Researchers from the University of St Andrews have identified a potential mechanism connecting the growth of glaciers in the Northern Hemisphere to the onset of ancient ice ages. Their findings, published in the Journal of Climate, suggest that the cooling of northern waters could have triggered changes in the ocean surrounding Antarctica, thereby influencing the global climate.
A decline in atmospheric carbon dioxide (CO₂) concentrations played a pivotal role in the development of ice ages. A significant portion of this carbon was sequestered in the oceans, with the Southern Ocean—encircling Antarctica—serving as a critical site for this process. For a long time, scientists struggled to explain how the expansion of ice sheets in the Northern Hemisphere—driven by natural shifts in Earth’s orbit—could enhance CO₂ absorption in the distant Southern Ocean.
The study’s authors link these processes to the movement of ocean waters between the hemispheres. As glaciers in the North grew, the adjacent waters of the North Atlantic cooled and gradually migrated southward. Upon reaching the Southern Ocean, these waters altered circulation patterns around Antarctica, creating conditions that facilitated greater CO₂ accumulation in the deep ocean layers.
To test this hypothesis, the researchers conducted computer simulations of ocean circulation. In one set of calculations, they cooled only the northernmost latitudes—simulating the impact of a massive ice sheet—and evaluated the response of the Southern Ocean. This localized cooling accounted for 74% of the total CO₂ absorption observed in a separate model that simulated cooling across the entire planet. According to the study’s lead author, Dr. Madison Shankle from the School of Earth and Environmental Sciences at the University of St Andrews, the research demonstrates a plausible link between Northern Hemisphere ice sheets and changes in Southern Hemisphere circulation that result in the removal of CO2 from the atmosphere. “Essentially, we have found evidence for a plausible mechanism connecting two seemingly disparate puzzles—Northern Hemisphere ice sheets and changes in Southern Hemisphere ocean circulation that drive CO2 uptake—which had previously been difficult to explain within the framework of past glacial cycles. Our research takes the next step: we have demonstrated how they work together through model simulations, which represents a significant advancement for the field,” she said.
Studying ancient glacial periods helps refine our understanding of Earth’s natural carbon cycle. Such data reveal how carbon dioxide moves between the atmosphere and the oceans, and how shifts in this balance affect global temperatures. The mechanism identified adds to our understanding of how the climate system functions and is crucial for assessing how the oceans and other natural processes might respond to the additional CO2 currently entering Earth’s system.
About the Author
