The role of anoxia in organic matter preservation in coastal sediments: relative stabilities of the major biochemicals under oxic and anoxic depositional conditions

Abstract

Sediment trap and core samples from two coastal environments, Dabob Bay (Washington State) and Saanich Inlet (British Columbia), which differ primarily in terms of bottom-water O 2 concentrations, were analysed for organic carbon, total nitrogen, amino acids, neutral sugars and lignin phenols. Comparison of these sites provides a test of the effects of anoxia on the preservation of sediment organic matter (OM). Biochemical compositions indicate lower concentrations of terrigenous OM in Saanich Inlet than in Dabob Bay. The benthic interface is an important site of diagenesis in both cases, with similar patterns of selective degradation. Although absolute reactivities at the benthic interface are consistently higher in Dabob Bay (oxic) than in Saanlich Inlet (anoxic), burial efficiencies for all measured OM components are indistinguisable under the two different regimes. Collectively, these results indicate that O 2 availability ultimately has little or no independent effect on OM preservation in these environments.