Abstract:
Compound-specific carbon isotopic (δ13C and Δ14C) data are reported for lipid
biomarkers isolated from Santa Monica Basin (SMB) and Santa Barbara Basin (SBB)
surface sediments. These organic compounds represent phytoplanktonic, zooplanktonic,
bacterial, archaeal, terrestrial, and fossil carbon sources. The lipids include long-chain
n-alkanes, fatty acids (as FAMEs), n-alcohols, C30 mid-chain ketols and diols, sterols,
hopanols, and ether-linked C4o-biphytanes of Archaea.
The data show that the carbon source for most of the biomarkers is marine
euphotic zone primary production or subsequent heterotrophic consumption of this
biomass. Two lipid classes represent exceptions to this finding. Δ14C values for the
n-alkanes are consistent with mixed fossil and contemporary terrestrial plant sources.
The archaeal isoprenoid data reflect chemoautotrophic growth below the euphotic zone.
The biomarker class most clearly representing marine phytoplanktonic production is the
sterols. It is suggested, therefore, that the sterols could serve as paleoceanographic
tracers for surface-water DIC.
The isotopic data are used to construct two algebraic models. The first calculates
the contributions of fossil and modem vascular plant carbon to 5MB n-alkanes. This
model indicates that the Δ14C of the modern component is +235% (post-bomb) or 0%
(pre-bomb). The second model uses these values to determine the origin of sedimentary
TOC. The results are comparable to estimates based on other approaches and suggest
that ~60% of SMB TOC is of marine origin, modern terrestrial and fossil sources
contribute ~10% each, and the remaining ~20% is of unknown origin.
