Our　understanding　of　climate　dynamics　during　millennial-scale　events　is　incomplete,　partially　due　to　the　lack　of　their　precise　phase　analyses　under　various　boundary　conditions.　Here　we　present　nine　speleothem　oxygen-isotope　records　from　mid-to-low-latitude　monsoon　regimes　with　subcentennial　age　precision　and　multi-annual　resolution,　spanning　the　Heinrich　Stadial　2　(HS2)　-　a　millennial-scale　event　that　occurred　at　the　Last　Glacial　Maximum.　Our　data　suggests　that　the　Greenland　and　Antarctic　ice-core　chronologies　require　+320-　and　+400-year　adjustments,　respectively,　supported　by　extant　volcanic　evidence　and　radiocarbon　ages.　Our　chronological　framework　shows　a　synchronous　HS2　onset　globally.　Our　records　precisely　characterize　a　centennial-scale　abrupt　＂tropical　atmospheric　seesaw＂　superimposed　on　the　conventional　＂bipolar　seesaw＂　at　the　beginning　of　HS2,　implying　a　unique　response/feedback　from　low-latitude　hydroclimate.　Together　with　our　observation　of　an　early　South　American　monsoon　shift　at　the　HS2　termination,　we　suggest　a　more　active　role　of　low-latitude　hydroclimate　dynamics　underlying　millennial　events　than　previously　thought.