An international team of scientists studying evidence preserved in speleothems in a coastal cave illustrate that more than three million years ago ̵
Scientists, including Professor Yeman Asmerom and Senior Scientist Victor Polyak of the University of New Mexico, the University of South Florida, the University of Ile Balears, and the University of Columbia, published their findings in today's edition of 19 . Analysis of deposits from the Artà Cave on the island of Majorca in the western Mediterranean has produced sea levels that serve as a target for future studies of ice sheet stability, calibration of the ice sheet model and forecasts for future sea level rise, scientists say.  Sea levels rise as a result of melting ice sheets, such as those that cover Greenland and Antarctica. How much and how fast the sea level will rise during warming is a question scientists have worked on. Reconstruction of changes in the ice sheet and sea level over past periods, when the climate was naturally warmer than today, provides a laboratory experiment on Earth to scale this matter, according to a USF doctor. student Oana Dumitru, the lead author who did much of her dating work at UNM under the direction of Asmer and Poleak.
"The limitation of sea-level rise models due to increased warming is critically dependent on actual measurements at past sea level." said Pole. "This study provides very stable measurements of sea level elevations during the Pliocene."
"We can use the knowledge gained from past warm periods to tune ice sheet models, which are then used to predict the future response of the ice sheet to current global warming," said the professor at the Department of Geological Sciences. USF
The project focuses on cave deposits known as phreatic overgrowths. Sediments are formed in coastal caves at the boundary between salt water and cave air each time ancient caves have been flooded by rising sea levels. At Artà Cave, located 100 meters from the shore, the water table is – and has been in the past – the same as the sea level, says Prof. Joan J. Fornos from the University of Ile Balears.
Scientists have discovered, analyzed and interpreted six of the geological formations found at elevations of 22.5 to 32 meters above the present sea level. Careful sampling and laboratory analyzes of 70 samples resulted in ages ranging from 4.4 to 3.3 million years BP (prior to present), indicating that cave deposits formed during the Pliocene era. Ages are determined using uranium-lead radiometric dating in the United Nations Radiogenic Isotope Laboratory.
"It was a unique rapprochement between the ideally suited natural environment developed by the team of cave scientists and the technical developments we have achieved over the years at our laboratory at the University of New Mexico," Asmerom said. "Reasonable investment in tools and techniques results in this kind of high-impact dividends.
" Changes in the sea level of the Artà Cave can be caused by the melting and rising of the ice sheets or the rise or fall of the island itself. "said Columbia University Assistant Professor Jackie Austerman, a member of the research team. It uses numerical and statistical models to carefully analyze how much uplift or descent may have occurred after the Pliocene and subtracted it from the elevation of the entities studied.  One key interval of particular interest during the Pliocene is the average Piacenza warm period – 3,264 to 3,025 million years ago – when temperatures were 2 to 3 degrees Celsius higher than pre-industrial levels. " marks the last time Earth's atmospheric CO2 was as high as it is today, providing important clues as to what the future holds for current anthropogenic warming, "says Onak.
This study found that during this period the global average sea level was above 16.2 meters (with an uncertainty range of 5.6 to 19.2 meters) above the present, which means that even if atmospheric CO2 stabilizes around current levels, the average global sea level is still likely to rise at least as much high, if not higher, they concluded scientists. In fact, it is likely to rise higher due to the increase in oceans volume due to rising temperatures.
"Given current melting patterns, this degree of sea level rise is likely to be caused by the collapse of both the Greenland and Western Antarctic ice regions," says Dumitru.
The authors also so they measure the sea level 23.5 meters higher than the current one about four million years ago during the climatic optimum of the Pliocene, when average global temperatures were up to 4 ° C higher than pre-industrial levels. "This is a possible scenario, if not actively and aggre a severe greenhouse gas reduction in the atmosphere, "Asmerom said.
Scientists detect stable sea levels during the last inter-glacial period
Limits on global mean sea level during Pliocene heat, Nature (2019). Doi: 10.1038 / s41586-019-1543-2, https://www.nature.com/articles/s41586-019-1543-2
The University of New Mexico
Scientists find evidence of past high sea level rise (2019, August 30)
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