Clumped-isotope thermometry of speleothems: understanding and correcting for large kinetic fractionation induced by CO2 degassing
Speleothem archives of delta18O provide important paleoclimatic information because carbonate del... more Speleothem archives of delta18O provide important paleoclimatic information because carbonate delta18O varies with environmental parameters such as cave temperature and the isotopic composition of local seepage water. Quantitative reconstruction of these two parameters remains challenging, however, because reliably separating paleotemperature from water composition effects is difficult, and because speleothems may have precipitated out of thermodynamic equilibrium. Clumped-isotope carbonate thermometry can
The Vil-car-1 flowstone core from Villars cave (SW France) provides one of the first European spe... more 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 UeTh 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& depletion in calcite d 18 O. Determining which specific environmental factors controlled such a large oxygen isotopic shift offers the opportunity to assess the impact of various factors influencing d 18 O variations in speleothem calcite. Oxygen isotope analyses of fluid inclusions indicate that drip water d 18 O remained within a very narrow range of AE1& from Late MIS6 to the MIS5 d 18 O optimum. The possibility of such a stable behaviour is supported by simple calculations of various effects influencing seepage water d 18 O.
This article presents isotopic measurements (d 18 O and dD) of precipitation and cave drip water ... more This article presents isotopic measurements (d 18 O and dD) of precipitation and cave drip water from two sites in southern France in order to investigate the link between rainfall and seepage water, and to characterize regional rainfall isotopic variability. These data, which are among the longest series in France, come from two rainfall stations in south-west France (Le Mas 1996, and Villars 1998; typically under Atlantic influence), and from one station in the south-east (Orgnac 2000-2012; under both Mediterranean and Atlantic influence). Rainfall isotopic composition is compared to drip water collected under stalactites from the same sites: Villars Cave (four drip stations 1999-2012) in the south-west, and Chauvet Cave (two drip stations 2000-2012) in the south-east, near Orgnac. The study of these isotopic data sets allows the following conclusions to be drawn about the rainfall/drip water relationships and about rainfall variability: (1) the cave drip water isotopic composition does not show any significant changes since the beginning of measurements; in order to explain its isotopic signature it is necessary to integrate weighted rainfall d 18 O of all months during several years, which demonstrates that, even at shallow depths (10-50 m), cave drip water is a mixture of rain water integrated over relatively long periods, which give an apparent time residence from several months to up to several years. These results have important consequences on the interpretation of proxies like speleothem fluid inclusions and tree-ring cellulose isotopic composition, which are used for paleoclimatic studies; (2) in the Villars Cave, where drip stations at two different depths were studied, lower d 18 O values were observed in the lower galleries, which might be due to winter season overflows during infiltration and/or to older rain water with a different isotopic composition that reaches the lower galleries after years; (3) local precipitation is characterized by local meteoric water lines, LMWL, with d 18 O/dD slopes close to 7 in both areas, and correlations between air temperature and precipitation d 18 O are low at both monthly and annual scales, even with temperature weighted by the amount of precipitation; (4) the mesoscale climate model REMOiso, equipped with a water isotope module, allows the direct comparison of modeled and http://dx.
Keywords: Pleistocene climate steppe bison seasonality oxygen isotope apatite Oxygen isotope anal... more Keywords: Pleistocene climate steppe bison seasonality oxygen isotope apatite Oxygen isotope analysis of phosphate in tooth enamel of mammals (δ 18 O p ) constitutes a valuable method to reconstruct past air temperatures in continental environments. The method is based on interdependent relationships between the δ 18 O of apatite phosphate, body fluids, environmental waters and air temperatures. Continuous tooth growth and absence of enamel remodelling in bovid teeth ensures a reliable record of the intra-annual variability of air temperature through an incremental δ 18 O analysis from apex to cervix. This method has been applied to Bison priscus dental remains of the late Middle Pleistocene from the fossiliferous layer of a cave at Coudoulous I in South-Western France (Layer 4). The stacked oxygen isotope signal obtained by combining 9 bison teeth shows sinusoidal variations (15.0‰ to 19.1‰ V-SMOW) of seasonal origin over 2.5 yr. The corresponding computed MAT of 9 ± 3°C is about 4°C lower than at present. Seasons appear more contrasted in Coudoulous I during Layer 4 deposition with summers as warm as present ones (19 ± 3°C) and significantly colder winters about 0 ± 3°C compared to 6 ± 1°C at present. Fig. 7. Diagram summarizing the published mean air temperature estimates for the Saalian (MIS 6) and Eemian (MIS 5e) periods deduced from the floral associations and the oxygen isotope compositions of phosphate from Bison tooth enamel (this study) in France. The data are from: Guiot (1990) for La Grande Pile 1, Fauquette et al. (1999) for La Grande Pile 2, Les Echets, Vienne and lac du Bouchet.
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Papers by K. Wainer