Carbon Dioxide Decline Linked To Ancient Glaciation

Carbon isotope ratios in algae-produced organic compounds provide evidence that 35 million years ago a dramatic decline in atmospheric carbon dioxide levels spurred Antarctic glaciation (Science, DOI: 10.1126/science.1203909). The idea of linking a drop in atmospheric CO₂ with glacier growth from the subsequent global cooling has been controversial and difficult to substantiate. Yale University’s Mark Pagani and colleagues extracted alkenones—long-chain unsaturated ethyl and methyl ketones produced by ancient ocean algae—from seafloor sediment cores and analyzed the molecules’ ¹³C to ¹²C ratios. These ratios provide a fingerprint of the atmospheric CO₂ levels present when the algae produced the alkenones via photosynthesis. The analysis by Pagani’s team suggests that atmospheric CO₂ decreased just before Antarctic ice shelves started forming. “Onset of Antarctic glaciation reflects a critical tipping point for Earth’s climate and provides a framework for investigating the role of atmospheric CO₂ during major climatic change,” the researchers conclude.