SATURDAY, MAY 04, 2024
SHASHWAT GUPTA RAY
VASCO: The warming in Antarctica weakens the monsoon while a cooler Antarctica results in a stronger monsoon, implying that in the current global warming scenario, warming of Polar Regions will adversely affect the Indian summer monsoon. This has been revealed in a study by scientists from National Centre for Polar and Ocean Research (NCPOR) Goa. The NCPOR scientists found this by analyzing a 145 thousand years old Indian summer monsoon record, and linking it with climatic changes in Antarctica.
But, how does the team know about the monsoon conditions of the past several hundred thousand years ago?
The NCPOR team of scientists led by Dr. Manish Tiwari, Scientist-F and In-charge (Paleoceanography) at NCPOR and his colleagues took the sediment cores from the bottom of the south-western tropical Indian Ocean. In the sediment, the team looked for fossilized shells of small organisms (sand grain-sized) called foraminifera, whose further analysis (oxygen and carbon isotopic ratios) revealed the past monsoon activities and gave an idea about the variations in its strength.
The team of scientists led by Dr Tiwari included Sidhesh Nagoji, Rahul Mohan and Vikash Kumar. This study published in the peer-reviewed journal ‘Polar Science’. The team explained the possibility that the increase in Antarctic temperature may propagate to the adjoining Southern Ocean including southern mid-latitudes (40-50 degrees South).
“It finally increases the sea surface temperature in Mascarene High region, which reduces the cross-equatorial pressure gradient and weakens the Indian Summer Monsoon. Mascarene High is an area in tropical Indian Ocean from where the Indian monsoon winds and moisture originate. The differences in pressure and temperature between Mascarene High and Indian Low (over the Indian subcontinent) govern the Indian Summer Monsoon strength,” Dr Tiwari told Herald.
Identifying and understanding the influencing factors of monsoon through past climatic studies will help in better understanding the mechanisms governing the present condition and a step forward towards more accurate monsoon prediction.
Analysing data of 145 thousand years was not a mean task. Informing about the challenges involved while studying such exhaustive data, Dr Tiwari said that to study past climate, one needs suitable natural archives such as marine sediment cores that preserve the changes occurring in the earth's climate layer by layer.
“For this study, we collected the sediment core on a scientific research cruise from the southern tropical Indian Ocean at a water depth of 3700 m. The core was then sub-sampled and several hundreds of samples were processed to separate tiny sand-sized microfossils under a stereo zoom microscope. These carefully selected microfossils were then analyzed for their isotopic and chemical composition using an Isotope Ratio Mass Spectrometer (IRMS) in the NCPOR. Thus, attaining these results included collecting samples from a remote oceanic region, and then putting in several years of painstaking work to generate and interpret the data,” he said.
According to him, the study signifies that a strong link exists between Antarctica and the Indian summer monsoon. The Antarctic/southern high latitude climate variability influences the Indian summer monsoon intensity.
“The periods of Antarctic warmth reduce the summer monsoon strength by modulating the adjoining oceanic temperature. It finally increases the sea surface temperature in the Mascarene High region of the southern tropical Indian Ocean, which reduces the cross-equatorial pressure gradient and weakens the Indian Summer Monsoon,” Dr Tiwari informed.
On the importance of this study for the common people and climate scientists, he said, “It is important for the general public to realise that the climatic changes occurring in the far-off regions can hit near home as well. People need to realise that global warming is a clear and present danger and can rear its ugly head at unexpected places such as adversely affecting the monsoon, which is the lifeline of India. Warming high-latitude regions like the Antarctic won't only contribute to ice melting and sea-level rise but can also influence remote climatic phenomena like the monsoon.
