Application of Laser Ablation Multi Collector Inductively Coupled Plasma Mass Spectrometry (LA MC ICPMS) for 230Th/U-dating of speleothems and paleoclimate reconstruction
Final Report Abstract
Stalagmite H-1 from Hüttenbläserschachthöhle, western Germany, was precisely dated using 64 MC-ICPMS 230Th/U-ages. The stalagmite grew during the last three major warm phases in the last 250,000 years, i.e., Marine Isotope Stages (MIS) 7, 5, and 1. During intermediate glacial periods no stalagmite growth occurred, probably due to the cool and/or dry climate conditions. So far, various algorithms for the calculation of speleothem age-depth models are used. This makes the comparability of speleothem age models from different studies difficult. In this project a general algorithm, especially designed for the calculation of stalagmite age-depth models and the corresponding uncertainty, was developed. The algorithm includes additional stratigraphic information and is able to automatically detect outliers and age inversions. Tests with modelled speleothem age-depth data revealed that the results of the algorithm are both very accurate and robust. The algorithm will be made available as a download to the scientific community. The age-depth model for stalagmite HBSH-1 was fitted with the newly developed algorithm. Due to the large number of 230Th/U-ages the chronology is both very robust and accurate. Stable oxygen and carbon isotopes as well as several trace elements were measured at high resolution. Stable oxygen isotopes reflect past temperature variability in the region of the cave. The stable carbon isotope signal reflects past precipitation intensity. Thus, the two records deliver precisely dated high-resolution records of past temperature and precipitation variability in western Germany. The trace element signals allow identification of the sections of HBSH-1 consisting of calcite rather than aragonite. This information is important for the interpretation of the age as well as the stable isotope data. Furthermore, the trace elements provide information about past variations in hydrology. The largest part of the stalagmite (70%) grew between ~135,000 and 70,000 years ago providing an almost continuous record for this climate phase. Stalagmite growth was only interrupted during three phases of very cold climate recorded in Greenland ice cores. This proves the supra-regional character of the climate signal recorded in stalagmite HBSH-1. Comparison with other climate records, such as global sea level, Greenland ice cores and Chinese stalagmite records reflecting the strength of the East Asian Monsoon, reveals generally warm and wet climate during periods of high sea level, warm climate in Greenland and strong East Asian Monsoon. On the millennial scale, however, the HBSH-1 record shows distinct differences to the other records. For instance, the evolution of temperature and precipitation during the Last Interglacial seems to be decoupled. The δ18O signal suggests the warmest temperatures at ~125,000 years. Based on the δ13C signal, however, the wettest climate conditions occurred much later, at ~120,000 years. This decoupled evolution of temperature and precipitation during MIS 5e is also predicted by a climate model simulation currently performed at Bristol University.
