Comparison of stable isotope time series of stalagmite and meteorological data from West Java, Indonesia

Abstract

Stable isotopic variations (i.e. δ 18O and δ 13C) of stalagmites have been widely recognized as a powerful tool to reconstruct the paleoclimate/environment of terrestrial areas. δ 18O and δ 13C values of a stalagmite calcite are known, however, to be cumulative signals of complex climatic and hydrogeological processes. In order to assess the reliability of stable isotopic ratios of stalagmites as climate proxies, we performed a systematic comparison between the temporal variation in annual precipitation amounts and temporal variation in δ 18O and δ 13C values of a stalagmite calcite. First, we analyzed a stalagmite collected in Ciawitali Cave, West Java, Indonesia. This finding is that the number of growth bands is coincident with uranium series disequilibrium age, within error. This is the first documentation of a stalagmite having annual bands in the Asian equatorial region. Next, we compared annual variations in δ 18O and δ 13C values in the growth bands with annual variations in precipitation amounts that have occurred since the 1950s at Cikidang station near the cave, showing significant negative correlations. This result suggests that δ 18O and δ 13C values in stalagmites calcite are effective proxies of ancient precipitation in this study area. Furthermore, based on travel time of dripwater in Ciawitali Cave (Yamada et al., 2008), this study performed the systematic comparison between temporal variation in annual precipitation amounts and those in δ 18O and δ 13C values of the stalagmite calcite, by taking the travel time of groundwater into account. Negative correlation disappears when the travel time is taken into consideration, suggesting that δ 18O and δ 13C values of the stalagmite calcite are immediately influenced by climatic conditions.