Weathering and the fallout plume of heavy oil from strong petroleum seeps near Coal Oil Point, CA. Academic Article uri icon


  • The Coal Oil Point (COP) seeps offshore Goleta, CA, are estimated to release 20-25 tons of oil daily, providing an ideal natural laboratory to investigate the fate of oil in the coastal ocean. To address the long-term fate of COP oil, we collected 15 sediment samples down current from the seeps and quantified petroleum content and individual biomarkers using traditional and comprehensive two-dimensional gas chromatography. Similarities in the distributions of hopane biomarkers link the oil in the sediments to fresh seep oil (n=5) and underlying reservoirs (n=3), although sediment oil is heavily weathered. The spatial distribution of oil forms a plume along the continental shelf that we suggest represents a chronic fallout pattern for heavy oil from the persistent surface slicks; average surface currents appear to modulate the distribution of the fallout over a period of 0.4-5 days. The extent of hydrocarbon loss is consistent for all sediments, indicating a common limit to oil weathering with contributions from evaporation, biodegradation, and dissolution. Considering the amount of oil and quantity of sediment impacted, we estimate a sediment oil burden of 0.3 x 10(12) to 3 x 10(12) g in the study area, equivalent to 8-80 spills of the Exxon Valdez accident of 1989.

publication date

  • May 15, 2009