Li/Mg ratio in scleractinian corals : a new powerful proxy for ocean paleo-temperatures ?

• Main Author: Cuny-Guirriec, Kristan
• Other Authors: Laboratoire des Sciences du Climat et de l'Environnement Gif-sur-Yvette (LSCE), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Direction de Recherche Fondamentale (CEA) (DRF (CEA)), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA), Université Paris-Saclay, Eric Douville, Edwige Pons-Branchu
• Format: Doctoral or Postdoctoral Thesis
• Language: French
• Published: HAL CCSD 2020
• Subjects: Climate change; Ocean; Paleo-Temperatures; New geochemical proxy; Li/Mg; Corals; Changement climatique; Océan; Paléo-Températures; Nouveaux traceurs géochimiques; Coraux; [SDU.STU.CL]Sciences of the Universe [physics]/Earth Sciences/Climatology; [SDU.STU.OC]Sciences of the Universe [physics]/Earth Sciences/Oceanography; Antarc*; Antarctic; Antarctique*
• Online Access: https://theses.hal.science/tel-02971509; https://theses.hal.science/tel-02971509/document; https://theses.hal.science/tel-02971509/file/82622_CUNY-GUIRRIEC_2020_archivage.pdf

The Li/Mg paleothermometer was here updated in a calibration including 15 species of coral from culture or various environmental context, from tropical areas to deep Antarctic waters. This work showed that this new proxy well defines the whole ocean temperature range from -1 to 29°C, with a precision of ± 1.0°C. However, presence of organic matter or diagenetic calcite in the skeleton can bias the reconstructed temperatures. A specific chemical cleaning and micro analysis can overcome these effects. Yet, uncertainties of reconstructed temperatures are higher for tropical corals from shallow waters, largely subjected to seasonal variation of environmental factors (e.g. SST, light, precipitations). Calcification and growth processes of these zooxanthellate species, controlled by their localisation in the lagoon and by seasonal variation, seem to alter the precision of the Li/Mg proxy. By combining Li/Mg and Sr/Ca ratios in a multi-proxy approach, these uncertainties can be considerably reduced, with a precision reaching ± 0.6°C. In a first application, general and local calibrations were compared in order to reconstruct the historical evolution of temperatures from analysis on a Siderastrea siderea, sampled alive in Martinique. The resulting temporal series covers the last two centuries and clearly shows the global warming affecting the Caribbean, in agreement with existing data. A second application was conducted on fossil deep-water corals from Mediterranean Sea, providing the first reconstruction of the temperature evolution of intermediate waters since 55.000 years, with a particularly cold signal during LGM, in response of the last glacial/interglacial cycle. La calibration du paléo-thermomètre Li/Mg a ici été revisitée pour 15 espèces de corail mises en culture ou issues de contextes environnementaux variés, allant des régions tropicales aux eaux profondes Antarctiques. Ces travaux de thèse ont montré que ce nouveau proxy retrace bien toute la gamme de température de l’océan allant de -1 à 29°C, avec une ...