Comparison of temperature proxies in tropical stalagmites
Abstract:Several new tools to reconstruct past temperatures with stalagmites have recently emerged, which we have compared for the first time using stalagmites from Northern Borneo (4.1°N, 114.9°E). Temperatures were inferred from 1) the partitioning of oxygen isotopes between fluid inclusion water and calcite (Dublyansky and Spötl, 2009, RCM), 2) the density of fluid inclusion water determined by liquid-vapor homogenization (Krüger et al., 2011, Chemical Geology), 3) noble gas concentrations in fluid inclusions (Vogel et al., 2013, G3), and 4) the carbonate isotopologue (or ‘clumped isotope’) composition of the calcite (Eiler, 2011, QSR). The temperature sensitivity of two of the proxies, fluid inclusion δ18O and clumped isotopes, is currently debated. The results of this study contribute also to these ongoing debates. We furthermore compare two different methods for measuring the isotopic composition of fluid inclusion water, namely isotope ratio mass spectrometry and cavity ring-down spectroscopy.
Stalagmite WR5 used for this study covers two glacial-interglacial cycles, from Marine Isotope Stage 12 to the beginning of Marine Isotope Stage 9 (460-330 ka). The sample has previously been used to infer past changes in precipitation (Meckler et al., 2012, Science). In addition to this old stalagmite we analyzed two recent samples in order to compare proxy data to measured cave temperatures. Within error, all methods yielded consistent temperature estimates and the results from the recent samples are in agreement with the modern cave temperature. We used the equation of Tremaine et al. (2011, GCA) for calculating temperatures from fluid inclusion δ18O and a new clumped isotope calibration obtained at ETH, based on synthetic calcites (Ziegler et al., in prep.). The results from WR5 suggest 4-5 °C temperature difference between the glacials and interglacials contained in our record, which is similar to the amplitude of reconstructed regional sea surface temperature records (e.g., de Garidel-Thoron et al., 2005, Nature) when considering sealevel-driven glacial-interglacial changes in cave elevation.