Environmental changes since 8.4 ka reflected in the lacustrine core sediments from Nam Co, central Tibetan Plateau, China

The Tibetan Plateau induces and enhances the Asian monsoon that influences the plateau itself, East China and even the whole of Asia. Pursuing the changing monsoon history and its impact in this environment-sensitive area is a key for understanding the climatic changes. Here, we present the initial results from core sediments in Nam Co, central Tibet, to elucidate the Holocene environment changes in this area. The studied lake (Nam Co) is the second largest lake, with an elevation of 4718 m, water area of 2015 km 2 and catchment area of 10 610 km 2 . By using echo-seismic profiling and hydro-echosounding, we investigated the bathymetric distribution of the whole lake. One 332 cm long PISTON core was successfully taken in the east part of the lake at 60 m water depth. Twelve AMS 14 C dates from top to bottom of this core established a good time sequence. TOC, TN, n-alkanes, grain size, clay minerals, Fe/Mn, Sr/Ba and CaCO 3 content were analysed with sampling intervals from 1 cm to 10 cm. Results showed that since 8400 yr BP, the environment changes in this region indicate three stages. The early stage (8400—6900 yr BP) was characterized by slight shifting from warm to cold with a cold-dry interval at 8100—7800 yr BP. The middle stage was from 6900 to 2900 yr BP, during which climate changed from warm-humid to cold-dry. However, around 2900 yr BP, the climate once was slightly cold but strongly dry. The late stage, from 2900 yr BP to present, was characterized by a general tendency toward cold-dry: the first temperature decline was around 1700—1500 yr BP, following which temperature increased once, before decreasing again around 600—300 yr BP, which might be the result of the `Little Ice Age'.