DISTRIBUTIONS OF N-ALKENES IN PEAT CORE RELATED TO PALEOCLIMATE CHANGE in HONGYUAN PEATLAND

This peat sedimentary sequence was systematically investigated with lipid molecular stratigraphy by gas chromatography-mass spectrometer (GC-MS). A variety of molecular fossils are found in this peat profile, including n-alkanes, n-alkanols and n-fatty acids and so on. The n-alkenes are from C₁₈ to C₂₈, hav-ing a maximum at C₂₇, with s second dominance at C₂₃ or C₂₅. In contrast to the n-alkenes analysed, the n-alkanes are characterized by the dominance of heavy-molecular-weight homologues (>C₂₂) at the same depth. According to the analysis, we found the high carbon number n-alkenes possibly are mainly derived from higher plants, while algae and microorganisms are secondly. The ratios of low molecular number to high molecular number n-alkenes(∑C₂₁^-/∑C₂₁⁺) and the ratios of n-alkenes to the corresponding carbon number n-alkanes such as C_24:1/C_24:0 and C_23:1/C_23:0 show the regular variations. ∑C₂₁^-/∑C₂₁⁺ has the same trend as the ratios of low molecular number to high molecular number n-alkanes (L/H-ALK) on the whole; on the contrary, C_24:1/C_24:0 and C_23:1/C_23:0 have an opposite trend. These results indicate n-alkenes especially these middle carbon number n-alkenes give microbial hydrogenation under the reductive condition resulting from the climatic change such as temperature. The results show n-alkenes proxies seem to bear significant climate information and possibly indicate temperature changes in the northeastern Qinghai-Tibet Plateau during the Holocene. In addition, (C₂₆ +C₂₇ +C₂₈)/(C₂₃+C₂₄ +C₂₅) n-alkene ratios display a defi-nite corresponding relationship with the vegetation in the region, possibly suggesting these n-alkenes not only have a relationship with the vegetation, but also are capable of microbial degradation of different vege-tation species. Climatic information from these n-alkens proxies is consistent with previous paleoclimate signals extracted from n-alkanes, n-alkanols and n-fatty acids of the same peat profile. These indicate n-al-kenes proxies can be an important proxy for studying the paleoclimate and global change.