Ancient Stalagmite Reveals Monsoon History in Meghalaya
Insights from Mawsmai Cave
Mawsmai Cave in Meghalaya (Photo: @KanedaAyaka / X)
Shillong, Nov 4: A stalagmite found deep within Meghalaya's Mawsmai Cave has provided scientists with a unique opportunity to explore the historical patterns of monsoon in northeastern India, revealing notable changes in rainfall intensity over millennia.
The analysis of a 6,000-year climate record from this cave deposit has enabled researchers to reconstruct the variations in the Indian Summer Monsoon (ISM) from 11,807 to 5,622 years ago, showcasing the impact of global climate systems and solar activity fluctuations on local rainfall.
This research, spearheaded by Yachna Verma and Anil K Gupta from IIT Kharagpur, along with Prasanta Sanyal from IISER Kolkata and co-authors Priyantan Gupta, Som Dutt, Pankaj Kumar, and Abhijit Mukherjee, was published in the journal Palaeogeography, Palaeoclimatology, Palaeoecology earlier this year.
Entitled 'Deciphering Holocene monsoon dynamics in northeastern India', the study focused on a stalagmite retrieved from Mawsmai Cave, situated about 60 km south of Shillong in the East Khasi Hills district of Meghalaya.
The Holocene epoch, which began roughly 11,700 years ago after the last Ice Age, is the current geological period.
To analyze ancient rainfall conditions, the team examined the stable oxygen isotope ratios of the stalagmite, along with its petrographic and mineralogical properties.
The results indicated that the Indian Summer Monsoon was significantly more vigorous during the early Holocene, particularly between 11,807 and 7,700 years ago, as evidenced by lower oxygen isotope values that suggested heightened monsoon activity.
However, between 7,700 and 5,622 years ago, there was a gradual decline in monsoon intensity, reflected in the rising oxygen isotope values in the stalagmite.
The researchers also noted several fluctuations in monsoon strength over centuries, indicating that rainfall patterns in northeastern India were influenced by climate processes beyond the region.
A key finding was the correlation between shifts in monsoon intensity and a series of North Atlantic climate events, known as Bond events 8, 7, 6, 5b, 5a, and 4.
These correlations imply potential links between North Atlantic climate variability and the Indian monsoon, mediated by changes in the Atlantic Meridional Overturning Circulation (AMOC), a crucial ocean current system that redistributes heat across the Atlantic.
The study also identified recurring climate patterns approximately every 118 and 110 years in the stalagmite record, aligning with Gleissberg solar cycles associated with long-term solar activity variations.
Researchers concluded that solar variability, along with interactions involving the Pacific Decadal Oscillation (PDO), ocean-atmosphere dynamics, and temperature differences between the Tibetan Plateau and the Indian Ocean, significantly influenced monsoon intensity during this timeframe.
The findings emphasize how regional rainfall patterns are shaped by the interplay of atmospheric, oceanic, and solar processes.
The Indian Summer Monsoon is vital for water supply, agriculture, and livelihoods across South Asia, making the understanding of its long-term variability crucial.
Northeastern India, with its unique geographical characteristics and climate sensitivity, provides essential insights into the evolution of monsoon systems.
The researchers highlighted that while earlier studies have utilized cave deposits and geological records to reconstruct historical monsoon patterns, integrating petrographic evidence with traditional geochemical indicators adds depth to the understanding of prehistoric climate conditions.
The stalagmite sample, measuring 11 cm in length, was collected from a chamber approximately 300 meters inside Mawsmai Cave, where humidity levels exceeded 95 percent.
The team expressed gratitude to the Meghalayan Adventure Association, led by B D Kharpan Daly, along with Ksan Kupar Mawlong and Kyrmen Skhembha Rani, for their assistance during fieldwork. Facilities for isotope analysis were provided by IISER Kolkata, while IIT Kharagpur supported the petrographic analysis.