Triple isotope (dD, d17O, d18O) study on precipitation, drip water and speleothem fluid inclusions for a Western Central European cave (NW Switzerland)
Quaternary Science Reviews 2015, Vol. 127, Pages 73-89
Deuterium (dD) and oxygen (d18O) isotopes are powerful tracers of the hydrological cycle and have been extensively used for paleoclimate reconstructions as they can provide information on past precipitation,temperature and atmospheric circulation. More recently, the use of 17O excess derived from precise measurement of d17O and d18O gives new and additional insights in tracing the hydrological cycle whereas uncertainties surround this proxy. However, 17O excess could provide additional information on the atmospheric conditions at the moisture source as well as about fractionations associated with transport and site processes. In this paper we trace water stable isotopes (dD, d17O and d18O) along their path from precipitation to cave drip water and finally to speleothem fluid inclusions for Milandre cave in northwestern Switzerland. A two year-long daily resolved precipitation isotope record close to the cave site is compared to collected cave drip water (3 months average resolution) and fluid inclusions of modern and Holocene stalagmites. Amount weighted mean dD, d18O and d17O are 71.0‰, 9.9‰, 5.2‰ for precipitation, 60.3‰, 8.7‰, 4.6‰ for cave drip water and 61.3‰, 8.3‰, 4.7‰ for recent fluid inclusions respectively. Second order parameters have also been derived in precipitation and drip water and present similar values with 18 per meg for 17O excess whereas d-excess is 1.5‰ more negative in drip water. Furthermore, the atmospheric signal is shifted towards enriched values in the drip water and fluid inclusions (D of ~ þ 10‰ for dD). The isotopic composition of cave drip water exhibits a weak seasonal signal which is shifted by around 8e10 months(groundwater residence time) when compared to the precipitation. Moreover, we carried out the firstd 17O measurement in speleothem fluid inclusions, as well as the first comparison of the d17O behaviour from the meteoric water to the fluid inclusions entrapment in speleothems. This study on precipitation,drip water and fluid inclusions will be used as a speleothem proxy calibration for Milandre cave in order to reconstruct paleotemperatures and moisture source variations for Western Central Europe.