Climatic and environmental controls of organic carbon accumulation on the California continental margin: A comparison of deep and shallow sites in the Late Quaternary Santa Barbara Basin

The Late Quaternary record of Santa Barbara Basin presents a unique opportunity for testing the relative importance of different environmental criteria for the preservation of organic carbon. Two piston cores from central/deep (569 m) and marginal/shallow (481 m) sites are located within and above the intermediate water mass, and record more consistently dysoxic and consistently oxygenated settings, respectively. Samples were analyzed at 20 cm (∼140 yr) increments for total organic carbon (TOC), CaCO3, C/N ratios, grain size and mass accumulation rates (MARs) of TOC and CaCO3. Comparison between the cores and paleoceanographic records show that anoxia was not a prerequisite for enhanced organic matter preservation. Covariation between C/N ratios and TOC or its MAR during cold, oxygenated intervals imply that TOC increased with the proportion of terrigenous vs. marine organic matter. During times of warmth and higher sea level, TOC increased when the C/N ratio became more marine in character.; There are notably similar gross stratigraphic trends between the two cores for all data sets, yet significance differences exist, indicating that local environmental controls are important in the preservation of organic matter. Both TOC profiles display asymptotic curves that decrease with depth with little variation lower in the core in spite of changes in laminations and benthic foraminiferal populations. MD2504, the shallow core, has sediments that are primarily coarser and organic components that are more marine in composition (including shell fragments). MD2503, the deep core, primarily has very fine-grained sediments originally deposited by the Santa Clara River that were winnowed off of the shelf by currents, removing the material, and redepositing them in the central basin. (Abstract shortened by UMI.)...