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810 years of monsoon history. A δ18O chronology as a contribution to the understanding of monsoon variability in Eastern Tibet (China).
Paper ID : 1066-ADA2013
Authors:
Jakob Wernicke *1, Jussi Griessinger2, Achim Braeuning2
1Kochstr. 4/4. 91054 Erlangen
2Institute of Geography, University of Erlangen-Nuremberg
Abstract:
In this study, we present a 810 years long δ18O chronology of Juniperus tibetica from Lhamcoka (E- Tibet; 4250m-4350m a.s.l.; 31°49'N/99°06'E). The tree stand is located at a steep south faced slope, which is framed by two glaciers. The water uptake by the trees is mainly dominated by monsoonal precipitation during the vegetation period. The oxygen signal in α- cellulose captures the oxygen signal of precipitation. Liu et al. (2008) have shown a temperature related depletion of δ18O westward. Their modelled δ18O values were validated by the findings of Grießinger (2011). Here, we assume a less depleted mean oxygen signal at the study site.

Bräuning (1999) already analysed the trees in respect to climate- proxy relationships. The late summer temperature (August, September) showed a highly significant correlation with the late wood density (MLD) and was therefore suitable for a late summer temperature reconstruction from 1600- 1999. Correlations of precipitation (MJJA and AS of the previous year) revealed only a significant correlation to tree-ring width. However, a qualitative moisture reconstruction was made from 1750- 1999. As demonstrated by Grießinger et al. (2011), stable oxygen isotopes have a strong correlation to summer monsoon precipitation. Thus, we will attempt to reconstruct the moisture conditions for Lhamcoka study site as well.

First results from a δ18O chronology of 5 trees (1880- 1996) are presented within this poster. The five isotope single mean curves show high correlations to the mean chronology of the tree stand, which is interpreted as a site specific signal, influencing all trees. As precipitation is the main source of oxygen in tree- rings, it can be regarded as the driving force of the joint δ18O variability. The common signal is justifying further efforts of expanding the chronology. Thus, oxygen is a promising proxy for the reconstruction of precipitation at the study site.



References:

Bräuning, A. (1999): Zur Dendroklimatologie Hochtibets während des letzten Jahrtausends. Dissertationes Botanicae, Band 312. Stuttgart.

Grießinger, J., Bräuning, A., Helle, G., Thomas, A., Schleser, G. (2011): Late holocene asian summer monsoon variability reflected by δ18O in tree-rings from Tibetan Junipers. Geophysical Research Letters 38, 1-5.

Liu, Z., Tian, L., Chai, X. & Yao, T. (2008): A model-based determination of spatial variation of precipitation 18O over China. Chemical Geology 249, 203- 212.
Keywords:
δ18O, Monsoon variability (precipitation), Eastern Tibet (China)
Status : Abstract Accepted