Moisture and vegetation variations in the extremely cold-dry area of the Tibetan Plateau during the past 5000 years

Climate change on the Tibetan Plateau (TP) and its response to the atmosphere circulation has been widely concerned. The extremely cold-dry area of the central-northern TP is vulnerable and particularly sensitive to the variations of Indian Summer Monsoon (ISM) and the Westerlies. However, records from the central-northern TP are still scarce, limiting our understanding of the natural variability of climate on the TP and its response to the atmosphere circulation. Here we present a high resolution palynological record from Buruo Co covering the last 5000 years. The palynological assemblage shows that the Artemisia-steppe predominated the Buruo Co region until it was replaced by the alternant domination of steppe and desert since 900 cal a BP. Our results show that the central-northern TP experienced relatively warm and humid conditions reflected by Artemisia-steppe before 3800 cal a BP linked with stronger ISM. And then, the vegetation variation reveals a stepwise long-term aridification on the central-northern TP, which was influenced by the gradually weakened ISM during 3800–3200 cal a BP. Subsequently, the strengthened dry Westerlies dominated this region since 3200 cal a BP. After 1000 cal a BP, the Buruo Co might slightly expanded, but the catchment still maintained relatively dry conditions, even though this region probably received small amount of external moisture supply under the low evaporation conditions. Besides, four drought intervals (4400–4100, 3850–3650, 3300–3000 and 1900–1400 cal a BP) and two relatively cold periods (3200–2800 and 400 cal a BP-Present) were detected. The climate and vegetation variations since mid-Holocene on the central-northern TP were mainly controlled by the summer insolation at 30°N and the solar activity. Also, it was associated with the position of Intertropical Convergence Zone and the climate oscillations of the North Atlantic mediated by the synergistic effect of ISM and the Westerlies.