PP009-0015
Neogene and Quaternary sea-level elevations using U-Pb dated phreatic overgrowths on speleothems from coastal caves on Mallorca Island
Tuesday, 8 December 2020
Poster
Oana-Alexandra Dumitru1,2, Jacqueline Austermann3, Victor J Polyak4, Joan J Fornos5, Yemane Asmerom4, Joaquín Ginés6, Angel Ginés6 and Bogdan P. Onac2, (1)Columbia University, Lamont-Doherty Earth Observatory, Palisades, NY, United States, (2)University of South Florida Tampa, School of Geosciences, Tampa, FL, United States, (3)Lamont -Doherty Earth Observatory, Columbia University, Department of Earth and Environmental Sciences, Palisades, NY, United States, (4)University of New Mexico, Department of Earth and Planetary Sciences, Albuquerque, NM, United States, (5)Universitat de les Illes Balears, Department de Ciencies de la Terra, Palma de Mallorca, Spain, (6)Universitat de les Illes Balears, Palma de Mallorca, Spain
Abstract:
Phreatic overgrowths on speleothems (POS) form at the air-water interface in littoral caves of Mallorca Island. They precipitate as CO2 degasses from brackish cave water that is hydrologically connected to the Mediterranean Sea. The precipitation mechanism of POS provides precise elevations of sea-level and their ages can be determined with the U-Pb method. Hence, POS are excellent sea level index points due to their clear relationship to sea level and absolute chronology. Here we document the position and timing of sea level during several key time intervals since the Upper Miocene until the Middle Pleistocene. We find that before and near the onset of the Messinian Salinity Crisis, the relative sea-level was at ~33.3 ± 0.25 m and ~31.8 ± 0.25 m above present level at 6.54 ± 0.37 Ma and 5.86 ± 0.60 Ma, respectively. These results may offer starting points on assessing whether sea-level drawdown in the western Mediterranean happened gradually or rapidly.
Local sea level estimates as inferred from POS can be translated into ice volume equivalent global mean sea level (GMSL) by correcting for glacial isostatic adjustment, long-term uplift or subsidence processes, and thermal expansion. The results presented here are not corrected for the latter one. We show that during the mid-Piacenzian Warm Period, which is a good analogue for future anthropogenic warming as temperatures were higher than pre-industrial levels and atmospheric CO2 concentration comparable to present-day, GMSL was about 17.4 m (6.8 – 20.3 m; 68% uncertainty range) higher than today. During the even warmer Pliocene Climatic Optimum, our results indicate that GMSL was 25.1 m (10.6 – 28.3 m) meters above the present level. We further estimate a GMSL of 6.4 m (-2.0 – 8.8 m) for the Pliocene-Pleistocene Transition at 2.63 ± 0.11 Ma that indicates an important lowering of sea level immediately after the Pliocene. New GMSL estimates of -1.1 m (-5.6 – 2.4 m) and 5 m (1.5 – 8.1 m) at 1.25 ± 0.09 Ma and 0.8 ± 0.16 Ma, respectively, correspond to the beginning and the end of Lower to Middle Pleistocene Transition period. Our robust POS data provide direct sea level estimates during several past warm periods that advance our understanding on the contribution of the cryosphere to changes in past sea level.
