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June 1st, 2007

Atmospheric CO2 pulses at the end of last ice age originated from the deep ocean

Tom Marchitto, Scott Lehman, Jaqueline Flückiger (former INSTAAR, now at ETH Zürich), and colleagues from Kent State and Lamont-Doherty have identified a mechanism for the enormous carbon dioxide increase in Earth's atmosphere at the end of the last ice age: abrupt changes in deep ocean circulation. The team analyzed sediment cores from the North Pacific, using radiocarbon (carbon 14) in benthic foraminifera shells as a tracer and chronometer to track the escape of carbon from the deep sea through the upper ocean and into the atmosphere during the last 40,000 years. They discovered two large CO2 "burps" about 18,000 years ago and 13,000 years ago. During both releases, the carbon delivered to the upper ocean and atmosphere was "very old," suggesting that it had been stored in the deep ocean and isolated from the atmosphere for thousands of years. Both events correspond closely in time with abrupt deep-sea circulation changes believed to have been caused by ice sheet melting in the North Atlantic. Thus, rapid changes in the ocean circulation system dramatically altered how carbon-rich deep water rose to the surface to release its carbon to the atmosphere. The teams' research helps improve not only understanding of why glacial times came and went in the past, but how the oceans may respond to future climate change.