HR: 1340h
AN: PP23B-1420    [Abstracts]
TI: East Asian Summer Monsoon Variability During Marine Isotope Stage 5 Based on Speleothem $\delta$$^{18}$O Records from Wanxiang Cave, Central China
AU: * Johnson, K R
EM: kathleen@earth.ox.ac.uk
AF: Department of Earth Sciences Oxford University, Parks Road, Oxford, OX1 3PR United Kingdom
AU: Ingram, B L
EM: ingram@eps.berkeley.edu
AF: Dept. of Earth and Planetary Science University of California, Berkeley, 307 McCone Hall, Berkeley, CA 94720-4767 United States
AU: Sharp, W D
EM: wsharp@bgc.org
AF: Berkeley Geochronology Center, 2455 Ridge Rd., Berkeley, CA 94709 United States
AU: Zhang, P
EM: pzzhang@lzu.edu.cn
AF: Center for Arid Environment and Paleoclimate Research College of Earth and Environmental Sciences , Lanzhou University, Lanzhou, 730000 China
AB: Speleothems collected from Wanxiang Cave, China (33.31$\deg$ N, 105.00$\deg$ E) provide high-resolution records of East Asian paleomonsoon variability. Wanxiang Cave is located in a key climatic location, near the northern limit of the summer monsoon. We present a simple model for interpreting $\delta$$^{18}$O shifts in speleothems from this region. The $\delta$$^{18}$O of speleothem calcite at this site is inversely related to monsoon intensity. We show that temperature has little effect on the $\delta$$^{18}$O of precipitation near Wanxiang Cave and is most likely canceled out by the $-$0.24$\permil$/øC temperature effect on calcite-water fractionation. Given this, the largest magnitude $\delta$$^{18}$O shift that could occur due only to changes in the composition of the oceanic source region, the amount of rainfall, and the amount of evaporation between full glacial conditions with a weak summer monsoon and full interglacial conditions with a strong summer monsoon is 5.5$\permil$. It is, therefore, necessary to invoke past changes in the summer:winter precipitation ratio and circulation changes to explain the nearly 7$\permil$ range observed in fossil speleothems from this site. We present detailed $\delta$$^{18}$O records from two stalagmites, WXSM 51 and WXSM 52, which formed during Marine Isotope Stages 5a-5b and 5c-5d. During the MIS 5d-5c transition, summer monsoon intensity increased steadily from 117.6 ka, with a peak in intensity occurring at 106.8 ka, concurrent with Greenland Interstadial 24. During the MIS 5b-5a transition, monsoon intensity increased abruptly at about 85.7 ka, when $\delta$$^{18}$O decreased by approximately 4$\permil$ in 200 years. The close agreement of the MIS 5c-5d record and the MIS 5a-5b record with global climate records such as the GISP2, Vostok, and SPECMAP records, and the Northern Hemisphere insolation curve, suggest that East Asian summer monsoon intensity varies in phase with global climate fluctuations and is largely controlled by solar variations in the Northern Hemisphere. The MIS 5a-5b and 5c-5d paleomonsoon records from Wanxiang Cave also agree well with other records of Asian monsoon variability indicating that $\delta$$^{18}$O of speleothems from Wanxiang cave is a valid proxy for past changes in monsoon intensity.
DE: 9320 Asia
DE: 9810 New fields (not classifiable under other headings)
DE: 4215 Climate and interannual variability (3309)
DE: 1035 Geochronology
DE: 1040 Isotopic composition/chemistry
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting