Carbon isotopic studies of individual lipids in organisms from the Nansha sea area, China

Carbon isotopes of individual lipids in typical organisms from the Nansha sea area were measured by the GC-IRMS analytical technique. δ13C values of saturated fatty acids in different organisms examined are from 25.6‰ to 29.7‰ with the average values ranging from 26.4‰ to 28.2‰ and the variance range of 1.8‰ between different organisms is also observed. Unsaturated fatty acids have heavy carbon isotopic compositions and the mean differences of 2.9‰–6.8‰ compared to the same carbon number saturated fatty acids. δ13C values of n-alkanes range from 27.5‰ to 29.7‰ and their mean values, ranging from 28.6‰ to 28.9‰, are very close in different organisms. The mean difference in δ13C between the saturated fatty acids and n-alkanes is only 1.5‰, indicating that they have similar biosynthetic pathways. The carbon isotopic variations between the different carbon-number lipids are mostly within ±2.0‰, reflecting that they experienced a biosynthetic process of the carbon chain elongation. At the same time, the carbon isotopic genetic relationships between the biological and sedimentary lipids are established by comparative studies of carbon isotopic compositions of individual lipids in organisms and sediments from the Nansha sea area, which provides scientific basis for carbon isotopic applied research of individual lipids.

Lipid Evidence for Oil Depletion by Sulfate-Reducing Bacteria during U Mineralization in the Dongsheng Deposit

Fatty acids were extracted from fluid inclusions, and analyzed for distribution and individual 613C values to determine if there exists sulfate-reducing bacteria （SRB） and what substrates SRB depleted during U mineralization in the Dongsheng deposit. The 10-methylhexadecanoic acid （10Mel6：0） has been detected from most of the samples using GC-MS based on relative retention time and co-injection of standard 10Me16：0 compound. Samples with higher 10Me16： 0 concentrations, show higher U contents. The presence of 10Mel6：0 along with iso-ω7-cis-heptadecenoic acid （i17：1ω7c） and ω7-cisoctadecenoic acid （18：1ω7c） in the fluid inclusions may indicate the occurrence of SRB during the U mineralization. Saturated fatty-acids and unsaturated fatty-acids detected in this study have individual δ^13C values from-30.3‰ to-28.5‰ and-30.5‰ to-27.9‰, respectively. These values are close to those of n-alkanes of the associated oils and the bulk oils, but significantly distinct from methane, thus the oils are concluded to have been used as substrate for the microorganisms to survive on. This proposal is supported by oil biodegradation and ore-stage calcite cement with δ^13C values from-1.4‰ to-17.2‰.