Artemisia/Chenopodiaceae ratio from surface lake sediments on the central and western Tibetan Plateau and its application

Artemisia and Chenopodiaceae are the two main pollen taxa in studies of lake sediments on the central and western Tibetan Plateau (TP). In this paper, we present Artemisia/Chenopodiaceae (A/C) ratios in pollen assemblages of surface sediments from 42 lakes on the central and western TP. Relationships between vegetation, climate and A/C ratio are investigated. The results show that the A/C ratio in the study region can distinguish desert from steppe vegetation. As a whole, the A/C ratio was higher than 1.2 in the steppe vegetation and lower than 1.2 in the desert vegetation zone. Statistical analysis revealed that the A/C ratio can be used as a moisture indicator on the TP. Based on the A/C ratio in pollen assemblages of sediment core TAN12-2 from Lake Tangra Yumco, we reconstructed the vegetation and climate history of the southern TP during the transitional period from the late glacial to the Holocene (17.5-10 cal kyr BP). From 17.5 to 16 cal kyr BP, desert vegetation occurred and climate was extremely dry. During 16-15 cal kyr BP, desert was replaced by steppe vegetation and climate became wetter. From 15 to 10 cal kyr BP, the lake basin of Tangra Yumco was covered by the steppe vegetation and climate tended to be more humid. Comparing our results with other lacustrine records on the TP, we found that the Indian summer monsoon (ISM) significantly affected the southern TP earlier than the northeastern TP.