Precipitation variability in the Indian Central Himalaya during last ca. 4,000 years inferred from a speleothem record: Impact of Indian Summer Monsoon (ISM) and Westerlies

We report the first high resolution stalagmite record from Indian Central Himalaya by using a combined oxygen and carbon isotopic study spanning the last 4000 years. In addition to the multi-decadal events, the stalagmite data also provide information on the variability in the intensity of precipitation [Indian Summer Monsoon (ISM) and Westerlies] in north Indian hills during the Late Holocene. The δ18O values show strong variability between −2.1‰ and −8.9‰. The extremely high variability points to the monsoon from two different sources compared to other similar aged caves which are primarily controlled by one monsoon, such as the East Asian Summer Monsoon (EASM; although ISM has penetrated into some parts in the areas of EASM in the past) or the Westerlies. Therefore, we suggest that the Westerlies played an important role in the Late Holocene climate of the Indian Himalaya. As the source of the Westerlies is Mediterranean/Atlantic, the North Atlantic Oscillation (NAO) which was responsible for comparatively stronger Westerlies in southern Europe, may have brought higher precipitation to the north Indian hills. The stronger Westerlies may also have resulted in the highest precipitation between 0.5 and 0.25 ka BP (1450–1700 AD; a part of the LIA) in contrast to the weakening of the Indian Summer Monsoon (ISM) in peninsular India. The stalagmite has also recorded the driest period, peaking at ∼3.2 ka BP which may be nearly synchronous with the final collapse of the Harappan culture in northwest India.