干旱区生态环境知识资源中心

Pookode Lake, Kerala, South India, a fresh water lake situated at an altitude of similar to 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 C-14 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 C-14 BP (similar to AD 650 cal.). The sediments older than 1500 C-14 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 C-14 BP (BC 4786-AD 1434 cal.) but this was interrupted by short, intense wet phases between similar to 3900 and similar to 1900 (similar to BC 4000-similar to AD 300 cal.), similar to 1400-similar to 760 (similar to AD 800-similar to AD 1200 cal.), and similar to 420-similar to 140 C-14 BP (similar to AD 1570-similar to 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. (C) 2013 Elsevier Ltd and INQUA. All rights reserved.