dioxide
believed to be responsible for global warming.
In recent years, the technique, called iron fertilisation, has been supported
by laboratory experiments and it has regularly been suggested that Antarctic
waters, which are well-endowed with algae, would be an ideal site for iron
fertilisation.
``The idea is, by adding small amounts of iron it encourages the growth of
phytoplankton," said Peter Sedwick, a biogeochemist at the Antarctic
Cooperative Research Centre. ``The phytoplankton captures carbon dioxide and
takes it down to the bottom of the ocean."
Buoyed by laboratory tests, scientists from the Hobart-based Antarctic CRC
and the University of Western Australia chose February, 1999, to test iron
fertilisation in Antarctic waters.
In collaboration with scientists from New Zealand and Britain, the
researchers fertilised 55 square kilometres of ocean off Antarctica with ferrous
sulphate - 20 times more iron than is usually there.
Tom Trull, a chemical oceanographer at the Antarctic CRC, said that over two
weeks the number of algae increased five-fold and absorbed 2000 tonnes of carbon
dioxide.
But despite the algal bloom, any changes in the color of the water were
imperceptible, he said.
``You could not see it with the naked eye," he said. ``It would have been
the clearest water you had seen in your life - clearer than the water from your
tap."
Dr Trull said the algae removed 2000 tonnes of carbon dioxide from the ocean,
paving the way for the oceans to suck a further 2000 tonnes of carbon dioxide
from the atmosphere. Although it took only two weeks for the algae to absorb
2000 tonnes of the greenhouse gas, it would take about two months for the oceans
to absorb an equivalent amount from the atmosphere, he said.
According to the Australian Greenhouse Office, there are about 1.2megatonnes
of carbon dioxide produced in Australia each day.
Although the Antarctic experiment used 10 tonnes of iron, Dr Trull said, the
same results would probably have been observed using only two tonnes.
Encouragingly, adding iron prompted an increase in a type of algae known as
diatoms. ``The present view is that diatoms are the most successful at taking up
carbon dioxide," Dr Trull said.
Diatoms, which have shells of silica, are not only efficient in absorbing
carbon dioxide, they also sink to the ocean floor, taking the greenhouse gas
with them.
Dr Trull said diatoms must sink to at least 60 metres for the carbon dioxide
to be effectively removed from the global carbon cycle.
Nevertheless, Dr Trull said iron fertilisation was not the absolute solution
to reducing atmospheric carbon dioxide. ``It's never going to be a panacea, it's
never going to be able to suck out massive amounts of carbon dioxide," he
said.
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