A Multiproxy Approach to study Vegetation and Temperature Changes since the Last Glacial in Central Vietnam.

Speleothems are invaluable archives of past climate variability and offer important insights into monsoon dynamics across Southeast Asia. Different isotope systems have been employed to characterise autumn monsoon in this region, but multiple influencing factors render the interpretation of isotope proxy records ambiguous. To gain novel insights into regional vegetation and temperature changes, novel proxies are required. Here, we combine traditional speleothem stable isotopes (δ¹⁸O and δ¹³C) with speleothem thermometry (TEX₈₆) and lignin oxidation products (LOP) analyses, to provide a more comprehensive understanding of past environmental changes in Central Vietnam. Specifically, we aim to:

1. Reconstruct cave air temperature variations using TEX₈₆.

2. Assess vegetation and environmental changes through LOP analysis.

3. Evaluate the response of these proxies to known climate forcing mechanisms, including Northern Hemisphere summer insolation, sea surface temperature anomalies, and shifts in the Intertropical Convergence Zone.

A stalagmite record from Central Vietnam, spanning the last glacial and onset of the Holocene (35 – 10 ka BP), provides a unique opportunity to reconstruct glacial to Holocene temperature changes and the response of regional hydroclimate and vegetation. Preliminary TEX₈₆ results suggest a temperature shift of at least 2°C from fully glacial to Holocene conditions. LOP results suggest that the vegetation in Central Vietnam changed from hardwood deciduous vegetation types (0.37 S/V, 0.33 C/V) to an increase in softwood vegetation types (0.1 S/V, 0.11 C/V), respectively.  Our findings have implications beyond Southeast Asia's paleoclimate. Validating these novel biomarker systems (TEX₈₆ and LOP) against more traditional stable isotope ratios (δ¹⁸O and δ¹³C), we aim to elucidate changes in moisture budget and sources, and seasonality.