Late Pleistocene-Holocene monsoon variations on climate, landforms and vegetation cover in southwestern India: An overview

Signatures of monsoon variability preserved in the Late Quaternary sediments of southwestern India have been decoded and addressed using biological proxies along with geochronological data. Barring sediments beyond the threshold for conventional 14C dating, Late Pleistocene sequences have been recognized both in Konkan and Kerala basins. Konkan area has only subsurface continental/lacustrine Late Pleistocene, whereas Kerala coast has mixed facies. The landscape as well as the vegetation cover has been substantially modified and the fossil contents and related palaeoenvironment provided ample evidence to demonstrate the landscape and vegetation dynamics since Late Pleistocene. Evidence of Myristica swamps until Late Pleistocene and its subsequent replacement by riparian forest towards Late Holocene in Konkan has been a significant impact of monsoon variations on the tropical rain forests. The prevalence of such freshwater swamps and a sensitive habitat indicated that Konkan had enjoyed an extended period of rainfall due to the combined effects of both SW and NE monsoons until the Late Pleistocene. The tropical rainforest cover along Kerala coast has shrunken considerably and pieces of evidence suggest that the entire terrain west of Sahyadri (Western Ghats) was under dense forest cover during the Holocene Climatic Optimum (9.0-6.0 k yrs BP) when the region had witnessed heavy precipitation much higher than that of the present. The forest land has been converted into major wetlands and present ecology is unsuitable to support evergreen forests and it can be concluded that coastal plains and associated landforms were covered by thick tropical evergreen forests which got destroyed by flooding towards Middle Holocene. Development of a chain of wetland system all along Kerala coast, loss of sheltered habitat and mangrove cover, and loss of sensitive freshwater Myristica swamps are some of the significant aspects brought in while addressing the monsoon variability in southwestern India.