Historical droughts in northern Vietnam captured by variability in speleothem δ18O

Abstract:

Speleothem records overlapping with the historical period offer valuable comparisons of documentary evidence with speleothem proxy data. These records provide opportunities to ‘ground-truth’ the paleo-record, fill in gaps in the historical record, and more confidently extent the paleo-record into deeper time. Here we present isotopic results from a stalagmite collected in northern Vietnam spanning 1200 to 1950 CE, a period with a rich historical record in Vietnam. This sample adds significantly to the relatively sparse paleoclimate record from Southeast Asia.

The record includes several multi-decadal positive excursions of ≥1 per mille in calcite δ¹⁸O. A preliminary age model, based on six U/Th ages, suggests possible correspondence to noted droughts from the historical record, including the Angkor Droughts, the Ming Dynasty Drought, the Strange Parallels Drought, and the Victorian Holocaust Drought. As modeling studies indicate a strong correlation between rainfall δ¹⁸O and both the intensity of summer monsoon winds and summer rainfall over northern Vietnam (e.g., Liu et al., 2014), these excursions are consistent with a decrease in regional precipitation.

The Vietnam record shows an overall negative trend during the Little Ice Age. The study site is located well south of the westerly wind belt, ruling out a shift between monsoonal and mid-latitude circulation systems as a likely explanation for the northern Vietnam record. We explore the correspondence between our record and other proxy data from Southeast Asia and suggest possible implications of the differences between Vietnamese and Chinese speleothem records during the Little Ice Age.

References cited:

Liu Z., Wen X., Brady E. C., Otto-Bliesner B., Yu G., Lu H., Cheng H., Wang Y., Zheng W., Ding Y., Edwards R. L., Cheng J., Liu W. and Yang H. (2014) Chinese cave records and the East Asia Summer Monsoon. Quaternary Science Reviews 83, 115–128.