It turns out that the modern ocean’s biological carbon pump is far more leaky than it was 20,000 years ago. At that time, a less leaky marine carbon pump helped keep the world locked into its glacial state.

The world’s ocean and atmosphere represent the most important circulatory pumping mechanism for the greenhouse gas carbon dioxide (CO₂) on centennial to millennial timescales. Atmospheric CO₂ is ‘inhaled’ through the sea surface and can be locked up by biological productivity that subsequently sinks deep into the ocean interior where it forms a major carbon reservoir. Eventually this sequestered CO₂ is leaked back into the atmosphere due to the slow turnover of the ocean by the overturning circulation. However, the slower this leak is, the more CO₂ will be stored in the deep ocean.

The study by Dr Luke Skinner from the Department of Earth Sciences in the University of Cambridge and an international team of scientists provides a much more accurate estimate of the Ice Age ocean’s total radiocarbon inventory than previously available. And, as a consequence they suggest that more than half of the decline in atmospheric CO₂ during that Ice Age may have resulted from less vigorous ocean overturning and a less leaky carbon pump.

As Luke Skinner says ‘the study serves as a reminder of the ocean's powerful role as a moderator of atmospheric CO₂ and global climate, though it is a sobering thought that even the natural CO₂ levels that helped to push the Earth in and out of past Ice Ages have already been outstripped by the release of manmade CO₂  into the atmosphere'.

Douglas Palmer, Sedgwick Museum

The research is published in the journal Nature Communications