Rapid reorganization of monsoon seasonality during the 2.8 ka event

Seasonal hydroclimate variability governs water availability, agricultural productivity, and societal resilience across monsoon Asia, yet its response to abrupt climatic extremes remains poorly constrained. Here we present seasonal-resolution δ¹⁸O and trace-element data from an annually laminated stalagmite in northern China, providing a direct reconstruction of East Asian summer monsoon (EASM) seasonality across the 2.8 ka extreme event. The records reveal rapid (<10 yr) transitions into multi-decadal weakened-monsoon states, marked by delayed onset and shortened midsummer rainfall stage, together with a shift from “W-shaped’’ to “V-shaped” δ¹⁸O seasonal cycle at the northern margin of the EASM domain. Our experiments with an isotope-enabled simulations show that North Atlantic cooling associated with weakened overturning circulation suppressed the Arabian Sea convection, displacing the westerly jet southward, shortening the core monsoon rainfall stage, and imparting northwestern westerly-dominated δ¹⁸O seasonality to the monsoon fringe. Comparison with contemporaneous historical and archaeological evidence indicates that the intensification of hydroclimate seasonality during dry-wet transitions may have imposed the decisive climatic stress precipitating the Shang dynasty’s decline. These results highlight altered monsoon seasonality, rather than mean aridity alone, as a critical dimension of past climate extremes and a key determinant of societal vulnerability.