A new study that traced the dynamics of Indian Summer Monsoon Rainfall (ISMR) over the 10000 years

A new study that traced the dynamics of Indian Summer Monsoon Rainfall (ISMR) over the 10000 years

Subject :Geography

Section : Atmosphere

Context: Regions surrounding northern Bay of Bengal (BoB) received higher precipitation than the other parts of India for the last 10200 years, says a new study that traced the dynamics of Indian Summer Monsoon Rainfall (ISMR) over the 10000 years

Concept:

• The Bengal Basin or the ‘Bengal region’ being located at the trajectory of the Bay of Bengal (BoB) branch of the ISM is very sensitive to changes in the ISM strength.
• Even a minor change in ISM strength may have adverse effects on the agrarian-based socioeconomic conditions of the region.
• However, no systematic long-term record (beyond the range of instrumental period) for the past ISM variability in the region was available.
• BSIP, an autonomous institute of 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 predates instrumental records (records taken before 19th Century).

The evolution of ISM:

• In the hydro-climatic history of the last 10.2 ka (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 – 5.6 ka by this region and the ISMR decreased since 4.3 ka.
• The ISM again got strengthened between 3.7 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 one, and had adverse impact of the ecosystem.

The inferences from the study

• The period witnessed the development and fall of numerous ancient civilizations around the world, many of which were associated with climate instability.
• They explored the drivers influencing the variability of the monsoon in the Indian part of the Bengal Basin and found that while the millennial-scale variations in the ISM rainfall may largely be attributed to changes in solar insolation and dynamics of Inter tropical Convergence Zone (ITCZ— area where the northeast and the southeast trade winds converge), the centennial scale variations may be collectively triggered by phenomena like North Atlantic Oscillation, El Nino Southern Oscillation and Indian Ocean Dipole.
• 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 Lake Ecosystem were strongly influenced by the ISM rainfall.