Stalagmite δ18O variations in southern India reveal divergent trends of Indian Summer Monsoon and East Asian Summer Monsoon during the last interglacial

Abstract

Indian monsoon variations for the period around ∼100ka have not been documented from terrestrial archives, while limited data do exist from the Indian Ocean. Some paleoceanographic studies have reported abrupt and stepwise changes in the monsoon intensity during the last deglaciation, but similar observations have not been possible for earlier periods such as the interglacial to glacial transition, mainly because of the coarse resolution (∼500 to 1000 years) provided by marine archives of that age. Here, we report a new δ18O data set from a stalagmite (3-ACN) that grew in the Belum caves, Andhra Pradesh, a semi-arid region in southern India, with a resolution of ∼85 years. Age assignment to different growth layers consistent with associated analytical errors indicates that the record could span ∼9ky during part of Marine Isotope Stage (MIS) 5d-c, from ∼108 to ∼99ka. δ18O variations in this stalagmite, if interpreted using the ‘amount effect’, i.e., 18O depletion of ∼1.5‰ per 100 mm increase in monsoon rainfall, indicate a step-like increase during the transition from the cooler stadial MIS 5d to warmer interstadial MIS 5c, signifying an abrupt reduction in monsoon rain. The new data presented highlight divergent trends between the Indian and the East Asian Summer Monsoons for a time period for which not many high-resolution comparisons are available.