Examining Carbon ‘Burps’ that Helped End the Last Ice Age
31.05.2010 - Atmosphere & Space, Water & Oceans, Flora & Fauna
The results of a recent study, published in the journal Science, suggest that carbon dioxide (CO2) was probably efficiently locked away in the deep ocean during the last ice age. Working on a marine sediment core recovered from the Southern Ocean seabed, the researchers radiocarbon-dated shells left behind by foraminifera (small marine creatures). By comparing the carbon-14 (14C) levels found in the shells with those contained in the atmosphere at the time, they found out how long the CO2 had been locked in the ocean.
Over the past two million years, the Earth has alternated between ice ages and warmer interglacials due to changes in the Earth's orbit around the sun. These changes, however, could only have acted as the 'pacemaker’ for the ice ages with help from large, positive feedbacks that turned this solar 'nudge' into a significant global energy imbalance. Changes in atmospheric CO2 were one of the most important of these positive feedbacks; however what drove these changes in CO2 has remained uncertain.
Yet because the ocean is a large, dynamic reservoir of carbon, scientists have suspected that changes in ocean circulation must have played a significant role in instigating large changes in CO2. They believe that more CO2 was locked up in the deep ocean during ice ages, and that pulses, or 'burps', of CO2 from the deep Southern Ocean helped trigger a global thaw every 100,000 years or so. If this theory is correct, we would expect to see large transfers of carbon from the ocean to the atmosphere at the end of each ice age.
As well as providing evidence for rapid release of carbon dioxide during deglaciation, the research illustrates how ocean circulation can change significantly over a relatively short period of time. The findings underline the fact that the ocean is a large and dynamic carbon pool and could have implications for proposals to pump carbon dioxide into the deep sea as a way of tackling climate change.
