1D Co‐Pi Modified BiVO4/ZnO Junction Cascade for Efficient Photoelectrochemical Water Cleavage

The most important factors dominating solar hydrogen synthesis efficiency include light absorption, charge separation and transport, and surface chemical reactions (charge utilization). In order to tackle these factors, an ordered 1D junction cascade photoelectrode for water splitting, grown via a simple low‐cost solution‐based process and consisting of nanoparticulate BiVO₄ on 1D ZnO rods with cobalt phosphate (Co‐Pi) on the surface is synthesized. Flat‐band measurements reveal the feasibility of charge transfer from BiVO₄ to ZnO, supported by PL measurements and photocurrent observation in the presence of an efficient hole scavenger, which demonstrate that quenching of luminescence of BiVO₄ and enhanced current are caused by electron transfer from BiVO₄ to ZnO. A dramatic cathodic shift in onset potential under both visible and full arc irradiation, coupled with a 12‐fold increase in photocurrent (ca. 3 mA cm^‐2) are observed compared to BiVO₄, resulting in ≈47% IPCE at 410 nm (4% for BiVO₄) with high solar energy conversion efficiency (0.88%). The reasons for these enhancements stem from enhanced light absorption and trapping, in situ rectifying electron transfer from BiVO₄ to ZnO, hole transfer to Co‐Pi for water oxidation, and facilitating electron transport along 1D ZnO.     

Na3V2(PO4)3 as the Sole Solid Energy Storage Material for Redox Flow Sodium‐Ion Battery

Redox flow batteries have considerable advantages of system scalability and operation flexibility over other battery technologies, which makes them promising for large‐scale energy storage application. However, they suffer from low energy density and consequently relatively high cost for a nominal energy output. Redox targeting–based flow batteries are employed by incorporating solid energy storage materials in the tank and present energy density far beyond the solubility limit of the electrolytes. The success of this concept relies on paring suitable redox mediators with solid materials for facilitated reaction kinetics and lean electrolyte composition. Here, a redox targeting‐based flow battery system using the NASICON‐type Na₃V₂(PO₄)₃ as a capacity booster for both the catholyte and anolyte is reported. With 10‐methylphenothiazine as the cathodic redox mediator and 9‐fluorenone as anodic redox mediator, an all‐organic single molecule redox targeting–based flow battery is developed. The anodic and cathodic capacity are 3 and 17 times higher than the solubility limit of respective electrolyte, with which a full cell can achieve an energy density up to 88 Wh L^?1. The reaction mechanism is scrutinized by operando and in‐situ X‐ray and UV–vis absorption spectroscopy. The reaction kinetics are analysed in terms of Butler–Volmer formalism.     

Corrosion and Alloy Engineering in Rational Design of High Current Density Electrodes for Efficient Water Splitting

Alongside rare‐earth metals, Ni, Fe, Co, Cu are some of the critical materials that will be in huge demand thanks to growth in clean‐energy sector. Herein scrap stainless steel wires (SSW) from worn‐out tires are employed as a support material for catalyst integration in the hydrogen evolution reaction (HER). In addition, SSW by corrosion engineering is exercised as an in situ formed freestanding robust electrode for the oxygen evolution reaction (OER). By superficial corrosion of SSW, inherent active species are unmasked in the form of Ni/FeOOH nanocrystallites displaying efficient water oxidation by reaching 500 mA cm^?2 at low overpotential (η₅₀₀) of 287 mV in 1 m KOH. Similarly, cathode scrap SSW with active (alloy) coatings of MoNi₄ catalyzes the HER at η_‐200 = 77 mV, with a low activation energy (E_a = 16.338 kJ mol^?1) and high durability of 150 h. Promisingly, when used in industrial conditions, 5 m KOH, 343 K, these electrodes demonstrate abnormal activity by yielding high anodic and cathodic current density of 1000 mA cm^?2 at η = 233 mV and η = 161 mV, respectively. This work may inspire researchers to explore and reutilize high‐demand metals from scrap for addressing critical material shortfalls in clean‐energy technologies.     

Effects of sediment pretreatment on the performance of sediment microbial fuel cells

In the present study, the effects of different pretreatment methods for sediments on the performance of sediment microbial fuel cells (SMFCs) were evaluated. Autoclaved (30 and 60 min), and heated (150 °C, 3 h) sediments demonstrated high power density, compared with control and heated (60 °C, 3 h) sediments. An SMFC with heated (60 °C, 3 h) sediment was found to easily form a biocathode. The power density of an SMFC with heated (150 °C, 3 h) sediment was 214 mW m(-2) on day 24. Furthermore, autoclaved (30 and 60 min) and heated (3 h, 60 and 150 °C) sediments accelerated the production of dissolved organic matter (DOM). The DOM in heated (60 °C, 3 h) sediments had larger molecular sizes. The present study demonstrates that SMFCs can have high power density and high loss on ignition removal efficiencies when produced from sediments by suitable pretreatment methods.     

Harnessing microbially generated power on the seafloor

In many marine environments, a voltage gradient exists across the water sediment interface resulting from sedimentary microbial activity. Here we show that a fuel cell consisting of an anode embedded in marine sediment and a cathode in overlying seawater can use this voltage gradient to generate electrical power in situ. Fuel cells of this design generated sustained power in a boat basin carved into a salt marsh near Tuckerton, New Jersey, and in the Yaquina Bay Estuary near Newport, Oregon. Retrieval and analysis of the Tuckerton fuel cell indicates that power generation results from at least two anode reactions: oxidation of sediment sulfide (a by-product of microbial oxidation of sedimentary organic carbon) and oxidation of sedimentary organic carbon catalyzed by microorganisms colonizing the anode. These results demonstrate in real marine environments a new form of power generation that uses an immense, renewable energy reservoir (sedimentary organic carbon) and has near-immediate application.     

Energy sources for chemolithotrophs in an arsenic- and iron-rich shallow-sea hydrothermal system

The hydrothermally influenced sediments of Tutum Bay, Ambitle Island, Papua New Guinea, are ideal for investigating the chemolithotrophic activities of micro-organisms involved in arsenic cycling because hydrothermal vents there expel fluids with arsenite (As(III)) concentrations as high as 950 μg L(-1) . These hot (99 °C), slightly acidic (pH ~6), chemically reduced, shallow-sea vent fluids mix with colder, oxidized seawater to create steep gradients in temperature, pH, and concentrations of As, N, Fe, and S redox species. Near the vents, iron oxyhydroxides precipitate with up to 6.2 wt% arsenate (As(V)). Here, chemical analyses of sediment porewaters from 10 sites along a 300-m transect were combined with standard Gibbs energies to evaluate the energy yields (-ΔG(r)) from 19 potential chemolithotrophic metabolisms, including As(V) reduction, As(III) oxidation, Fe(III) reduction, and Fe(II) oxidation reactions. The 19 reactions yielded 2-94 kJ mol(-1) e(-) , with aerobic oxidation of sulphide and arsenite the two most exergonic reactions. Although anaerobic As(V) reduction and Fe(III) reduction were among the least exergonic reactions investigated, they are still potential net metabolisms. Gibbs energies of the arsenic redox reactions generally correlate linearly with pH, increasing with increasing pH for As(III) oxidation and decreasing with increasing pH for As(V) reduction. The calculated exergonic energy yields suggest that micro-organisms could exploit diverse energy sources in Tutum Bay, and examples of micro-organisms known to use these chemolithotrophic metabolic strategies are discussed. Energy modeling of redox reactions can help target sampling sites for future microbial collection and cultivation studies.     

Corrosion-enhancing potential of Shewanella putrefaciens isolated from industrial cooling waters

Microbially influenced corrosion (MIC) is catalysed by a series of metabolic activities of selected micro-organisms, notably by oxidation of cathodic hydrogen by hydrogenase, by hydrogen sulphide and by reduction of ferric iron. The sulphate-reducing bacteria are considered to be the most common catalyst of MIC, whereas the role of other bacteria has been neglected. This study examined the corrosive potential of the facultative sulphide producer, Shewanella putrefaciens , isolated from an industrial cooling water system. Shewanella putrefaciens was shown to reduce ferric iron and sulphite under anaerobic conditions and with ferric iron being the preferred electron acceptor. The isolate could utilize cathodic hydrogen as an energy source, especially when using sulphite as a terminal electron acceptor. In pure culture corrosion experiments, the highest mass loss of mild steel was observed in the presence of sulphite as sole electron acceptor, although mass loss was also detected where ferric iron was the sole electron acceptor. Our data indicate that S. putefaciens plays a role in MIC as it was able to catalyse a variety of corrosion-promoting reactions and to corrode mild steel under pure culture conditions.     

Increased Power in Sediment Microbial Fuel Cell: Facilitated Mass Transfer via a Water-Layer Anode Embedded in Sediment

We report a methodology for enhancing the mass transfer at the anode electrode of sediment microbial fuel cells (SMFCs), by employing a fabric baffle to create a separate water-layer for installing the anode electrode in sediment. The maximum power in an SMFC with the anode installed in the separate water-layer (SMFC-wFB) was improved by factor of 6.6 compared to an SMFC having the anode embedded in the sediment (SMFC-woFB). The maximum current density in the SMFC-wFB was also 3.9 times higher (220.46 mA/m²) than for the SMFC-woFB. We found that the increased performance in the SMFC-wFB was due to the improved mass transfer rate of organic matter obtained by employing the water-layer during anode installation in the sediment layer. Acetate injection tests revealed that the SMFC-wFB could be applied to natural water bodies in which there is frequent organic contamination, based on the acetate flux from the cathode to the anode.     

Anaerobic methanotrophic community of a 5346‐m‐deep vesicomyid clam colony in the Japan Trench

Vesicomyidae clams harbor sulfide‐oxidizing endosymbionts and are typical members of cold seep communities where active venting of fluids and gases takes place. We investigated the central biogeochemical processes that supported a vesicomyid clam colony as part of a locally restricted seep community in the Japan Trench at 5346 m water depth, one of the deepest seep settings studied to date. An integrated approach of biogeochemical and molecular ecological techniques was used combining in situ and ex situ measurements. In sediment of the clam colony, low sulfate reduction rates (maximum 128 nmol mL^?1 day^?1) were coupled to the anaerobic oxidation of methane. They were observed over a depth range of 15 cm, caused by active transport of sulfate due to bioturbation of the vesicomyid clams. A distinct separation between the seep and the surrounding seafloor was shown by steep horizontal geochemical gradients and pronounced microbial community shifts. The sediment below the clam colony was dominated by anaerobic methanotrophic archaea (ANME‐2c) and sulfate‐reducing Desulfobulbaceae (SEEP‐SRB‐3, SEEP‐SRB‐4). Aerobic methanotrophic bacteria were not detected in the sediment, and the oxidation of sulfide seemed to be carried out chemolithoautotrophically by Sulfurovum species. Thus, major redox processes were mediated by distinct subgroups of seep‐related microorganisms that might have been selected by this specific abyssal seep environment. Fluid flow and microbial activity were low but sufficient to support the clam community over decades and to build up high biomasses. Hence, the clams and their microbial communities adapted successfully to a low‐energy regime and may represent widespread chemosynthetic communities in the Japan Trench. In this regard, they contributed to the restricted deep‐sea trench biodiversity as well as to the organic carbon availability, also for non‐seep organisms, in such oligotrophic benthic environment of the dark deep ocean.     

Physicochemical Conditioning of Dredged Heavy Metal‐Polluted Sediment in Suspension

The remediation of heavy metal‐polluted aquatic sediment by solid‐bed bioleaching requires a material well permeable to air and water. Freshly dredged sediment is nearly impermeable and needs previous conditioning to make it suitable for solid‐bed leaching. This conditioning – in practice carried out by planting sediment packages with helophytes – comprises water removal by evapotranspiration, abiotic and microbial oxidation of sediment‐borne reduced compounds, acidification, as well as structural changes improving the sediment permeability. The rate of this process seems to be limited by the transport of oxygen into the sediment bed. For a better understanding of the physicochemical processes occurring during conditioning, sediment oxidation was studied in a stirred suspension to minimize transport limitations. Freshly dredged, silty, anoxic, heavy metal‐polluted sediment from the Weisse Elster River (Germany) was suspended in water and then continuously stirred and aerated at 20 °C. Aerobic conditions appeared within a few hours. The redox potential increased from – 400 to + 220 mV, at first very quickly and later more slowly. Sediment‐borne inorganic sulfur compounds were oxidized to sulfate (S⁰ mainly within two days and sulfide within ten days), which reduced the pH from 7.2 to 5.9. A successive oxidation of FeS to Fe(II) sulfate, the oxidation of Fe(II) to Fe(III) followed by Fe(III) oxyhydrate formation caused the dissolved Fe to sharply increase and thereafter rapidly decrease. Ammonium was completely oxidized in a nitrification process to form nitrate, further decreasing the pH to 5.5. The acidification increased the solubility of Mn, Zn, Mg, Ca, and K. The increase in dissolved Mn rules out any oxidation of Mn(II) to Mn(IV) since Mn(IV) would have been insoluble under the prevailing pH and redox conditions. Sediment oxidation did not proceed in a well‐defined, redox‐potential‐directed order, but individual (partly microbially) oxidation processes superimposed each other. Physicochemical conditioning of suspended sediment was completed after 20 days while conditioning in a solid bed would require months or even years. These different rates result from transport limitations in the solid bed. Sediment conditioning in a solid bed could therefore possibly be accelerated by prior sediment aeration.     

Fatty acid oxidation in anoxic marine sediments: the importance of hydrogen sensitive reactions

In anoxic marine sediments fatty acids may be oxidized directly by sulfate reducing bacteria, or may be oxidized by pathways which result in hydrogen production. Some of these latter reactions are quite sensitive to hydrogen concentrations ... in other words if hydrogen concentrations become elevated, fatty acid oxidation will cease. Thus sulfate reducers may actually play two important roles in the metabolism of fatty acids in marine sediments. The sulfate reducers both can utilize fatty acids directly, and also can oxidize hydrogen and thus control hydrogen partial pressures in the sediments. Therefore sulfate reducers may act indirectly to facilitate fatty acid oxidation by hydrogen-producing pathways. We carried out a series of incubations of slurried salt marsh sediment under high and low hydrogen partial pressures and in the presence and absence of molybdate to investigate the relative importance of sulfate reducers and other bacteria mediating hydrogen-sensitive reactions. Our results suggest that both classes of bacteria contribute significantly to fatty acid turnover in marine sediments. Studies of low molecular weight fatty acid turnover in sediment must explicitly recognize that manipulation of sediment (including addition of molydbate to inhibit sulfate reducers) may have a large impact on hydrogen partial pressures in sediment, and may thus significantly alter the pathways and/or rates of fatty acid turnover.     

Electric coupling between distant nitrate reduction and sulfide oxidation in marine sediment

Filamentous bacteria of the Desulfobulbaceae family can conduct electrons over centimeter-long distances thereby coupling oxygen reduction at the surface of marine sediment to sulfide oxidation in deeper anoxic layers. The ability of these cable bacteria to use alternative electron acceptors is currently unknown. Here we show that these organisms can use also nitrate or nitrite as an electron acceptor thereby coupling the reduction of nitrate to distant oxidation of sulfide. Sulfidic marine sediment was incubated with overlying nitrate-amended anoxic seawater. Within 2 months, electric coupling of spatially segregated nitrate reduction and sulfide oxidation was evident from: (1) the formation of a 4–6-mm-deep zone separating sulfide oxidation from the associated nitrate reduction, and (2) the presence of pH signatures consistent with proton consumption by cathodic nitrate reduction, and proton production by anodic sulfide oxidation. Filamentous Desulfobulbaceae with the longitudinal structures characteristic of cable bacteria were detected in anoxic, nitrate-amended incubations but not in anoxic, nitrate-free controls. Nitrate reduction by cable bacteria using long-distance electron transport to get privileged access to distant electron donors is a hitherto unknown mechanism in nitrogen and sulfur transformations, and the quantitative importance for elements cycling remains to be addressed.     

Bifunctional Electrocatalytic Activity of Boron‐Doped Graphene Derived from Boron Carbide

A single material that can perform water oxidation and oxygen reduction reactions (ORR), also called bifunctional catalyst, represents a novel concept that emerged from recent materials research and that has led to applications in new‐generation energy‐storage systems, such as regenerative fuel cells. Here, metal/metal‐oxide free, doped graphene derived from rhombohedral boron carbide (B₄C) is demonstrated to be an effective bifunctional catalyst for the first time. B₄C, one of the hardest materials in nature next to diamond and cubic boron nitride, is converted and separated in bulk to form heteroatom (boron, B) doped graphene (BG, yield ≈7% by weight, after the first cycle). This structural conversion of B₄C to graphene is accompanied by in situ boron doping and results in the formation of an electrochemically active material from a non‐electrochemically active material, broadening its potential for application in various energy‐related technologies. The electrocatalytic efficacy of BG is studied using various voltammetric techniques. The results show a four‐electron transfer mechanism as well as a high methanol tolerance and stability towards ORR. The results are comparable to those from commercial 20 wt% Pt/C in terms of performance. Furthermore, the bifunctionality of the BG is also demonstrated by its performance in water oxidation.     

Biogeochemical controls on microbial diversity in seafloor sulphidic sediments

The ultimate fate of hydrothermal sulphides on the seafloor depends on the nature and rate of abiotic and microbially catalysed reactions where sulphide minerals are exposed to oxic seawater. This study combines organic and inorganic geochemical with microbiological measurements across a suboxic transition zone of highly altered sulphidic sediments from the Trans‐Atlantic Geotransverse hydrothermal field to characterize the reaction products and microbial communities present. There is distinct biogeochemical zonation apparent within the sediment sequence from oxic surface layers through a suboxic transition zone into the sulphide material. The microbial communities in the sediment differ significantly between the biogeochemical horizons sampled, with the identified microbes inferred to be associated with Fe and S redox cycling. In particular, Marinobacter species, organisms associated with circumneutral Fe oxidation, are dominant in a sulphide lens present in the lower core. The dominance of Marinobacter‐related sequences within the relict sulphide lens implies that these organisms play an important role in the alteration of sulphides at the seafloor once active venting has ceased.     

On the energetics of chemolithotrophy in nonequilibrium systems: case studies of geothermal springs in Yellowstone National Park

Chemolithotrophic micro‐organisms are important primary producers in high‐temperature geothermal environments and may catalyse a number of different energetically favourable redox reactions as a primary energy source. Analysis of geochemical constituents followed by chemical speciation and subsequent calculation of reaction free energies (ΔG_rxn) is a useful tool for evaluating the thermodynamic favourability and potential energy available for microbial metabolism. The primary goal of this study was to examine relationships among geochemical gradients and microbial population distribution, and to evaluate the utility of energetic approaches for predicting microbial metabolism from free‐energy calculations, utilizing as examples, several geothermal habitats in Yellowstone National Park where thorough geochemical and phylogenetic analyses have been performed. Acidic (pH ～ 3) and near‐neutral (pH ～ 6–7) geothermal springs were chosen for their range in geochemical properties. Aqueous and solid phase samples obtained from the source pools and the outflow channels of each spring were characterized for all major chemical constituents using laboratory and field methods to accurately measure the concentrations of predominant oxidized and reduced species. Reaction free energies (ΔG_rxn) for 33 oxidation–reduction reactions potentially important to chemolithotrophic micro‐organisms were calculated at relevant spring temperatures after calculating ion activities using an aqueous equilibrium model. Free‐energy values exhibit significant variation among sites for reactions with pH dependence. For example, free‐energy values for reactions involving Fe³⁺ are especially variable across sites due in large part to the pH dependence of Fe³⁺ activity, and exhibit changes of up to 40 kJ mol^?1 electron from acidic to near neutral geothermal springs. Many of the detected 16S rRNA gene sequences represent organisms whose metabolisms are consistent with exergonic processes. However, sensitivity analyses demonstrated that reaction free energies do not generally represent the steep gradients in local geochemical conditions resulting from air–water gas exchange and solid phase deposition that are important in defining microbial habitats and 16S rRNA gene sequence distribution within geothermal outflow channels.     

Influence of cathodic protection of mild steel on the growth of sulphate‐reducing bacteria at 35°C in marine sediments

In order to protect metallic structures from marine corrosion, cathodic protection using sacrificial anodes or impressed current is widely used. In aerated seawater steel is considered to be protected when a cathodic potential of — 800 mV/SCE (Saturated Calomel Electrode) is applied. However, in many cases, this potential must be lowered due to the presence and activity of microorganisms such as acid‐producing bacteria or sulphate‐reducing bacteria (SRB). SRB are obligate anaerobes using sulphate as an electron acceptor with resultant production of sulfides. Some SRB are able to use hydrogen as an electron donor causing thereby depolarization of steel surfaces.

An experiment was performed in marine sediments to determine the relationship between cathodically produced hydrogen and growth of SRB in marine sediments both at ambiant temperature (Therene, 1988) and at 35°C. Results concerning the latter experiments are reported here.

Analytical techniques included microbiological analyses, lipid biomarker studies and electrochemical measurements including AC impedance spectroscopy. Results indicated a change in the bacterial community structure both on the steel and sediment as a function of time and potential. The results also showed that cathodically‐produced hydrogen promoted the growth of SRB with the Desulfovibrio genus predominating.     

Aquaculture of Posidonia australis Seedlings for Seagrass Restoration Programs: Effect of Sediment Type and Organic Enrichment on Growth

Seeds of the seagrass Posidonia australis are desiccation sensitive and as there is no seed dormancy seeds cannot be stored for use in restoration projects. To realize the restoration potential of seed‐based restoration of Posidonia, this study investigated preconditioning seedlings of Posidonia in aquaculture facilities before transplanting to extend the restoration window from a few weeks (for fresh seed) to months or even years (for preconditioned seedlings). Here, we tested two levels of organic matter addition, 0 and 1.5% sediment dry weight and three sediment types; two heterogeneous sediments typical of low‐energy marine environments (1) unsorted calcareous and (2) unsorted silica, and a homogeneous sediment typical of high‐energy marine habitats (3) well‐sorted silica. We then evaluated seedling survival, biomass and development over a period of 7 months in tank culture. There was 100% survival over the 7‐month experimental period for seedlings. Seedling leaf, root, rhizome, and total biomass increased when organic matter was added to unsorted calcareous and unsorted silica sediment but not well‐sorted silica sediment, although this increase was significant only after 7 months of growth. The characteristics of the sediment also influenced seedling root length and architecture. Root length and number of lateral root branches were greatest in unsorted sediments and when organic matter was present. This study demonstrates that tank culture of P. australis enabled seedlings to be available for restoration purposes for at least 7 months, and with modification of the sediment composition, larger P. australis seedlings with more substantial root systems can be produced.     

Tuning Multimetallic Ordered Intermetallic Nanocrystals for Efficient Energy Electrocatalysis

Ordered intermetallic alloys have attracted extensive attention as advanced electrocatalysts for polymer electrolyte membrane fuel cells (PEMFCs) reactions with much improved activity and stability. Here, latest progress in tuning intermetallic Pt‐ and Pd‐based nanocrystals with tunable morphology and structure for catalyzing both the cathodic reduction of oxygen and anodic oxidation of fuels (e.g., methanol, ethanol and formic acid) in PEMFCs is highlighted. Making/tuning interesting intermetallic PtM (M = Fe, Co, Pb, Cu, etc.)‐based nanocrystals for boosting oxygen reduction reaction with high activity and stability by using/controlling high‐temperature annealing treatment is discussed. In all the reported Pt‐based intermetallic nanocrystals, controlling the degree of ordering under the proper high temperature treatment is the key for achieving the optimized electrocatalysis. In order to search for cheaper catalysts, the progress on making Pd‐based intermetallic nanocrystals is also discussed. Furthermore, future research directions are proposed and discussed to further enhance the efficiency of such unique intermetallic multimetallic nanocatalysts. This report aims to demonstrate the potential of ordered intermetallic strategy for boosting electrocatalysis and stimulating more research efforts in this field.     

Archaeal and bacterial communities in geochemically diverse hot springs of Yellowstone National Park, USA

Microbiological and geochemical surveys were conducted at three hot springs (Obsidian Pool, Sylvan Spring, and ‘Bison Pool’) in Yellowstone National Park (Wyoming, USA). Microbial community structure was investigated by polymerase chain reaction (PCR) amplification of 16S rRNA gene sequences from DNA extracted from sediments of each hot spring, followed by molecular cloning. Both bacterial and archaeal DNA was retrieved from all samples. No Euryarchaea were found, but diverse Crenarchaea exist in all three pools, particularly affiliating with deep‐branching, but uncultivated organisms. In addition, cloned DNA affiliating with the Desulphurococcales and Thermoproteales was identified, but the distribution of taxa differs in each hot spring. The bacterial community at all three locations is dominated by members of the Aquificales and Thermodesulfobacteriales, indicating that the ‘knallgas’ reaction (aerobic hydrogen oxidation) may be a central metabolism in these ecosystems. To provide geochemical context for the microbial community structures, energy‐yields for a number of chemolithoautotrophic reactions are provided for >80 sampling sites in Yellowstone, including Obsidian Pool, Sylvan Spring, and ‘Bison Pool’. This energy profile shows that the knallgas reaction is just one of many exergonic reactions in the Yellowstone hot springs, that energy‐yields for certain reactions can vary substantially from one site to the next, and that few of the demonstrated exergonic reactions are known to support microbial metabolism.     

Not all aragonitic molluscs are missing: taphonomy and significance of a unique shelly lagerstätte from the Jurassic of SW Britain

The Blue Lias Formation at Lyme Regis (Dorset, UK) includes an exceptional pavement of abundant large ammonites that accumulated during a period of profound sedimentary condensation. Ammonites were originally composed of aragonite, an unstable polymorph of calcium carbonate, and such fossils are typically prone to dissolution; the occurrence of a rich association of aragonitic shells in a condensed bed is highly unusual. Aragonite dissolution occurs when pore‐water pH is reduced by the oxidization of hydrogen sulphide close to the sediment‐water interface. Evidence suggests that, in this case, the oxygen concentrations in the overlying water column were low during deposition. This inhibited the oxidation of sulphides and the associated lowering of pH, allowing aragonite to survive long enough for the shell to be neomorphosed to calcite. The loss of aragonite impacts upon estimates of past biodiversity and carbonate accumulation rates. The preservational model presented here implies that diagenetic loss of aragonite will be greatest in those areas where dysoxic‐anoxic sediment lies beneath an oxic waterbody but least where the sediment and overlying water are oxygen depleted. Unfortunately, this implies that preservational bias through aragonite loss will be greatest in those biotopes which are typically most diverse and least where biodiversity is lowest due to oxygen restriction.