PhD defense



"High resolution climate records from modern and last interglacial periods derived from giant clam shells (Tridacnidae) in Sulawesi, Indonesia"

18th of December 2017 - Amphitheatre Building n°34, LS2N - Faculty of Sciences and Technology - University of Nantes


Abstract :

"Giant clam shells (Tridacnidae family) were used to reconstruct climatic conditions during past interglacial periods in Indonesia's Sulawesi Island. Geochemical analyzes on modern shells have shown that these species actually record variation of the environment (temperature, salinity, precipitation and nutrient availability) in which they live. The main results of this PhD are the reproducibility of the geochemical signal tracers (18O, 13C and Mg/Ca) in two different species, as well as the recording of the climatic anomalies related to the La Niña phenomenon in 2010. Uranium-series dating revealed reefs formed at the beginning of the last interglacial period (MIS-5) and the penultimate interglacial or MIS-7. Comparison between modern and fossil reconstructions gave the following main results: 1) colder average temperature conditions with reduced seasonality for both periods (beginning of MIS-5 and MIS-7) due to drier conditions. 2) These parameters respond systematically to a decrease / increase of the sea level and testify the strong interaction between the atmospheric and ocean circulation in the region 3) The interannual variability of SST / SSS presents oscillations in the same amplitude as today for the MIS-5 period, however for MIS 7, interannual variability is reduced by around 50% compared to the current interglacial 4) The Mg/Ca ratio has a strong taxonomic variation, additional studies are needed to remove the biological factor related to geochemical signal. 5) Ba/Ca and 13C present a potential use as tracers of upwelling processes and/or variations in salinity."