Scientists Discover Evidence for Past High-Level Sea Rise

Monday, September 2, 2019 - 14:56

Scientists have discovered evidences for past high-level sea rise at current atmospheric carbon dioxide levels.

According to the SciTechDaily reports, scientists from the University of New Mexico, the University of South Florida, Universitat de les Illes Balears and Columbia University published their findings in today’s edition of the journal Nature.

Scientists believed that the analysis of deposits from Artà Cave on the island of Mallorca in the western Mediterranean Sea produced sea levels that serve as a target for future studies of ice sheet stability, ice sheet model calibrations and projections of future sea-level rise.

The project focused on cave deposits known as phreatic overgrowths on speleothems. The deposits form in coastal caves at the interface between brackish water and cave air each time the ancient caves were flooded by rising sea levels. In Artà Cave, which is located within 100 meters of the coast, the water table is – and was in the past – coincident with sea level, says Professor Joan J. Fornós of Universitat de les Illes Balears.

The scientists discovered, analyzed, and interpreted six of the geologic formations found at elevations of 22.5 to 32 meters above present sea level. Careful sampling and laboratory analyses of 70 samples resulted in ages ranging from 4.4 to 3.3 million years old BP (Before Present), indicating that the cave deposits formed during the Pliocene epoch. The ages were determined using uranium-lead radiometric dating in UNM’s Radiogenic Isotope Laboratory.

One key interval of particular interest during the Pliocene is the mid-Piacenzian Warm Period – some 3.264 to 3.025 million years ago – when temperatures were 2 to 3º Celsius higher than pre-industrial levels. “The interval also marks the last time the Earth’s atmospheric CO2 was as high as today, providing important clues about what the future holds in the face of current anthropogenic warming,” said USF Department of Geosciences Professor Bogdan Onac.

This study found that during this period, global mean sea level was as high as 16.2 meters (with an uncertainty range of 5.6 to 19.2 meters) above present. This means that even if atmospheric CO2 stabilizes around current levels, the global mean sea level would still likely rise at least that high, if not higher, the scientists concluded. In fact, it is likely to rise higher because of the increase in the volume of the oceans due to rising temperature.

The authors also measured sea level at 23.5 meters higher than present about four million years ago during the Pliocene Climatic Optimum, when global mean temperatures were up to 4°C higher than pre-industrial levels. “This is a possible scenario if active and aggressive reduction in greenhouse gases into the atmosphere is not undertaken,” added Columbia University Assistant Professor Jacky Austermann, a member of the research team.

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