A recent press release from IIT Kharagpur, India, dated July 06, 2023, highlights a groundbreaking discovery made by scientists from IIT Kharagpur and Academia Sinica, Taipei. The research team has found compelling evidence of triple oxygen isotopes in intertrappean fossil woods, indicating exceptionally high annual rainfall during the catastrophic volcanism eruption of the Deccan Traps, which took place approximately 66 million years ago. This massive volcanic event led to the extinction of nearly 80% of all animal species, including the dinosaurs. The study's findings suggest a substantial increase in tropical rainfall, reaching 1600 mm per year, on the island of India during the terminal Cretaceous period.
Advertisement
Prof. Anindya Sarkar of Geology and Geophysics at IIT Kharagpur, who led the research, stated, "The Deccan Trap lavas erupted all across central and western India, releasing massive amounts of CO2 from the Earth's deep interior. This increased the atmospheric CO2 concentration to as high as 1000 ppm. Land and ocean temperatures rose by approximately 13°C and 4°C, respectively, creating an extremely hot and inhospitable environment. Surprisingly, the rainfall patterns remained relatively unaffected both before and after this high CO2 phase. This ancient scenario serves as an analogue for what our future greenhouse earth might become."
The study also highlights the alarming increase in CO2 emissions from fossil fuels, which have raised the atmospheric CO2 concentration to around 420 ppm in 2023. Climate models indicate that a doubling of CO2 levels will intensify atmospheric circulation and result in increased rainfall. However, experts warn that the rapid rate of global warming and climate change may have irreversible consequences, potentially leading to another mass extinction event.
Advertisement
The Intergovernmental Panel on Climate Change's (IPCC) 2023 AR6 report projects a manifold increase in annual wettest day precipitation across all continents if CO2 emissions and global warming continue unabated. Monsoonal precipitation associated with tropical cyclones over India is predicted to increase by 40%. These predictions, derived from climate models, can only be validated through the study of past rainfall records during natural warming phases with high CO2 emissions.
To analyze the past rainfall, the research team utilized a novel technique involving laser beams and NanoSIMS (Nanoscale Secondary Ion Mass Spectrometry) to examine the oxygen isotopes within fossilized trees found in the sediments of the intertrappean lakes. This method allowed them to infer the isotopic composition of the lake water derived from rainfall. The results showed a remarkable preservation of the cellular structures in these fossil trees, resembling those of modern trees.
The study sheds light on the significance of understanding past precipitation in a high CO2 and warmer global climate, as interpretations and predictions from climate models often vary due to insufficient data from the geological past. By analyzing intertrappean sediments from the Deccan Traps, which covered over 500,000 sq. km of the Indian subcontinent, the researchers gained insights into the magnitude of tropical precipitation during the enhanced greenhouse period of the Cretaceous era.
Prof. Sourendra Bhattacharya, a co-author of the study, emphasized the implications of the findings, stating, "Our data suggests that these fossil trees recorded annual rainfall of 1800-1900 mm, compared to the modern average of 1000-1200 mm over large parts of peninsular India. These findings align precisely with the IPCC's predictions for extreme warming scenarios, where the planet experiences a 4°C increase."
