Scientists at the University of St Andrews have identified a previously unknown process that may help explain how Earth entered past ice ages. Their computer simulations suggest that the growth of ice sheets in the Northern Hemisphere could have altered ocean circulation as far away as Antarctica, increasing the Southern Ocean’s capacity to remove carbon dioxide (CO2) from the atmosphere and potentially intensifying global cooling.
The research offers a possible explanation for how the expansion of Northern Hemisphere ice sheets influenced Southern Hemisphere sea ice and ocean circulation. These southern changes are known to have played an important role in reducing atmospheric CO2, a key factor in the development of ice ages. Until now, scientists have struggled to explain how processes in distant parts of the world could become so closely connected.
One factor that supported Earth’s past ice ages was a decline in atmospheric CO2, partly because more carbon was stored in the ocean. Much of this process was controlled by changes in the Southern Ocean surrounding Antarctica. However, a major question remained: how could the expansion of Northern Hemisphere ice sheets—initially caused by natural variations in Earth’s orbit—lead to greater carbon uptake in the distant Southern Ocean?
How northern ice sheets could affect Antarctica
The researchers propose that the answer lies in the movement of seawater between the hemispheres. As large ice sheets spread across northern regions, they cool waters near the North Atlantic Ocean. Over time, those colder waters can circulate southward and eventually reach the Southern Ocean.
If the cooling is strong enough, it could alter ocean circulation around Antarctica and increase the amount of CO2 stored in the deep ocean. As atmospheric CO2 levels fall, global temperatures may decline further, potentially intensifying an ice age.
To investigate this possibility, the research team used computer simulations of ocean circulation. Instead of lowering temperatures across the entire planet, the researchers cooled only the northernmost latitudes to mimic the effects of large ice sheets. They then examined how the Southern Ocean responded.
The results indicated that cooling the far north alone produced 74% more CO2 drawdown than a simulation in which the entire planet cooled. This suggests that temperature changes in the Northern Hemisphere could have a substantial effect on the Southern Ocean and its ability to store carbon.
A missing link in the ice-age climate puzzle
The simulations support a possible connection between the expansion of Northern Hemisphere ice sheets and changes in Southern Ocean circulation. They suggest that colder water originating in the North Atlantic could eventually influence circulation around Antarctica, helping remove CO2 from the atmosphere and contributing to the global cooling associated with past ice ages.
For decades, much of the research into ice-age climate change has focused on the Southern Ocean because of its important role in regulating atmospheric CO2. Scientists have only recently begun to recognize how changes in distant ocean regions may affect these processes.
Lead author Dr Madison Shankle, from the School of Earth and Environmental Sciences at the University of St Andrews, explained the significance of the findings:
“Essentially, we have presented evidence of a plausible mechanism that connects two distant pieces of the puzzle: northern hemisphere ice sheets and southern hemisphere ocean circulation changes that drive CO2 drawdown — this has been difficult to explain in theories about Earth’s past ice ages. In our research, we have taken the step of actually demonstrating that they work in model simulations, which is a major step forward for the field.”
What ancient ice ages reveal about today’s climate
Understanding how past ice ages developed gives scientists a way to study Earth’s natural carbon cycle. These periods show how carbon moves between the atmosphere and the ocean, and how changes in that balance influence global temperatures.
By identifying possible mechanisms that contributed to reductions in atmospheric CO2, research into ancient ice ages can provide a more complete picture of how Earth’s climate system operates.
This knowledge is also important today, as scientists work to understand how the oceans and other natural systems will respond to the additional CO2 entering the Earth system.
Source: www.sciencedaily.com
