Sulfate reduction rates in the sediments of the Mediterranean continental shelf inferred from combined dissolved inorganic carbon and total alkalinity profiles

Wurgaft, Eyal; Findlay, Alyssa; Vigderovich, Hanni; Herut, Barak; Sivan, Orit

doi:10.1016/j.marchem.2019.03.004

Cited by 17 publications

(28 citation statements)

References 83 publications

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“…Since marine methane flux settings have diagenetic systems different than sites without methane fluxes (e.g., Formolo and Lyons, 2013), the sulfide burial rate at diffusive methane flux settings could differ from the global average (Dickens, 2011). For example, nearly quantitative precipitation of all reduced sulfur by AOM was reported for an iron-rich, non-steady-state setting (Hensen et al, 2003) and more recently, and two thirds of sulfide produced via AOM and OSR at the SMTZ was inferred to undergo burial (Wurgaft et al, 2019). Availability of reactive iron (for sulfide burial) as well as the ratio of burial versus oxidation of the sulfide produced at the SMTZ is thus an important parameter in determining the impact of methane induced carbon cycling at diffusive methane flux settings.…”

Section: Importance Of Dic Outflux To the Water Column: Implication Tmentioning

confidence: 99%

Dissolved Inorganic Carbon Pump in Methane-Charged Shallow Marine Sediments: State of the Art and New Model Perspectives

et al. 2020

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Methane transport from subsurface reservoirs to shallow marine sediment is characterized by unique biogeochemical interactions significant for ocean chemistry. Sulfate-Methane Transition Zone (SMTZ) is an important diagenetic front in the sediment column that quantitatively consumes the diffusive methane fluxes from deep methanogenic sources toward shallow marine sediments via sulfate-driven anaerobic oxidation of methane (AOM). Recent global compilation from diffusion-controlled marine settings suggests methane from below and sulfate from above fluxing into the SMTZ at an estimated rate of 3.8 and 5.3 Tmol year −1 , respectively, and wider estimate for methane flux ranges from 1 to 19 Tmol year −1. AOM converts the methane carbon to dissolved inorganic carbon (DIC) at the SMTZ. Organoclastic sulfate reduction (OSR) and deep-DIC fluxes from methanogenic zones contribute additional DIC to the shallow sediments. Here, we provide a quantification of 8.7 Tmol year −1 DIC entering the methane-charged shallow sediments due to AOM, OSR, and the deep-DIC flux (range 6.4-10.2 Tmol year −1). Of this total DIC pool, an estimated 6.5 Tmol year −1 flows toward the water column (range: 3.2-9.2 Tmol year −1), and 1.7 Tmol year −1 enters the authigenic carbonate phases (range: 0.6-3.6 Tmol year −1). This summary highlights that carbonate authigenesis in settings dominated by diffusive methane fluxes is a significant component of marine carbon burial, comparable to ∼15% of carbonate accumulation on continental shelves and in the abyssal ocean, respectively. Further, the DIC outflux through the SMTZ is comparable to ∼20% of global riverine DIC flux to oceans. This DIC outflux will contribute alkalinity or CO 2 in different proportions to the water column, depending on the rates of authigenic carbonate precipitation and sulfide oxidation and will significantly impact ocean chemistry and potentially atmospheric CO 2. Settings with substantial carbonate precipitation and sulfide oxidation at present are contributing CO 2 and thus to ocean acidification. Our synthesis emphasizes the importance of SMTZ as not only a methane sink but also an important diagenetic front for global DIC cycling. We further underscore the need to incorporate a DIC pump in methane-charged shallow marine sediments to models for coastal and geologic carbon cycling.

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Section: Importance Of Dic Outflux To the Water Column: Implication Tmentioning

confidence: 99%

Dissolved Inorganic Carbon Pump in Methane-Charged Shallow Marine Sediments: State of the Art and New Model Perspectives

et al. 2020

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“…The most abundant clay mineral is montmorillonite (with a smaller fraction of illite and kaolinite), which makes silica, alumina, and ferric iron oxides the main chemical components in the bulk sediment (Nir, 1984). Although methane is not expected in the upper several meters of the sediments due to the oligotrophic characteristics the SE Mediterranean Sea surface water, methane was observed in several cores collected from SG-1 (Sela-Adler et al, 2015;Vigderovich et al, 2019;Wurgaft et al, 2019). They identified the SMTZ in the upper few meters of the sediments, conducted an isotopic analysis of the methane and concluded that most of the methane is from biogenic source and that it is being produced in situ.…”

Section: Study Sitementioning

confidence: 99%

“…All four samples, collected from different depths, show an identical composition. Wurgaft et al (2019) determined the content of calcite, clays, and quartz, in a different core collected from the same station, by 4-6%, 50-70%, and 15-25%, respectively. Measurements of iron fractions using chemical extractions ( Figure 2D) show that goethite, hematite and akageneite (Fe ox2 ) are the most abundant Fe minerals in the sediment, with concentrations of 2.2% wt/dry sediment at the top of the sediment, decreasing to 1.4% wt/dry sediment at 500 cm depth.…”

Section: Sediment Compositionmentioning

confidence: 99%

The Effect of Early Diagenesis in Methanic Sediments on Sedimentary Magnetic Properties: Case Study From the SE Mediterranean Continental Shelf

2020

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“…Iron-coupled AOM in natural lake sediments was indicated using isotope porewater depth profiles (Sivan et al, 2011), rate modeling based on these profiles (Adler et al, 2011), microbial profiles (Bar-Or et al, 2015) and directly from a set of sediment slurry incubation experiments (Bar-Or et al, 2017). The few microbial studies on iron-coupled AOM (mainly in cultures) showed either the involvement of methanogenic/methanotrophic archaea (Scheller et al, 2016;Ettwig et al, 2016;Rotaru and Thamdrup, 2016;Cai et al, 2018;Yan et al, 2018) or a cooperation between methanotrophs and methanogens (Bar-Or et al, 2017).…”

Section: Fe 3+mentioning

confidence: 99%

Evidence for microbial iron reduction in the methanic sediments of the oligotrophic southeastern Mediterranean continental shelf

Vigderovich

Liang²,

Herut

et al. 2019

Biogeosciences

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Abstract. Dissimilatory iron reduction is probably one of the oldest types of metabolisms that still participates in important biogeochemical cycles, such as those of carbon and sulfur. It is one of the more energetically favorable anaerobic microbial respiration processes and is usually coupled to the oxidation of organic matter. Traditionally this process is thought to be limited to the shallow part of the sedimentary column in most aquatic systems. However, iron reduction has also been observed in the methanic zone of many marine and freshwater sediments, well below its expected zone and occasionally accompanied by decreases in methane, suggesting a link between the iron and the methane cycles. Nevertheless, the mechanistic nature of this link (competition, redox or other) has yet to be established and has not been studied in oligotrophic shallow marine sediments. In this study we present combined geochemical and molecular evidences for microbial iron reduction in the methanic zone of the oligotrophic southeastern (SE) Mediterranean continental shelf. Geochemical porewater profiles indicate iron reduction in two zones, the uppermost part of the sediment, and the deeper zone, in the layer of high methane concentration. Results from a slurry incubation experiment indicate that the deep methanic iron reduction is microbially mediated. The sedimentary profiles of microbial abundance and quantitative PCR (qPCR) of the mcrA gene, together with Spearman correlation between the microbial data and Fe(II) concentrations in the porewater, suggest types of potential microorganisms that may be involved in the iron reduction via several potential pathways: H2 or organic matter oxidation, an active sulfur cycle, or iron-driven anaerobic oxidation of methane. We suggest that significant upward migration of methane in the sedimentary column and its oxidation by sulfate may fuel the microbial activity in the sulfate methane transition zone (SMTZ). The biomass created by this microbial activity can be used by the iron reducers below, in the methanic zone of the sediments of the SE Mediterranean.

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Sulfate reduction rates in the sediments of the Mediterranean continental shelf inferred from combined dissolved inorganic carbon and total alkalinity profiles

Cited by 17 publications

References 83 publications

Dissolved Inorganic Carbon Pump in Methane-Charged Shallow Marine Sediments: State of the Art and New Model Perspectives

Dissolved Inorganic Carbon Pump in Methane-Charged Shallow Marine Sediments: State of the Art and New Model Perspectives

The Effect of Early Diagenesis in Methanic Sediments on Sedimentary Magnetic Properties: Case Study From the SE Mediterranean Continental Shelf

Evidence for microbial iron reduction in the methanic sediments of the oligotrophic southeastern Mediterranean continental shelf

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