Science News

Antarctic CO2 deposits shown to have existed in the Ice Age

Twenty thousand years ago, humans were still nomadic hunters and gatherers, and low concentrations of CO2 in the atmosphere had allowed the Earth to fall into the grip of an ice age. Despite decades of research, the reasons why the CO2was so low during the ice age have been vexingly difficult to piece together.

New research, published this week in Nature, involving researcher Eric Galbraith of the Institute of Environmental Science and Technology (ICTA-UAB), shows that a big part of the answer lies at the bottom of the world. Sediment samples from the seafloor, more than 3 km beneath the surface of the ocean near Antarctica, support a long-standing hypothesis that there was more CO2 dissolved in the deep Southern Ocean at times when the CO2 was low.

“The chemical fingerprint left in the sediments is a long-sought smoking gun that there was increased carbon storage in the deep sea when the atmospheric CO2 was lower,” according to Sam Jaccard at the University of Bern, the study’s lead author.

Researchers now know that extra carbon was trapped in the deep sea by the build-up of dead organic matter from above, as long suspected and they state that the build-up and release of CO2 stored in the deep ocean during the ice age was driven by what was happening in the ocean around Antarctica.

The new work also shows that these same processes were probably behind a series of natural – ~20 part per million (ppm) – wobbles in atmospheric CO2 concentrations. Researchers declare that these natural CO2 wobbles were probably caused by changes in the amount of dust sprinkled over the ocean surface, which fertilizes the growth of phytoplankton, and by changes in the release of carbon from the deep ocean by changing ocean currents.

Eric Galbraith, ICREA researcher at ICTA-UAB says that whereas the natural wobbles of 20 ppm took thousands of years to occur, atmospheric CO2 concentrations have risen by 20 ppm over just the last 9 years due to human emissions. “The current rate of CO2 increase is just so fast that it’s hard to compare it with natural variations,” says Dr Galbraith, who adds that “we are entering territory for which we don’t have a good climatic analogue in the past”.