Signatures of Holocene Hydrological Processes from Sedimentary Archives in Southwestern India: Case Studies from Wetlands of Kerala Coast

The subsurface sediments of the Kerala coast provided signatures of hydrological processes that have influenced in the modifications and conversion of larger part of the lowland and the forest cover into a major wetland system during the Holocene which in turn has transformed into one of the best carbon sinks in the Indian subcontinent. The most significant and well recognized signature is the paleoflood event during the Early to Middle Holocene coinciding with the Holocene Climate Optimum (HCO). The excessive rainfall seems to have flooded the entire forest area in the coastal plains and the forests that flourished in the abandoned river channels and other low-lying areas in the midland. Formation of peat and peat land development in the inland region, but not far away from the coast, towards the Middle Holocene has been another important imprint of the hydrological process. Occurrence of peat sequence of 1-3 m at shallower depths stands testimony to such episodes. The other recognized imprints include the erosion and reworking of older sediments that contain the Neogene pollen elements and development of bay head deltas and other alluvial deposits in the mouth of the rivers. The mangrove dynamics too provided sufficient evidence of their prevalence, stability and decreasing tendency depending up on the hydrological regimes during the Holocene. Though episodes related to mud bank formation, as of now, are restricted to recent times, sediment archives, dated as Late Holocene, revealed scope for decoding the signatures of hydrological and geological processes associated with the monsoon vicissitudes.