Scientists uncover evidence of past sea-level rise

An international team of scientists, studying evidence preserved in the form of speleothems in a coastal cave, shows that there are more than three million years – at a time when the Earth was warmer from two to three degrees Celsius as the pre-industrial era – the sea level was 16 meters higher than today. Their findings represent important implications for understanding and predicting the rate of sea level rise today in the face of global warming.

Scientists, including Professor Yemane Asmerom and Senior Research Scientist Victor Polyak of the University of New Mexico, University of South Florida, University of Balearic Islands and the University of New Mexico. Columbia University, published their findings in this day's edition of the journal Nature. Analysis of the Artà cave deposits on the island of Majorca in the western Mediterranean has made it possible to determine the sea level that will serve as a target for future studies on ice cap stability, calibration of the model of the ice cap and projections of rising sea levels, scientists said.

Sea levels rise as ice patches melt, such as those covering Greenland and Antarctica. However, the question scientists have been working on is how fast and how fast sea level will rise during warming. The reconstruction of the icecap and sea level changes in previous periods, when the climate was naturally warmer than today, is a laboratory experiment on the scale of the sea. Earth allowing to study this issue, according to the Ph.D. of the USF. The main student, Oana Dumitru, who has done most of her dating work at the UNM under the leadership of Asmerom and Polyak.

"Binding models for sea-level rise due to increased warming essentially depend on actual measurements of past sea level," said Polyak. "This study provides very robust measurements of sea level heights during the Pliocene."

"We can use the knowledge gained from previous warm periods to adjust ice cap models that are then used to predict the future reaction of the ice cap to current global warming," said Professor Bogdan Onac, a professor in the Department of Climate Change. USF geosciences.

The project focuses on cave deposits known as phreatic overgrowth on speleothems. Deposits are formed in coastal caves at the interface of brackish water and cave air whenever ancient caves are flooded by rising sea levels. In Artà cave, unless 100 meters from the coast, the water table coincides with the sea level and coincides with it, explains Professor Joan J. Fornós of the University of the Balearic Islands.

Scientists discovered, analyzed and interpreted six of the geological formations discovered at an altitude of 22.5 to 32 meters above sea level today. Careful sampling and laboratory analyzes of 70 samples yielded ages between 4.4 and 3.3 million BP years (before present), indicating that cave deposits were formed during the Pliocene period. The ages were determined with the aid of radiometric uranium-lead dating in the laboratory of radiogenic isotopes of the UNM.

"It was a unique convergence between a perfectly adapted natural environment, developed by the team of cave scientists, and the technical advances made over the years in our laboratory at the University of New Mexico," said Asmerom. "Sound investments in instrumentation and techniques produce this type of high-impact dividend."

"The changes in sea level in the Artà cave can be caused by the melting and growth of the ice sheets or by the uprising or even collapse of the island," said the deputy professor of the island. Columbia University, Jacky Austermann, member of the research team. She used numerical and statistical models to carefully analyze the level of uplift or subsidence that could have occurred since the Pliocene and subtracted from the elevation of the formations on which they surveyed .

A key period of special interest during the Pliocene is the warm period of the Piacenzian – some 3,264 to 3,225 million years ago – when temperatures were 2 to 3 ° C above pre-industrial levels. "This interval also marks the last time that the Earth's atmospheric CO2 was as high as today, providing important clues to what the future will hold in the face of current human warming," he said. Onac.

This study revealed that during this period, the mean sea level reached 16.2 meters (with an uncertainty range of 5.6 to 19.2 meters) above the current value. This means that even if atmospheric CO2 stabilizes around current levels, the world's average sea level would probably increase at least as much if not more, scientists said. In fact, it is likely that the increase will increase due to the increase in ocean volume due to rising temperatures.

"Given the current melting patterns, this sea-level rise would most likely be caused by a collapse of the ice sheets of Greenland and West Antarctic," said Dumitru.

The authors also measured sea level 23.5 meters higher than about four million years ago during the Pliocene climatic optimum when global average temperatures were 4 ° C above pre-industrial levels. . "This is a possible scenario if the active and aggressive reduction of greenhouse gases in the atmosphere is not undertaken," Asmerom said.