Suboxic, early diagenetic processes in surficial sediments near a deepwater ocean outfall, Sydney, Australia

Abstract

Triplicate boxcores collected from three sample locations, near the Malabar deepwater ocean outfall on the continental margin adjacent to Sydney, were analysed on a total and a size-normalized basis (<63 μm fraction) to establish the extent of heavy metal enrichment. No heavy metal enrichment near the outfall is observable in total sediment samples, but an enrichment in Ag, Cu, Pb and Zn is detectable in the sediment fine fraction and in weak acid leachable bulk sediment concentrations. Trace metal profiles for the fine fraction indicate that chemical remobilization, and physical sediment mixing and resuspension influence downcore trace metal distributions. Ratios of solid and dissolved-phase porewater Fe, Mn and Cu indicate that oxidation of sewage organic matter and suboxic sulphide reduction influence dissolved-phase trace metal concentrations in sediments near the outfall. Suboxic, early diagenesis results in an increased dissolved-phase benthic flux of Cu near the outfall, with organic matter reduction likely to be the major diagenetic process.