Past Climate and Sea-level Reconstruction Using Cave Deposits from Mallorca, Spain

The potential impacts of the increasing temperature on the water resources, as well as the hazards associated with the sea-level rise in the low-elevation coastal zones of the Mediterranean Sea, makes this region vulnerable to current climate change due to global warming. Hence, accurate projections of the future hydroclimate scenarios in this area are crucial. Long-term information on climate and sea-level variability cannot be obtained by direct observations or using short instrumental records. However, various geological archives may provide valuable data that can be then used to assess the models used for future predictions. This thesis presents results on past climate and sea-level reconstruction using cave deposits from Mallorca Island in the western Mediterranean basin and is structured in two parts, as follows. The first part deals with speleothem-based paleoclimate reconstruction. Stable isotopic analyses of precipitation, cave drip water, and groundwater from sites in Mallorca are performed in order to enhance our understanding of the processes controlling the isotopic variability and the sources of moisture in the modern climate system. Then, the obtained isotopic data is used to explain past changes recorded in the oxygen isotopic profile of a stalagmite (CAM-1) collected from Campanet Cave. Combining the growth history with the isotopic record and mineral changes of CAM-1 provides evidence of dramatic climatic shifts in the western Mediterranean over the past 121,000 years. The second part of the thesis presents evidence of past sea-level based on phreatic overgrowths on speleothems from caves on the same island. These deposits are suitable for U-Pb radiometric dating and they proved to be valid and precise sea-level index points. Sea-level snapshots over a number of key intervals throughout the Cenozoic Era are presented. Samples CP-04 and AR-02i from Coves Petites and Coves d’Artà, respectively, provide evidence of sea-level stands prior and at the onset of the Messinian Salinity Crisis (5.97 - 5.33 million years ago; Ma), a major event in the history of the Mediterranean Sea. Six other POS samples collected from Coves d’Artà, formed during the Pliocene Epoch, between 4.39 and 3.27 Ma. To infer the global mean sea level (GMSL) from these local observations, the POS elevations are corrected for glacial isostatic adjustment and long-term deformation due to sediment loading. Hence, sample AR-02 documents a GMSL of 23.5 meters above present sea level (mapsl) and its growth is coincident with the Pliocene Climatic Optimum, a time interval when the annual temperatures were about 4 ºC warmer than pre-industrial period. A GMSL of 16.2 mapsl is reported from sample AR-02 for the Mid-Piacenzian Warm Period, an interval during the Late Pliocene. This has been used as an analogue for future anthropogenic warming since atmospheric CO2 conditions were comparable to present-day values (~400 ppm) and estimated global mean temperatures were 2-3 °C higher compared to the pre-industrial period. Another POS sample (AR-19) collected from the same cave at 14 mapsl, returned an age of 2.63 ± 0.11 Ma, overlapping with the Plio-Pleistocene transition. Finally, samples DR-D4v from Coves del Drac and SBB25-01 from Cova de Sa Bassa Blanca, precipitated during the transition from early to mid Pleistocene (~1.25 - 0.7 Ma) and mark GMSL of -1.1 mapsl and 5 mapsl at 1.25 ± 0.09 Ma and 0.8 ± 0.16 Ma, respectively. Collectively, these data will serve as critical inputs for future climate model development and calibration that will improve confidence in sea-level projections