Geochemical patterns in sediments near offshore production platforms

Abstract

Patterns of the geochemical characteristics of sediments adjacent to three production platforms (22–150 m water
depths) in the northwestern Gulf of Mexico were determined by the presence of the structure, the amount and type of materials
discharged from the structure, and the local hydrographic setting. Sediments close to platforms (<500 m) were enhanced in
coarse-grain materials primarily derived from discharged muds and cuttings. Hydrocarbon and trace metal (Ag, Ba, Cd, Hg, Pb,
and Zn) contaminants were associated with these coarse-grain sediments. Contaminants were asymmetricallly distributed
around each platform in response to the prevailing currents. Contaminant concentrations at most locations were below levels
thought to induce biological responses. At a few locations close to one platform, trace metal (i.e., Cd, Hg) concentrations
exceeded levels thought to induce biological effects. In deep water (>80 m), sediment trace metal contaminant patterns were
stable over time frames of years. A few metals (Pb, Cd) exhibited evidence of continued accumulation in sediments over the
history of the platform.