A large array of proxy records suggests that the "4.2 ka event" marks an approximately 300-year long period (∼ 3:9 to 4.2 ka) of major climate change across the globe. However, the climatic manifestation of this event, including its onset, duration, and termination, remains less clear in the Indian summer monsoon (ISM) domain. Here, we present new oxygen isotope (δ18O) data from a pair of speleothems (ML.1 and ML.2) from Mawmluh Cave, Meghalaya, India, that provide a high-resolution record of ISM variability during a period (∼ 3:78 and 4.44 ka) that fully encompasses the 4.2 ka event. The sub-annually to annually resolved ML.1 δ18O record is constrained by 18 230Th dates with an average dating error of ±13 years (2σ) and a resolution of∼ 40 years, which allows us to characterize the ISM variability with unprecedented detail. The inferred pattern of ISM variability during the period contemporaneous with the 4.2 ka event shares broad similarities and key differences with the previous reconstructions of ISM from the Mawmluh Cave and other proxy records from the region. Our data suggest that the ISM intensity, in the context of the length of our record, abruptly decreased at ∼ 4:0 ka (∼ ±13 years), marking the onset of a multi-centennial period of relatively reduced ISM, which was punctuated by at least two multi-decadal droughts between ∼ 3:9 and 4.0 ka. The latter stands out in contrast with some previous proxy reconstructions of the ISM, in which the 4.2 ka event has been depicted as a singular multicentennial drought.
Bibliographical noteFunding Information:
Acknowledgements. We thank Giovanni Zanchetta and the two anonymous reviewers for their comments that helped improve the original paper. We thank Digambar Singh Chauhan, Chetan Singh Chauhan, Aditya Singh Kathayat, Geetan-jali Kathayat, Neha Pant, Sanjay Melkani, Clive Dunnai, Ardy Dunnai, and Ceejey Dunnai for their assistance during the fieldwork. This work is supported by grants from the Natural Science Foundation of China to Gayatri Kathayat (NSFC 41703007), Hai Cheng (NSFC 41731174 and 4157020432), R. Lawrence Edwards and Hai Cheng (NSF 1702816), and Haiwei Zhang (NSFC 41502166).