Global warming may affect Antarctic’s ability to absorb carbon

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.