Speleothem record of the last 180 ka in Villars cave (SW France): Investigation of a large delta O-18 shift between MIS6 and MIS5

The Vil-car-1 flowstone core from Villars cave (SW France) provides one of the first European speleothem records extending back to 180 ka, based on U-Th TIMS and MC-ICP-MS measurements. The core offers a continuous record of Termination II and the Last Interglacial. The penultimate deglaciation is characterized by a prominent 5 parts per thousand depletion in calcite delta O-18. Determining which specific environmental factors controlled such a large oxygen isotopic shift offers the opportunity to assess the impact of various factors influencing delta O-18 variations in speleothem calcite. Oxygen isotope analyses of fluid inclusions indicate that drip water delta O-18 remained within a very narrow range of +/- 1 parts per thousand from Late MIS6 to the MIS5 delta O-18 optimum. The possibility of such a stable behaviour is supported by simple calculations of various effects influencing seepage water delta O-18. Although this could suggest that the isotopic shift in calcite is mainly driven by temperature increase, attempts to quantify the temperature shift from Late MIS6 to the MIS5 delta O-18 optimum by assuming an equilibrium relationship between calcite and fluid inclusion delta O-18 yield unreasonably high estimates of similar to 20 degrees C warming and Late MIS6 cave temperatures below 0 degrees C; this suggests that the flowstone calcite precipitated out of thermodynamic equilibrium at this site. Using a method proposed by Guo et al. (submitted for publication) combining clumped isotope measurements, fluid inclusion and modern calcite delta O-18 analyses, it is possible to quantitatively correct for isotopic disequilibrium and estimate absolute paleotemperatures. Although the precision of these absolute temperature reconstructions is limited by analytical uncertainties, the temperature rise between Late MIS6 and the MIS5 optimum can be robustly constrained between 13.2 +/- 2.6 and 14.6 +/- 2.6 degrees C (1 sigma), consistent with existing estimates from Western Europe pollen and sea-surface temperature records. (C) 2010 Elsevier Ltd. All rights reserved.