Indian Summer Monsoon During the Medieval Climate Anomaly With a Steady Trend From 1140 to 1250 CE

A high-resolution U-Th dated speleothem record from Bylliat cave, Meghalaya, spanning ∼722 to 1250 CE, provides new insights into dynamics of the Indian Summer Monsoon (ISM) through the Medieval Climate Anomaly (MCA). The δ¹⁸O values, supported by petrographic analyses, indicate extreme events in the ISM behavior. Our data report a distinctly wet phase between ∼722 and 775 CE, followed by a marked decline in precipitation from ∼775 to 850 CE. Subsequently, a prolonged drought-like condition prevailed between ∼850 and 890 CE. From ∼890 to 980 CE, the northeastern Himalaya witnessed return of wetter conditions, whereas from ∼1140 to 1250 CE the monsoon was relatively stable, analogous to modern ISM patterns in a non-El Niño scenario. Multidecadal ISM variability in the MCA appears to have been primarily modulated by solar activity, and consequent latitudinal migration of the Intertropical Convergence Zone. In contrast, subdecadal ISM variability was closely linked to changes in the El Niño-Southern Oscillation. The pronounced wet conditions from the eighth to thirteenth centuries are believed to have promoted agricultural expansion and crop diversification across India. However, these climatic conditions may also have influenced patterns of cultural and political change, particularly in the eastern regions of the subcontinent.