Origins of lipid biomarkers in Santa Monica Basin surface sediment: A casestudy using compound-specific Delta C-14 analysis

Compound-specific Delta C-14 values are reported for 31 different lipid bio marker molecules obtained from Santa Monica Basin and Santa Barbara Basin s urface sediments. These organic compounds represent phytoplanktonic, zoopla nktonic, bacterial, archaeal, terrestrial higher plant, and fossil carbon s ources. The lipid classes include the following: long-chain n-alkanes, fatt y acids (as methyl esters; FAMEs), n-alcohols, C-30 midchain ketols and dio ls, sterols, hopanols, and C-40 isoprenoid side chains from the ether-linke d glycerols of Archaea. The data show that the carbon source for the majori ty of the biomarkers is marine euphotic zone primary production or subseque nt heterotrophic consumption of this biomass. A small amount of benthic inc orporation of C-14-depleted dissolved inorganic carbon was identified for t he bacterial hopanols and C-15, linear and branched-chain fatty acids. Howe ver, there is no apparent uptake of C-14-depleted dissolved inorganic carbo n in Santa Monica Basin by the bacteria, including filamentous Beggiatoa sp p., that produce C-18:1 omega7 fatty acid. Two of the lipid classes did not reflect carbon originally fixed by marine photoautotrophs. These were the n-alkanes, for which the Delta C-14 data are consistent with mixed fossil c arbon and contemporary terrestrial higher plant sources, and the archaeal i soprenoids, for which the Delta C-14 data are consistent with chemoautotrop hic growth below the euphotic zone. Copyright (C) 2001 Elsevier Science Ltd .