现代环境研究室知识库

Knowledge of late Holocene precipitation variability in the northwestern Yunnan Province is important for understanding the Indian summer monsoon (ISM) dynamics. In this study, we present a proxy record of the ISM precipitation history at Lake Lugu covering the last 2,900 years based on grain size and carbon/nitrogen (C/N) ratio in the northwestern Yunnan Province. The results show centennial variations in ISM precipitation, with two remarkably dry intervals from 750 to 1167 AD and from 1733 AD to the present and two relatively wet intervals from 898 BC to 750 AD and from 1167 to 1733 AD. A comparison between the record at Lake Lugu and the pollen record at Lake Erhai (both in the northwestern Yunnan Province) suggests that dry climate conditions prevailed during the Medieval Warm Period (MWP) and over the last 100-200 years, whereas relatively humid conditions prevailed during the Little Ice Age (LIA). These characteristics are generally similar to those of the climate patterns in extensive areas dominated by the ISM (e.g., southwestern-southern China, southeastern-southern Tibetan Plateau, northeastern India Himalayas, southern Oman, and equatorial eastern Africa), but anti-phased with the climate patterns in the wide areas dominated by the East Asian summer monsoon (EASM) (e.g., northern-northeastern China and north-central Japan). We speculate that both the variations in the sea surface temperature (SST) over the tropical Indo-Pacific Ocean, the ocean atmosphere coupling processes and the migration of the mean position of the Intertropical Convergence Zone (ITCZ) should be responsible for the hydroclimatic contrasts over the Asian summer monsoon (ASM) region on centennial timescales during the last 2,000 years. (C) 2015 Elsevier B.V. All rights reserved.