"The most interesting findings are firstly that atmospheric carbon dioxide is strongly correlated with Antarctic temperature and secondly that it begins to increase a few thousand years prior to large abrupt warming events in Greenland," researchers Jinho Ahn and Edward Brook told environmentalresearchweb. "We also see some links between increases in carbon dioxide and changes in ocean circulation that might release carbon dioxide from the deep ocean."
Ahn and Brook used carbon dioxide data from the Byrd ice core, which was taken in Antarctica in the 1960s, along with δ18O levels in the ice to act as a proxy for site temperature. They used methane concentrations to correlate this data with Greenland ice cores.
Evidence from marine sediment proxies collected from the Iberian margin and the Chile margin showed that carbon dioxide rose most rapidly when North Atlantic Deep Water shoaled and stratification in the Southern Ocean decreased.
"The pattern of carbon dioxide variations fits a conceptual framework that explains abrupt climate changes as consequences of shifts in ocean circulation patterns that influence whether heat is transported northward or southward," said Ahn. "The correlation of rising carbon dioxide, rising temperature in Antarctica, and delay of warming in Greenland all are consistent with what models predict would happen in response to a slowdown of surface to deep circulation in the North Atlantic. So the carbon dioxide data help us understand this whole phenomenon of abrupt change."
Changes in North Atlantic Deep Water formation could affect carbon dioxide levels in the atmosphere by altering both physical and biological processes in the ocean and on land, say the researchers. Mechanisms could include an increase in Southern Ocean sea surface temperatures, decreased salinity in the North Atlantic and less stratification in the Southern Ocean.
According to Brook, if future climate change causes a similar change in North Atlantic circulation, there may be an extra release of carbon dioxide from the deep ocean. "But this is speculative because conditions during the glacial period were different," he stressed.
Now the team is involved with the West Antarctic Ice Sheet (WAIS) Divide ice core project, which they hope will provide them with records of environmental change with "the highest possible time resolution" for the last 100,000 years or so. "We think we can get much more detail about how carbon dioxide behaved if we can get an ice core that will provide better and more samples," said Ahn. "The core we used was actually collected in the late 1960s and a lot of it has been used already."