Indian summer monsoon variability in southern India during the last deglaciation: Evidence from a high resolution stalagmite δ18O record

Abstract We present a high resolution record of Indian summer monsoon (ISM) variability during the last deglacial period. The record is based on high precision measurements of oxygen isotopes (δ 18 O) in 263 sub-samples from a ~ 18 cm long stalagmite (VSPM1) sample collected from the Valmiki cave in the southern India. The chronological framework is based on high precision U-Th dating in 8 sub-samples at regular intervals. The stalagmite exhibits a variable growth rate ranging from ~ 0.03 to 0.80 mm/yr with 9 years as an average sampling resolution for δ 18 O. X-ray diffraction analysis shows that the sample is composed of aragonite mineral. The δ 18 O record provides a strong evidence of abrupt changes in ISM activity between approximately 15,610 and 13,160 yr BP (before 1950 AD). Highly negative δ 18 O values at ~ 15,610 and 15,250 yr BP are suggestive of a wet climate followed by less negative δ 18 O at ~ 15,240 to 14,750 yr BP indicating relatively dry climate. These dry and arid conditions are punctuated by two wet events at 15,030 and 14,910 yr BP. A marked increase in δ 18 O between approximately 14,660 and 14,370 yr BP suggests weakening in ISM activity, followed by a gradual decrease in δ 18 O between 14,370 and 13,560 yr BP indicating strengthening of ISM. However we cannot rule out the possibility of some past flooding event influencing δ 18 O of VSPM1. Wavelet analysis of δ 18 O time series suggests strong influence of solar forcing on ISM activity. The amplitude variance of δ 18 O reveal decadal to centennial scale variability in monsoonal activity during the last deglaciation.