Antarctica at the centre of the ice age CO2 mystery

.A new study published in Nature involving ICTA-UAB researcher Eric Galbraith demonstrates the existence of increased carbon storage in the deep Southern Ocean during the Ice Age, when the atmospheric CO₂ was lower.

.Researchers warn about the high rate of CO₂ increase in the atmosphere

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 CO₂ was 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 –Universidad Autònoma de Barcelona (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 nine 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”.