beach in the Seychelles

Corals record huge rise in sea level after ice collapse

Fossil corals from the tropical islands of Seychelles may help scientists predict the future of the Antarctic ice sheet.

An examination of the fossils shows that global mean sea level about 125,000 years ago—when the average global temperature was only slightly warmer that it is now—peaked at 20 to 30 feet above current levels.

In fact, sea levels rose enough to submerge the locations of many of today’s coastal cities. Understanding what caused seas to rise then could help protect those cities today.

Geochemist Andrea Dutton in  Seychelles
Geochemist Andrea Dutton in Seychelles, where fossil corals reveal that previous sea levels were nearly twice the height of the survey stake pictured. (Credit: U. Florida)
researchers examine a limestone outcrop in Seychelles
Dutton (right) and Jody Webster of the University of Sydney (left) study a limestone outcrop containing fossil corals in Seychelles. (Credit: U. Florida)

The rapid retreat of an unstable part of the Antarctic ice sheet was a major contributor to that sea-level rise, says Andrea Dutton, a geochemist at the University of Florida.

“This occurred during a time when the average global temperature was only slightly warmer than at present,” she says.

For the study, published in Quaternary Science Reviews, researchers evaluated fossil corals in Seychelles because sea level in that region closely matches that of global mean sea level. Local patterns of sea-level change can differ from global trends because of variations in the Earth’s surface and gravity fields that occur when ice sheets grow and shrink.

The findings show that while sea-level rise in the Last Interglacial period was driven by the same processes active today—thermal expansion of seawater, melting mountain glaciers, and melting polar ice sheets in Greenland and Antarctica—most were driven by polar ice sheet melt.

The study also suggests the Antarctic ice sheet partially collapsed early in that period.

“Following a rapid transition to high sea levels when the last interglacial period began, sea level continued rising steadily,” Dutton says. “The collapse of Antarctic ice occurred when the polar regions were a few degrees warmer than they are now—temperatures that we are likely to reach within a matter of decades.”

Several recent studies by other researchers suggest that process may have already started.

“We could be poised for another partial collapse of the Antarctic ice sheet,” Dutton says.

The National Science Foundation supported the work.

Source: University of Florida