A multi-proxy reconstruction of monsoon variability in the late Holocene, South India.

Abstract: Pookode Lake, Kerala, South India, a fresh water lake situated at an altitude of ∼770 m.a.s.l., receives predominantly rains from the south-west monsoon. A sediment core 125 cm long was investigated for sediment texture, dating and geochemical composition. Radiocarbon dates obtained on the organic carbon rich sediments of the Pookode Lake range in age from the mid-Holocene to more recent (6240–565 14C BP; BC 4786 to AD 1434 cal.). Geochemical data of the sediment cores were corroborated with phytolith and pollen studies. Although phytoliths occur in the entire sediment core, pollen assemblages start occurring only since 1500 14C BP (∼AD 650 cal.). The sediments older than 1500 14C BP were not suitable for the preservation of the pollen assemblages. There is a major change in the lake hydrology, indicating lacustrine conditions subsequent to 1500 BP. Occurrence of diatoms in the upper sediment layers of the sediment core indicates shallowing of the lake. Both the Medieval Warm Period (MWP) and the Little Ice Age (LIA) are represented in the Pookode Lake sediment core. Sediment texture, chemical weathering intensity (CWI) values supported by phytolith and pollen assemblages, indicate that overall warm and dry conditions prevailed during 6200–420 14C BP (BC 4786–AD 1434 cal.) but this was interrupted by short, intense wet phases between ∼3900 and ∼1900 (∼BC 4000–∼AD 300 cal.), ∼1400–∼760 (∼AD 800–∼AD 1200 cal.), and ∼420–∼140 14C BP (∼AD 1570–∼ AD 1860 cal.). The wet events resulted from the strengthening of south-west monsoon (SWM) causing rising water levels and brief expansion of the Pookode Lake margin. [Copyright &y& Elsevier]