Characteristics And Climatic Implications Of Biomarkers In Modern Soils Along North-south Transection Of East Asia And Lacustrine Sediments

Present use of fossil molecules to reconstruct paleoclimate and ancient human activities has become an important part of molecular stratigraphy. Fossil Molecules have the characteristics of stable compounds, long-time preservation and wide distribution, providing great information on climatic and environmental changes, provenience of parent materials, redox degree of organic matters, development status of bacteria and microorganisms in ancient environments, different ecology and vegetation systems, past water salinity, and thermal evolution degree of organic matter. Many types of biomarkers have been reported, such as alkanes, aromatics, alkanoic acids, alkanols, alkenones and esters. Most researches mainly focused on the category, concentration, relative abundance of biomarker compounds, and the compositions of stable isotopes such as monomer carbon, hydrogen, oxygen and nitrogen. The research areas have reached aerosol, marine sediments, lacustrine and peat sediments, glacier, ancient vegetation, loess, cave, stalagmite, and estuarine sediments (rocks). These researches show that molecular fossils should be significant in the study of modern soils, which are effective in revealing past climate change and environment conditions.China spans over 33° latitudes from north to south with large solar radiation and temperature increases. In this paper, the molecular fossils of modern soils were taken from various temperature and humidity regions in China from south to north (extended northward to part of Mongolia), and humidity-differenct regions from southeast to northwest, aiming at understanding of how some organic compounds change with climatic conditions (temperature and humidity), such as n-alkanes, n-alkyl-ketone, macrocyclic alkanes and long-chain branched alkanes. We find the predominance of main peaks of long-chain n-alkanes (nC₂₉, nC₃₁, nC₃₃) and short-chain ones (nC₁₆, nC₁₇, nC₁₈) records information of soil generation in warm num(?) and cold dry re(?) The proportion of n-alkancs (nC₁₆+nC₁₇+nC₁₈) to (nC₂₉+nC₃₁+nC₃₃) varies in good agreem ent with moisture-heat conditions and thus probably can be served as a new index for climate chan ge The ratios of C₂₁^-/nC₂₂⁺, nC₁₇/nC₃₁ and (nC₁₅+nC₁₇+nC₁₉) / ( nC₂₇+nC₂₉ +nC₃₁) of n-alka(?)e indicating respectively input ratios of lower bacterial alga, aquatic organisms, and higher pla(?)ns and terraneous organisms, co-vary well in different climate regions from forest to grassland (?) desert, suggesting that they have also reflected the difference of climates between monsoon regi(?) and inland one. The C₂₂^-/C₂₂⁺ ratio of n-alkan-2-one records largely the discrepancy of temperature from north to south of China bordered by Qinling Mountains. The C₂₁^-/C₂₂⁺ ratio of n-alkan-3-ones changes well with climatic factors , such as temperature and humidity. We calculated the proportions of the C₁₈/C₂₀/C₂₂ components for the macrocyclic alkanes and those of the C₁₉/C₂₁/C₂₃ components for the methylated macrocyclic alkanes. Based on the distribution characteristics of these biomarkers, we suggest that they record information related to climate change.The biogenic source of series A-D long-chain branched alkanes may be derived from some kinds of special epiphyte that most likely live in weak oxic-anoxic and moisture-heat environments, suggesting their distribution record as well some information on climatic change.It is useful to enlarge the deep and scope in studying environmental change by the study for change of biomarkers proxies in lacustrine layer. Abundant lipids were recognized in the lacustrine sediments of Maogou section in the Linxia Basin, including n-alkanes, isoprene and n-alkenones. The ratios of nC₂₇/nC₃₁ of n-alkanes and the predominance of main peaks of n-alkan-2-one indicatewarm-humid climate in miocene (24.6-11 Ma). The predominance of main peaks of n-alkan-2-one and the relative abundance of isoprene evidently record the drop of temperture with passage of time in 13Ma .All of climate indexes reflect the occur of dry climate in 8Ma. The ratios of (nCn-nC2i)/(nC27- nC3i), nC27/nC3i of n-alkanes and the predominance of main peaks of n-alkan-2-one indicate a passage of warm-humid climate after 8Ma. All these researches of climate in research region record commonly the climate respond of global climate change and uplift of the Tibetan Plateau, which are similar to the process of climate change with the study of inorganic proxies. These researches show that molecular fossils should be significant in the study of environment conditions of lacustrine sediments.In one word, All these researches demonstrate that the distributions of lipids molecules in modern soils of East Asian record well signals of climates from quite different climatic regions, and can be served as important climatic proxies to reveal climatic change. The parameters and indexes of molecular fossils in the Linxia Basin indicate the change of dry environment.