Hydroclimate variability of western Thailand during the last 1400 years

Ancient teak log coffins found in Namjang (NJ) Cave, Pang Ma Pha district of Mae Hong Son province in Northwestern (NW) Thailand, were dated using a combination of C-14 dating and cross-dating techniques The longest tree-ring width chronology (ie, the CoffinNJ index) in Thailand covered a 477-year period from 106 BC to AD 371 The ages of the NJ log coffins fell within the log coffin culture epoch in NW Thailand The NJ coffins are considered to belong to the second component of the log coffin culture period in NW Thailand, which began from approximately 2100 BP to 1200 BP Spectral analysis of the CoffinNJ index displayed a decadal periodicity of 112 years, similar to the well-known 11-year periodic change in the sunspot cycle A positive relationship (r = 031, p < 0035) was observed between the CoffinNJ index and sunspot number for the entire period from 110 BC to AD 370, particularly during the period of AD 191–370 (r = 048, p < 0045) Comparisons with speleothem proxies sensitive to changes in solar activity showed relationships between the CoffinNJ index and speleothem parameters (layer thickness: r = − 050, p < 0001 and δ18O: r = 040, p < 0001) The results confirmed that the ancient teak trees in this study might have responded, at least partly, to solar variation The ring widths of the teak log coffins proved to be a promising proxy for studying the evolution of coffin culture and past climate change in this area

The potential of teak log coffins collected from Namjang Cave in Northwestern Thailand for studying the coffin culture and paleoclimate in Southeast Asia

Thailand is a predominantly agricultural country. An understanding of the dominant driver of decadal-scale changes in Thailand monsoon (TM) rainfall trends is particularly important in terms of agro-meteorological information and monsoon predictions. In this study, a 194-year tree ring chronology of teak trees in northwestern Thailand was developed. Correlations between the tree ring width index (i.e., the Susa index) and climate variables confirmed that this index can be used as a proxy for rainfall in the early monsoon season from May to July. Similar variations with other regional tree ring chronologies confirmed the reliability of the climate signals embedded in the tree ring widths. The possible relationship between the Susa index–based TM rainfall and the Pacific Decadal Oscillation (PDO) was examined. Spectral analysis showed statistically significant PDO periodicities of between 22 and 24 years. The spatial correlations detected across the key regions of the PDO revealed associations with the north Pacific sea surface temperature during recent decades. The long-term relationships between the Susa index and the PDO were nonstationary at the decadal timescale. Positive correlations were found for AD 1824–1875 and AD 1900–1955, whereas negative relationships prevailed for AD 1876–1899 and 1956–2017. The El Nino Southern Oscillation–related anomalous TM was indeed stronger during both the warm and cold phases of the PDO. The PDO is therefore identified as a driving factor of decadal climate variability. This study leads the way to understanding the changes in the TM-PDO relationship over time and demonstrates the utility of teak tree ring width as a potential proxy for PDO teleconnection.

Effects of the Pacific Decadal Oscillation on Thailand monsoon rainfall derived from a 194-year tree ring width chronology of teak trees from northwestern Thailand

Application of novel proxies, such as the stable isotope compositions and noble gas concentrations of fossil drip water trapped as inclusions in stalagmites, have the potential to provide unique constraints on past hydroclimate states and surface temperatures. Geochemical analysis of inclusion waters, however, requires an understanding of the three‐dimensional spatial distribution of dominantly liquid‐ versus air‐filled inclusions in a given stalagmite. Here we couple neutron computed tomography and medium‐ to high‐resolution X‐ray computed tomography to map out the three‐dimensional calcite density and distribution of liquid‐ versus air‐filled inclusions within a Sierra Nevada stalagmite (ML‐1), which formed during the last deglaciation (18.5 to 11.7 ka). Comparison of coupled neutron computed tomography‐X‐ray computed tomography results with a time series of stalagmite calcite fabrics indicates that although highest density calcite contains abundant liquid (fluid)‐filled inclusions, calcite density and fabric overall were secondary controls on the liquid inclusion distribution (LID). Furthermore, a multistatistical evaluation of the stalagmite time series indicates a significant relationship at the multicentury‐ to millennial‐scale between LID and calcite δO and δC that suggests a potential link between LID and water availability to the cave.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2018GC008140

Mapping Fluid-Filled Inclusions in Stalagmites Using Coupled X-Ray and Neutron Computed Tomography: Potential as a Water Excess Proxy

Stalagmites provide one of the few high-quality proxy records of the Thailand monsoon. The Namjang (NJ) cave (19°40′30″N, 98°12′12″E; 923 m a.s.l.), which is situated in the data-scarce region of northwestern Thailand, serves as a unique and important site that offers great potential for multi-proxy climate reconstruction. We present new data on stable oxygen isotopic (δ18O) compositions and growth rates of aragonite stalagmites based on an in situ cave and climate monitoring study performed between August 2012 and October 2013. The dominant factors that control the variations in the δ18O values of rainfall, drip water, and modern aragonite precipitate as well as the variations in the modern speleothem deposition rates and drip water hydrochemical properties were determined to correctly interpret the climatic signals of the parameters that are derived from speleothems. The intraseasonal variations in rainfall δ18O values were faithfully recorded from cave drip water isotopic signals. The monthly mean values of δ18O in cave drip water were lower in the rainy season and higher in the dry seasons and shifted from approximately − 4 in the early rainy months to approximately − 6‰ in the late rainy months. These variations have implications for the use of speleothem δ18O from the NJ cave as a proxy of the seasonal variations in monsoon rainfall δ18O and changes in moisture source trajectories. The deposition rates of modern speleothem deposits are primarily controlled by drip water flow rates, which are linked to the amount of water recharge in the cave during the summer monsoon season. There was a significant correlation between the drip rate and amount of carbonate precipitation for the drip sites NJ-1 (r = 0.54, p < 0.040) and NJ-1202 (r = 0.76, p < 0.004). Combinations of different parameters and proxies from this area could provide the potential for the further development of multi-proxy climate reconstructions over different time scales.

Oxygen isotopic compositions of meteoric precipitation, drip water, and aragonitic stalagmite deposition from the Namjang cave in northwestern Thailand: implications for multi-proxy climate reconstruction

Warisa Paisonjumlongsri

Papers

Stalagmites from western Thailand : preliminary investigations and challenges for palaeoenvironmental research