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Monterey Bay Studies

Monterey Bay Studies


Monterey Bay National Marine Sanctuary Project, 1999

Oil Residues on the Coastline of Monterey Bay National Marine Sanctuary

by Keith A. Kvenvolden, Frances D. Hostettler, Robert J. Rosenbauer, Thomas D. Lorenson, Paul R. Carlson, Erika J. Clesceri, Augusta Warden, and William T. Castle


Oil residues can often be observed on the shores of the Monterey Bay National Marine Sanctuary. We have undertaken a detailed organic geochemical study of several such residues and have compared our results with those obtained from nearby inland and offshore oil seeps and from produced crude oils from California. Distributions of acyclic and cyclic aliphatic hydrocarbons and carbon isotopic compositions of whole oil residues were used for the comparisons. All samples have unusually heavy carbon isotopic compositions, ranging from -21.9 to -23.7 per mil (PDB), characteristic of crude oils sourced from the Miocene Monterey Formation of California. Our coastal oil residues all contain the terpane biomarker, 28,30-bisnorhopane, a compound also characteristic of crude oil from the Monterey Formation. An inland and an offshore seep with carbon isotopic compositions of -22.0 and -22.1 per mil (PDB), respectively, are within the range of values obtained for the coastal residues; however, aliphatic hydrocarbon distributions in the seeps do not correlate well with distributions in the coastal residues. Because the coastal oil residues apparently are extensively distributed within the Sanctuary, we believe that their source is likely natural and not spilled oil products. Although we have been unable as yet to identify the specific natural sources, our geochemical results suggest that the original source is the Miocene Monterey Formation.

This abstract is from Monterey Bay National Marine Sanctuary Symposium, Sanctuary Currents '98, Human Influences on the Coastal Ocean, Poster Session, 1998.

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