HR: 16:30h
AN: PP34A-03    [Abstracts]
TI: Modern Stable Isotope Systematics in Heshang Cave, China: Implications for Speleothem Based Paleoclimate Reconstructions
AU: * Johnson, K R
EM: kathleen.johnson@uci.edu
AF: Dept. of Earth System Science, University of California, Irvine 3206 Croul Hall, Irvine, CA 92697-3100, United States
AU: Hu, C
EM: chaoyonghu@hotmail.com
AF: Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Wuhan, 430074, China
AU: Henderson, G
EM: Gideon.Henderson@earth.ox.ac.uk
AF: Dept. of Earth Sciences, University of Oxford Parks Road, Oxford, OX1 3PR, United Kingdom
AB: Stable isotope (δ¹⁸O and δ¹³C) records from speleothems collected in Heshang Cave, China (30.44°N, 110.42°E) contain detailed information about past variability in East Asian monsoon rainfall. In particular, HS4, a 2.5 m long, annually laminated stalagmite, which grew continuously since the early Holocene until it was collected in 2001, contains seasonal variations in δ¹⁸O and δ¹³C (and trace elements) which may provide information about past seasonal and inter-annual monsoon variability. To investigate the modern environmental controls on seasonal geochemical variations preserved in Heshang Cave speleothems, an intensive environmental and hydrochemical monitoring program was initiated in late 2003. Here we present stable isotope data (δD and δ¹⁸O) from cave drip waters collected at two locations every ten days during this period. In addition, we present δ¹⁸O and δ¹³C results from calcite precipitated on glass slides in monthly intervals over a two year period. This data suggests that modern calcite is forming in isotopic equilibrium in Heshang Cave and that seasonal variations in speleothem δ¹⁸O are caused by both seasonal variations in drip water composition, which are closely related to rainfall, and seasonal temperature variations within Heshang Cave, which are closely related to outside temperature. The most negative speleothem δ¹⁸O values are observed during the peak of the summer monsoon, reflecting the low rainfall δ¹⁸O (because of the amount effect) and high cave temperatures at this time. We expect this relationship to remain constant in the past, and thus δ¹⁸O can serve as a useful time marker to tie other seasonal geochemical variations to the annual cycle. Seasonal δ¹³C variations in Heshang Cave speleothems are most likely reflecting changes in the fraction of CO₂ degassing that occurs either above the cave as prior calcite precipitation or on the speleothem surface. The highest δ¹³C values occur during the summer monsoon season, suggesting perhaps that temperature, growth rate, and drip rate, which all peak at this time, may play a role. We hope to deconvolve these controls using a multi-proxy approach which includes trace element, in addition to stable isotope analysis.
DE: 1041 Stable isotope geochemistry (0454, 4870)
DE: 1806 Chemistry of fresh water
DE: 1854 Precipitation (3354)
DE: 3344 Paleoclimatology (0473, 4900)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting