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Indian monsoon was more intense 6,000 years ago: study

  • Y.Mallikarjun
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Sea-dwelling fossil shells reveal 60,000-year-old link relating to climate change

Shells of surface-dwelling fossil Foraminifera (Globigerinoides Ruber) used to infer past sea surface temperature. These shells contain signatures of past sea surface temperature by way of oxygen isotope composition.— photo: By arrangement
Shells of surface-dwelling fossil Foraminifera (Globigerinoides Ruber) used to infer past sea surface temperature. These shells contain signatures of past sea surface temperature by way of oxygen isotope composition.— photo: By arrangement

Link dating back to 60,000 years between sea surface temperature of Northeast Indian Ocean (NEIO) and North Atlantic climate oscillations, probably through ocean atmospheric connection, was found by researchers.

In a study on oxygen isotopes deposited in fossil shells in the ocean sediment through AMS radiocarbon dating, it was also found that the Indian monsoon was much more intense 6,000-8,000 years ago than the present period. In the study carried out by scientists from CSIR-National Geophysical Research Institute here, researchers from the School of Geography Science, Nanjing Normal University and the School of Earth Science and Engineering, Nanjing University, Nanjing, China collaborated in dating the fossils.

A paper relating to the study was published in ‘Marine Geology’, an Elsevier publication.

According to Dr. S.Masood Ahmad, Chief Scientist at NGRI and the lead author, the fossil shells (foraminifera) found at a water depth of more than 3,000 metres were collected for the study. He said that using oxygen isotopes deposited in fossil shells, the temperature details of the sea water of the past thousands of years could be studied.

“We have seen using well-dated sediment cores from NEIO that there was a connection between its sea surface temperature and North Atlantic climate oscillations”.

He said that studies in the past had shown that changes in Indian southwest and northeast monsoon even on shorter time-scales were associated with cold and warm events in the North Atlantic. He said that cold winds from Northern polar region have influenced low latitude regions like the Indian Ocean during last glacial period (20,000 to 60,000 years ago). This had happened at intervals of every 4,000-5,000 years through atmosphere.

Stating that the Indian monsoon was much more intense 6,000-8,000 years ago, Dr. Masood said the freshwater influxes were much more intense than the present influxes like the Ganges and Brahmaputra. “There might be some reasons for it. We are trying to establish them,” he added. Such studies would not only throw light on past monsoon behaviour but also help in developing predictive models, Mr. Masood added.


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