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A caver explores speleothem encrustations, a type of mineral deposit, in a coastal cave on the Mediterranean island of Mallorca. Researchers studying the deposits have found evidence that sea level was about one meter above present-day levels around 81,000 years ago, a time preceded by rapid ice melting, on the order of 20 meters of sea level change per thousand years. (Credit: Tony Merino)

U. IOWA (US)—New findings about the close link between changes in sea level and Earth’s climate challenge theories about the rates of ice accumulation and melting during the Quaternary Period—the time interval ranging from 2.6 million years ago to the present.

Jeffrey Dorale, assistant professor of geoscience at the University of Iowa, and colleagues collected data on speleothem encrustations, a type of mineral deposit, in coastal caves on the Mediterranean island of Mallorca and found that sea level was about one meter above present-day levels around 81,000 years ago.

The research challenges other studies that indicate sea level was as low as 30 meters—the ice equivalent of four Greenland ice sheets—below present-day levels. Their findings are reported in the journal Science.

Dorale says the sea level high stand of 81,000 years ago was preceded by rapid ice melting, on the order of 20 meters of sea level change per thousand years and the sea level drop following the high water mark, accompanied by ice formation, was equally rapid.

“Twenty meters per thousand years equates to one meter of sea level change in a 50-year period,” Dorale says. “Today, over one-third of the world’s population lives within 60 miles of the coastline. Many of these areas are low-lying and would be significantly altered—devastated—by a meter of sea level rise. Our findings demonstrate that changes of this magnitude can happen naturally on the timescale of a human lifetime. Sea level change is a very big deal.”

Dorale also notes that although their findings disagree with some sea level estimates, such as those from Barbados and New Guinea that come from ancient coral reefs, they are in agreement with data gathered from other sites such as the Bahamas, the U.S. Atlantic coastal plain, Bermuda, the Cayman Islands, and California.

“There has been a long-standing debate on this issue, but our data is pretty robust,” he says. “The key to our research is two-fold. First, the speleothem approach we employed is novel and extremely precise compared to other methods of sea-level reconstruction. Second, Mallorca appears to be particularly well suited to the task, because neither tectonics nor isostasy—geological forces of crustal motion—over-complicate the record. It’s really close to the ideal scenario. It’s also a heck of a nice place to do fieldwork.”

Researchers from the University of Iowa, University of South Florida, Tampa; Universitat de les Illes Balears, Mallorca, Spain; and University of Rome III, Italy contributed to the work, which was supported by the National Science Foundation.

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