North American ice sheets caused majority of post-Ice Age sea-level rise
The study overturns decades of scientific consensus that had pointed to Antarctica as the main contributor. Researchers found that between 8,000 and 9,000 years ago, the retreat of North American ice sheets alone raised sea levels by more than 30 feet (around 10 meters). In contrast, Antarctica's contribution during this period was relatively minor.
"This requires a major revision of the ice melt history during this critical time interval," said Torbjorn Tornqvist, Vokes Geology Professor at Tulane 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."
The North Atlantic region plays a central role in global climate regulation, powering currents such as the Gulf Stream that help moderate temperatures across Northwestern Europe. Tornqvist noted that while an influx of freshwater from melting ice can weaken these currents, the new data indicate that the system showed surprising resilience in the past.
"Clearly, we don't fully understand yet what drives this key component of the climate system," Tornqvist said.
Reconstructing ancient sea levels from more than 8,000 years ago has long posed challenges because it often requires offshore drilling. A key breakthrough occurred when former Tulane postdoctoral researcher Lael Vetter identified ancient marsh sediments buried near the Mississippi River. Radiocarbon dating of these samples extended the sea-level timeline back over 10,000 years.
Building upon that discovery, former PhD student Udita Mukherjee combined the Mississippi Delta record with complementary data from Europe and Southeast Asia. The global comparison revealed stark differences in sea-level rise rates that only an expanded North American ice melt could account for.
"This research provides a stark reminder of the complexities of our climate system and melting ice sheets," said Mukherjee, now a postdoctoral fellow at the University of Hong Kong. "Broadening our focus beyond North America and Europe to include valuable high-quality data from Southeast Asia was critical for this study. By embracing a truly global perspective in climate studies, we can enhance our understanding and work together towards a sustainable future."
The research was supported by the U.S. National Science Foundation, with collaborators from the University of Ottawa, Memorial University in Canada, Maynooth University in Ireland, and the University of South Florida.
Research Report:Sea-level rise at the end of the last deglaciation dominated by North American ice sheets
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