Indian summer monsoon variability in northeastern India during the past two millennia

We have produced oxygen isotopes record from a speleothem from the Mawmluh cave, northeastern India showing sudden shifts in speleothem oxygen isotope values, indicating abrupt changes in the Indian summer monsoon (ISM) during ~212 BCE to 1986 CE. Moderate to strong ISM conditions prevailed during ~212 BCE to 400 CE, strong ISM during 400 and 500 CE and from 640 to 1060 CE, whereas weak ISM conditions prevailed during 520-540 CE, 820-850 CE and 940-980 CE and after 1060 CE. A sudden weakening of the ISM occurred at ~500 CE. The interval from 1060 to 1986 CE witnessed decreased precipitation than the earlier millennium. The latter phase of the Medieval Climate Anomaly (MCA; 1060 to 1200 CE) was quite drier in contrast to the earlier intervals. The ISM was generally weak during the Little Ice Age (LIA; 1350 to 1850 CE) with short-term pulses of high precipitation when sun-spot activity was high. The data shows the weakest ISM condition during 1640 to 1740 CE (Maunder Minimum ) of the last two millennia. Variations in extra-tropical northern hemisphere temperatures due to volcanic activity and solar insolation, and accompanying northward/southward shifting of the Inter-Tropical Convergence Zone played a pivotal role in modulating the strength of the ISM during the past two millennia.