Laboratory for Environmental and Sedimentary Geochemistry (LESG)

Speleothem Studies – Tibetan Plateau

Another area of research in our group is a paleoclimate study of the Qinghai-Tibetan Plateau using annually growth-banded cave calcite formations (speleothems). This project is being conducted by graduate student Kathleen Johnson for her dissertation. The climate of this region is under the influence of the East Asian monsoon system, an important component of the global climate system. This long-term record will allow us to document high frequency (annual to decadal) climate signals such as those caused by ENSO and the East Asian monsoon system, which may aid in the prediction of anomalous monsoons. Kathleen is collecting the speleothems for analyses of stable isotopes, growth band thickness, crystallography, mineralogy, and fluid inclusions. Kathleen has also been dating the samples using U-Th methods at the Berkeley Geochronology Center , with our collaborators Warren Sharp and Ken Ludwig. One stalagmite began growing 316,000 years ago, and continued growth until the last glacial maximum (20,000 years ago). Six major growth hiatuses are observed in this stalagmite, indicating that calcite precipitation stopped for extended time periods, most likely due to very cold and dry conditions in the region. Kathleen has begun very high-resolution sampling of the stalagmite (~300 micron sample width) using a new, state-of-the-art computer-controlled micromilling instrument recently obtained in our laboratory for oxygen and carbon isotope analyses.

PUBLICATIONS:

Johnson, K.R., and Ingram, B.L. (2003) Spatial and temporal variability in the stable isotope systematics of modern precipitation in China: Implications for Paleoclimate reconstruction. Earth and Planetary Science Letters (in press).