Variability and environmental significance of organic carbon isotopes in Ganzi loess since the last interglacial on the eastern Tibetan Plateau

Abstract

The stable carbon isotope composition of total organic matter (δ13Corg) in loess deposits has been widely used as a valuable proxy for reconstructing terrestrial paleovegetation. Aeolian loess is widely distributed on the high Tibetan Plateau (TP); however, little is known about the variability and paleoenvironmental implications of the δ13Corg of Tibetan loess. We conducted detailed δ13Corg and total organic carbon analyses of the Ganzi loess sequence on the eastern TP since the last interglacial (LIG). Our results indicate that the δ13Corg values of loess during glacial periods were lower than those during interglacial periods, with more negative values associated with the cold stages since the LIG on the eastern TP. The reconstruction of vegetation from the δ13Corg data indicated that C3/C4 mixed vegetation was dominated by C3 vegetation, and that the relative abundance of C4 vegetation during the glacial stages was much lower than that during MIS 5 and MIS 3. The high relative abundance of C4 plants during MIS 5 and MIS 3 suggested an increased proportion of C4 plants during the warm period. Since the LIG, the change in the abundance of C3/C4 vegetation in the Ganzi region has been mainly controlled by climate change at the glacial–interglacial scale. The combined effect of temperature, precipitation, and atmospheric CO2 caused changes in the paleovegetation on the eastern TP.