A new study has revealed that a fundamental shift in the Indian monsoon has occurred over the last few millennia, from a steady humid monsoon that favoured lush vegetation to extended periods of drought.
The study led by researchers at the Woods Hole Oceanographic Institution (WHOI) could increase our understanding of the monsoon’s response to climate change. To assemble the 10,000-year record, the team looked to both what the land and the ocean could tell them. Contained within the sediment core’s layers are microscopic compounds from the trees, grasses, and shrubs that lived in the region and remnants of plankton fossils from the ocean.
“The geochemical analyses of the leaf waxes tell a simple story,” said Liviu Giosan of the Woods Hole Oceanographic Institution who designed the study.
“About 10,000 years ago to about 4,500 ago, the Godavari River drained mostly terrain that had humidity-loving plants. Stepwise changes starting at around 4,000 years ago and again after 1,700 years ago changed the flora toward aridity-adapted plants. That tells us that central India — the core monsoon zone — became drier,” the researcher explained. This was supported by analysis of plankton fossils.
“What the new paleo-climatic information makes clear is that the shift towards more arid conditions around 4,000 years ago corresponds to the time when agricultural populations expanded and settled village life began,” said Dorian Fuller’s of the Institute of Archaeology, University College London.
“Arid-adapted food production is an old cultural tradition in the region, with cultivation of drought-tolerant millets and soil-restoring bean species,” Fuller stated.
Together, the geological record and the archaeological evidence tell a story of the possible fate of India’s earliest civilisations.
Cultural changes occurred across the Indian subcontinent as the climate became more arid after approximately 4,000 years.
In the already dry Indus basin, the urban Harappan civilisation failed to adapt to even harsher conditions and slowly collapsed. But aridity favoured an increase in sophistication in the central and south India where tropical forest decreased in extent and people began to settle and do more agriculture.
“If you know what’s happening in the central monsoon zone, you know more or less what’s happening in the rest of India. Our biggest problem has been a lack of evidence from this region to extend the short, existing records,” said Camilo Ponton, a student in the MIT-WHOI Joint Programme in Oceanography and lead author of the study.
The finding was recently published in Geophysical Research Letters, Holocene Aridification of India.