Some 14,000 years ago, algal blooms in the Southern Ocean helped to massively reduce the global carbon dioxide content of the atmosphere—as has now been revealed by new analyses of ancient DNA published by a team from the Alfred Wegener Institute (AWI) in the journal Nature Geoscience. In the ocean around the Antarctic continent, these algal blooms had a significant impact on global carbon dynamics. The current and expected future decline in sea ice in this region now poses a serious threat to these algae, which could incur global consequences.