Py-GC/MS Analysis Method for Aliphatic Biomarker in Desert Lake Sediment and Its Application in Paleoclimatic Study

Methylene chain backbone compounds (MCCs) in lake sediments are sensitive to climate change, and changes in environmental conditions could promote the transformation of MCCs lipids between free and bound states, hence providing a series of biomarkers for paleoclimate reconstruction. In previous studies, free MCCs lipids were typically extracted by mixed solvents, bound MCCs lipids with chemical bonding or physical adsorption could not be obtained by organic solvent extraction, and the indicator information of the characteristics of bound components on paleoclimate change was missing.

To study the suitable analytical conditions for bound MCCs lipids, and establish proxy based on bound MCCs lipids to provide an effective tool for paleoclimate reconstruction of terrestrial ecosystems.

Optimized analytical method of pyrolysis gas chromatography-mass spectrometry (Py-GC/MS) was established and used to evaluate the bound MCCs in typical Desert Lake sediment.

Total of 71 bound MCCs compounds were identified and analyzed based on fine characterization of organic matter composition in the sediments of the Yiheshariwusu Lake in Inner Mongolia. Pyrolysis temperature was the main factor affecting the distribution characteristics of bound MCCs in sediment. Low pyrolysis energy under 450℃ led to insufficient resolution of bound MCCs. At 550℃ and 650℃, total bound n-alkanes, n-alkenes, and n-alkan-2-ones were on-line separated, identified and analyzed. The average chain length characteristics of bound n-alkanes at 550℃ and the carbon isotope of free n-alkanes as a traditional climate substitute index δ¹³C_27-33 had the best correlation (R=0.83, n=11, p < 0.01).

Proxy ACL_25-31 of bound n-alkanes respond to the change characteristics of regional effective precipitation, identify the drought periods around 5.6ka and 3.9ka in the region, reflect the intensity change of East Asian summer monsoon, and correspond to the change of effective precipitation in the mid-latitude of the northern hemisphere.