Never mind Antarctica: North American ice sheets caused dramatic rise in sea level after the last ice age

This article was adapted from an announcement by Tulane University.

Melting ice sheets in North America drove the rise in global sea level at the end of the last ice age more than scientists previously thought, according to new research published this week in Nature Geoscience.

The findings challenge decades of conventional wisdom about how Earth emerged from its last great freeze and could reshape how scientists view future climate risks.

“This study shows that we still have a lot to learn about how ice, ocean currents, and the solid Earth respond to changes in climate,” said Brad Rosenheim, professor of geological oceanography at the USF College of Marine Science and a co-author of the recent study.

For years, scientists believed Antarctic melt drove much of the post-glacial sea level rise, but the new study finds North American ice sheets were the dominant source, contributing over 30 feet of sea level rise between 8,000 and 9,000 years ago.

“Our results suggest that there was likely a much higher input of freshwater into the North Atlantic during the last deglacial period,” Rosenheim said. “This calls into question whether anticipated melt of glaciers from human activities will be sufficient to collapse or even slow down the Atlantic Meridional Overturning Circulation.”

The Atlantic Meridional Overturning Circulation (AMOC), a key climate regulator, influences global weather and helps keep the climate in Northwestern Europe mild.

“This requires a major revision of the ice melt history during this critical time interval,” said Torbjörn Törnqvist, professor of geology at Tulane University and co-author of the study. “The amount of freshwater that entered the North Atlantic Ocean was much larger than previously believed, which has several implications.”

Decades of research has shown that an influx of freshwater can weaken the currents of the AMOC, including the Gulf Stream, potentially leading to cooler European climates and altered rainfall patterns in places like the Amazon. But the study suggests the system was more resilient in the past than some recent projections indicate.

“Clearly, we don’t fully understand yet what drives this key component of the climate system,” Törnqvist said.

Measurements for the study were made possible by the USF College of Marine Science’s Marine Environmental Chemistry Lab, where researchers analyzed stable carbon isotope values of basal peat samples used in reconstructing sea level curves. These sea level curves were then fed into models that account for the solid Earth response to sea level changes.

The research was funded by the U.S. National Science Foundation and included additional co-authors from the University of Ottawa and Memorial University in Canada and Maynooth University in Ireland.