Holocene climate dynamics and ecological responses in Kaas Plateau, Western Ghats, India: Evidence from lacustrine deposits

The Kaas lake is one of the unique sedimentary basins in the Northern region of the Western Ghats escarpment of India and preserves paleoclimate signals of the Holocene in its cover sequence over the lateritic basement. The signatures preserved in the lacustrine deposits, such as pollen, non-pollen palynomorphs, diatoms, and geochemistry of the sediments, were decoded and used to reconstruct the Holocene environmental changes of the Kaas Plateau in the Western Ghats. The main stages in the lake's evolution indicate the following: (1) low nutrient level and strongly changeable water levels in the early Holocene, (2) persistence of the oligotrophic state of the lake up to the last 2000 yr, and (3) strong cultural eutrophication of the lake in the recent period (c. 1000 years). The localized depression or a seasonal-lake favoured freshwater accumulation since 8.0 kyr BP and was probably dried sometimes after 2.0 kyr BP. A late Holocene peak of planktonic diatom and high organic recovery at the top level in the recent past (c. 1000 years) represents an event of eutrophication, possibly due to human impact. Being a seasonal lake, the plateau surface allowed clay accumulation with an extremely slow rate of 2.5 cm/10 kyr. Diatoms, pollen, and non-pollen palynomorphs together showed periodic fluctuations in lake hydrology, which was probably in response to climate-controlled vegetation on the Kaas Plateau. The diatom and sediment anomalies point to an ecological shift towards the mid–Holocene, supporting the hypothesis of increased Southwest Monsoons during the early Holocene around 8.0 kyr BP and the relative weakening of Northeast Monsoon after 2.5 kyr BP.