Abrupt changes in Indian summer monsoon strength during the last similar to 900 years and their linkages to socio-economic conditions in the Indian subcontinent

摘要

Abrupt shifts in Indian summer monsoon (ISM) precipitation largely affected regional hydrometeorology, accelerating socio-economic and cultural adaptations of agrarian economies in South Asia in the last millennium. Linking ISM variability to human history in the Indian subcontinent is still limited by the scarcity of high-resolution paleoclimatic data for the period encompassing the last 1000 years or earlier. We present a new high resolution oxygen isotope proxy record from the Wah Shikar cave, northeastern India and identified abrupt shifts in the ISM that had profound impact on human societies during the last similar to 900 yrs. The ISM was strong during the Medieval Climate Anomaly (MCA) and the Current Warm Period (CWP), and show multiple shifts during the Little Ice Age (LIA). The abrupt shifts in the ISM were more frequent during warm intervals, showing a secular trend with few exceptions during the cold periods. Intervals of prolonged summer monsoon weakening are correlated to the decline of major dynasties in India, possibly due to decrease in agriculture productivity, declining economy and societal crisis. Changes in atmospheric temperature due to volcanic eruptions and sun spot activity have played major role in the onset of the LIA and other prolonged weak intervals of the ISM during the last similar to 900 yrs.