scholarly journals Anaerobic oxidation of methane alters sediment records of sulfur, iron and phosphorus in the Black Sea

2016 ◽  
Author(s):  
Matthias Egger ◽  
Peter Kraal ◽  
Tom Jilbert ◽  
Fatimah Sulu-Gambari ◽  
Célia J. Sapart ◽  
...  
Keyword(s):  
Lake Sediments ◽  
Pore Water ◽  
Black Sea ◽  
The Black Sea ◽  
Anaerobic Oxidation Of Methane ◽  
Anaerobic Oxidation ◽  
Fe Oxide ◽  
Fe Oxides ◽  
Oxidation Of Methane ◽  
High Concentrations

Abstract. The surface sediments in the Black Sea are underlain by extensive deposits of iron (Fe) oxide-rich lake sediments that were deposited prior to the inflow of marine Mediterranean Sea waters ca. 9000 years ago. The subsequent downward diffusion of marine sulfate into the methane-bearing lake sediments has led to a multitude of diagenetic reactions in the sulfate-methane transition zone (SMTZ), including anaerobic oxidation of methane (AOM) with sulfate. While the sedimentary cycles of sulfur (S), methane and Fe in the SMTZ have been extensively studied, relatively little is known about the diagenetic alterations of the sediment record occurring below the SMTZ. Here we combine detailed geochemical analyses of the sediment and pore water with multicomponent diagenetic modeling to study the diagenetic alterations below the SMTZ at two sites in the western Black Sea. We focus on the dynamics of Fe, S and phosphorus (P) and demonstrate that diagenesis has strongly overprinted the sedimentary burial records of these elements. Our results show that sulfate-mediated AOM substantially enhances the downward diffusive flux of sulfide into the deep limnic deposits. During this downward sulfidization, Fe oxides, Fe carbonates and Fe phosphates (e.g. vivianite) are converted to sulfide phases, leading to an enrichment in solid phase S and the release of phosphate to the pore water. Below the sulfidization front, high concentrations of dissolved ferrous Fe (Fe2+) lead to sequestration of downward diffusing phosphate as authigenic vivianite, resulting in a transient accumulation of total P directly below the sulfidization front. Our model results further demonstrate that downward migrating sulfide becomes partly re-oxidized to sulfate due to reactions with oxidized Fe minerals, fueling a cryptic S cycle and thus stimulating slow rates of sulfate-driven AOM (~ 1–100 pmol cm−3 d−1) in the sulfate-depleted limnic deposits. However, this process is unlikely to explain the observed release of dissolved Fe2+ below the SMTZ. Instead, we suggest that besides organoclastic Fe oxide reduction, AOM coupled to the reduction of Fe oxides may also provide a possible mechanism for the high concentrations of Fe2+ in the pore water at depth. Our results reveal that methane plays a key role in the diagenetic alterations of Fe, S and P records in Black Sea sediments. The downward sulfidization into the limnic deposits is enhanced through sulfate-driven AOM with sulfate and AOM with Fe oxides may provide a deep source of dissolved Fe2+ that drives the sequestration of P in vivianite below the sulfidization front.

scholarly journals Anaerobic oxidation of methane alters sediment records of sulfur, iron and phosphorus in the Black Sea

2016 ◽  
Vol 13 (18) ◽  
pp. 5333-5355 ◽  
Author(s):  
Matthias Egger ◽  
Peter Kraal ◽  
Tom Jilbert ◽  
Fatimah Sulu-Gambari ◽  
Célia J. Sapart ◽  
...  
Keyword(s):  
Lake Sediments ◽  
Black Sea ◽  
Solid Phase ◽  
The Black Sea ◽  
Anaerobic Oxidation Of Methane ◽  
Anaerobic Oxidation ◽  
Fe Oxide ◽  
Fe Oxides ◽  
Oxidation Of Methane ◽  
High Concentrations

Abstract. The surface sediments in the Black Sea are underlain by extensive deposits of iron (Fe)-oxide-rich lake sediments that were deposited prior to the inflow of marine Mediterranean Sea waters ca. 9000 years ago. The subsequent downward diffusion of marine sulfate into the methane-bearing lake sediments has led to a multitude of diagenetic reactions in the sulfate-methane transition zone (SMTZ), including anaerobic oxidation of methane (AOM) with sulfate. While the sedimentary cycles of sulfur (S), methane and Fe in the SMTZ have been extensively studied, relatively little is known about the diagenetic alterations of the sediment record occurring below the SMTZ.Here we combine detailed geochemical analyses of the sediment and porewater with multicomponent diagenetic modeling to study the diagenetic alterations below the SMTZ at two sites in the western Black Sea. We focus on the dynamics of Fe, S and phosphorus (P), and demonstrate that diagenesis has strongly overprinted the sedimentary burial records of these elements. In line with previous studies in the Black Sea, we show that sulfate-mediated AOM substantially enhances the downward diffusive flux of sulfide into the deep limnic deposits. During this downward sulfidization, Fe oxides, Fe carbonates and Fe phosphates (e.g., vivianite) are converted to sulfide phases, leading to an enrichment in solid-phase S and the release of phosphate to the porewater. Below the sulfidization front, high concentrations of dissolved ferrous Fe (Fe2+) lead to sequestration of downward-diffusing phosphate as authigenic vivianite, resulting in a transient accumulation of total P directly below the sulfidization front.Our model results further demonstrate that downward-migrating sulfide becomes partly re-oxidized to sulfate due to reactions with oxidized Fe minerals, fueling a cryptic S cycle and thus stimulating slow rates of sulfate-driven AOM ( ∼  1–100 pmol cm−3 d−1) in the sulfate-depleted limnic deposits. However, this process is unlikely to explain the observed release of dissolved Fe2+ below the SMTZ. Instead, we suggest that besides organoclastic Fe oxide reduction and reactivation of less reactive Fe oxides by methanogens, AOM coupled to the reduction of Fe oxides may also provide a possible mechanism for the high concentrations of Fe2+ in the porewater at depth. Our results reveal that methane plays a key role in the diagenetic alterations of Fe, S and P records in Black Sea sediments. The downward sulfidization into the limnic deposits is enhanced through sulfate-driven AOM with sulfate, and AOM with Fe oxides may provide a deep source of dissolved Fe2+ that drives the sequestration of P in vivianite below the sulfidization front.

Mn(II) carbonate authigenesis marks the benthic SMTZ and is fueled by Mn-driven anaerobic oxidation of methane: A Black Sea evidence

2021 ◽  
Author(s):  
Tiantian Sun ◽  
Michael E Böttcher ◽  
Jens Kallmeyer ◽  
Tina Treude ◽  
Marko Lipka ◽  
...  
Keyword(s):  
Pore Water ◽  
Black Sea ◽  
Dissolved Inorganic Carbon ◽  
Sediment Cores ◽  
The Black Sea ◽  
Anaerobic Oxidation Of Methane ◽  
Potential Contribution ◽  
Anaerobic Oxidation ◽  
Upward Migration ◽  
Geochemical Composition

<p>In the Black Sea, sediment cores covering the last brackish-limnic transition were recovered and investigated for anaerobic biogeochemical processes controlling sulfur, carbon, and metal cycling. The development of a sulfate-methane transition zone (SMTZ) is nowadays found below the brackish zone in the limnic part of the sediments that limits the upward migration of biogenic methane into surface sediments and the water column. The position of the SMTZ may have changed in the past due to dynamic fluxes of dissolved species in the pore water. Besides dissolved sulfate, metal-bearing minerals have been shown to serve as potential reactants, also converting CH<sub>4</sub> into dissolved inorganic carbon (DIC). The pore water and sediment stable isotope (C, S, O) and geochemical composition were investigated, as well as in-situ microbial rates of sulfate reduction and total anaerobic oxidation of CH<sub>4</sub> (AOM) obtained from sediment incubations for the identification of a potential contribution of manganese-bearing minerals to AOM in the limnic part of the sediments (Mn-AOM). In the limnic Black Sea sediments Mn-AOM is causes an upward flux of dissolved Mn whereas intense SO<sub>4</sub>-AOM located in shalower sediments leads to an increase in pH and a maximum in DIC concentrations in the SMTZ. The resulting change in saturation states leads to the precipitation of mixed MnCa-carbonate solid-solutions (‘rhodochrozitization front’) and the development of a zone enriched in excess sedimentary Mn(II). We further argue that these authigenic fronts may survive changes in pore water composition and are stable in the anoxic sedimentary record, marking the position of paleo-SMTZs. The persisting formation of this geochemical marker has advantage in application over the transient development of a sulfidization front of metastable mackinawite, that is fromed by the reaction of downard migrating sulfide with upward diffusing Fe(II), originating from SO<sub>4</sub>-AOM and Fe-AOM, respectively.</p>

Archaea mediate anaerobic oxidation of methane in deep euxinic waters of the Black Sea

2003 ◽  
Vol 67 (7) ◽  
pp. 1359-1374 ◽  
Author(s):  
Stuart G Wakeham ◽  
Cynthia M Lewis ◽  
Ellen C Hopmans ◽  
Stefan Schouten ◽  
Jaap S Sinninghe Damsté
Keyword(s):  
Black Sea ◽  
The Black Sea ◽  
Anaerobic Oxidation Of Methane ◽  
Anaerobic Oxidation ◽  
Oxidation Of Methane

scholarly journals Manganese/iron-supported sulfate-dependent anaerobic oxidation of methane by archaea in lake sediments

2019 ◽  
Author(s):  
Guangyi Su ◽  
Jakob Zopfi ◽  
Haoyi Yao ◽  
Lea Steinle ◽  
Helge Niemann ◽  
...  
Keyword(s):  
Lake Sediments ◽  
16S Rrna Gene Sequencing ◽  
Electron Acceptors ◽  
Rrna Gene ◽  
Anaerobic Oxidation Of Methane ◽  
Anaerobic Oxidation ◽  
Sequencing Data ◽  
Oxidation Of Methane ◽  
Freshwater Habitats ◽  
Rrna Gene Sequencing

AbstractAnaerobic oxidation of methane (AOM) by methanotrophic archaea is an important sink of this greenhouse gas in marine sediments. However, evidence for AOM in freshwater habitats is rare, and little is known about the pathways, electron acceptors and microbes involved. Here, we show that AOM occurs in anoxic sediments of a lake in southern Switzerland (Lake Cadagno). Combined AOM-rate and 16S rRNA gene-sequencing data suggest thatCandidatusMethanoperedens archaea are responsible for the observed methane oxidation. Members of the Methanoperedenaceae family were previously reported to conduct nitrate- or iron/manganese-dependent AOM. However, we demonstrate for the first time that the methanotrophic archaea do not necessarily rely upon these oxidants as terminal electron acceptors directly, but mainly perform canonical sulfate-dependent AOM, which under sulfate-starved conditions can be supported by metal (Mn, Fe) oxides through oxidation of reduced sulfur species to sulfate. The correspondence of high abundances of Desulfobulbaceae andCandidatusMethanoperedens at the same sediment depth confirm the interdependence of anaerobic methane-oxidizing archaea and sulfate-reducing bacteria. The relatively high abundance and widespread distribution ofCandidatusMethanoperedens in lake sediments highlight their potentially important role in mitigating methane emissions from terrestrial freshwater environments to the atmosphere, analogous to ANME-1, -2 and -3 in marine settings.

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