Changes in vegetation and environment in Yamzhog Yumco Lake on the southern Tibetan Plateau over past 2000 years

Abstract

High-resolution palynological analyses of the sediment of Yamzhog Yumco Lake can potentially provide new insight into vegetation change and climate dynamics of the southern Tibetan Plateau over the past 2000 years. The chronology, presented herein, is based on 210Pb and AMS 14C dates from the macro-remains of plants. Reconstruction of vegetation types, temperature and moisture indices indicate that the vegetation was alpine meadow, under relatively wet and cool conditions, from approximately 100 to 780 CE Later, the vegetation between approximately 780 and 1400 CE was alpine steppe, with a warmer and drier climate prevailing during the Medieval Warm Period (MWP). Then, the vegetation during the period from approximately 1400 to 1890 CE reverted back to alpine meadow, under relatively cold and moist climate conditions, which may have corresponded to the Little Ice Age (LIA). Since the 20th century, an alpine steppe has dominated the landscape, developed under a dry climate with a lower effective moisture. Climate records from Yamzhog Yumco Lake have confirmed a cold-moist/warm-dry climate oscillation on the southern Tibetan Plateau over the past 2000 years. Comparison of pollen records with other climatic records suggests that the climate changes in the southern Tibetan Plateau were generally similar to those in the northern Tibetan Plateau, as well as those in westerly-dominated Central Asia. Additionally, climate patterns were found to be the opposite of those in the East Asian monsoon controlled region. The temperature variations inferred from the records correlate well with changes in the solar irradiance and Northern Hemispheric temperature, which suggests a possible link between solar forcing and climate variabilities over the last 2000 years on the southern Tibetan Plateau. In addition, the enhancement and southward shift of the westerlies is determined to have significantly contributed to the high moisture conditions on the southern Tibetan Plateau during the LIA.