scholarly journals Sedimentary Transport Influences on Diagenetic Processes at the Amazon Continental Shelf, Brazil

2019 ◽  
pp. 1-16
Author(s):  
Fabio Aprile ◽  
Gilmar W. Siqueira ◽  
Assad Darwich ◽  
Georg Irion
Keyword(s):  
Trace Elements ◽  
Organic Matter ◽  
Continental Shelf ◽  
Trace Element ◽  
Pore Water ◽  
Coastal Zone ◽  
Iron Reduction ◽  
Net Production ◽  
Diagenetic Processes ◽  
Physical Chemical

This research aimed to correlate the sedimentary transport with the diagenetic processes in the coastal zone and Amazon Continental Shelf (ACS). Physical and physical-chemical parameters, trace element contents (Cr, Pb, Ni, Zn and Hg), and O2, CO2 and iron flux were determined in sediment and pore water. Sedimentary incubation (96 hours) and algorithms were applied to determine the variation of the activity coefficient (ΔI) and ionic strength (Fi) of the predominant chemical species, and to estimate the net production and mineralization of the organic matter (ΔCO2T) in the system. There are not many studies applying incubation tests to identify the diagenetic processes, especially in fluvial-marines sediments. The results showed a strong zonation associated to the transport and deposition processes, influenced mainly by the grain-size and texture of sediment and fluvial streams. The distribution of trace elements followed the trend of the sedimentary pattern, with higher levels of metals in the deposits of clay minerals and organic matter. A factor of weight (Fw), calculated to establish the degree of importance of each parameter under the distribution and mobility of trace elements, suggests that the mobility of Cr, Ni and Zn is controlled by depth, clay and organic compounds contents, and concentration of dissolved oxygen. The vertical flow of O2 and CO2 and the Fe2+/Fe3+ ratio in the pore water suggest a predominance of organic matter oxidation in the sedimentary layer between 0.0 and 0.2 m, with partially anaerobic mineralization of the sediments below 0.4 m. Increases in trace element concentrations were observed in iron reduction zones, indicating processes of desorption of oxides and hydroxides of Fe and mineralization of organic matter. The extrapolation of the results of the incubation test to the studied system allowed to establish three hypotheses related to the diagenetic processes: 1) the flow of marine currents may be allowing the aerobic oxidation in the sandy sediments, with the nitrification route more accentuated than the ammonification route; 2) in the region of the coastal zone and inner continental shelf the routes of oxidation and reduction may be alternating according to the physical-chemical factors and seasonality; 3) in the coastal zone and inner shelf the net mineralization rate exceeded the net production rate of the organic matter (ΔCO2T >0).

scholarly journals Radium-228-derived ocean mixing and trace element inputs in the South Atlantic

2020 ◽  
Author(s):  
Yu-Te Hsieh ◽  
Walter Geibert ◽  
E. Malcolm S. Woodward ◽  
Neil J. Wyatt ◽  
Maeve C. Lohan ◽  
...  
Keyword(s):  
Trace Elements ◽  
Continental Shelf ◽  
Trace Element ◽  
Vertical Mixing ◽  
South Atlantic ◽  
Open Ocean ◽  
The South ◽  
Horizontal Mixing ◽  
Cape Basin ◽  
Argentine Basin

Abstract. Trace elements play important roles as micronutrients in modulating marine productivity in the global ocean. The South Atlantic around 40° S is a prominent region of high productivity and a transition zone between the nitrate-depleted Subtropical Gyre and the iron-limited Southern Ocean. However, the sources and fluxes of trace elements to this region remain unclear. In this study, the distribution of the naturally occurring radioisotope 228Ra in the water column of the South Atlantic (Cape Basin and Argentine Basin) has been investigated along a 40° S zonal transect to estimate ocean mixing and trace element supply to the surface ocean. Ra-228 profiles have been used to determine the horizontal and vertical mixing rates in the near-surface open ocean. In the Argentine Basin, horizontal mixing from the continental shelf to the open ocean shows an eddy diffusion of Kx = 1.7 ± 1.4 (106 cm2 s−1) and an integrated advection velocity w = 0.6 ± 0.3 cm s−1. In the Cape Basin, horizontal mixing is Kx = 2.7 ± 0.8 (107 cm2 s−1) and vertical mixing Kz = 1.0–1.5 cm2 s−1 in the upper 600 m layer. Three different approaches (228Ra-diffusion, 228Ra-advection and 228Ra/TE-ratio) have been applied to estimate the dissolved trace-element fluxes from shelf to open ocean. These approaches bracket the possible range of off-shelf fluxes from the Argentine margin to be: 3.8–22 (× 103) nmol Co m−2 d−1, 7.9–20 (× 104) nmol Fe m−2 d−1 and 2.7–6.5 (× 104) nmol Zn m−2 d−1. Off-shelf fluxes from the Cape margin are: 4.3–6.2 (× 103) nmol Co m−2 d−1, 1.2–3.1 (× 104) nmol Fe m−2 d−1 and 0.9–1.2 (× 104) nmol Zn m−2 d−1. On average, at 40° S in the Atlantic, vertical mixing supplies 0.4–1.2 nmol Co m−2 d−1, 3.6–11 nmol Fe m−2 d−1, and 13–16 nmol Zn m−2 d−1 to the euphotic zone. Compared with atmospheric dust and continental shelf inputs, vertical mixing is a more important source for supplying dissolved trace elements to the surface 40° S Atlantic. It is insufficient, however, to provide the trace elements removed by biological uptake. Other inputs (e.g. particulate, or from winter deep-mixing) are required to balance the trace element budgets in this region.

scholarly journals Trace elements in New Zealand ferromanganese nodules: implications for deep sea environments

2021 ◽  
Author(s):  
◽  
Andrea Davies
Keyword(s):  
Trace Elements ◽  
New Zealand ◽  
Trace Element ◽  
Pore Water ◽  
Deep Sea ◽  
Sediment Composition ◽  
Ferromanganese Nodules ◽  
Sediment Profiles ◽  
Element Enrichment ◽  
Trace Element Enrichment

<p>Ferromanganese nodules are authigenic marine sediments that form over millions of years from the precipitation of Fe oxyhydroxides and Mn oxides from seawater (hydrogenetic-type growth) and sediment pore-water (diagenetic-type growth). Fe-Mn (oxyhydr)oxides grow in layers about nuclei, effectively scavenging minor metals such as Ni, Cu and Co from the waters they grow in. The uptake of different elements into the ferromanganese nodules reflects their environment and mechanism of growth, and these deposits are of interest both as a potential source of metals of economic interest, and as records of changing ocean conditions. This study investigates the composition of 77 ferromanganese nodules from the seafloor around New Zealand. Samples analysed come from locations several thousand kilometres apart under the same water mass (Lower Circumpolar Deep Water – LCDW), but with varying depth, current velocity, and sediment type. The outermost 1 mm rim of each nodule, representing near-modern growth, was sampled to compare with modern environmental parameters including substrate sediment composition and chemical and physical oceanography. Major, minor, and trace element analysis of nodule rims were undertaken, and the authigenic and detrital components examined via leaching experiments to evaluate their relative influence on growth mechanisms. Overall, New Zealand ferromanganese nodules are hydrogenetic in origin. However, there are systematic variations in composition that reflect variable diagenetic influence. Hydrogenetic endmember compositions are defined by samples from two localities in the Southern Ocean that have no evidence for diagenetic influence. Diagenetic influence on nodule composition is exemplified by samples from the two locations in the Tasman Sea, but also include nodules from the Campbell nodule field. Nodules from the Campbell nodule field come from two transects perpendicular to the Campbell Plateau, and the Deep Western Boundary Current (DWBC). Both sediment composition and nodule rim chemistry vary systematically across both transects. Areas closest to the slope have sediment profiles indicating high energy, erosive environments, continental-sourced sand components, and are dominated by nodules with hydrogenetic chemical characteristics similar to those of the Southern Ocean. Further from the slope, the sediment profiles indicate silt dominated sediments of a more oceanic crustal provenance, lower energy environment, and increased influence of oxic diagenetic processes on the major, minor and trace element profiles of the nodules. No hydrothermal contribution was identified in the chemistry of any of the nodules analysed. The physical and chemical properties of the sediment, along with current velocities, were found to be the key influences in diagenetic enrichment in the nodules. The influence of seawater chemistry was difficult to determine due to the lack of direct analyses in the area. Ferromanganese nodule chemistry is a function of the nodule environment, including water body, sediment composition and depth. The authigenic components of nodules can therefore be used to investigate the deep-sea environment. The redox conditions of sediments and the productivity of the overlying water will affect the trace metal constituents of the pore-waters of a sediment (Kuhn et al., 2017). Sediments with a larger fraction of labile organic matter may result in trace element enrichment of the pore-water. Sediments below the CCD will be higher in trace elements than sediments below the CCD (U1413, U1406B, U1402, U1398, U1398, and U1378) due to carbonate matter acting as a dilutant that can limit the supply of trace elements mobilised in the pore-water during diagenesis (Glasby, 2006). Terrigenous clasts such as quartz (Chester, 1990), will also reduce trace element enrichment in the pore-water due to their low reactivity, e.g. for the sediment U1406B, which has a high lithic component (Table 3.2). Sediments with a higher biogenic silica component (such as U1373, U1374, and U1378) (Table 3.2, Table 3.4) are predicted to produce nodules with higher trace element contents (ISA, 2010). In contrast to both the CCZ and Indian Ocean nodules, the Campbell nodule field samples formed above the CCD, and hence in sediments that include a significant carbonate component. This minimises the trace element pore-water enrichment and can account for the lower Cu+Ni+Co contents observed in the Campbell nodule field nodules compared with those that formed below the CCD (CCZ and Indian Ocean).</p>

Trace element availability to plants in agricultural soils, with special emphasis on fertilizer inputs

1994 ◽  
Vol 2 (2) ◽  
pp. 133-146 ◽  
Author(s):  
Bal Ram Singh
Keyword(s):  
Trace Elements ◽  
Organic Matter ◽  
Atmospheric Deposition ◽  
Trace Element ◽  
Plant Species ◽  
Soil Ph ◽  
Agricultural Soils ◽  
Considerable Proportion ◽  
Short And Long Term

Fertilizers, along with atmospheric deposition, are believed to contribute more than all other factors to the trace element burden of cultivated soils. This review will discuss trace elements in commercial fertilizer in relation to their transfer to soil–plant systems. Also, background levels in soils and the concentrations of trace elements in soils, phosphate rocks, and commercial fertilizers will be presented. Results from several short and long-term experiments indicated that the application of phosphate fertilizers to agricultural soils generally resulted in an increase of trace elements in soils and that the increase was most pronounced for Cd. The corresponding increase in plants was quite variable, ranging from no increase at all to a significant increase. The concentration of trace elements in plant species also showed a wide variation. The distribution and partitioning of trace elements among chemical associations in soils varied considerably for different elements. The highest percentage of Cd in soils, as estimated by sequential extraction, was associated with exchangeable fractions (25–41%), but the highest fraction of Zn (47%) was associated with resistant minerals. Uptake of trace elements by plants and solubility and mobility of these elements in the soil were affected to a greater extent by the plant species grown and soil pH, organic matter, and soil texture. Soil pH showed a significant but inverse relationship with the concentrations of most of the trace elements in plants. The addition of organic matter generally immobilized the trace elements in soils and caused reduction in plant uptake of most elements. A considerable proportion (up to 50%) of the total uptake of trace elements, and especially of Cd, was a result of atmospheric deposition. Ecological implications of contaminants in fertilizers and the resultant need for research are described.Key words: accumulation in soils, fertilizers, plant availability, soil properties, trace elements.

Inorganic geochemistry of the type Caradoc series (Sandbian to middle Katian, Upper Ordovician), Onny valley, Shropshire, UK

2013 ◽  
Vol 150 (4) ◽  
pp. 699-727 ◽  
Author(s):  
R. HANNIGAN ◽  
M. E. BROOKFIELD
Keyword(s):  
Trace Elements ◽  
Continental Shelf ◽  
Shallow Water ◽  
Trace Element ◽  
Depositional Environment ◽  
Upper Ordovician ◽  
Physical Weathering ◽  
Minor Elements ◽  
Sandstone Formation ◽  
Western Side

AbstractThe geochemistry and petrology of the type section of the Caradoc Series in the Onny valley indicate that it was deposited on a marginal basin continental shelf similar to the western side of the present Sea of Japan. The lower beds form a transgressive–regressive sequence in which the rocks become less mature upwards. All the coarser sediments above the basal quartzites and conglomerates are greywackes in which the apparent muddy and ferrous matrix is due to the breakdown of unstable minerals and particles. Higher values of Na2O and Na/K ratios are found in the coarser shallow-water sandstones of the Horderley Sandstone Formation and decrease markedly in the succeeding beds, accompanied by an increase in K2O. Higher values of carbonate-corrected (and hence related) other major and minor elements like SiO2, CaO, P2O5, MnO and most trace elements correlate with the transgressive systems and maximum flooding surfaces of the three sequences recognized where they are related to condensation at those horizons. Chemical Indices of Alteration (CIA) suggest that the Horderley Sandstone Formation underwent greater predepositional physical weathering than lower and higher beds, which is compatible with the petrography, and were deposited during a cool phase within overall warm Sandbian–Katian times. Trace element ratios suggest an oxic to suboxic depositional environment.

scholarly journals Benthic alkalinity and DIC fluxes in the Rhône River prodelta generated by decoupled aerobic and anaerobic processes

2019 ◽  
Author(s):  
Jens Rassmann ◽  
Eryn M. Eitel ◽  
Cécile Cathalot ◽  
Christophe Brandily ◽  
Bruno Lansard ◽  
...  
Keyword(s):  
Pore Water ◽  
Iron Reduction ◽  
Iron Sulfide ◽  
Dissolved Inorganic Carbon ◽  
River Mouth ◽  
Total Alkalinity ◽  
Pore Waters ◽  
Rhône River ◽  
Net Production ◽  
Rhone River

Abstract. Estuarine regions are generally considered a net source of atmospheric CO2 as a result of the high organic carbon (OC) mineralization rates in the water column and their sediments. Yet, the intensity of anaerobic respiration processes in the sediments tempered by the reoxidation of reduced metabolites controls the net production of alkalinity from sediments that may partially buffer the metabolic CO2 generated by OC respiration. In this study, a benthic chamber was deployed in the Rhône River prodelta and the adjacent continental shelf (Gulf of Lions, NW Mediterranean) to assess the fluxes of total alkalinity (TA) and dissolved inorganic carbon (DIC) from the sediment. Concurrently, in situ O2 and pH microprofiles, electrochemical profiles, pore water and solid composition were measured in surface sediments to identify the main biogeochemical processes controlling the net production of alkalinity in these sediments. The benthic fluxes of TA and DIC, ranging between 14 and 74 mmol m−2 d−1 and 18 and 78 mmol m−2 d−1, respectively, were up to 8 times higher than the DOU fluxes (10.4 ± 0.9 mmol m−2 d−1) close to the river mouth, but their intensity decreased offshore, as a result of the decline in OC inputs. Low nitrate concentrations and strong pore water sulfate gradients indicated that the majority of the TA and DIC was produced by sulfate and iron reduction. Despite the complete removal of sulfate from the pore waters, dissolved sulfide concentrations were low due to the precipitation and burial of iron sulfide minerals (12.5 mmol m−2 d−1 near the river mouth), while soluble organic-Fe(III) complexes were concurrently found throughout the sediment column. The presence of organic-Fe(III) complexes together with low sulfide concentrations and high sulfate consumption suggests a dynamic system driven by the variability of the organic and inorganic particulate input originating from the river. By preventing reduced substances from being reoxidized, the precipitation and burial of iron sulfide decouples the iron and sulfur cycles from oxygen, therefore allowing a flux of alkalinity out of the sediments. In these conditions, the sediment provides a source of alkalinity to the bottom waters which mitigates the effect of the benthic DIC flux on the carbonate chemistry of coastal waters.

Diagenetic processes and nutrient fluxes at the sediment-water interface, northern Adriatic Sea, Italy

1995 ◽  
Vol 46 (1) ◽  
pp. 55 ◽  
Author(s):  
A Barbanti ◽  
MC Bergamini ◽  
F Frascari ◽  
S Miserocchi ◽  
M Ratta ◽  
...  
Keyword(s):  
Organic Matter ◽  
Pore Water ◽  
The Other ◽  
Nutrient Concentrations ◽  
Nutrient Fluxes ◽  
Water Interface ◽  
Po River ◽  
Northern Adriatic ◽  
Diagenetic Processes ◽  
Decomposition Of Organic Matter

Early diagenetic processes that control pore-water chemistry and nutrient fluxes at the sediment-water interface were studied in late summer 1989 and spring 1990 at four sites influenced by fine sediments of the Po River. Parameters on the solid fraction (grain size and C, N and P) and pore- water profiles of SO42-, NO3-, NH3, alkalinity, PO43-, Fe, Mn, Ca and Mg were determined. Data interpretation was supported by application of kinetic and stoichiometric modelling. Nutrient fluxes were calculated by Fick's first law. In the prodelta station the pore-water profiles showed large depletion in SO42- ions, jointly with the increase with depth of alkalinity, NH3 and PO43- concentrations, thus indicating anaerobic decomposition of organic matter, mainly due to bacterial sulfate reduction. At the other three sites the results were completely different. Nutrient concentrations in pore water were one order of magnitude lower. The peaks of alkalinity, NH3 and PO43- values near the interface and the constant presence of SO42- ions indicate aerobic decomposition of organic matter in the uppermost sediment. Nutrient fluxes showed much higher values in the prodelta station, whereas fluxes in the remaining stations decreased southward. In addition, seasonal variations produced higher summertime fluxes. The clear-cut difference in diagenetic processes as a function of the distance from the main Po River mouth can be explained by the rapid burial of sediments rich in organic matter and inorganic compounds in the prodelta station. At the other stations, the lower sedimentation rate and more efficient bioturbation and resuspension processes cause a prolonged exposure of sediments to aerobic metabolization reactions before burial.

Molecular characterization of dissolved organic matter in pore water of continental shelf sediments

2009 ◽  
Vol 73 (11) ◽  
pp. 3337-3358 ◽  
Author(s):  
Frauke Schmidt ◽  
Marcus Elvert ◽  
Boris P. Koch ◽  
Matthias Witt ◽  
Kai-Uwe Hinrichs
Keyword(s):  
Organic Matter ◽  
Dissolved Organic Matter ◽  
Continental Shelf ◽  
Molecular Characterization ◽  
Pore Water ◽  
Shelf Sediments

scholarly journals Trace elements in New Zealand ferromanganese nodules: implications for deep sea environments

2021 ◽  
Author(s):  
◽  
Andrea Davies
Keyword(s):  
Trace Elements ◽  
New Zealand ◽  
Trace Element ◽  
Pore Water ◽  
Deep Sea ◽  
Sediment Composition ◽  
Ferromanganese Nodules ◽  
Sediment Profiles ◽  
Element Enrichment ◽  
Trace Element Enrichment

<p>Ferromanganese nodules are authigenic marine sediments that form over millions of years from the precipitation of Fe oxyhydroxides and Mn oxides from seawater (hydrogenetic-type growth) and sediment pore-water (diagenetic-type growth). Fe-Mn (oxyhydr)oxides grow in layers about nuclei, effectively scavenging minor metals such as Ni, Cu and Co from the waters they grow in. The uptake of different elements into the ferromanganese nodules reflects their environment and mechanism of growth, and these deposits are of interest both as a potential source of metals of economic interest, and as records of changing ocean conditions. This study investigates the composition of 77 ferromanganese nodules from the seafloor around New Zealand. Samples analysed come from locations several thousand kilometres apart under the same water mass (Lower Circumpolar Deep Water – LCDW), but with varying depth, current velocity, and sediment type. The outermost 1 mm rim of each nodule, representing near-modern growth, was sampled to compare with modern environmental parameters including substrate sediment composition and chemical and physical oceanography. Major, minor, and trace element analysis of nodule rims were undertaken, and the authigenic and detrital components examined via leaching experiments to evaluate their relative influence on growth mechanisms. Overall, New Zealand ferromanganese nodules are hydrogenetic in origin. However, there are systematic variations in composition that reflect variable diagenetic influence. Hydrogenetic endmember compositions are defined by samples from two localities in the Southern Ocean that have no evidence for diagenetic influence. Diagenetic influence on nodule composition is exemplified by samples from the two locations in the Tasman Sea, but also include nodules from the Campbell nodule field. Nodules from the Campbell nodule field come from two transects perpendicular to the Campbell Plateau, and the Deep Western Boundary Current (DWBC). Both sediment composition and nodule rim chemistry vary systematically across both transects. Areas closest to the slope have sediment profiles indicating high energy, erosive environments, continental-sourced sand components, and are dominated by nodules with hydrogenetic chemical characteristics similar to those of the Southern Ocean. Further from the slope, the sediment profiles indicate silt dominated sediments of a more oceanic crustal provenance, lower energy environment, and increased influence of oxic diagenetic processes on the major, minor and trace element profiles of the nodules. No hydrothermal contribution was identified in the chemistry of any of the nodules analysed. The physical and chemical properties of the sediment, along with current velocities, were found to be the key influences in diagenetic enrichment in the nodules. The influence of seawater chemistry was difficult to determine due to the lack of direct analyses in the area. Ferromanganese nodule chemistry is a function of the nodule environment, including water body, sediment composition and depth. The authigenic components of nodules can therefore be used to investigate the deep-sea environment. The redox conditions of sediments and the productivity of the overlying water will affect the trace metal constituents of the pore-waters of a sediment (Kuhn et al., 2017). Sediments with a larger fraction of labile organic matter may result in trace element enrichment of the pore-water. Sediments below the CCD will be higher in trace elements than sediments below the CCD (U1413, U1406B, U1402, U1398, U1398, and U1378) due to carbonate matter acting as a dilutant that can limit the supply of trace elements mobilised in the pore-water during diagenesis (Glasby, 2006). Terrigenous clasts such as quartz (Chester, 1990), will also reduce trace element enrichment in the pore-water due to their low reactivity, e.g. for the sediment U1406B, which has a high lithic component (Table 3.2). Sediments with a higher biogenic silica component (such as U1373, U1374, and U1378) (Table 3.2, Table 3.4) are predicted to produce nodules with higher trace element contents (ISA, 2010). In contrast to both the CCZ and Indian Ocean nodules, the Campbell nodule field samples formed above the CCD, and hence in sediments that include a significant carbonate component. This minimises the trace element pore-water enrichment and can account for the lower Cu+Ni+Co contents observed in the Campbell nodule field nodules compared with those that formed below the CCD (CCZ and Indian Ocean).</p>

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

2019 ◽  
Vol 16 (16) ◽  
pp. 3165-3181 ◽  
Author(s):  
Hanni Vigderovich ◽  
Lewen Liang ◽  
Barak Herut ◽  
Fengping Wang ◽  
Eyal Wurgaft ◽  
...  
Keyword(s):  
Organic Matter ◽  
Continental Shelf ◽  
Microbial Activity ◽  
Iron Reduction ◽  
Sulfur Cycle ◽  
Anaerobic Oxidation Of Methane ◽  
Upward Migration ◽  
Oxidation Of Methane ◽  
Microbial Iron Reduction ◽  
Dissimilatory Iron Reduction

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.

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

2019 ◽  
Author(s):  
Hanni Vigderovich ◽  
Lewen Liang ◽  
Barak Herut ◽  
Fengping Wang ◽  
Eyal Wurgaft ◽  
...  
Keyword(s):  
Organic Matter ◽  
Continental Shelf ◽  
Iron Reduction ◽  
Sediment Cores ◽  
Iron Concentration ◽  
Sulfur Cycle ◽  
Geochemical Data ◽  
Anaerobic Oxidation Of Methane ◽  
Oxidation Of Methane ◽  
Microbial Iron Reduction

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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