Earth’s Ice Sheets More Stable Than Once Thought
May 17, 2013

Ancient Geodynamics Indicate Earth’s Ice Sheets More Stable Than Thought

April Flowers for - Your Universe Online

For decades, researchers have used ancient shorelines to predict the stability of today´s largest ice sheets in Greenland and Antarctica. High shoreline markings from three million years ago as Earth was going through a warm period were thought to be evidence of a high sea level due to ice sheet collapse at the time — an assumption that has led many scientists to believe that if the world´s largest ice sheets collapsed in the past, they will do so again. Global warming is adding to this fear.

However, a groundbreaking new study spearheaded by researchers at the University of Chicago challenges this thinking.

Led by David Rowley, CIFAR Senior Fellow and professor at the University of Chicago, the research team used the east coast of the US as their laboratory. They found that the Earth´s hot mantle pushed up segments of ancient shorelines over millions of years. This made the shorelines appear higher now than they originally were millions of years ago.

"Our findings suggest that the previous connections scientists made between ancient shoreline height and ice volumes are erroneous and that perhaps our ice sheets were more stable in the past than we originally thought," says Rowley. "Our study is telling scientists that they can no longer ignore the effect of Earth's interior dynamics when predicting historic sea levels and ice volumes."

Rowley´s team of international scientists included Alessandro Forte from the Université du Québec à Montréal, Jerry Mitrovica  from Harvard, and a former CIFAR-supported post-doctoral fellow Rob Moucha from Syracuse. Their findings were published online in the journal Science.

"This study was the culmination of years of work and deep collaboration by researchers in CIFAR's program in Earth System Evolution," explains Rowley. "For this study, each of us brought our individual expertise to the table: Rob and Alex worked on simulations of Earth's mantle dynamics, Jerry provided calculations on how glaciers warp Earth's surface, and I shaped our understanding of the geology of the landscape we were looking at. This study would not have been possible without CIFAR."

CIFAR is the Canadian Institute for Advanced Research, which was established in 1982 as an independent research institute. CIFAR is comprised of nearly 400 researchers representing more than 100 academic institutions in 16 countries.

The researchers focused on the coastline from Virginia to Florida, an area which has an ancient scarp tens of meters above present-day sea level. Previously, research groups have concluded from this shoreline that the Greenland, West Antarctic and a fraction of the East Antarctic ice sheets collapsed three million years ago during a warm period, raising the sea level by at least 115 feet. The findings from Rowley´s team, however, suggest that these ice sheets — particularly the world´s largest, the East Antarctic — were probably more stable than previously thought.

Computer simulations were used to follow the movement of mantle and tectonic plates that occurred over time. The simulation´s prediction of how the shoreline would have moved matched with observations made by geologists mapping this region. The team wants to continue their research by making similar simulations and predictions for other locations around the world.

"The paper is important because it shows that no prediction of ancient ice volumes can ever again ignore the Earth's interior dynamics," explains Rowley. "It also provides a novel bridge between two disciplines in Earth science that rarely intersect: mantle dynamics and long-term climate. It is the kind of study that changes how people think about our past climate and what our future holds."