Changes of provenance of loess deposits in Nyingchi, southeastern Tibetan Plateau: Implications for paleoclimates since the last glacial

Abstract

Paleoenvironmental conditions on the southeastern Tibetan Plateau (TP) during the last glacial period are still unclear. Here, we present a loess record (LZP) in the Yarlung Zangbo River (YZR) valley of the southeastern TP, extending over the past 33 ka. Based on grain size, magnetic susceptibility, major and trace elements, sources of loess during different periods were discriminated. Combined with bulk biogeochemical properties (TOC and δ13Corg), as well as comparisons to regional paleoclimate records, the paleoclimate and environmental implications of the LZP loess were further revealed. During 33.4–24.5 ka and 8.4–0.5 ka, loess deposits were mainly derived from nearby river valley while undergoing a relatively strong Indian summer monsoon (ISM). The period of 24.5–15.4 ka witnessed a notable decrease in the contribution of nearby sources and an increase in the contribution of distant materials. The dramatic changes in loess provenance may be due to the development of a paleo-dammed lake in the YZR valley, coupled with the impact of a weak ISM. The sediment contribution of nearby sources increased during 15.4–8.4 ka due to shrinkage or disappearance of the paleo-dammed lake and enhanced ISM. Furthermore, four warmer and wetter events occurred at 31–29 ka, 26.8–25 ka, 22.3–21 ka and 15.5–14 ka were revealed by the LZP record and correspond to enhanced ISM. Our research indicates the complex responses of loess deposits in the southeastern TP to global climate change and local environmental events.