Global climate events may have driven abrupt shifts in Indian Summer Monsoon: Study

New Delhi (NVI): The Global climate events like the Roman Warm Period, Medieval Climate Anomaly, and the Little Ice Age may have driven abrupt shifts in the Indian Summer Monsoon (ISM) in past 3,200 years, according to a new study.

These events also had a significant impact on India’s landscape, vegetation, and socio-economic growth.

The study by Wadia Institute of Himalayan Geology (WIHG), an autonomous institute of the Department of Science & Technology (DST), shows the calculations of Total organic carbon (TOC), Total Nitrogen (TN) and depleted carbon isotope ratio values during the interval 1200 to 550 BCE which indicated wet monsoon conditions in the North-Western Himalaya.

“This condition prevailed till 450 AD, coinciding with the Roman Warm Period (RWP), followed by reduced precipitation and a weak ISM till 950 AD, But the ISM became comparatively stronger during the Medieval Climate Anomaly (MCA) between 950 to 1350 AD,” it added.

During the Little Ice Age, there was a pronounced reduction in ISM precipitation, as indicated by relatively low C/N ratio and decreased TOC content. The findings pointed out to revival of wet climatic conditions with a strong ISM around 1600 AD following the Little Ice Age, which prevails in present times, the study stated.

The study was carried out with lake sediments from Rewalsar Lake in Mandi, Himachal Pradesh could resolve the long debate among scientists about whether events causing monsoon variability in the past were local or global. Also, the sediments from this lake preserve signature that can be used as proxies to understand monsoon variability in the past.

This recent study was published in the journal ‘Quaternary International’, in which researchers obtained grain size data, stable isotope ratios of carbon and nitrogen, total organic carbon (TOC), and total nitrogen data from the sediments of the lake.

They retrieved a sediment core of 15-meter length from the center of the lake at a water depth of about 6.5 meters using piston corer, which was used as a sample.

The chronology of Rewalsar Lake sediment was then established based on the Accelerator Mass Spectrometry (a form of mass spectrometry to separate a rare isotope from an abundant neighbouring mass) (AMS) 14C radiocarbon dates of fourteen samples and the age ranges from approximately 2950 years to 200 years ago.

However, the variability of ISM in historical past needs to be ascertained and the study will help understand present, and future behaviour of ISM as climate shifts and water supply has dictated flourish and demise of ancient civilizations.

-RJV