The prolonged weak monsoon event in East Asia and the interhemispheric seesaw: implications for persistent AMOC forcing at the mid-late Holocene transition

The interhemispheric seesaw at lower latitudes is well established from the last glaciation to the early Holocene. This phenomenon is driven by variations in the Atlantic Meridional Overturning Circulation (AMOC) and the associated latitudinal migration of the Intertropical Convergence Zone (ITCZ). However, the persistence of this phenomenon and the mechanisms involved during the late Holocene, a period characterized by minimal and stable global ice volume, remain unclear. This study presents a new 5.3-year-resolution stalagmite δ¹⁸O record from central China spanning 4.4–3.0 ka BP. Our data reveal a multi-centennial weak Asian summer monsoon (ASM) event spanning 4.4–3.5 ka BP that is inversely correlated with intensified South American summer monsoon (SASM) activity. This antiphase relationship mirrors the pattern observed during the Little Ice Age (LIA), suggesting a consistent seesaw mechanism. Further analysis shows that an AMOC slowdown coupled with a southward shift in the ITCZ created this hemispheric antiphase during both events. El Niño-like conditions further strengthened the ASM–SASM antiphase relationship during both the 4.4–3.5 ka event and the LIA. Unlike the typical AMOC–solar correlation observed during the LIA, the weakened AMOC during the 4.4–3.5 ka event coincided with strong solar activity. Our results emphasize the persistent seesaw pattern during the mid-to-late Holocene transition, which is driven by changes in the AMOC and El Niño-Southern Oscillation (ENSO) rather than solar activity.