The West Antarctic Ice Sheet made a greater contribution to sea level rise millions of years ago than previously thought; an important insight that helps predict the future more accurately.

Right now we hear it all around us: glaciers in Antarctica are retreating, ice shelves are thinning and sea ice is melting. The result is that the sea level will rise sharply in the coming century. But that’s not the first time. That happened millions of years ago, during the Miocene, too. In a new study researchers have taken a closer look at events during this era. Because what exactly can we learn from this?

Miocene

The Early Miocene – a time period from about 18 to 16 million years ago – is characterized by both warm and cold periods. During these warmer periods, the sea level rose to as much as 60 meters. According to researcher Francesca Sangiorgi of Utrecht University, it is very important to closely study these warm periods during the Miocene. “The circumstances at the time are very similar to the situation that will be by the end of this century,” she explains in conversation with Scientias.nl from. “Consider, for example, comparable CO2 concentrations and global temperatures.”

sea ​​level rise

So while we know that sea levels rose as much as 60 meters at the time, the relative contributions of the larger East Antarctic Ice Sheet (EAIS) and the smaller West Antarctic Ice Sheet (WAIS) to this past sea level rise have been uncertain until now. “Many assumed that the WAIS was relatively small during the early Miocene, including during the cold periods,” Sangiorgi said. The rigorous sea level rise would in that case be mainly due to the decay of the larger EAIS. But while geological data show major sea-level rises, ice sheet models suggest that parts of the EAIS — even during the warmest periods of the Miocene — stood proudly.

Study

In a new study, researchers decided to map the ins and outs of the Antarctic ice sheets during the early Miocene. The research team drilled into sediments in the Ross Sea to find layers that correspond to the coldest and warmest periods. It leads to a surprising discovery. “By finding microfossils and other material deposited by the WAIS in the sediment wells far out to sea, we concluded that the WAIS was much larger during the Early Miocene than previously thought,” Sangiorgi said.

Larger surface

It means that the West Antarctic Ice Sheet covered a larger area during cold spells in the Early Miocene. And so the WAIS probably played a bigger role in sea level rise during the warm periods than expected. This was possible because in the past a significantly larger portion of the land area below the WAIS was above sea level, resulting in more ice being found on this part of the continent than today. This is evidenced by the large amount of eroded material found in the drill core. “There was more land—and therefore more ice—above water,” Sangiorgi sums up.

Future

According to the researcher, this new insight not only helps to understand the past, but also to better predict the future of the Antarctic ice sheets. “The more we know about how the ice sheets reacted in past warm climates, the better we can map the future,” she explains. “We know that the Antarctic ice sheets are melting. That melt is still increasing, with the result that the sea level is rising. However, to properly predict the future, we need a lot of data. That is why we have now studied how the ice sheets behaved in the past during long warm and cold periods. That way we can better understand how they reacted in the past. And from that we can infer how they may react in the future. Although history never repeats itself in exactly the same way, it does at least give us a global picture.”

West Antarctica

What can we learn from the past? At the moment, West Antarctica in particular is struggling with wasting ice. And this is mainly due to the fact that – in contrast to the situation during the Miocene – large parts of the ice sheet are now below sea level. This increases the sensitivity to changing ocean conditions of the West Antarctic Ice Sheet. “So the geography is simply different now,” says Sangiorgi. “Most of the ice sheet is now underwater, in direct contact with the ‘warm’ ocean. This makes it melt faster.” The study of the deep past of the West Antarctic ice sheet thus also shows its vulnerability to warming.

sea ​​level rise

If we’re not careful, that vulnerability to warming could translate into yet another rigorous sea level rise. “If the entire WAIS melts, it could lead to a sea level rise of up to three or four meters,” Sangiorgi says. “The good news is that the large ice sheets are relatively slow to respond to environmental changes. This means that if we act quickly, we can still prevent large-scale ice loss in many areas. The bad news is that the low-lying areas of the ice sheet have a ‘tipping point’ have, and we don’t quite understand where this ‘point of no return’ lies.”

According to the researcher, we can’t wait any longer. “We have to keep warming ‘limited’,” she emphasizes. “And that means cutting our emissions in half by 2030. At the same time, we will need to do more research on the WAIS. We still know very little. And that while we need as much data as possible to properly reconstruct the past. If we can then better model the past, we can also make better predictions for the future.”