Hydrocarbon geochemistry of the Puget Sound region—I. Sedimentary acyclic hydrocarbons

Hydrocarbon compositions have been determined for ²¹⁰Pb-dated sediment cores collected at 23 sites within the inland marine waters of northwestern Washington State, U.S.A. Concentrations of total aliphatic hydrocarbons (TAH) and an unresolved complex mixture (UCM) are significantly higher in surface sediments near urban areas than at all other locations with a chronology that indicates a predominantly anthropogenic origin. Concentrations of chromatographically resolvable alkanes are comparatively uniform; the major constituents are plant wax n-alkanes and a naturally-occurring suite of fossil isoprenoid and n-alkanes. Pristane concentrations decrease sharply near the sea-sediment interface suggesting rapid degradation of a plankton-derived component. A saturated multibranched, but nonisoprenoid, C₂₀ hydrocarbon and two novel mono-olefinic analogs have been isolated along with a previously unreported suite for four acyclic multibranched C₂₅ polyenes. Structural and distributional similarities between the C₂₀ and C₂₅ multibranched hydrocarbons suggest that they may be structurally homologous and share a common source.