Using computer simulations, the researchers looked at past glacial periods and noted that previous increases in sea ice levels might have significantly altered the circulation of the ocean, leading to a reverse greenhouse effect as carbon dioxide levels in the ocean increased and levels in the air decreased.
“One key question in the field is still what caused the Earth to periodically cycle in and out of ice ages,” Malte Jansen, a University of Chicago professor and the study's co-author, said in a statement. “We are pretty confident that the carbon balance between the atmosphere and ocean must have changed, but we don’t quite know how or why."
Since the last major ice age ended at the close of the Pleistocene epoch, about 11,700 years ago, glaciers have periodically grown and then gotten smaller. Researchers believe that changes to the Earth's orbit may have been partly responsible for some of the Earth's cooling, while changes in how carbon was divided between the atmosphere and the ocean could also have contributed to the process. According to the study, a mini-ice age that occurred roughly 12,800 years ago may have been caused by an asteroid impact that "rocked the Northern Hemisphere" and led to the Younger Dryas climate event.
Jansen noted that the Southern Ocean around Antarctica "plays a key role in ocean circulation" due to the deep waters in the region, leading it to have "outsize[d] consequences."
“What this suggests is that it’s a feedback loop,” said the study's lead author, Alice Marzocchi. “As the temperature drops, less carbon is released into the atmosphere, which triggers more cooling.”
“What surprised me is how much of this increased storage can be attributed to physical changes alone, with Antarctic sea ice cover being the key player,” Marzocchi added, noting that future studies of the ocean and the role it plays in the carbon cycle could help simulate "future environmental change.”