A Record of Vegetation Change in Chinese Loess Plateau Inferred From Biomarker Study

A knowledge of the response of terrestrial vegetation to climate change in the past is central to the construction of global carbon budgets, and to the prediction of the terrestrial biosphere response to anthropogenically forced climate change in the future. The Chinese loess-paleosol sequence constitutes an important record of variation in Asian monsoon climate during the past. Long-chain n-alkanes are biomarkers from high plants and thus can reflect vegetation cover. The typical loess profile in central Chinese Loess Plateau was sequentially sampled at 10cm interval for 5m, in order to understand the relationship between vegetation (type and biomass) and climate during the past 40k years. There is significant difference in the concentration of n-alkanes between Holocene and last glacial. Total alkane concentration is higher in marine stage 3 samples than in last glacial maximum (LGM) and Holocene samples. Individual n-alkane presents even clearer clue. n-C31 concentration is significantly higher in stage 3 samples than LGM and Holocene samples. n-27, 29 and 33 has the same trend but with less variation. It was argued that the Chinese loess plateau experienced wet weather during stage 3. Our data seems to support it. n-alkane concentration is low in LGM samples, related with the cold and dry weather. The variation of n-alkane concentration in Holocene samples may be due to anthropogenic intervention. ACL (average chain length) shows high value in last glacial. It may be related with differential preservation of long-chain alkanes. CPI (carbon preference index) also has a higher value in last glacial but show variation. The ratio of n-C33/n-C32 is obviously higher in last glacial. The primary result is encouraging. Further work on the carbon isotopes of individual n-alkanes will help trace the C3/C4 vegetation change during the last 40ka.