The Tibetan Plateau (TP) is primarily influenced by the northern hemispheric middle latitude Westerlies and the Indian summer monsoon (ISM). The extent, long-distance effects and potential long-term changes of these two atmospheric circulations are not yet fully understood. Here, we analyse modern airborne pollen in a transition zone of seasonally alternating dominance of the Westerlies and the ISM to develop a pollen discrimination index (PDI) that allows us to distinguish between the intensities of the two circulation systems. This index is applied to interpret a continuous lacustrine sedimentary record from Lake Nam Co covering the past 24 cal kyr BP to investigate long-term variations in the atmospheric circulation systems. Climatic variations on the central TP widely correspond to those of the North Atlantic (NA) realm, but are controlled through different mechanisms resulting from the changing climatic conditions since the Last Glacial Maximum (LGM). During the LGM, until 16.5 cal kyr BP, the TP was dominated by the Westerlies. After 16.5 cal kyr BP, the climatic conditions were mainly controlled by the ISM. From 11.6 to 9 cal kyr BP, the TP was exposed to enhanced solar radiation at the low latitudes, resulting in greater water availability.

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 km² and catchment area of 10 610 km². 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 ¹⁴C 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 CaCO₃ 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'.