Branched aliphatic alkanes of shell bar section in Qarhan Lake,Qaidam Basin and their paleoclimate significance

Biomarkers of paleolake deposits from Qarhan Salt Lake in Qaidam Basin,northwest China were sys-tematically analyzed and the A―C series compounds of branched aliphatic alkanes with quaternary substituted carbon atom(BAQCs) were identified. The homologous distinguished three series,A―C,were identified as 5,5-diethylalkanes,6,6-diethylalkanes and 5-butyl,5-ethylalkanes series,and their relative abundance was A > B > C. Series A and C were characterized by odd carbon numbers,whereas series B was characterized by even carbon numbers. The high values of series A corresponded with the high values of series B and C. Therefore,it can be concluded that series A,B and C possess a similar biological origin. The abundance of series A was relatively low in the lower part of the section compared with that in the upper part,implying that these series originated from bacteria and/or algae more prevalent in fresh-mesohaline water,and such kinds of bacteria and/or algae are most likely to be thermophilous species. The A25/nC25 ratio differences in the section show that such branched aliphatic alkanes can be treated as one kind of environmental change proxy for paleolake evolution and may provide important information for the climate reconstruction of the Late Pleistocene.

Difference in Tree Growth Responses to Climate at the Upper Treeline: Qilian Juniper in the Anyemaqen Mountains

Three ring-width chronologies were developed from Qilian Juniper （Sabina przewalskii Kom.） at the upper treeline along a west-east gradient in the Anyemaqen Mountains. Most chronological statistics, except for mean sensitivity （MS）, decreased from west to east. The first principal component （PC1） Ioadings indicated that stands in a similar climate condition were most important to the variability of radial growth. PC2 Ioadings decreased from west to east, suggesting the difference of tree-growth between eastern and western Anyemaqen Mountains. Correlations between standard chronologies and climatic factors revealed different climatic influences on radial growth along a west-east gradient in the study area. Temperature of warm season （July-August） was important to the radial growth at the upper treeline in the whole study area. Precipitation of current May was an important limiting factor of tree growth only in the western （drier） upper treeline, whereas precipitation of current September limited tree growth in the eastern （wetter） upper treeline. Response function analysis results showed that there were regional differences between tree growth and climatic factors in various sampling sites of the whole study area. Temperature and precipitation were the important factors influencing tree growth in western （drier） upper treeline. However, tree growth was greatly limited by temperature at the upper treeline in the middle area, and was more limited by precipitation than temperature in the eastern （wetter） upper treeline.