Antarctica’s ice has a history of rapid and unexpected changes

During the early Miocene era, about 19 million years ago, Antarctica’s ice sheets underwent rapid and frequent growth and recession, posing a potential parallel to Earth’s future climate trajectory if current carbon emission trends persist. 

Understanding these ice sheets’ historical patterns is crucial, as their future behavior under a warming climate holds significant global implications, including potential sea level rises of over 50 meters and impacts on ocean currents, marine ecosystems, and regional climates.

Rapidly fluctuating ice sheets

Recent research led by the University of Wisconsin–Madison and international collaborators reveals new insights into this period. The study found that between 19.2 and 18.8 million years ago, Antarctic ice sheets fluctuated multiple times within just a few thousand years. 

These changes are more rapid than the expected Milankovitch cycles, which typically influence Earth’s climate and ice sheets over much longer spans.

“Our observation of this rapid volatility of the Antarctic ice sheets raises the interesting question of what’s causing it,” said lead author Nicholas Sullivan, a 2022 PhD graduate from UW–Madison.

Sediment cores

This discovery was made possible by the Antarctic Drilling Project (ANDRILL), an international initiative that retrieved sediment records from beneath the Antarctic seabed, providing valuable data on past climatic conditions.

“We could clearly see the influence of long-term climate cycles on ice sheet extent in the rock and sediment cores we recovered in 2007, but our initial observations weren’t detailed enough to detect shorter-term changes,” explained co-author Richard Levy, a professor at Victoria University of Wellington and principal scientist at GNS Science, New Zealand.

Critical insights 

The new analysis enables the documentation of past ice sheet changes over remarkably short periods, even as brief as five centuries. 

Stephen Meyers, a UW–Madison geoscience professor who collaborated with Sullivan, praises the sediment records as a remarkable archive, noting their content of small gravel bits shed from icebergs, which indicate ice sheet proximity to specific seafloor areas.

Sullivan’s research, which initially sought to identify Milankovitch cycles in the sediment, uncovered variations in gravel abundance, hinting at ice sheets’ recurring advancements and retreats in intervals as short as 1,200 years. 

Ice sheet behavior 

The precise triggers for these frequent changes remain uncertain, but the team proposes several theories, including the possibility of ice sheets becoming extremely heavy and collapsing, or friction-generated heat under thick ice sheets temporarily accelerating their movement.

These findings underscore the complexity of factors influencing ice sheet behavior, beyond just Earth’s orbital changes, especially in the context of ongoing global warming. 

Study implications 

While the early Miocene is not a perfect analogy for today’s climate, the study suggests that Antarctica’s ice sheets could undergo rapid and unexpected changes in the future if greenhouse gas emissions and global temperatures continue to rise.

“It was long thought that Antarctica’s ice sheets remained large and stable over long periods of time. But the closer we look, the more we realize just how sensitive the ice sheets are to environmental change,” said Levy.

This insight is key as we consider the pace at which we need to adapt to future sea level rise driven by melt and retreat of our planet’s ice sheets.”

The study is published in the journal Proceedings of the National Academy of Sciences.

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