Climatic reconstruction of the last 200ka from the isotopic study of South France speleothems
This work aims to characterise the climatic variations of the last 200 ka through the study of four South France speleothems dated by the U-Th method. Between 175 and 165ka, the high resolution of the Villars Cave flowstone core (Vil-car-1) base record yields for the first time in the region, millennial climatic events. During Termination II, the isotopic composition of the same record shows a spectacular drop of the 18Oc of -5 ‰. The confrontation of these data with fluid inclusions 18Odw and calcite 47 suggests that (1) if isotopic equilibrium was satisfied, the Termination II warming is around 20°C, (3) if we consider that kinetic effect occurred, the warming amplitude should be about 14°C (corrected from kinetic effects). A stalagmite from a neighbour site didn't record such an amplitude of variation during Termination II: it reminds us the strong influence of the cave karstic system on speleothems isotopic signals. According to the study of 3 speleothems, the MIS5 was globally a warm and humid period with an alternation of warmer and more humid episodes and colder and drier ones. The latters are synchronous with cooling events in the North Atlantic Ocean. For MIS3, this study allows us to give precise ages to the Dansgaard-Oeschger (DO) cycles 14 end and 13 and 12 limits, thanks to a high resolution precisely dated by MCICPMS record. The end of the identified DO is synchronous to an abrupt cooling (short permafrost settlement). The growth cessation of this sample synchronous to the two others stalagmites growth cessation confirms an important cooling during MIS3 at 30ka.
Accès au document
|Lien externe vers le document:|