Organic matter reactivity and sedimentation rates in the ocean

Tóth, D.; Lerman, Abraham

doi:10.2475/ajs.277.4.465

Cited by 166 publications

(67 citation statements)

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“…6a) imply a somewhat lower organic matter processing efficiency at low oxygen levels. First-order degradation rate constants for oxic and anoxic degradation both show a significant relationship with the square of sediment accumulation rates (Toth and Lerman, 1977;Reimers and Suess, 1983), but with an offset between oxic and anoxic degradation. This offset might suggest more efficient mineralization under oxic conditions, but this interpretation has been questioned because of differences in methodology and differences in the age of the material degraded (Middelburg et al, 1993).…”

Section: The Effect Of Bottom-water Oxygen On Sedimentary Organic Mattermentioning

confidence: 99%

Coastal hypoxia and sediment biogeochemistry

2009

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Abstract. The intensity, duration and frequency of coastal hypoxia (oxygen concentration <63 µM) are increasing due to human alteration of coastal ecosystems and changes in oceanographic conditions due to global warming. Here we provide a concise review of the consequences of coastal hypoxia for sediment biogeochemistry. Changes in bottomwater oxygen levels have consequences for early diagenetic pathways (more anaerobic at expense of aerobic pathways), the efficiency of re-oxidation of reduced metabolites and the nature, direction and magnitude of sediment-water exchange fluxes. Hypoxia may also lead to more organic matter accumulation and burial and the organic matter eventually buried is also of higher quality, i.e. less degraded. Bottom-water oxygen levels also affect the organisms involved in organic matter processing with the contribution of metazoans decreasing as oxygen levels drop. Hypoxia has a significant effect on benthic animals with the consequences that ecosystem functions related to macrofauna such as bio-irrigation and bioturbation are significantly affected by hypoxia as well. Since many microbes and microbial-mediated biogeochemical processes depend on animal-induced transport processes (e.g. re-oxidation of particulate reduced sulphur and denitrification), there are indirect hypoxia effects on biogeochemistry via the benthos. Severe long-lasting hypoxia and anoxia may result in the accumulation of reduced compounds in sediments and elimination of macrobenthic communities with the consequences that biogeochemical properties during trajectories of decreasing and increasing oxygen may be different (hysteresis) with consequences for coastal ecosystem dynamics.

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Section: The Effect Of Bottom-water Oxygen On Sedimentary Organic Mattermentioning

confidence: 99%

Coastal hypoxia and sediment biogeochemistry

2009

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“…A rough proportionality between net sedimentation rate and depth-integrated sulfate reduction was found by modeling sulfate gradients for a wide range of sediment types (Toth & Lerman 1977). The overall mineralization of organic matter, however, gradually shifts from sulfate reduction toward aerobic respiration with decreasing sedimentation rates (e.g.…”

Section: Introductionmentioning

confidence: 99%

Anaerobic mineralization in marine sediments from the Baltic Sea-North Sea transition

Jørgensen¹,

Bang²,

Blackburn³

1990

Mar. Ecol. Prog. Ser.

161

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Mineralization was studied withln the upper 2 m of sediments from the Belt Sea, Kattegat, and Skagerrak at 15 to 200 m water depth. Radiotracer measurements of sulfate reduction rates were related to porewater chemistry (SO,'-, HC03-, P O~~-, NH4+, H2S, and CH,), to solid-phase chemistry (C, S , N, and Fe), and to bacterial distributions. Sulfate penetrated 0.9 to > 3 . 5 m into the sediment. Sulfate reduction rates decreased > 100-fold from m a m a of 6 to 74 nmol cm-3 d-' at the surface to between 0.1 and 1 nmol cm-3 d-' at 1 to 2 m depth. Between 8 and 88 O/O of the total, depth-integrated sulfate reduction took place within the uppermost 0 to 15 cm of the sediment. Maxlma of sulfate reduction or bacterial densibes at the sulfate-methane transition indicated a zone of anaerobic methane oxidation 0.8 to > 2.5 m below the surface. The fraction of the iron pool, which was bound in pyrite, was 17 to 42 %, even in the presence of > 1 mM H2S. Only 4 to 32 % of the H2S produced from sulfate reduction was permanently buried as FeS2 while the rest was reoxidized. Sediment accumulation rates determined from 'I0pb age determinations were 0.3 to 6.2 mm yr-'. The total deposition of organlc carbon, determined from the sum of organic C mineralized by aerobic and anaerobic respiration plus net burial of organic C, was 16.7 to 52.3 mm01 m-' d-'. This was equivalent to about 50 % of the primary productivity in the water column. The net burial rates of organic C were 1.5 to 26 mm01 m-' d-' corresponding to 9 to 50 ' % of the deposited organic C. The bunal of pyritic sulfur corresponded to 9 to 37 O/u of the reducing equivalentes buried as organic C.

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“…In laboratory studies of bacterial sulfate reduction, the magnitude of the instantaneous fractionation between sulfate and sulfide is inversely proportional to the rate of sulfate reduction (Goldhaber and Kaplan, 1974). The rate of sulfate reduction is positively correlated with the sedimentation rate and with the organic carbon accumulation rate (Toth and Lerman, 1977;Berner, 1978;Canfield, 1991), suggesting that variations in the latter could result in deviation of the Leg 129 IW data from that of organic-rich sediments. For example, movement of a site from a low-productivity zone into a higher productivity area (e.g., equatorial zone) would result in an increased rate of deposition of organic carbon, greater sulfate reduction rates, and consequently lower isotopic fractionation.…”

Section: Discussionmentioning

confidence: 97%

Sulfur in Pacific Deep-Sea Sediments (Leg 129) and Implications for Cycling of Sediment in Subduction Zones

Alt¹,

Burdett²

1992

Proceedings of the Ocean Drilling Program

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The mineralogy of S-bearing phases, S-contents, and S-isotopic compositions of sediments and interstitial waters were determined for three cores drilled during Leg 129 in the western Pacific. Pelagic clays, chalks, and radiolarites generally contain 350-1200 ppm S, with essentially all S present as sulfate. Volcanogenic turbidite units contain about 400 ppm S, with about 10%-20% of total sulfur as pyrite-S and the remainder as sulfate. A single claystone from the base of Hole 802A has high pyrite-S content (1200 ppm) and contains a component of metalliferous sediment. The single analyzed chert has the highest sulfur content (4020 ppm) with essentially all sulfur present as pyrite-S. Sulfate in pore waters ranges from seawater concentrations to nearly zero, and has δ 34 S values ranging from seawater values (+20‰) to slightly enriched in 34 S (+28‰). Pyrite sulfur has 34 S values of -4.8‰to -37. l‰ These general trends are attributed to bacterial reduction of seawater sulfate, but the data do not fit simple models for downward diffusion of sulfate or closed-system reduction of buried sulfate. These complications are due to variations in the δ 34 S of seawater sulfate in the past, uptake of sulfate by thaumasite (Ca3Si(OH) 6 CO 3 Sθ4-12H 2 O) without isotopic fractionation in the Unit II tuff in Hole 802A, the presence of cherts that act as barriers to diffusion, and possible variations in the magnitude of isotopic fractionation during bacterial sulfate reduction.The average sediment from Leg 129 contains around 850 ppm S (85% as sulfate, 15% as sulfide), with a bulk δ 34 S of+12‰ The bulk sulfur isotopic composition of deep-sea sediment is highly dependent on the proportion of pyrite-sulfur present, which varies depending on the sedimentary environment and history. The sedimentary sulfur component during subduction thus likely varies from near seawater values (+20‰) to possibly strongly negative values (-20‰).

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Organic matter reactivity and sedimentation rates in the ocean

Cited by 166 publications

References 0 publications

Coastal hypoxia and sediment biogeochemistry

Coastal hypoxia and sediment biogeochemistry

Anaerobic mineralization in marine sediments from the Baltic Sea-North Sea transition

Sulfur in Pacific Deep-Sea Sediments (Leg 129) and Implications for Cycling of Sediment in Subduction Zones

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