The respective characteristics of millennial-scale changes of the India summer monsoon in the Holocene and the Last Glacial

Abstract

There has been no proxy climate record simultaneously showing the identified millennial-scale change events of the India summer monsoon (ISM) during the period from the Last Glacial period to the Holocene, although these abrupt changes have been shown in separate records. This deficiency prevents further understanding of the potentially different characteristics of the ISM rapid changes. Here, we present a 33,300-year record of the ISM reconstructed from the stable carbon isotopic composition of cellulose in peat deposits collected near the Tibetan Plateau, reflecting the millennial-scale history of abrupt changes in the ISM intensity from the cold late Last Glacial to the warm Holocene epoch. Our record shows that, corresponding to the abrupt cooling (warming) events that occur in the high northern latitudes, the ISM intensity abruptly decreases (increases), which provides additional evidence for the teleconnection between low-latitude monsoonal variability and the rapid temperature fluctuation of high northern latitudes. However, this relationship behaves differently in the cold and warm stages. In the cold late Last Glacial period, a one-to-one response is often seen, but in the warm Holocene, the ISM often shows only partial responses to the rapid cooling events. In particular, more than half of the abruptly weakening events in the ISM occur in the Holocene, and the amplitudes of declines are larger in the warm stage than in the cold stage, which reveals that extreme change events in the ISM have occurred much more in the warm Holocene and may have once influenced the development of ancient civilizations. We consider that the various characteristics of the abrupt changes in the ISM during the warm and cold stages may have derived from different combinations of climatic drivers within the two stages. These results provide a historical record of the considerable changes in ISM and resultant effects on human society, and so provide a background for concerns over contemporary climate change.