The Lipid Biomarkers Preserved In Stalagmite And Their Potential Significance In Reconstruction Of Paleoclimate During Quaternary

Lying in the North Hemispheric Subtropical High, the middle reaches of the Yangtze, as a key passage of the East Asian monsoon, is climatologically characterized by the energy exchange between the trade wind and westerlies as well as water-vapor convergence of the Southeast and Southwest monsoons. This transitional belt may be highly susceptible to different climatic forcings. Not only has been the belt heavily effected by frequent reciprocation between the Asian winter and summer monsoons, it can also sensitively response to the interaction of seesaw-fashion shared by the Southeast monsoon and Southwest monsoon, both of which is part of the Asian summer monsoon system. As a result, it is an ideal location to study past global changes and regional sea-land coupling.The stalagmites, as the products of interactive processes among the atmosphere, hydrosphere, biosphere and lithosphere, are the most valuable geological archive for investigating the continental paleoenvironments and paleoclimates with two advantages: (1) high resolution time scales available for secondary carbonate and (2) the least possibility of alteration after deposition because of the protection of carbonate minerals. In current research developed for stalagmites, most of them focused on the inorganic constituent, but know little about the trace constituents - organic materials although it is as important as inorganics.Molecular fossils, or called biomarkers, refer to the organic compounds preserved in geological body, which have specific biological origins. This characteristic makes these compounds especially important to geochemical studies. With the progress of modern analytical technique, organic geochemists obtain much valuable information from the molecular fossils preserved in sediments in lakes or oceans, in contrast researches on molecular fossils in loess, read earth and peat are rare and no one reports his work on stalagmites.Here in this paper, a stalagmite (HS-2) collected from Heshang cave in Qingjiang Hubei was studied for reconstruction of paleoclimatic condition during the period of ca 10-21 ka B.P. . Lipid compounds were identified by gas chromatography-mass spectrometer analysis, and the abundance and distribution pattern of organic homologues were showed in mass chromatograms. The iipid extracts from this stalagmite present the mixed sources from autochthonous and allochthonous organisms. With the distribution parameters and coefficients of abundance, we attribute LMW alkanol to microbes lived in soil overlapping the cave, and HMW alkanol to land plants supported by the soil. However, the contribution to n-alkanes is too complicated to easily associate LMW series and HMW series with microbe and land plants repectively, although most of n-alkanes are transported from soil. Fatty acids, more sensitive to degradation and alteration than n?alkanol and n-alkane, are attributed to in situ microbes flourishing on stalagmite carbonates and preserved through such a long geological time with the protection from carbonate minerals.Because molecular fossils have strong ties with their biological precursors, we suggest the abundance of certain molecular fossils or the distribution pattern of organic homologues which are attributed to a common precursor can be used to distinguish different climatic condition on the basis of creature adjusting to climate. The correlation between paleoclimatic conditions indicated by organic records and those by oxygen isotopic signals prove the potential significance of the application of molecular fossils. Our work also revealed that the molecular signatures should be helpful to interpret 5 C data recovered from carbonate minerals.With the high resolution time scale constrained by the TIMS U-Th dating, we establish the phase relation between subtropical and high-latitude climate variation. The synchroneity with Greenland warming during the last deglaciation, which support evidences from Southern South China Sea and tropical Indian Ocean, while conflict with evidences from the equatorial Pac...