HR: 08:15h
AN: PP31A-02    [PDF]
TI: A Multi-Proxy Speleothem Based Record of Asian Monsoon Variability During the Last Glacial Period
AU: * Johnson, K R
EM: kathleen@eps.berkeley.edu
AF: University of California, Berkeley, Department of Earth and Planetary Science 307 McCone Hall, Berkeley, CA 94720-4767 United States
AU: Ingram, B L
EM: ingram@eps.berkeley.edu
AF: University of California, Berkeley, Department of Earth and Planetary Science 307 McCone Hall, Berkeley, CA 94720-4767 United States
AU: Sharp, W
EM: wsharp@bgc.org
AF: Berkeley Geochronology Center, 2455 Ridge Rd., Berkeley, CA 94709 United States
AU: Zhang, P
EM: pzzhang@lzu.edu.cn
AF: Lanzhou University, College of Earth and Environmental Science, Lanzhou, 730000 China
AB: Speleothems are well suited for paleoclimatic reconstruction as they preserve paleoclimate proxy data in highly resolvable growth bands and can be precisely dated using U-series dating. Variations in stable isotope composition, trace element composition, and growth band thickness along speleothem growth axes reflect past variations in precipitation and temperature. Oxygen isotopes in speleothems collected from higher latitudes have been widely utilized as paleothermometers due to the strong correlation between $\delta$$^{18}$O of precipitation and surface temperature in these regions. Oxygen isotopes in speleothems from lower latitudes or monsoon regions, however, may be more useful as paleoprecipitation proxies, due to the dominance of the amount effect in these regions. Speleothems collected from Wanxiang Cave, China (33.31$\deg$ N, 105.00$\deg$ E.) provide high-resolution records of the Southeast Asian Monsoon variability during the Late Pleistocene. The speleothems are well dated by U-series TIMS methods. The favorable ($^{230}$Th/$^{232}$Th) activity ratios (350-3000) result in the need for only very minor detritus corrections. Wanxiang Cave is located near the northern limit of the summer monsoon, where oxygen isotopes in modern precipitation are largely controlled by the amount of precipitation. Previous records show that the Asian monsoon intensity has varied dramatically during the past, exhibiting increased intensity during interglacial or interstadial periods and decreased intensity during glacial or stadial periods. We present $\delta$$^{18}$O records from Marine Isotope Stages 5a-5b and the last Deglaciation, which suggest that globally warmer periods were characterized by a more intense Asian Monsoon. Large shifts in speleothem $\delta$$^{18}$O occurred at the same time as rapid climate changes observed in Greenland, Antarctica, and the marine record. Due to the complicated systematics of stable isotopes in precipitation in the monsoon regions, we use trace element and uranium isotopic data to support our interpretation of $\delta$$^{18}$O as a paleomonsoon proxy. Initial ($^{234}$U/$^{238}$U) ratios and U, Sr, and Ba concentration are positively correlated with $\delta$$^{18}$O in the speleothems. This lends support to the use of $\delta$$^{18}$O in speleothems as a paleoprecipitation proxy, since during drier periods, when $\delta$$^{18}$O of precipitation is high, evaporative enrichment and increased residence time of vadose groundwaters is expected to lead to increased trace element concentrations and a greater degree of $^{234}$U leached out of crystal lattices. We also present growth band thickness data that support our results. Through this multiproxy approach to paleoclimate reconstruction, there is a strong potential for improvement in the understanding and, hence, applicability of stable isotope and trace element variations in cave calcite deposits from monsoon regions.
DE: 1035 Geochronology
DE: 1040 Isotopic composition/chemistry
DE: 1065 Trace elements (3670)
DE: 3344 Paleoclimatology
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2003 Fall Meeting