Science:
Although the Southern Ocean surrounding Antarctica has been
taking up about half of the atmospheric carbon dioxide emitted
by human activities, its capacity is starting to decrease,
according to Samuel Jaccard of ETH Zürich in Switzerland.
Carbon dioxide sequestration is very effective in the Antarctic
because phytoplankton that grow in its nutrient-rich waters
absorb CO
2 from the atmosphere and carry it with them to the
ocean floor when they die. In addition, CO
2 is more soluble in colder waters, and the southern
winds that churn up the water allow more of the gas to be
absorbed. Over the past few decades, however, the ocean's
capacity to sequester atmospheric CO
2 appears to be lessening. Using two deep cores
collected from the Southern Ocean, Jaccard and colleagues have
been able to study the evolution of the carbon sink stretching
back a million years. What they have found is a regular
glacialâinterglacial cycle, in which more CO
2 is released from the deep ocean as the climate
warms and less as the climate cools. How to apply what they've
learned about the past to what will happen in the future is
still unknown; computer climate models are not yet
sophisticated enough to deal with all the variables, which
include the growing ozone hole, the melting of ice sheets, and
the strengthening of the southern winds.
