They might be tens of thousands of kilometers apart, but ice coverage at the North and South Poles may be more closely related than once thought. Scientists have tapped into geological records to model historical ice sheet changes at either end of the globe and, for the first time, demonstrated how the melting of one has influenced the other over the past 40,000 years.
“Polar ice sheets are not just large, static mounds of ice,” explains senior author of the study Natalya Gomez, from the University of McGill. “They evolve on various different time scales and are in constant flux, with the ice growing and retreating depending on the climate and the surrounding water levels. They gain ice as snow piles up on top of them, then spread outwards under their own weight, and stream out into the surrounding ocean where their edges break off into icebergs.”
This toing and froing between the climate and ice sheet coverage has been playing out long before we were around to see it, and certainly before we had the scientific tools to study it. The researchers drew on geological records such as sediment cores from the ocean floor and historical data on land exposure and shorelines to examine changes in the ice sheets over the past 40,000 years, building models that simulated these shifts in both hemispheres simultaneously, for the first time.
What’s useful about studying this period of time is that it covers the peak of the last Ice Age, 26,000 to 20,000 years ago, and therefore incorporates a range of colder and warmer periods. According to the team, the Antarctic ice sheet experienced significant losses in this period, which could only be explained by retreating ice sheets at the opposite end of the globe and the resulting changes in sea levels.
“We found a very variable signal of ice-mass loss over the last 20,000 years, left behind by icebergs breaking off Antarctica and melting down in the surrounding oceans,” says Michael Weber, from the Department of Geochemistry and Petrology at the University of Bonn. “This evidence could hardly be reconciled with existing models until we accounted for how the ice sheets in both hemispheres interact with one another across the globe.”
Because the team studied a timeframe that covered cooler periods along with the warming the world is currently experiencing, they say this new understanding can help us understand the ramifications of future climate change.
“The scale and complexity of ice sheets and the oceans, and the secrets of the Earth’s past climate that are locked up in the geological record are fascinating and inspiring,” says Gomez. “Our results highlight how interconnected the Earth system is, with changes in one part of the planet driving changes in another. In the modern era, we haven’t seen the kind of large ice sheet retreat that we might see in our future warming world. Looking to records and models of changes in Earth’s history can inform us about this.”
The research was published in the journal Nature.
Source: McGill University