Compilations have been made of sulfate reduction rates and oxic respiration rates over the entire range of marine sedimentation rates, and sedimentary environments, including several euxinic sites These data show, consistent with the findings of Jorgensen (1982, Nature, 296, 643-645), that sulfate reduction and oxic respiration oxidize equal amounts of organic carbon in nearshore sediments As sedimentation rates decrease, oxic respiration, becomes progressively more important, and in deep-sea sediments 100-1000 times more organic carbon is oxidized by oxic respiration than by sulfate reduction By contrast, nearly as much organic carbon is oxidized by sulfate reduction in euxinic sediments as is oxidized by the sum of sulfate reduction and oxic respiration in normal marine sediments of similar deposition rate This observation appears at odds with the enhanced preservation of organic carbon observed in euxinic sediments However, only small reductions in (depth-integrated) organic carbon decomposition rates (compared to normal marine) are required to give both high organic carbon concentrations and enhanced carbon preservation in euxinic sediments Lower rates of organic carbon decomposition (if only by subtle amounts) are explained by the diminished ability of anaerobic bacteria to oxidize the full suite of sedimentary organic compounds

Sulfate reduction and oxic respiration in marine sediments: implications for organic carbon preservation in euxinic environments

Chemical processes at the sediment-water interface.

Amino acid analyses were performed on a suite of potential organic matter sources to coastal marine environments. They yielded no source-indicati.ve compositional parameters, but microbes produced markedly higher carbon-normalized yields than did vascular plant tissues. Sediment trap samples collected monthly for a year at 30 and 60 m in Dabob Bay, Washington, were also analyzed, as were subsamples from a sediment core taken at the same site. Amino acid yields from the trap samples exhibited spring and fall maxima that coincided with blooms, and a winter minimum that resembled yields in underlying sediments. Amino acids in all samples were primarily of marine origin and low yields in winter traps resulted from low planktonic production, selective amino acid loss, and resuspension of amino acid-depleted sediments. Nonprotein amino acid levels and the fraction of total N represented by amino acids are indices of diagenetic alteration. Amino acids accounted for 13-37% of the total 0rgani.c C and 30-8 1% of the total N in the 30-m samples, and, on average, 10 and 37% of sedimentary C and N. Midwater amino acid fluxes also displayed a winter minimum and spring and fall maxima; they were more pronounced than fluxes of bulk particles or C, due to a lesser influence of resuspension. On average, -80% of the total midwater particulate amino acid flux was lost prior to incorporation in surface sediments. Amino acids were degraded selectively and represented 35 and 7 1% of the C and N remineralized at the benthic interface. The labile fraction closely resembled fresh plankton in its amino acid composition and carbon-normalized yield. Although trapping of poisoned zooplankton may have caused some artificially high amino acid yields, diagenesis was apparently the primary control on calculated reactivities. Among the amino acids, reactivity patterns indicated relative preservation of diatom cell-wall protein. Within the sediments, amino acids were again degraded preferentially relative to organic C and N, but no downcorc compositional changes were observed. Midw.ater and sediment burial fluxes ofplanktonic amino acids represented, respectively, - 13 and 2.5% of annual mean amino acid production by primary producers.

https://aslopubs.onlinelibrary.wiley.com/doi/pdf/10.4319/lo.1992.37.4.0703

Sources and reactivities of amino-acids in a coastal marine-environment

Sediment trap and net plankton samples were collected monthly for a year at three depths in a marine bay (Dabob Bay, Washington). These materials and subsamples from a sediment box core were analyzed for lignin oxidation products as well as elemental and stable carbon isotope compositions. The sediment core was compositionally uniform over its entire 50-cm length. The elemental and lignin compositions of the sediment trap and core samples indicate nitrogen-rich (atomic C : N = 7.5) plankton-derived organic matter mixed with vascular plant debris. At most, vascular plant debris accounts for 10% (nonwinter months) to 35% (winter months) of the total organic carbon in the upper water column (30 m) sediment trap samples and consists predominantly of gymnosperm wood along with some nonwoody gymnosperm tissues and angiosperm woods. Bulk land-derived organic matter in Dabob Bay contains a maximum of 50% vascular plant debris and comprises an average of one-third of the total organic carbon in the sediment trap samples and two-thirds of the total organic carbon in the underlying sediments. Lignin in the sediment trap and core samples shows evidence (from elevated vanillic acid:vanillin ratios) of white-rot fungal degradation before (but not after) introduction to the water column at the study site. Vascular plant debris introduced to the bay has already lost almost half of its initial bulk polysaccharide. Glucose yields are particularly low whereas rhamnose and fucose are obtained in excess of expected yields and must have additional sources. Lignin and neutral sugars together account for ~20% of the total organic carbon in the sediment trap and core samples. Overall, the sediments of Dabob Bay compositionally resemble the gymnosperm wood-rich particulate material introduced to the overlying water column during winter and poorly record the input of plankton and other types of vascular plant debris during nonwinter months.

https://aslopubs.onlinelibrary.wiley.com/doi/pdf/10.4319/lo.1988.33.5.1116

Organic matter sources to the water column and surficial sediments of a marine bay

A database containing published rates of sediment and pore-water transport and biogeochemical transformations has been established to derive empirical predictive equations to calibrate and parameterize global diagenetic models. Rates of sediment accumulation, organic carbon burial, organic matter decomposition via aerobic and anaerobic pathways and bioturbation (in terms of bioturbation coefficients) can be predicted quite well using exponential relationships with water depth as an independent variable. The relationships are corrected for skewness to reduce the bias inherent in the back transformation from a lognormal to an arithmetic estimate. 
 
Bioturbation is shown to be the dominant mode of sediment transport in the upper centimeters of oceanic sediments. The derived empirical relationships are combined with bathymetric maps to estimate globally integrated rates of benthic processes. Ocean margin sediments account for about 85% of the materials accumulating in the ocean and about 80–90% of the mineralization in marine sediments.

J.T. Bennett

Papers

210Pb-derived sediment accumulation and mixing rates for the greater Puget Sound region

Mixing and cycling of uranium, thorium and 210Pb in Puget Sound sediments