DISTRIBUTION AND SOURCES OF POLYCYCLIC AROMATIC HYDROCARBONS (PAHS) IN THE SANTA BARBARA BASIN

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous organic pollutants originating from both natural and anthropogenic sources through petrogenic, pyrogenic, and biogenic pathways. Their persistence, toxicity, and use as a proxy to trace the anthropogenic combustion of fossil fuels make PAHs widely studied. Sediment samples from the Santa Barbara Basin were extracted and analyzed to assess PAHs using concentration distributions, diagnostic ratios, and principal component analysis (PCA). The Santa Barbara Basin hosts a complex array of PAHs from anthropogenic sources and natural sources such as oil seepages and wildfires. The high sedimentation rates (≈ 4 mm/yr near the sediment surface) combined with limited sediment redistribution produce a high-resolution sediment record that is varved down to ca. 1700 AD and laminated for at least 2500 years. In addition to varves, distinguishable terrigenous flood layers and marine turbidites were also investigated as their distinctive depositional characteristics affected the environmental fate of specific PAHs. A total of 25 parent and alkylated PAHs were identified and quantified by gas chromatography/mass spectrometry (GC/MS) in selected ion mode. Two biogenic PAHs, perylene and retene, provided the most informative concentration values. Perylene concentrations increased in depth down core dramatically in sediments dating older than 300 AD suggesting perylene creation from the in situ degradation of organic matter. However, a small increase in perylene concentrations in modern sediments from the late 1960s to the early 1970s suggests an alternative input. Increased retene concentrations in flood layers and turbidites suggest these lithologies were more effective in transporting pyrogenic PAHs and could be interpreted as a proxy for wildfires. A shift in key diagnostic ratios reveal the dominant presence of petroleum PAHs in older sediments change to a strong combustion and/or petroleum combustion signal starting in the latter half of the 20th century. PCA was the best way to elucidate a modern, anthropogenic signature from all the samples and a lithological signature of flood layers. Modern sediments showed a strong, positive relationship to principal component group one. Flood layers showed a strong relationship with principal component group two.