A 2700-year high resolution pollen record of climate change from varved Sugan Lake in the Qaidam Basin, northeastern Tibetan Plateau

摘要

A 2700-year high resolution pollen record from annually-varved Sugan Lake in the Qaidam Basin at 2793. m a.s.l was obtained to examine vegetation and climatic change on the NE Tibetan Plateau. Pollen data shows that Sugan Basin was constantly covered by open desert-steppe vegetation dominated by Chenopodiaceae, Artemisia, Poaceae and Ephedra. However, large variations in Artemisia/Chenopodiaceae (A/C) ratios suggest regional moisture fluctuations over the last 2700. years, including a dry and relatively stable climate prior to 300. AD, relatively wet climate from 300 to 1200. AD with variability during 1100-1200. AD, and unstable climate since 1200. AD with relatively moister climate during 1250-1400. AD and 1700-1800. AD. However, other proxies (varve thickness, Chironomid taxa, isotopes of oxygen in precipitated carbonate) show fresher water when regional moisture was lower inferred from A/C ratio. This inconsistency suggests the possible difference of in-lake lithology/environment and regional moisture change. Fresh water into the lake from ice melting on the surrounding mountains might have contributed to the in-lake lithology and environment variation. The effective moisture changes in the Basin are in opposite phases to snow accumulation records from Dunde ice core (5325. m a.s.l) and to the monsoon intensity inferred from Dongge Cave, suggesting that the regional topography might have played an important role in mediating moisture changes at regional scale. Pollen data from Sugan Lake shows the shift of moisture at 1200. AD, from stable to variable conditions. This event is well correlated with other paleoclimate proxies in China and other parts of the world; however, the mechanisms behind these patterns require further investigation.