Meghalaya cave stalagmite reveals 6,000-year monsoon history in Northeast India
A study of a stalagmite from Mawsmai Cave shows how solar activity and North Atlantic climate events influenced ancient rainfall patterns.
A stalagmite recovered from Mawsmai Cave in Meghalaya has provided a 6,000-year climate record of monsoon changes in northeastern India, according to The Assam Tribune. The research, which examined the Indian Summer Monsoon (ISM) between 11,807 and 5,622 years ago, was published in the journal Palaeogeography, Palaeoclimatology, Palaeoecology.
The study was led by Yachna Verma and Anil K Gupta of IIT Kharagpur, alongside Prasanta Sanyal of IISER Kolkata and co-authors Priyantan Gupta, Som Dutt, Pankaj Kumar, and Abhijit Mukherjee. Researchers analysed the stable oxygen isotope composition and mineralogical characteristics of the 11-cm-long stalagmite to reconstruct ancient rainfall.
Findings indicate the ISM was considerably stronger during the early Holocene, specifically between approximately 11,807 and 7,700 years ago. The monsoon then weakened gradually between 7,700 and 5,622 years ago, as reflected by rising oxygen isotope values in the cave deposit.
The researchers identified links between monsoon fluctuations and North Atlantic climate events known as Bond events 8, 7, 6, 5b, 5a, and 4. This suggests connections between the Indian monsoon and the Atlantic Meridional Overturning Circulation (AMOC), a system of ocean currents.
The study also found recurring climate patterns at intervals of 110 and 118 years, which correspond with Gleissberg solar cycles. Solar variability, the Pacific Decadal Oscillation (PDO), and temperature differences between the Tibetan Plateau and the Indian Ocean were noted as factors influencing monsoon intensity.
The stalagmite was collected from a chamber 300 metres inside Mawsmai Cave, located around 60 km south of Shillong in the East Khasi Hills district. The researchers noted that combining petrographic evidence with geochemical indicators provides an additional dimension to understanding prehistoric climate conditions.