The indian monsoon variability during the last two millennia and links to the tropical equatorial Pacific

This study examines the variability of the Indian summer monsoon rainfall (ISMR) during the last two millennia using a near-annually resolved speleothem oxygen isotope record from Kadapa cave in peninsular India. Our results show that the monsoon precipitation variations experienced a wet phase during the dark age cold period (DACP; ~250–800 CE) as evidenced from the progressive depletion of the δ18O values; followed by high amplitude variability during the medieval warm period (MWP; ~ 900–1300 CE), and drier monsoon conditions with enriched δ18O values during the edge of the little ice age (LIA; ~ 1500–1850 CE). It is further noted that the monsoon precipitation variability as observed in the Kadapa speleothem record during the last two millennia is corroborated by other speleothem and sediment records from the Indian subcontinent and adjoining oceanic areas. Analyses of reconstructed climate proxies, suggest that the intertropical convergence zone (ITCZ) during the DACP was stable and located relatively northward with pronounced La Niña conditions prevailing in the tropical Pacific. On the other hand, the high amplitude monsoon precipitation variations during the MWP appear to have resulted from multi-decadal fluctuations in the latitudinal position of the ITCZ, accompanied by enhanced activity of ENSO. Additionally the low monsoon precipitation during the LIA is found to be closely linked to a southward shift of the ITCZ, with precipitation reductions during the edge of LIA associated with volcanic cooling. Enriched and depleted δ18O values are consistent with the instrumental records of weakening and revival of monsoon precipitation during 1850–2000 CE and post-2000 CE, respectively.