31 May 2024  |   09:53pm IST

Joint Indo-China study traces history of weakening monsoon back to 12 million years

Scientists from Qingdao, Beijing, Hamburg, Panjim and Hyderabad were part of this international study
Joint Indo-China study traces history of weakening monsoon back to 12 million years


PANJIM: Even as India and China are slugging it out on the Himalayas and the Indian Ocean for regional supremacy, ocean scientists from Beijing and Goa have collaborated for an international study that examine the erratic rains caused by weak monsoon, which we have been witnessing in recent times due to climate change, traced back as far as 12 million years.

This study titled, ‘Weakening of the South Asian summer monsoon linked to inter-hemispheric ice-sheet growth since 12 Ma’, gives insights into the changing pattern of the monsoon system, caused by climate warming. It has been published in the journal ‘Nature Communications’.

The study has been co-authored by Zhengquan Yao and Xuefa Shi, from the First Institute of Oceanography, Ministry of Natural Resources, Qingdao, China; Zhengtang Guo from Key Laboratory of Cenozoic Geology and Environment, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China along with B Nagender Nath from CSIR-National Institute of Oceanography (NIO), Goa and others.

 “The study’s objective was to understand the longterm evolutionary pattern of South Asian monsoon system. Here we had a geological archive; the deepest part of the archive had an age of 12 million years,” said Nath, former NIO chief scientist.

 “The archive is a sediment core drilled in the Maldives inner Sea which is a carbonate platform in the Northern Indian Ocean as a part of International Ocean Discovery Program (IODP) expedition,” the senior scientist said.

 “The study was designed to address changes in sea level and currents, along with monsoon evolution in the Indian Ocean. The expedition had researchers from all the member countries. IODP India (nodal agency being MoES-NCPOR, Goa) nominated me to participate. My then employer CSIR-NIO too had encouraged my participation,” he said.

In view of the fluctuating nature of rainfall that has become more frequent in recent decades, this past study assumes importance. A weakening of southwest monsoon on longer time periods has been inferred from this sediment core study, which is driven by the increase in ice sheet growth in the Southern Hemisphere and in Greenland.

 “This weakening of monsoon can be traced to two different periods - 12 million years and 4 million years ago, when the strength of the Southwest Monsoon wind and the North Westerly ‘shamal’ winds decreased,” Nath said.

However, in shortterm, the intensity of the monsoon could increase due to temperature warming and reduction of ice sheet thickness in Polar Regions.

 “We found that there was a decrease in the dust deposition at 12 million years and 4 million years ago, which is due to the weakening of the monsoon winds,” the former NIO Chief Scientist added.

When asked why there was collaboration with the Chinese, Nath said, “This was part of a major international programme with participation from member countries. Like India, China too is a member country in the IODP.”

 “In the expedition 359, myself and the first author of the paper Dr Zhengquan Yao were part of the Sedimentology group on board the drilling vessel JOIDES Resolution. This project was proposed by Dr Yao and he wanted to collaborate with us in view of our familiarity with the geology of the Northern Indian Ocean. We provided key inputs in identifying the source regions of mineral dust supply,” he said.


Iddhar Udhar