Leaf wax n-alkane distributions in Chinese loess since the Last Glacial Maximum and implications for paleoclimate

Leaf wax n-alkanes have been recently introduced into loess deposits for paleovegetation and paleoclimate reconstruction. However, the paleoclimate significance of some n-alkane parameters such as chain-length ratios (L/H, C-27/C-31, C-29/C-31, and (C-27 + C-29)/(C-31 + C-33)) remains to be clarified. In order to evaluate the validity of those proxies in loess deposits, leaf wax n-alkanes were analyzed from a northwest-southeast transect on the Chinese Loess Plateau since the Last Glacial Maximum (LGM). The n-alkanes show a bimodal distribution between C-14 and C-33 with Carbon number maxima (C-max) at C14 or C-16, and at C-31 or C-33, indicative of both terrestrial plant and microbial origin. L/H variations are in good agreement with climate changes both temporally and spatially, i.e. the higher L/H ratio the warmer and wetter climate and vice versa. Therefore, the L/H ratio in Chinese loess can serve as an efficient proxy for paleoclimate. By comparing long-chain n-alkane ratios with pollen records, we suggest that the generally used woody plant proxies (C-27 and C-29) and grass proxies (C-31 and C-33) are not applicable to Chinese loess. As the Chinese Loess Plateau was dominated by herbs in both the LGM and the Holocene, the long-chain n-alkane ratios may mainly reflect changes in the species composition of local vegetation. For a better understanding of leaf wax n-alkanes in Chinese loess, further studies are required to investigate the n-alkane distributions in both the major plant species and their associated surface soils on the Chinese Loess Plateau. (C) 2015 Elsevier Ltd and INQUA. All rights reserved.