Environmental evolution and southwest monsoon changes in mid-Holocene recorded by lake sediments in Erhai Lake

Abstract

IN recent years, much progress has been made in the research of the temporal and spatial changes of East Asian monsoon[1s ' I . To research the environmental evolution and monsoon variations in Holocene in the region of Southwest China, a 310-cm continuous lake sediments core in Erhai Lake, Yunnan Province was sampled with Livingston sampler on July 6, 1996. The lake sediments were separated at 2-cm intervals and the core samples were analyzed with chronology, stable isotope ratios of organic carbon and diatoms determination. Three 14C ages are ( 4 473 + 40) a B. P. (98-102 cm) , (5 825 + 85) a B. P. (144-148 cm) and (7 754 + 45) a B. P . (198-202 cm) . By 137Cs dating, the sedimentation rate is about 0 . 3 mm/a and this result is close to the 14c dating results. The average sedimentation rates indicate that the core samples of 0-210 cm stand for the past 8 . 1 ka sedimentation. Here we first present the environmental evolution and southwest monsoon changes recorded by lake sediments from Erhai Lake, Yunnan Province in mid-Holocene (8.1-3.0 ka B. P. ) . This period coincided with the Holocene Megatherma1 period in East Asian monsoon. The stable isotope ratios ( 6 13c) of organic carbon are related to the source of organic carbon in lake