Spatial distribution and sources of organic matter and pollutants in the SE Mediterranean (Levantine basin) deep water sediments

Astrahan, Peleg; Silverman, Jacob; Gertner, Yaron; Herut, Barak

doi:10.1016/j.marpolbul.2017.01.006

Cited by 23 publications

(12 citation statements)

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“…The bottom seawater along the continental shelf is well oxygenated and sulfate concentrations at the water-sediment interface are ∼ 30 mmol L −1 (Sela- Adler et al, 2015). The central and eastern regions of the Levantine Basin have relatively low total organic carbon (TOC) content (∼ 0.1 %-1.4 %; Almogi-Labin et al, 2009;Sela-Adler et al, 2015;Astrahan et al, 2017) as compared to the Western Mediterranean Basin and offshore the Nile River delta (1 %-2 %). Along the Egyptian coast, the TOC in surface sediments on the shelf reach maximum values of 1.5 % (Aly Salem et al, 2013).…”

Section: Study Sitementioning

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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Section: Study Sitementioning

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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“…The sediments are mostly clay silts between 30-50 m water depth, while the clay fraction dominates at >50 m water depth (Nir, 1984;Sandler and Herut, 2000). The organic carbon content in the central and eastern regions of the Levantine Basin is relatively low (∼0.1-1.4%; (Almogi-Labin et al, 2009;Sela-Adler et al, 2015;Astrahan et al, 2017). However, biogenic methane was found at some locations in shallow sediments (Sela-Adler et al, 2015).…”

Section: Study Site and Samplingmentioning

confidence: 99%

Iron oxides impact sulfate-driven anaerobic oxidation of methane in diffusion-dominated marine sediments

et al. 2022

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Microbial iron (Fe) reduction by naturally abundant iron minerals has been observed in many anoxic aquatic sediments in the sulfidic and methanic zones, deeper than it is expected based on its energetic yield. However, the potential consequence of this “deep” iron reduction on microbial elemental cycles is still unclear in sediments where diffusion is the dominant transport process. In this contribution, we experimentally quantify the impact of iron oxides on sulfate-driven anaerobic oxidation of methane (S-AOM) within the sulfate methane transition zone (SMTZ) of marine diffusive controlled sediments. Sediments were collected from the oligotrophic Southeastern (SE) Mediterranean continental shelf and were incubated with 13C-labeled methane. We followed the conversion of 13C-labeled methane as a proxy of S-AOM and monitored the sediment response to hematite addition. Our study shows microbial hematite reduction as a significant process in the SMTZ, which appears to be co-occurring with S-AOM. Based on combined evidence from sulfur and carbon isotopes and functional gene analysis, the reduction of hematite seems to slow down S-AOM. This contrasts with methane seep environments, where iron oxides appear to stimulate S-AOM and hence attenuate the release of the greenhouse gas methane from the sediments. In the deep methanic zone, the addition of iron oxides inhibits the methanogenesis process and hence methane gas production. The inhibition effect deeper in the sediment is not related to Fe-AOM as a competing process on the methane substrate, since Fe-AOM was not observed throughout the methanic sediments with several iron oxides additions.

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“…The continental shelf narrows from south to north and is built mainly of Pliocene-Quaternary Nile-derived sediments, whose rate of sedimentation decreases with increasing distance from the Nile Delta and from the shoreline (Nir, 1984;Sandler and Herut, 2000). While the highest levels of total organic carbon (TOC) (1 -2%) in sediments were found in the Western Mediterranean Basin and offshore the Nile River delta, the central and eastern deep water regions of the Levantine Basin have relatively low TOC levels (0 -0.5%) (Astrahan et al, 2017). Along the Egyptian coast, maximal contents of TOC in surface sediments on the shelf is up to 1.5% (Aly Salem et al, 2013), while in the Israeli shelf sediments (< 100 m depth) the TOC levels vary between < 0.1 -1% (Almogi-Labin et al, 2009).…”

Section: Study Sitementioning

confidence: 99%

Evidence for microbial iron reduction in the methanogenic sediments of the oligotrophic SE Mediterranean continental shelf

Vigderovich

Liang

Herut

et al. 2019

Preprint

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Abstract. Dissimilatory iron reduction is probably one of the earliest metabolisms, which still participates in important biogeochemical cycles such as carbon and sulfur. Traditionally, this process is thought to be limited to the shallow part of the sediment column, as one of the energetically favorable anaerobic microbial respiration cascade, usually coupled to the oxidation of organic matter. However, in the last decade iron reduction has been observed in the methanogenic depth in many aquatic sediments, suggesting a link between the iron and the methane cycles. Yet, the mechanistic nature of this link has yet to be established, and has not been studied in oligotrophic shallow marine sediments. In this study we present first geochemical and molecular evidences for microbial iron reduction in the methanogenic depth of the oligotrophic Southern Eastern (SE) Mediterranean continental shelf. Geochemical pore-water profiles indicate iron reduction in two zones, the traditional zone in the upper part of the sediment cores and a deeper second zone located in the enhanced methane concentration layer. Results from a slurry incubation experiment indicate that the iron reduction is microbial. The Geochemical data, Spearman correlation between microbial abundance and iron concentration, as well as the qPCR analysis of the mcrA gene point to several potential microorganisms that could be involved in this iron reduction via three potential pathways: H2/organic matter oxidation, an active sulfur cycle or iron driven anaerobic oxidation of methane.

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Spatial distribution and sources of organic matter and pollutants in the SE Mediterranean (Levantine basin) deep water sediments

Cited by 23 publications

References 50 publications

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

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

Iron oxides impact sulfate-driven anaerobic oxidation of methane in diffusion-dominated marine sediments

Evidence for microbial iron reduction in the methanogenic sediments of the oligotrophic SE Mediterranean continental shelf

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