Seasonally resolved stable isotope chronologies from northern Thailand deciduous trees

Abstract

Despite the existence of a number of climate proxies, the terrestrial expression of tropical climate variability over the past few centuries remains poorly resolved. We explore the applicability of stable isotope dendroclimatology as a tool for chronology and paleo-hydrology reconstruction on deciduous trees from monsoonal northern Thailand. Analysis of 11 trees coming from 4 different regions of northern Thailand yielded 7 records with varying degrees of δ18O and δ13C seasonality. We develop age models for trees lacking visible rings based on the seasonality of the δ18O and find agreement to within ≤ 3 years with radiocarbon age estimates. We use the isotopic age models to reconstruct estimates of growth rates and find a significant positive correlation between growth and amplitude of the oxygen and carbon seasonal isotopic signals. A comparison of a reconstructed dendro-isotopic index from Pangmapa with regional rainfall records indicates significant correlations consistent with the locally derived patterns but with decreased representation of the variance. Individual isotopic chronologies stemming from different tree species share common trends, which are also consistent with patterns of rainfall variability. We see an increase in the amplitude of the seasonal δ18O cycle along with an increase in δ18Omax over the past few decades suggesting a tracking of the recent drying trend of Thailand's monsoon.