Extreme events in the Indian monsoon during the Bølling–Allerød interstadials as documented in a core monsoon zone speleothem record

Major shifts in the Indian Summer Monsoon (ISM) are evident in a U-Th-dated composite δ¹⁸O record from Kailash Cave (KGC) in central India. The composite oxygen isotope record combines previously published data with the present data from sample KG-1, ranging in age from 14.62 to 12.97 thousand year before the Present (1950) (kyr BP), during the Bølling-Allerød (B-A) interstadials. Petrographic analysis of KG-1, spanning ∼14.44 to 13.98 kyr BP, reveals long-term coherence between the stable isotope values and petrographic elements. The KGC record shows an increase in ISM intensity with high-frequency δ¹⁸O variability during the Bølling (14.62–14.02 kyr BP), followed by stabilization in the Allerød (14.02–12.97 kyr BP) with low-frequency oscillations. At the onset of the B-A interstadials, coincident warming (cooling) in the northern (southern) hemisphere induced a bipolar see-saw effect, displacing the Intertropical Convergence Zone northward and intensifying the ISM. Multi-centennial to millennial ISM variations are driven by atmospheric temperature over the Tibetan Plateau (TP) and equatorial Indian Ocean (IO) sea surface temperature (SST) fluctuations. High-frequency monsoon shifts at multidecadal to centennial scales likely reflect extreme wet-dry episodes linked to changes in solar activity, temperature of TP and IO SST. These findings suggest that solar activity, in conjunction with coupled ocean-atmosphere interactions, have played a pivotal role in driving ISM variability during the B-A interstadials. Additionally, the increased greenhouse gas concentrations during this period might have triggered extreme climatic events, more prevalent in the warmer Bølling, serving as a modern analogue for current global warming scenario.