Origins of lipid biomarkers in Santa Monica Basin surface sediment: A case study using compound-specific Δ~(14)C analysis

摘要

Compound-specific Δ~(14)C values are reported for 31 different lipid biomarker molecules obtained from Santa Monica Basin and Santa Barbara Basin surface sediments. These organic compounds represent phytoplanktonic, zooplanktonic, bacterial, archaeal, terrestrial higher plant, and fossil carbon sources. The lipid classes include the following: long-chain n-alkanes, fatty acids (as methyl esters; FAMEs), n-alcohols, C_(30) midchain ketols and diols, sterols, hopanols and C_(40) isoprenoid side chains from the ether-linked glycerols of Archaea. The data show that the carbon source for the majority of the biomarkers is marine euphotic zone primary production or subsequent heterotrophic consumption of this biomass. A small amount of benthic incorporation of ~(14)C-depleted dissolved inorganic carbon was identified for the bacterial hopanols and C_(15) linear and branched-chain fatty acids. However, there is no apparent uptake of ~(14)C-depleted dissolved inorganic carbon in Santa Monica Basin by the bacteria, including filamentous Beggiatoa spp., that produce C_(18:1ω7) fatty acid. Two of the lipid classes did not reflect carbon originally fixed by marine photoautotrophs. These were the n-alkanes, for which the Δ~(14)C data are consistent with mixed fossil carbon and contemporary terrestrial higher plant sources, and the archeal isoprenoids, for which the Δ~(14)C data are consistent with chemoautotrophic growth below the euphotic zone.