A potential of multi-proxy approach for studying Thailand summer monsoon rainfall based on tree rings and stalagmite from northwestern Thailand

Abstract:

Thailand is a country in the Southeast (SE) Asian peninsula. The country has been regarded as a transition zone between the Indian and the western North Pacific monsoons. Climate data from the country is a key for advancing our understanding of monsoon climate in the transition zone area.

Previously, high-resolution climate signals preserved within δ¹⁸O, growth rate, and grey level were successfully extracted from stalagmite NJ-1, collected from Namjang (NJ) cave in the Mae Hong Son province of northwestern (NW) Thailand [Cai et al., 2010; Muangsong et al., 2011]. Present-day climate and cave monitoring in NW Thailand were carried out from August 2012 to October 2013 to investigate the climatic controls on rainfall and stalagmite isotopic properties. The δ¹⁸O of rainfall, stalagmite drip water as well as modern stalagmite precipitated on glass plates generally exhibited seasonal response to seasonal monsoon rainfall δ¹⁸O. Theses have implications for the use of isotopic composition of natural climate proxies from NW Thailand as a proxy of seasonal climate as well as the study of seasonal changes in moisture trajectories.

Among the limited number of tree species suitable for tree-ring studies, teak (Tectona grandis Linn.) trees have great potential for dendrochronology in SE Asia. There are young teak trees growing out a few meters from NJ cave that uptake a common source water of published stalagmite NJ-1. In this study, the unique signals of cellulose δ¹⁸O detected in Thai teak were presented. Intra-seasonal and inter-annual variations of tree-ring cellulose δ¹⁸O provided detailed insights into seasonal monsoon climate. Comparisons of tree-ring cellulose δ¹⁸O with speleothem proxies from the same locality and tree-ring indices from wider geographical areas provide a basis for developing a multi-proxy approach. This is the first study in Thailand with a precise high resolution examination of δ¹⁸O in Thai teak as a climate signal, and this is the first preliminary study on a comparison between two natural proxies from a single location. These findings demonstrated the potential of stable isotope climatology from tree rings and stalagmites, and provided an additional basis for seasonal rainfall reconstruction in this region.