After the last Ice Age peaked about 18,000 years ago, levels of atmospheric carbon dioxide rose about 30 percent. Scientists believe that the additional CO2 -- the source of which was thought to be the deep ocean -- played a key role in warming the planet and melting the continental ice sheets. But a new study suggests that the deep ocean was not an important source of carbon during glacial times. The finding will force researchers to reassess their ideas about the fundamental mechanisms that regulate atmospheric CO2 over long time scales....