δ13C Values of loess total carbonate: A sensitive proxy for Asian summer monsoon in arid northwestern margin of the Chinese loess plateau

摘要

We measured carbon isotope ratio of loess total carbonates (δ~(13)Cic) from the Jingyuan loess profile in the arid northwestern portion of the Chinese Loess Plateau (CLP), in order to examine the effectiveness and sensitivity of loess total carbonate δ~(13)Cic values as a potential paleoenvironmental indicator. The δ~(13)Cic record in the loess profile shows large variations ranging from -1‰ to -7‰, during the past 70ka. The most negative δ~(13)Cic peaks coincide with paleosol formation; S_0, L_1SS_1 and L_1SS_2, which occurred under relatively wetter climatic conditions during middle Holocene and marine δ~(18)O stages 3. On the other hand, the least negative δ~(13)Cic values responded to loess accumulation during relative drier phases of LGM and marine δ~(18)O stages 4. While δ~(13)Cic variations in the loess profile in arid area demonstrate a clear correlation with changes of total organic carbon isotope (δ~(13)Coc) of bulk sediments which has been widely used as a proxy for the past monsoon precipitation intensity, the δ_(13)Cic values in the loess profile are more sensitive to the changes of paleohabitat controlled by the Asian monsoon variation in the arid area. We propose that carbon isotope compositions of total carbonates in loess profile can serve as a sensitive and reliable proxy for the Asian summer monsoon in the arid northwestern Chinese Loess Plateau.