Holocene monsoon and sea-level variability from coastal lowlands of Kerala, SW India

Abstract

The widespread Early Holocene sea-level rise observed along the global coastal realms reinvigorated the need to decipher sea-level variability on a local and regional scale, yet limited attempts were made on simultaneously addressing sea-level and climate variability. The southwest coast of India is endowed with several geomorphic features providing cues on the paleosea-level and climate variability engrossed with its sedimentary sequence in the lowlands. In view of this, the present study aims to decipher the Holocene sea-level and climate variability based on geochemical and palynological proxies supported by 10 AMS radiocarbon ages on a 32 m long sediment core (L7) raised from Upper Kuttanad Kole wetlands (Kuttoor), Kerala, Southwest India.The study demonstrated high sea-level along with warm and wet climate due to Indian summer monsoon (ISM) intensification during 9.69–7.56 ka corroborating with the Holocene Climate Optimum (HCO). However, a break in the sediment deposition is observed between 7.56 and 3.51 ka, the reason for which is yet to be fully understood. During 3.51–2.55 ka, the gradual weakening of ISM has been invoked with an intermittent monsoon spell during 3.20–3.40 ka. After 2.55 ka the sediment core records occurrence of coarser clastics indicating sediment deposition by the migrating distributary channel of the Pamba-Manimala rivers. The high sea level during HCO attests that the core location plausibly represented the southward extension of the Vembanad lagoon which transformed into part of the terrestrial system due to the gradual sea regression during the mid-late Holocene period followed by deposition of alluvial sediments from the hinterland rivers.