Sulfidic Environments Research Articles

Electrochemical properties and hydrogen barrier properties of mixed sulphide-iron compounds

Sulphide-iron compounds are the corrosion product in hydrogen sulphide environment. When the surface of steel is covered by sulphide-iron compounds, the corrosion rate of steel becomes unpredictable. The effect on the corrosion resistance of sulphide-iron compounds layer is explored by controlling the proportion of single crystalline sulphide-iron compounds. In this study, single crystalline pyrite and pyrrhotite were synthesised through hydrothermal method. The pyrite and pyrrhotite were then mixed with ratios of 7:3, 1:1 and 3:7. The results revealed that ion selectivity was changed from cation to anion as the pyrrhotite content increased. What's more, the impedance value of the mixed sulphur iron compounds gradually decreased and the corrosion current density increased, which indicated that corrosion resistance reduced with the increasing of pyrrhotite content. As the pyrrhotite content increased, hydrogen permeation current and hydrogen content exhibited a gradual decrease, which showed an overall improvement in its hydrogen barrier properties.

A new species of Erinaceusyllis (Annelida: Syllidae) discovered at a wood-fall in the eastern Clarion-Clipperton zone, central Pacific ocean

In the deep sea, organic falls provide temporary localized enrichments of organic matter to the otherwise nutrient-poor abyssal seafloor. Areas where organic falls land become ephemeral patches of increased biodiversity. Often rich in opportunistic species which are tolerant to the sulfidic environment formed from anaerobic breakdown of organic matter. On a wood-fall at abyssal depths in the eastern Clarion-Clipperton Zone, the novel species Erinaceusyllis simonlledoi (Annelida: Syllidae) was discovered in high abundance. This study entails the first description of a novel syllid species found in high density on a naturally occurring organic fall. Phylogenetic position was investigated using three genetic markers (16S, 18S, COI) and morphology was studied through light- and scanning electron microscopy. Genetic data and morphological analysis supported placement in the syllid genus Erinaceusyllis. Distinguishing features were lack of eyes, dorsal brooding of one egg per egg-bearing segment, lack of visible papillae across the body, incomplete fusion of palps, bidentate chaetae, as well as pyriform antennae and tentacular cirri. Erinaceusyllis simonlledoi sp. nov. is highly similar to a species found on hydrothermal vents belonging to the closely related genus Sphaerosyllis. The similarity between the two species, as well as findings of unspecified Sphaerosyllis species in various types of sulfidic habitats evoke questions of a possible syllid lineage adapted to sulfidic environments.

Optimization of heat treatment of 30Kh13 steel for oil industry to operate in hydrogen sulfide environment: analysis of accelerated and standard tests

Optimization of heat treatment of 30Kh13 steel for oil industry to operate in hydrogen sulfide environment: analysis of accelerated and standard tests

Microbiome flexibility enhances the resilience of the potentially invasive coral Tubastraea aurea to abrupt environmental changes: Insights from a shallow water hydrothermal vent transplantation study

To comprehend the effects of potentially invasive coral Tubastraea aurea on marine ecosystems, it is crucial to understand their adaptive strategies to survive environmental changes and perturbations. Therefore, a cross-transplantation study was conducted to assess the microbiome's role in the resilience of T. aurea to sudden environmental changes.Hydrographic analyses revealed distinct ecological conditions at two sites: a hydrothermal vent (HV) site, characterized by harsh environmental conditions serving as a natural laboratory for future oceanic changes, and a regular coastal site Fulong (FU). Both sites showed significant differences in pH, temperature, and dissolved oxygen. Using Oxford Nanopore Technologies, we examined bacterial dynamics in coral tissue, mucus and ambient sediment samples following cross-transplantation experiments. We observed a rapid shift in dominant bacterial groups post-transplantation with transplanted corals acquiring microbiomes similar to native corals from their respective sites within 16 days. The bacteria Endozoicomonas euniceicola and Ruegeria profundi were dominant in both native and transplanted corals, suggesting their critical role in coral resilience. Furthermore, the enrichment of certain bacterial taxa post-transplantation suggests that opportunistic species also contribute to host acclimatization. Functional profiling data indicated that there was site-specific adaptation because corals had acquired beneficial bacterial assemblages to assist them cope with environmental stressors. More specifically, there was a switch towards sulfur and nitrogen metabolism in corals that moved to high sulfidic environments, while corals transplanted into normal coastal environments showed enriched photoautotrophic processes due to their symbionts. Our study underscored the highly flexible microbiome of T. aurea and its pivotal role in facilitating host resilience to environmental perturbations, particularly in the context of its potential invasiveness. Hence, these findings contribute to the understanding of coral-microbiome dynamics and emphasize the necessity of considering microbially-mediated resilience in managing potentially invasive coral species in marine ecosystems around the world, especially as ocean conditions continue to change.

The fracture and perforation failure analysis of downhole tubes

：The downhole tubes were fractured and perforated after 5 years of shut-in due to high water cuts. This study employs a comprehensive array of analytical techniques to investigate the mechanisms behind fractures and perforations. Utilizing non-destructive testing (NDT), direct reading spectrometer, tensile strength testing machine, impact testing machine, optical microscope (OM), macroscopic fracture morphology observation, scanning electron microscope (SEM) and energy spectrum analysis (EDS), and sulfide stress corrosion cracking (SSCC) was studied. The reason for the fracture of the tubing is that under the condition of low pH value, high hydrogen sulfide environment, the tubing is fractured due to stress concentration caused by cracks in the outer thread relief groove. The perforation of the inner tube wall was caused by gradual wall thickness reduction under the influence of H2S, CO2, and Cl−, resulting in fouling and eventual perforation. To prevent tube corrosion during long-term shut-in, it is recommended to inject crude oil or diesel into the well.

Rhodoquinone-dependent electron transport chain is essential for Caenorhabditis elegans survival in hydrogen sulfide environments

Hydrogen sulfide (H2S) has traditionally been considered as an environmental toxin for animal lineages; yet, it plays a signaling role in various processes at low concentrations. Mechanisms controlling H2S in animals, especially in sulfide-rich environments, are not fully understood. The main detoxification pathway involves the conversion of H2S into less harmful forms, through a mitochondrial oxidation pathway. The first step of this pathway oxidizes sulfide and reduces ubiquinone (UQ) through sulfide-quinone oxidoreductase (SQRD/SQOR). Because H2S inhibits cytochrome oxidase and hence UQ regeneration, this pathway becomes compromised at high H2S concentrations. The free-living nematode C. elegans feeds on bacteria and can face high sulfide concentrations in its natural environment. This organism has an alternative ETC that uses rhodoquinone (RQ) as the lipidic electron transporter and fumarate as the final electron acceptor. In this study, we demonstrate that RQ is essential for survival in sulfide. RQ-less animals (kynu-1 and coq-2e KO) cannot survive high H2S concentrations, while UQ-less animals (clk-1 and coq-2a KO) exhibit recovery, even when provided with a UQ-deficient diet. Our findings highlight that sqrd-1 uses both benzoquinones and that RQ-dependent ETC confers a key advantage (RQ regeneration) over UQ in sulfide-rich conditions. C. elegans also faces cyanide, another cytochrome oxidase inhibitor, whose detoxification leads to H2S production, via cysl-2. Our study reveals that RQ delays killing by the HCN-producing bacteria Pseudomonas aeruginosa PAO1. These results underscore the fundamental role that RQ-dependent ETC serves as a biochemical adaptation to H2S environments, and to pathogenic bacteria producing cyanide and H2S toxins.

Impact of mineral and non-mineral sources of iron and sulfur on the metalloproteome of Methanosarcina barkeri.

Methanogens often inhabit sulfidic environments that favor the precipitation of transition metals such as iron (Fe) as metal sulfides, including mackinawite (FeS) and pyrite (FeS2). These metal sulfides have historically been considered biologically unavailable. Nonetheless, methanogens are commonly cultivated with sulfide (HS-) as a sulfur source, a condition that would be expected to favor metal precipitation and thus limit metal availability. Recent studies have shown that methanogens can access Fe and sulfur (S) from FeS and FeS2 to sustain growth. As such, medium supplied with FeS2 should lead to higher availability of transition metals when compared to medium supplied with HS-. Here, we examined how transition metal availability under sulfidic (i.e., cells provided with HS- as sole S source) versus non-sulfidic (cells provided with FeS2 as sole S source) conditions impact the metalloproteome of Methanosarcina barkeri Fusaro. To achieve this, we employed size exclusion chromatography coupled with inductively coupled plasma mass spectrometry and shotgun proteomics. Significant changes were observed in the composition and abundance of iron, cobalt, nickel, zinc, and molybdenum proteins. Among the differences were alterations in the stoichiometry and abundance of multisubunit protein complexes involved in methanogenesis and electron transport chains. Our data suggest that M. barkeri utilizes the minimal iron-sulfur cluster complex and canonical cysteine biosynthesis proteins when grown on FeS2 but uses the canonical Suf pathway in conjunction with the tRNA-Sep cysteine pathway for iron-sulfur cluster and cysteine biosynthesis under sulfidic growth conditions.IMPORTANCEProteins that catalyze biochemical reactions often require transition metals that can have a high affinity for sulfur, another required element for life. Thus, the availability of metals and sulfur are intertwined and can have large impacts on an organismismal biochemistry. Methanogens often occupy anoxic, sulfide-rich (euxinic) environments that favor the precipitation of transition metals as metal sulfides, thereby creating presumed metal limitation. Recently, several methanogens have been shown to acquire iron and sulfur from pyrite, an abundant iron-sulfide mineral that was traditionally considered to be unavailable to biology. The work presented here provides new insights into the distribution of metalloproteins, and metal uptake of Methanosarcina barkeri Fusaro grown under euxinic or pyritic growth conditions. Thorough characterizations of this methanogen under different metal and sulfur conditions increase our understanding of the influence of metal availability on methanogens, and presumably other anaerobes, that inhabit euxinic environments.

Isotopically light Mo in sediments of methane seepage controlled by the benthic Fe–Mn redox shuttle process

Methane seepage has been extensively observed in various continental margin settings. It has profound effects on the marine redox environment and the molybdenum (Mo) cycles in marine sediments. Therefore, there has been much recent attention on the redox-sensitive behavior of Mo in methane seepage environments. However, the characteristics of the Mo isotope composition in the cold-seep system remain poorly understood. In this study, we performed geochemical analyses, including Mo content and isotope composition, on sediment samples (core QDN-MS6) from the “Haima” cold-seep deposit area in the South China Sea. The analysis reveals a significant concentration of authigenic pyrite in the mid-section of QDN-MS6 core (373–403 cm). Moreover, the δ34S value in this interval is notably elevated with high total sulfur/total organic carbon ratio. Additionally, the sediments in the mid-section exhibits substantial enrichment in Mo (enrichment factors of Mo ranging from 5.29 to 39.32). This implies that the sediments in the mid-section are influenced by sulfate-driven anaerobic oxidation of methane. Most notably, the sediments in the mid-section displayed distinct low δ98Mo values (with an average of −0.7‰). After careful consideration, we ruled out the influence of organic matter, an oxic environment, a weakly sulfidic environment, and incomplete removal of thiopolybdate as contributing factors. Based on δ56Fe-Fe/Al ratios, (Mo–U) enrichment factors, and As enrichment factors, we propose that the “benthic Fe-Mn redox shuttle process” is the primary cause of the observed light δ98Mo signatures in sediments. This newly identified mechanism sheds light on Mo isotope cycling in methane seepage environments and enhances our understanding of the Mo isotope cycling process.

Enrichment pattern of tungsten in sediments under methane seepage environments: Applicability as a proxy for tracing and reconstructing (paleo-)methane seepage

The release of hydrogen sulfide by sulfate-driven anaerobic oxidation of methane (SD-AOM) during methane seepage activities has a strong impact on the evolution of marine redox conditions and the cycles of redox-sensitive elements (e.g. Mo and U). Consequently, the sedimentary enrichment or depletion of these elements is often used to trace and reconstruct (paleo-)methane seepage activity. In recent years, tungsten (W) has shown promise as an indicator of marine redox changes, but its applicability to trace methane seepage activity is unknown. This study identified significant differences in the W content of sediments in methane seepage environments compared to suboxic environments not influenced by methane seepage and oxic environments in the South China Sea. The sediments subjected to methane seepage were characterized by low W contents, similar to those of euxinic Black Sea sapropels. It is believed that the sulfidic environment resulting from SD-AOM is the primary cause of W depletion in sediments subjected to methane seepage. By examining W's interaction with its twin element, Mo, we present WMo enrichment patterns in various environments. In methane seepage environment (sulfidic environments), sediments had high MoEF (> 10) and low WEF (< 2) with a high Mo/W molar ratio (> 10); in suboxic environments not influenced by methane seepage, sediments exhibited a WMo enrichment pattern similar to the UCC (the MoEF and WEF values are predominantly below 1 and 2, respectively, with a low Mo/W molar ratio, <1.5); in oxic environments (enrichment of FeMn (oxy)hydroxides), sediments exhibited high MoEF (2 < MoEF < 10) and high WEF (> 2), with a medium Mo/W molar ratio (1.5–10). This further indicates that the Mo/W molar ratio has great potential in tracing and reconstructing (paleo-)methane seepage activities.

Effect of hydrogen on steels in hydrogen sulfide-containing and other environments at gas facilities

The impact of hydrogen sulfide raw materials on steel equipment and pipelines is known and is associated not only with internal corrosion processes, but also with the hydrogenation of carbon and low-alloy steels used. Penetration of hydrogen into steel can lead to the loss of its strength properties and subsequent destruction of gas pipelines operated under high pressure conditions. The manifestations of cracking characteristic of hydrogen sulfide environments, which are a consequence of the penetration of hydrogen into steel, are the most dangerous from the point of view of the safety and reliability of the operation of facilities for the production and transportation of corrosive gas. The effect of H2S on the decrease in ductility of the main types of structural steels was studied based on the results of simulation tests. The formation of blisters (bloatings) and cracks on the surface of steels due to the effect of hydrogen on steel was recorded. The study of the phase composition and properties of corrosion products was carried out in order to assess their possible influence on the processes of steel hydrogenation. The formation of evenly distributed on the surface and the densest corrosion deposits will hinder both the corrosion processes and the penetration of hydrogen into steel. A decrease in the plastic properties of steel is also observed when exposed to hydrogen, which can be transported both separately and together with methane through the main gas pipelines. The main possible means of protecting steels that are unstable to hydrogenation is the use of corrosion inhibitors. It was established that the most effective corrosion inhibitors with rational technologies of application and dosage can protect steels from penetration of hydrogen into them and their destructive effect.

Emerging Behaviour of Alloy Steel Microstructure in Hydrogen Sulphide Environment - A Review

Alloy steel is known to be different from carbon steel due to the presence of the alloying element in varying compositions which is usually done for the purpose of modifying and improving the performance of the steel. However, a major problem with the alloy steel is that it usually exhibits different behavior in terms of the microstructures and the mechanical properties, especially, in sulphide environment. Thus, this study focused on the different microstructure of alloy steel and their performance in different environment with strong emphasis in sulphide environment. It was established in the study that a major problem of alloy steel in hydrogen sulphide environment is the sulphide stress cracking which is attributed to the presence of hydrogen and its absorption by the alloy steel. Hence, this study provides a potential guide and information on the capacity of the grades of alloy steel that can thrive in sulphide environment.

Effect of sulfide on the physiological energetics of Mercenaria mercenaria

Marine sulfide is mainly produced by the reduction of sulfate. Eutrophication and anoxic conditions caused by tidal fluctuations have accelerated the production of sulfide and widened its distribution. Sulfide has toxic effects on aquatic animals, and it has important effects on physiological activities such as feeding and respiration in buried bivalves. The aim of this study was to estimate the impact of sulfide on the energy budget of the intertidal bivalve Mercenaria mercenaria. Acute toxicity experiments were first conducted on small (SS), medium (MS), and large (LS) size clams, and then clearance rate (CR), absorption efficiency (AE), respiration rate (RR), and ammonia excretion rate (ER) were measured at 24, 48, 72, and 96 h using 0 (control group), safe concentration (low sulfide group), and 96 h half-lethal concentration (high sulfide group) as sulfide concentration gradients, and scope for growth (SFG) was calculated. The results indicated that sulfide reduced the CR, AE, RR, and ER of M. mercenaria, and these indicators were lower in the high sulfide group than in the low sulfide group. The sulfide concentration and exposure time had significant effects on CR, AE, RR, and SFG. The CR of the SS low sulfide group reached its maximum value at 48 h, and the CR of the LS low sulfide and high sulfide groups reached their maximum values at 96 h and 48 h, respectively. SFG experienced a significant decrease with the extension of time, and for both MS and LS, the SFG of sulfide-treated groups was negative at all times, with the exception of 24 h. These results suggest that M. mercenaria exhibits metabolic inhibition and metabolic compensation in response to sulfide exposure. This study provides important insights for comprehending the physiological response of buried bivalves in sulfide environments and provides a scientific fundation for implementing corresponding culture measures.

Stainless Steel in Municipal Sewage-How to Recognize Favorable Corrosion Conditions.

While chromium-nickel steel is known to be extremely resistant to corrosion, the occurrence of certain factors can unfortunately initiate an uncontrolled corrosion process. This paper presents samples made of 304 stainless steel containing delta ferrite that have been exposed to wastewater for 18 months. Samples placed above the surface of the wastewater (A-series) were intensively corroded. Samples half-submerged in the wastewater and periodically fully submerged at higher effluent flows through the screenings and grit separator (B-series) only suffered minor mechanical erosion. No significant changes in the tested surface were observed on samples fully submerged in wastewater (C-series). The results indicated that the observed pitting corrosion of samples placed above the surface of the wastewater was a consequence of the presence of bacteria in a wet hydrogen sulfide environment. The fluorescence in situ hybridization method showed that either the sludge taken from the wastewater, or from the surface of samples submerged in wastewater exhibited increased amounts of bacteria from the δ-proteobacteria class, indicating the presence of microorganisms involved in the reduction of sulfur or sulfate compounds. A new approach to microbiological evaluation by determining classes of bacteria may be a promising tool for evaluating wastewater in terms of aggressiveness and recognizing favorable corrosive conditions.

Study of the protection of carbon steel with an inhibitory composition in hydrogen sulfide environments by electrochemical methods

Study of the protection of carbon steel with an inhibitory composition in hydrogen sulfide environments by electrochemical methods

Sedimentary Environment and Organic Accumulation of the Ordovician–Silurian Black Shale in Weiyuan, Sichuan Basin, China

The sedimentary environment and organic matter enrichment relationship of the Upper Ordovician Wufeng Formation black shale, Guanyinqiao mudstone, and Lower Silurian Longmaxi Formation black shale in the Sichuan Basin of Weiyuan are analyzed using geochemical methods such as organic carbon, sulfur, major elements, and trace elements. The experimental results illustrate that the upper section of the Wufeng Formation and the lower section of the Longmaxi Formation are organic matter enrichment layers. The presence of P indicates a high productivity level in the Sichuan Basin from the Late Ordovician to the Early Silurian. In addition, indicators such as V/Cr, Ni/Co, and S/C suggest that the Wufeng Formation was deposited under anoxic reductive conditions, that the ice age Guanyinqiao segment was in an oxygen-rich to oxygen-poor environment, and that the Longmaxi Formation was in a sulfidic environment. Mo/TOC indicates that the Wufeng Formation shale was controlled by a restricted basin and that the Guanyinqiao segment and the Longmaxi Formation were in a medium-to-weak retention environment. The weak correlation of TOC with P/Al and Al indicates that the level of primary productivity and terrigenous detritus had a minor effect on the organic matter enrichment of the Wufeng and Longmaxi Formation black shale. Conversely, the positive correlation of TOC with V/Cr and Ni/Co illustrates that the anoxic reductive sedimentary environment is the main factor affecting the organic matter enrichment of the Wufeng and Longmaxi Formation black shale. Based on these studies, the development model of organic-rich shales of the Ordovician–Silurian in Weiyuan, Sichuan Basin is proposed. This paper may provide a reference for shale gas exploration in the Wufeng–Longmaxi Formation and a sedimentary response to the major geological events of Ordovician–Silurian.

From two sensors to a single sensor: Better understanding of oxygen–sulfide interfaces

AbstractIntense biogeochemical transformations in sediments and biofilms may occur over sub‐mm distances. Our current understanding of those transformations in such narrowly stratified environments has been facilitated by the introduction of microsensors. Until now most studies have been conducted using individual sensors for the various chemical species, and careful vertical alignment of the sensor tips is then essential for the meaningful interpretation of the resulting data. For instance, the determination of total dissolved sulfide (TDS) at high resolution requires perfect alignment of sensors for H2S and pH, as the pKa for H2S is close to ambient pH. In this study, we show how a recently developed TDS sensor and a new combined H2S/O2microsensor can improve the analysis of sulfidic environments including the oxygen–sulfide interface. The TDS sensor does not require pH correction unlike the conventional H2S sensor, and it thus eliminates the need for a simultaneous pH measurement. The combined sensor allows for perfect alignment of H2S and O2micro profiles and makes it possible to not only more accurately estimate fluxes, but also to determine overlapping zones of oxygen and dissolved sulfide at very high resolution.

Pyrite-bearing non-marine ostracods from the Lower Cretaceous Maracangalha Formation, Recôncavo Basin, NE Brazil: Depositional controls and paleoecological implications

Ostracods are aquatic microcrustaceans which use calcium dissolved in water to synthesize their carapaces, along with a low magnesium content. Depending on the conditions of the depositional environment and diagenetic processes, ostracods can be preserved in the fossil record, with or without alteration of the original chemical composition. In this study, samples from shales, siltstones and silty sandstones of the Maracangalha Formation (Recôncavo Basin) along the Gameleira and Manguinhos (Ilha de Itaparica) and Praia da Falha (Ilha dos Frades) outcrops, Baía de Todos os Santos, were analyzed. Results show that the pattern of ostracod carapaces preservation was controlled by distinct sedimentological processes. In the Manguinhos and Praia da Falha outcrops, ostracod specimens show total or partial replacement of the carapace by pyrite, with the more expressive pyritization observed in shale from Manguinhos. In the Gameleira outcrop, on the other hand, no pyritized carapaces were observed. Results of the Energy Dispersive Spectrometry (EDS) from Manguinhos and Praia da Falha outcrops indicate the presence of Fe and S pointing to pyrite mineralization. The Scanning Electron Microscopy (SEM) images revealed the euhedral and framboidal habit of pyrites present in the carapaces. The low recovery of specimens from Gameleira and Praia da Falha, as well as the abundance of specimens in Manguinhos, seem to have depositional controls. At Gameleira and at Praia da Falha, facies associated with low-to-high density turbidity currents may have hampered preservation, thus low recovery of ostracods. Despite the occurrence of fragmented carapaces, the anoxic conditions of the Manguinhos shale samples allowed a better preservation of specimens. The Manguinhos facies are interpreted as relatively deep lacustrine deposits. The presence of framboidal pyrite suggests early conditions of diagenesis at low burial depths. Pyrite mineralization may have occurred through a hydrogen sulfide environment, rich in organic matter, with dissolution of the carbonate carapace through the acidic pH of the medium and relative rapid post-mortem burial. The sedimentary facies described, along with the taphonomic results of ostracod preservation, corroborate a lacustrine environment with occasional sediment gravity flows to the Maracangalha Formation.

A new extremophile ostracod crustacean from the Movile Cave sulfidic chemoautotrophic ecosystem in Romania

Sulfidic cave ecosystems are remarkable evolutionary hotspots that have witnessed adaptive radiation of their fauna represented by extremophile species having particular traits. Ostracods, a very old group of crustaceans, exhibit specific morphological and ecophysiological features that enable them to thrive in groundwater sulfidic environments. Herein, we report a peculiar new ostracod species Pseudocandonamovilaensis sp. nov. thriving in the chemoautotrophic sulfidic groundwater ecosystem of Movile Cave (Romania). The new species displays a set of homoplastic features specific for unrelated stygobitic species, e.g., triangular carapace in lateral view with reduced postero-dorsal part and simplification of limb chaetotaxy (i.e., loss of some claws and reduction of secondary male sex characteristics), driven by a convergent or parallel evolution during or after colonization of the groundwater realm. P.movilaensis sp. nov. thrives exclusively in sulfidic meso-thermal waters (21 °C) with high concentrations of sulphides, methane, and ammonium. Based on the geometric morphometrics-based study of the carapace shape and molecular phylogenetic analyses based on the COI marker (mtDNA), we discuss the phylogenetic relationship and evolutionary implication for the new species to thrive in groundwater sulfidic groundwater environments.

Effect of surfactant on the morphology and anti-tarnishing behaviour of Ag coatings electrodeposited from a novel cyanide-free thiosulphate-based electroplating bath

In the present course of study, mirror-bright silver (Ag) coatings are electrodeposited via pulse galvanostatic route from a cyanide-free thiosulphate-based bath containing cetrimonium bromide (CTAB) as a surfactant. Cyclic voltammetry (CV) and chronoamperometry studies are performed to analyze the mode of nucleation occurring in the presence and absence of CTAB during the deposition of Ag. The electrochemical studies and the corresponding SEM micrographs suggest that in the presence of CTAB, Ag nucleates in the progressive mode. The XRD and EDS analysis confirm the presence of elemental Ag in the deposited coatings. The SEM studies show the morphological variations that occur in the presence and absence of CTAB. The cross-sectional SEM suggests that in the presence of CTAB, a continuous and uniform coating of an average thickness of ∼3.5 µm is deposited. However, in the absence of CTAB, the deposited coating is non-uniform and has a lower thickness. A static immersion test in Na2S environment, followed by EIS measurements, are carried out to study the effect of CTAB on the anti-tarnishing behaviour of Ag coatings. The XPS spectra show that in the absence of CTAB there is a higher concentration of S(2p) and the coatings turn black due to the formation of tarnished layer over them. Therefore, it can be concluded that the coatings deposited in the presence of CTAB have a uniform and compact morphology and are less prone to tarnishing by the sulphide environment. On that account, the bath containing CTAB can be used for producing mirror-bright and tarnish-resistant Ag coatings for long-term aesthetic usage.

Molecular evidence for the production of labile, sulfur-bearing dissolved organic matter in the seep sediments of the South China Sea

Cold seeps with methane-rich fluids leaking out of the seafloor usually support massive biomass of chemosynthetic organisms and associated fauna. A substantial amount of methane is converted to dissolved inorganic carbon by microbial metabolism, and this process also releases dissolved organic matter (DOM) into pore water. Here, pore water samples from “Haima cold seeps” sediments and the non-seep reference sediments in the northern South China Sea were analyzed for optical properties and molecular compositions of pore water DOM. Our results showed that the relative abundance of protein-like DOM, H/Cwa and molecular lability boundary percentage (MLBL%) in the seep sediments were significantly higher than those in the reference sediments, indicating that more labile DOM related to unsaturated aliphatic compounds is produced in the seep sediments. Spearman's correlation of the fluoresce and molecular data suggested that the humic-like components (C1 and C2) mainly constituted the refractory compounds (CRAM, highly unsaturated and aromatics compounds). In contrast, the protein-like component (C3) had high H/C ratios featuring high degree of DOM lability. The amount of S-containing formulas (CHOS and CHONS) was greatly elevated in the seep sediments, likely caused by abiotic and biotic sulfurization of DOM in the sulfidic environment. Although the abiotic sulfurization was proposed to have a stabilizing effect on organic matter, our results implied that the biotic sulfurization in the cold seep sediments would increase DOM lability. Overall, the labile DOM accumulated in the seep sediments is closely linked to methane oxidation, which not only support heterotrophic communities and but also likely have an impact on carbon and sulfur cycling in the sediments and the ocean.