A section through the Dharamjali stalagmite that the authors studied
Newswise —
Recent investigation carried out by Cambridge University has revealed proof — preserved within an aged stalagmite extracted from a cave in the Himalayas — of multiple extended and severe droughts that could have caused the downfall of the Bronze Age Indus Civilization.
The commencement of this dry spell — commencing approximately 4,200 years ago and extending for more than 200 years — corresponds with the restructuring of the city-developing Indus Civilization that encompassed current Pakistan and India.
The investigation distinguished three prolonged dry spells — each lasting from 25 to 90 years — throughout this parched period. "We discover explicit confirmation that this duration was not a brief emergency but a gradual alteration of the environmental circumstances in which the Indus population resided," affirmed Professor Cameron Petrie, co-author of the study and part of Cambridge's Department of Archaeology.
The scientists mapped out past precipitation patterns by scrutinizing growth strata in a stalagmite procured from a cave adjacent to Pithoragarh, India. By gauging various environmental markers — such as oxygen, carbon, and calcium isotopes — they acquired a representation demonstrating the corresponding rainfall during specific seasons. Furthermore, they employed Uranium-series dating techniques of great accuracy to determine the timing and length of the arid periods.
"Numerous indications enable us to assemble the characteristics of these dry spells from different perspectives — and verify that they align," stated Alena Giesche, the study's primary author, who carried out the study while pursuing her doctorate in Cambridge's Department of Earth Sciences.
Giesche and her colleagues distinguished discrete intervals of substandard precipitation in both the summer and winter seasons. "The proof of drought affecting both planting seasons is exceedingly meaningful for comprehending the influence of this epoch of climatic transformation on human societies," commented Petrie. He also mentioned that the dry spells during this duration extended for longer durations, to the extent that the third one would have lasted for multiple generations.
The outcomes reinforce the current proof that the deterioration of the Indus metropolises was connected to shifts in climate. "However, what remained puzzling up until this point was knowledge of the duration of the droughts and the specific seasons during which they occurred," Giesche explained. "That additional information is genuinely vital when we reflect on cultural recollection and how people adjust to environmental changes."
As Petrie put it: "The archaeological proof reveals that throughout a two-century period, the early occupants adopted several measures to adjust and sustain their lifestyle amid this fresh reality." In the course of this transformation, more sizable urban regions were deserted in preference for less populous rural establishments located towards the eastern frontier of the territory inhabited by Indus communities. Concurrently, cultivation was modified to depend more on summer crops, especially drought-resistant millets, and the populace shifted to a lifestyle that appeared to be more autonomous.
David Hodell, a co-author of the study from Cambridge's Department of Earth Sciences, explains that megadroughts have recently been widely cited to account for various cultural changes, including those in the Indus Valley. "However, the connections are typically vague due to the challenges of comparing climatic and archaeological data," he said. This situation is now changing because "paleoclimate records are becoming increasingly advanced in pinpointing alterations in precipitation on a seasonal and yearly basis, which have a direct impact on people's choices," Hodell added.
The team is now planning to widen their climate reconstructions to the western territories of the Indus River Region, where the winter rainfall system becomes more significant than the Indian Summer Monsoon. "What we really require are additional records like this, from a west-to-east aligned stretch across the region where the summer and winter monsoons intermingle - and, most importantly, covering the onset of this dry period," said Giesche.
Prof Sebastian Breitenbach, co-author and palaeoclimatologist at Northumbria University, pointed out that "we presently have a significant knowledge gap on our maps spanning across Afghanistan and Pakistan, where the Indian summer monsoon and the Westerlies overlap." He further stated that "unfortunately, the current political climate is unlikely to allow for this type of research in the near future."
David Hodell, the study's co-author from Cambridge’s Department of Earth Sciences, believes that there is still a lot of work that needs to be done by both palaeoclimatologists and archaeologists. He stated, "We are fortunate to have the two departments situated next to each other here in Cambridge."
The TwoRains Project, which was funded by the European Research Council (ERC) and is a collaboration between Cambridge and Banaras Hindu University, has been focused on answering the question of how the interaction of different rain zones affected the Indus Civilization.
RSS