Study traces higher rainfall in northern Bay of Bengal than in other parts of India for last 10,000 years

New Delhi: Regions surrounding the northern Bay of Bengal (BoB) received higher precipitation than the other parts of India for the last 10,200 years, said a new study that traced the dynamics of the Indian Summer Monsoon Rainfall over 10,000 years.

Agriculture in India is heavily dependent on the Indian Summer Monsoon Rainfall (ISMR). According to the Ministry of Science and Technology, the Bengal Basin or the 'Bengal region' being located at the trajectory of the Bay of Bengal branch of the ISMR is very sensitive to changes in the ISMR strength. Even a minor change in its strength may have adverse effects on the agrarian-based socioeconomic conditions of the region. However, no systematic long-term record (beyond the range of the instrumental period) for the past ISM variability in the region was available.

The BSIP, an autonomous institute of the Department of Science and Technology (DST), for the first time, reconstructed the history of the ISM variability from this region by using both biotic and abiotic proxies that predate instrumental records (records taken before 19th century). In the hydro-climatic history of the last 10,200 years of the Bengal region published in the journal "Palaeogeography, Palaeoclimatology, Palaeoecology", a team of scientists show that a heavy ISMR was witnessed during 10.2 ka-5.6 ka by this region and the ISMR decreased since 4.3 ka. The ISM again got strengthened between 3.7 ka and 2.1 ka following which it switched to a drier mode for some time.

The ISM regained its strength during 0.2-0.1 ka. Of the weakened phases, weakening around 4.3 ka was the most severe, and had an adverse impact on the ecosystem.

The study can help understand long-term trends of climate change impact on the ecosystem and may help mitigate future climate extremities.

The scientists collected sediment samples from the bed of a dried lake in the northern part of the Bengal Basin and standard techniques were followed for building the age-depth model of sedimentary sequence and measuring different palaeo- climatological parameters. They also compared the proxy-based results with a few palaeo-model outputs from the Palaeo Modelling experiments for different time spans to validate the results of this study. The numerical models provided insights into the spatio-temporal dimensions of climate change and helped analyse the dynamic relations between different climatic components under specific boundary conditions. Combining these datasets, they investigated the timing, regional coherence and causes of Holocene ISM variability in the Bengal region.

Focusing on monsoonal variability in the Indian part of the Bengal Basin, the scientists combined both biotic (phytoliths, NPPs and stable carbon isotopes) and abiotic (environmental magnetic parameters, and grain size data) proxy data to understand the ecosystem response to past hydroclimatic changes. They inferred that changes in the Lake Ecosystem were strongly influenced by the ISM rainfall.