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May
10, 2007 A study released
today provides
some of the first solid evidence that warming-induced changes in ocean
circulation at the end of the last Ice Age caused vast quantities of
ancient
carbon dioxide to belch from the deep sea into the atmosphere.
Scientists
believe the carbon dioxide (CO2) releases helped propel the world into
further
warming. The study, done by researchers at the Atmospheric CO2,
also produced by
burning of fossil fuels, is thought to be largely responsible for
current
warming. However, scientists have known for some time that the gas also
goes
through natural cycles. By far most of the world's mobile carbon is
stored in
the oceans—40 trillion metric tons, or 15 times more than in
air, soil and
water combined. But how this vast marine reservoir interacts with the
atmosphere has been a subject of debate for the last 25 years. The
study
indicates what many scientists have long suspected, but could not
prove:
sometimes the oceans can release massive amounts of CO2 into the air as
they
overturn. "The lesson is that abrupt changes in ocean circulation in
the
past have affected the oceans' ability to keep carbon dioxide out of
the
atmosphere," said geologist Thomas Marchitto of the The researchers
found the
evidence in a core of Pacific Ocean sediment brought up from 705
meters--about
2,300 feet—off the coast of The upwelling and
release of this
carbon dioxide matches well with rapid warming and rises in atmospheric
CO2
shown in glacial ice cores from Exactly what caused
the upwelling
is not clear, but many scientists believe the world was already
undergoing a
natural warming cycle, possibly due to a slight periodic change in
earth's
orbit. This suddenly ended the last Ice Age, in turn changing ocean
currents
and wind patterns. The hypothesis favored by paper's authors is that
sudden
disintegration of northern ice sheets during this initial warming
slowed or
halted deep "Once the CO2
started
rising, it probably helped the warming process along—but
exactly how much, we
can't say," said Robert Anderson, a Lamont-Doherty expert in ocean
circulation who was not involved in the study. "And there is still huge
uncertainty as to how the oceans will respond to current warming."
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