Using ammonium pore water profiles to assess stoichiometry of deep remineralization processes in methanogenic continental margin sediments

Burdige, David J.; Komada, Tomoko

doi:10.1002/ggge.20117

Cited by 15 publications

(11 citation statements)

References 71 publications

(162 reference statements)

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“…These and all variables used in the model equations are defined in Table 2. This model is based on a similar model presented in Burdige and Komada (2013), although there are four fundamental changes to the model presented here.…”

Section: Description Of the Model A Equations And Numerical Solutionsmentioning

confidence: 99%

“…The biogeochemical reactions included in the model are listed in Table 1. With the exception of ACP, the kinetic expressions used in the model for these processes have been described previously (Burdige and Komada 2013).…”

Section: Description Of the Model A Equations And Numerical Solutionsmentioning

confidence: 99%

“…The ratio of the basal methane flux to the DIC flux (J lbM /J lbDIC ≈ 4.5; see Table 4) would argue against the predominance of a deep biogenic source because such a deep source should result in a flux ratio close to 1, based on the stoichiometry of methanogenesis in Table 1. Although methane derived from a decomposing hydrate source is expected to have little accompanying DIC (see discussions in Burdige and Komada 2013), an upward flux of thermogenic methane not associated with a currently decomposing hydrate is also expected to have little accompanying DIC (Snyder et al 2007). However, the nonzero value of the upward ammonium flux (J lbA ) argues against thermogenic methane production because at the temperatures of thermogenic methane production, ammonium is unstable and reacts with CO 2 to form methane and N 2 (Zhu, Shi, and Fang 2000).…”

Section: A Carbon Budget For Sbb Sediments and The Significance Ofmentioning

confidence: 99%

“…However, the nonzero value of the upward ammonium flux (J lbA ) argues against thermogenic methane production because at the temperatures of thermogenic methane production, ammonium is unstable and reacts with CO 2 to form methane and N 2 (Zhu, Shi, and Fang 2000). Little ammonium is also expected to accompany a methane flux from a decomposing deep hydrate (Burdige and Komada 2013). However, if we assume that the methane, DIC, and ammonium fluxes are initially the result of a deep biogenic source, and that the low DIC flux is the result of some accompanying deep uptake process, the total carbon remineralized by such a deep biogenic source should be roughly two times the upward methane flux (∼2J lbM ).…”

Section: A Carbon Budget For Sbb Sediments and The Significance Ofmentioning

confidence: 99%

“…In past work, we examined the impact of such deep methane fluxes on pore-water profiles in SMB sediments (Burdige and Komada 2011) and the relationship between these deep methane fluxes and upward fluxes of other remineralization end products such as dissolved inorganic carbon (DIC) or ammonium (Burdige and Komada 2013). Here we extend our examination of these processes using an expanded version of the reaction-transport (RT)…”

Section: Introductionmentioning

confidence: 99%

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Carbon cycling in Santa Barbara Basin sediments: A modeling study

Burdige¹,

Komada²,

Magen³

et al. 2016

J Mar Res

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The primary input of organic matter to almost all marine sediments comes from deposition at the sediment surface. However, in many continental margin settings, reduced carbon can also be added to sediments from below-for example, from "deep" geologic hydrocarbon reservoirs derived from ancient source rocks or from the decomposition of deeply buried gas hydrate deposits. To examine the impact of these two differing reduced carbon inputs on sediment biogeochemistry, a modified reaction-transport model for anoxic marine sediments is described here and applied to data from sediment cores in Santa Barbara Basin to a depth of 4.6 m. Excellent model fits yield results consistent with previous studies of Santa Barbara Basin and other continental margin sediments. These results indicate that authigenic carbonate precipitation in these sediments is not centered around the sulfatemethane transition zone (SMTZ), as is seen in many other sedimentary environments but occurs at shallower depths in the sediments and over a relatively broad depth range. Sulfate profiles are linear between the surface sediments (upper ∼20 cm) and the top of the SMTZ (∼105 cm) giving the appearance of refractory particulate organic carbon (POC) burial and conservative sulfate behavior in this intermediate region. However, model results show that linear profiles may also occur when high rates of sulfate reduction occur near the sediment surface (as organoclastic sulfate reduction [oSR]) and in the SMTZ (largely as anaerobic oxidation of methane) with low, but nonzero, rates of oSR inbetween. At the same time, linearity in the sulfate profile may also be related to downward pore-water advection by compaction and sedimentation plus a decrease with depth in sulfate diffusivity because of decreasing porosity. These model-determined rates of oSR and methanogenesis also result in a rate of POC loss that declines near-continuously in a logarithmic fashion over the entire sediment column studied. The results presented further here indicate the importance of a deep methane flux from below on sediment biogeochemistry in the shallower sediments, although the exact source of this methane flux is difficult to ascertain with the existing data.

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Section: Description Of the Model A Equations And Numerical Solutionsmentioning

confidence: 99%

Section: Description Of the Model A Equations And Numerical Solutionsmentioning

confidence: 99%

Section: A Carbon Budget For Sbb Sediments and The Significance Ofmentioning

confidence: 99%

Section: A Carbon Budget For Sbb Sediments and The Significance Ofmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Carbon cycling in Santa Barbara Basin sediments: A modeling study

Burdige¹,

Komada²,

Magen³

et al. 2016

J Mar Res

Self Cite

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Pore Water Geochemistry and Quantification of Methane Cycling

2023

South China Sea Seeps

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Owing to numerous scientific cruises in the past two decades, pore water data from more than 250 sites within gas hydrate and cold seep areas of the South China Sea have been reported. These investigated sites are mainly distributed in the Dongsha–Taixinan, Shenhu, and Qiongdongnan areas of the northern South China Sea, together with a few sites from the Beikang Basin of the southern South China Sea. Pore water geochemical profiles at these sites have been used to indicate fluid sources that are linked to gas hydrates and methane seepage, to distinguish the anaerobic oxidation of methane (AOM) from organoclastic sulfate reduction, to reveal fluid flow patterns, and to quantify the rates of AOM. As the pore water data accumulate over a broad area of the SCS, recent attempts have been made to quantify regional sulfate and methane cycling in the subseafloor of the northern South China Sea. This quantitative assessment on a regional scale highlights the importance of deep-sourced methane in governing subseafloor carbon and sulfur cycling along continental margins.

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