EXPLORING THE DRIVERS AND CYCLES OF PAST MONSOON VARIABILITY IN VIETNAM

Southeast Asia occupies a nexus between three major branches of the Asian monsoon system. Multiple dynamical climate features, including the ITCZ, Pacific Walker Circulation (PWC) and tropical storms, modulate monsoon rainfall in this region over varying time scales. An intermittently laminated core from a karst pond in northern Vietnam was analyzed at ~3 year resolution. Over the last 650 years, oxygen-isotope inferred hydroclimate was significantly correlated with the reconstructed Southern Oscillation Index of precipitation (SOIpr), suggesting a prolonged La Niña-like state existed during the Little Ice Age with significant decade-long drought and pluvial events superimposed on the general trend. Many of these droughts are coincident with those identified elsewhere in SE Asia and the tree-ring inferred Monsoon Asia Drought Atlas. Application of the multi-taper method to the detrended isotope record reveals several cycles exceeding the 95% confidence interval, including periodicities at 76, 44, and 3-9 years. These cycles may be linked to the AMO, PDO and ENSO, respectively, highlighting the role of dynamical oscillations in monsoon rainfall variability in SE Asia.