Indian monsoon's past analysed by scientists

By Helen Briggs
BBC Environment Correspondent

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image captionA flooded street in Amritsar, after heavy monsoon rainfall struck the northern Indian city

Fossils from the ocean floor are yielding clues to the Indian monsoon millions of years ago.

Samples drilled from beneath the Indian Ocean are being used to reconstruct past rainfall and temperature records.

Scientists are studying how the Indian monsoon behaved in the past, to shed light on the impact of climate change.

The research will lead to a better understanding of how the monsoon over India might change, said Dr Kate Littler of the University of Exeter.

As part of the larger-scale Asian monsoon, the monsoon over India is formed due to intense heat from the Sun in late spring, which warms the Northern Indian Ocean, along with the plains of northern India and the Tibetan Plateau.

This results in 75% of the year's rain falling between June and September.

Simulations of future climate generally suggest a 5-10% increase in monsoon rainfall over India, which could influence the economy and agriculture.

image copyrightKate Littler
image captionKate Littler with the sediment cores

Palaeoclimatology - the study of changes in climate taken on the scale of the entire history of Earth - can give valuable clues to how the Earth might respond to future climate change.

Dr Littler was part of an expedition to the Indian Ocean, Bay of Bengal and the Andaman Sea on a scientific drill ship belonging to the UK International Ocean Discovery Program.

The team of international scientists collected sediment samples from the deep-sea at several locations.

These are being analysed to reconstruct what the regional and global climate was like during the period when the small fossilised marine creatures contained in the sediments lived.

"We wanted to capture the whole evolution of the India monsoon from when it intensified about 8 million years ago," said Dr Littler.

"By analysing these hard-to-reach deep-sea sediments we will make important discoveries about the behaviour of the Indian monsoon in the deep past, and how its behaviour and intensity may change in the near future.

"The data will give us a holistic idea of the past behaviour of the monsoon."

Some of the samples came from sites that had never been drilled before.

Others contained volcanic ashes, which can be matched to ancient volcanic eruptions, helping in dating the sediments.

Their chemistry, geology and biology will be analysed to build up a record of how the annual Indian monsoon cycle has historically been affected by climate change.

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