The past as a window into the future

This is from Science News magazine, 9/28/19.

Caves offer glimpse of sea level rise
By Lucas Laursen

Link to Science News article

Link to longer article in University of Southern Florida newsroom

Even longer article with charts, text excerpts, etc.

The future of sea level rise may be written into the walls of coastal Spanish caves.

Mineral “bathtub rings” deposited inside the limestone Artà Caves on the island of Mallorca show how high seas rose during the Pliocene Epoch – when Earth was about as warm as it’s expected to bet by 2100. Those deposits suggest that seas were around 16 meters (52.5 ft.) higher on average than they are today, researchers report August 30 in Nature.

That measurement provides the most precise peek yet into what may be in store as climate change causes ice sheets to melt and oceans to rise over hundreds to thousands of years. Previous estimates of sea levels during the Pliocene, 5.3 million to 2.6 million years ago, gave similar results. But those relied on more indirect dating methods or failed to incorporate information about the subsequent rise and fall of Earth’s crust.

For the new research, Oana-Alexandra Dumitru, a geochemist at the University of South Florida in Tampa, and colleagues turned to aragonite and calcite deposits on stalactites and stalagmites in the Artà Caves – “a very protected environment,” Dumitru says. Called phreatic overgrowths, the deposits accumulate as brackish seawater laps against rock. Similar features have been found on the island of Sardinia and in Mexico and Japan.

Seawater washing into the caves left behind mineral deposits at heights from 14.7 to 23.5 meters (48.2 to 77.1 feet) above today’s sea level, Dumitru’s team found. One deposit corresponds with a warm period that lasted from about 3.3 million to 3 million years ago. Global temperatures during that time were 2 to 3 degrees Celsius warmer than in modern, preindustrial times – and resemble forecasts for the year 2100. Global mean sea levels then were 16.2 meters (53.1 feet) higher than today, Dumitru’s team calculates.

“We still may not know exactly how much sea level rose,” says Alan Haywood, a paleoclimatologist at Leeds University in England. But with results like these, “we’re getting more confidence that we’re in the right ballpark.”

[Chuck Almdale]