Vegetation response to South Asian Monsoon variations in Konkan, western India during the Late Quaternary: Evidence from fluvio-lacustrine archives

Abstract

The palaeobotanical and palynological data along with physical proxies obtained from Konkan, western India, have been addressed while ascertaining the vegetation response to monsoon variations since Late Pleistocene (∼53,000 yrs BP). The retrieved plant fossil assemblage, being a sensitive indicator of climate changes, has important implications in palaeoclimate study of the Late Pleistocene as it is the first of its kind in the entire 7500 km long coastline of India. The plant fossil assemblage of the lacustrine sediments forms potential evidence for the prevalence of wet evergreen forest in the Late Pleistocene (∼44,000 yrs BP). This scenario was attributed to prevalence of an extended period of rainfall of both the Southwest (SW) and Northeast (NE) monsoon in Konkan, although the Indian subcontinent was under the influence of active tectonic processes. Numerous fossil plant taxa are now confined to freshwater Myristica swamps of Southeast Asia in general and that of southwestern India in particular suggesting that these areas maintain a similar monsoon trend to that existing prior to 44,000 yrs BP. On the other hand, the NE monsoon did not reappear during the Early Holocene, when the SW monsoon became strong along the Konkan coast. Many of the plant species of the fossil assemblage have been displaced from Konkan as a response to weakening of the monsoons since the Late Pleistocene and towards the Last Glacial Maximum (LGM). The aridity/reduced rainfall since Late Pleistocene, including the LGM, and limited terrestrial accumulation in the Early Holocene suggests an ecological shift and subsequent replacement of evergreen forest cover and a possible break in sedimentation. Palynological evidence of the Late Holocene (<3000 yrs BP) fluvio-lacustrine sediments reveals that the evergreen forest could not reappear/rejuvenate in Konkan due to such climatic stress, in contrast to southwestern India and Sri Lanka where extended rainfall was still prevalent. The hypothesis of an extended period of monsoonal rains prior to 44,000 yrs BP in the present humid tropical parts of Konkan holds significance, as data on paleosols and vertebrate fossils from the semi-arid/arid parts of western India indicate relatively wet climate and wetland flood plains.