- School of Marine Science & Policy
700 Pilottown RD
University of Delaware
Lewes, DE 19958 - 302-645-4208
George W Luther
University of Delaware, School of Marine Science and Policy, Faculty Member
A solid‐state Au/Hg voltammetric microelectrode was used to monitor the development of seasonal anoxia in Delaware coastal bays which have deep holes with stratification. Since fish kills and harmful algal blooms have occurred over the... more
A solid‐state Au/Hg voltammetric microelectrode was used to monitor the development of seasonal anoxia in Delaware coastal bays which have deep holes with stratification. Since fish kills and harmful algal blooms have occurred over the years here, water circulators were installed in October 2003 to improve water quality. We conducted in situ determination of temperature, salinity, pH, dissolved O2 and H2S to document the circulators' function which was evaluated by comparing in situ data obtained before and after their installation. Stratification at both sites was similar in 2004 to that in previous years. Furthermore, the circulators did not oxygenate the water column but did bring some H2S to the surface waters. We found that O2 concentrations in the surface waters and H2S concentrations in the bottom waters were similar in different years. Thus, the H2S conditions were not abated and water quality was still a problem.
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... DOI: 10.1080/02786826.2011.580392 Bryan R. Bzdek a , Christopher A. Zordan a , George W. Luther III b & Murray V. Johnston a pages 1041-1048. ... Smith, JN, Barsanti, KC, Friedli, HR, Ehn, M., Kulmala, M., Collins, DR, Scheckman,... more
... DOI: 10.1080/02786826.2011.580392 Bryan R. Bzdek a , Christopher A. Zordan a , George W. Luther III b & Murray V. Johnston a pages 1041-1048. ... Smith, JN, Barsanti, KC, Friedli, HR, Ehn, M., Kulmala, M., Collins, DR, Scheckman, JH, Williams, BJ and McMurry, PH 2010. ...
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Abstract Copepoda is the most diverse and abundant taxon at deep-sea hydrothermal vents, contributing significantly to the biodiversity and thus is important in maintaining ecosystem functioning. To date we lack knowledge on meiofauna,... more
Abstract Copepoda is the most diverse and abundant taxon at deep-sea hydrothermal vents, contributing significantly to the biodiversity and thus is important in maintaining ecosystem functioning. To date we lack knowledge on meiofauna, specifically copepod community dynamics, in the entire region of the Eastern Lau Spreading Center. We explore abundance and diversity of copepods associated with foundation species thriving at distinct physiochemical regimes at the active vent site ABE. Diffuse flow habitats within ABE are dominated by three foundation species: (1) the snail Alviniconcha hessleri, exposed to average vent fluid temperatures of ∼24 °C, (2) the snail Ifremeria nautilei at ∼12 °C, and (3) the mussel Bathymodiolus septemdierum in average temperatures of ∼6 °C. In each habitat, three samples were taken using a quantitative collection device (mussel-pot). Copepod abundance ranged from 1 to 30 ind. per 10 cm2, with no significant differences between the three habitats. A total of 18 copepod species were identified. In the Alviniconcha habitat, the vent endemic dirivultid copepod Stygiopontius lauensis dominated the community, representing >90% of the individuals. Species richness and Shannon diversity were significantly higher in the Bathymodiolus habitat, correlated with lower temperatures, lower hydrogen sulfide concentrations and higher oxygen concentrations. This increase in diversity was driven by a community mostly comprised of habitat generalists including genera reported from shallow coastal waters, shallow vents, and peripheral vent environments. This study provides the first quantification of biodiversity and community structure of copepods along a physiochemical stress gradient at a relatively stable Southwest Pacific vent site prospective for deep-sea mining.
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The transformation between iodate (IO3−), the thermodynamically stable form of iodine, and iodide (I-), the kinetically stable form of iodine, has received much attention because these species are often dependent on the oxygen... more
The transformation between iodate (IO3−), the thermodynamically stable form of iodine, and iodide (I-), the kinetically stable form of iodine, has received much attention because these species are often dependent on the oxygen concentration, which ranges from saturation to non-detectable in the ocean. As suboxic conditions in the ocean’s major oxygen minimum zones indicate that IO3− is minimal or non-detectable, the incorporation of IO3− into carbonate minerals has been used as a redox proxy to determine the O2 state of the ocean. Here, I look at the one and two electron transfers between iodine species with a variety of oxidants and reductants to show thermodynamics of these transformations. The IO3− to IO2− conversion is shown to be the controlling step in the reduction reaction sequence due to thermodynamic considerations. As IO3− reduction to IO2− is more favorable than NO3− reduction to NO2− at oceanic pH values, there is no need for nitrate reductase for IO3− reduction as othe...
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Dataset: Pump Profiler Casts - HRS1415Data from in situ pump profiler system collected on R/V Hugh R. Sharp cruise HRS1415 in August 2014 For a complete list of measurements, refer to the full dataset description in the supplemental file... more
Dataset: Pump Profiler Casts - HRS1415Data from in situ pump profiler system collected on R/V Hugh R. Sharp cruise HRS1415 in August 2014 For a complete list of measurements, refer to the full dataset description in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: https://www.bco-dmo.org/dataset/718887NSF Division of Ocean Sciences (NSF OCE) OCE-115538
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Abstract Formation rates for various products of hydrogen sulfide oxidation by δ-MnO2 were studied as a function of pH, temperature, concentration of the reactants, temperature and ionic strength at the environmentally-relevant... more
Abstract Formation rates for various products of hydrogen sulfide oxidation by δ-MnO2 were studied as a function of pH, temperature, concentration of the reactants, temperature and ionic strength at the environmentally-relevant conditions. The main goals of this work were studying the effects of these parameters on speciation of zero-valent sulfur, including individual polysulfides and revealing the mechanism of its formation. A reaction between hydrogen sulfide and manganese dioxide is the fastest environmentally-relevant abiotic process of polysulfides formation, reactive sulfur species, which participate in complexation of metals, pyrite formation, sulfurization of organic matter and may serve as a substrate for microorganisms. In the pH range of 7.0 to 10.5, zero-valent sulfur accounted for >55% of the sulfur in the products of hydrogen sulfide oxidation, while at pH ≥7.5, the formation rates of polysulfide zero-valent sulfur were higher than those of particulate zero-valent sulfur formation. Speciation of polysulfides on the initial stage of the reaction shows significant shift toward the higher polysulfides compared to their speciation calculated under assumption of thermodynamic equilibrium in both H2S - Sn2- - S8(aq) - α-S8 and H2S - Sn2- - S8(aq) - S8(coll) systems. We suggest that the shift in the speciation of polysulfide system results from the presence of a short-living highly reactive sulfur atoms, which are formed on the first stage of the reaction: two-electron transfer from hydrogen sulfide to manganese dioxide. Results of this study provide constraints on the rates of polysulfide formation at the redox interfaces of the stratified aquatic systems, and allows quantitative assessment of their role in sulfur cycling.
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... that the chemical speciation (probably due to precipitation of FeS) was changed as the waters were cooled. ... 5) from that at 2500 meter water depth (250 atmospheres). ... Luther, III, GW; Bono, Α.; Taillefert, M; Cary, SC In... more
... that the chemical speciation (probably due to precipitation of FeS) was changed as the waters were cooled. ... 5) from that at 2500 meter water depth (250 atmospheres). ... Luther, III, GW; Bono, Α.; Taillefert, M; Cary, SC In Electrochemical Methods for the Environmental Analyses of ...
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We have used solid‐state Au/Hg voltammetric electrodes to understand redox and biogeochemical processes in hot spring and deep sea hydrothermal environments. These electrodes are non‐specific and have the capability of measuring... more
We have used solid‐state Au/Hg voltammetric electrodes to understand redox and biogeochemical processes in hot spring and deep sea hydrothermal environments. These electrodes are non‐specific and have the capability of measuring simultaneously a suite of chemical species including several of the principal redox species involved in early diagenesis (O2, Mn2+, Fe2+, H2S/HS−, and I−) as well as some Fe species (FeS and Fe3+) and sulfur species (Sx2− and S2O$\rm{ _3^{2 - } )}$. Here we demonstrate how in situ data obtained in complex environments can be used to study specific iron and sulfur reactions and processes at (sub)millimeter to centimeter resolution and over short time scales. Examples include the oxidation of Fe2+ by O2 produced by cyanobacterial mats in Yellowstone National Park hot springs and the formation of S2O$\rm{ _3^{2 - } }$ in diffuse flow waters from the hydrothermal vents at Lau Basin. In one example, profiles of redox species in cyanobacterial mats from Yellowstone National Park hot springs show that in the light dissolved Fe2+ is completely removed from the source waters as cyanobacterial mats produce O2 and oxidize the Fe2+. Performing kinetic experiments in the dark and light at the depth of maximum O2 production indicates that the decay of Fe2+ follows a zero order rate law consistent with photosynthesis as the source of O2. These dynamic environments show how kinetic data can be obtained in situ and be used to understand the interactions between biology and chemistry. We know of no other analytical technique that can provide this information in both clear and turbid waters on the time scales (seconds) observed.
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Significance The Fe-catalyzed oxidation of sulfide by dioxygen in hydrothermal vent plumes is shown to be a source of reactive oxygen species (ROS) to the deep ocean. ROS are a class of powerful oxidants, the most reactive of which can... more
Significance The Fe-catalyzed oxidation of sulfide by dioxygen in hydrothermal vent plumes is shown to be a source of reactive oxygen species (ROS) to the deep ocean. ROS are a class of powerful oxidants, the most reactive of which can react with recalcitrant organic molecules at near diffusion limited rates. ROS production in hydrothermal systems may be comparable to the known photochemical yields of ROS in surface waters. The discovery of this abundant hydrothermal source of ROS demonstrates a mechanism for the alteration of refractory organic matter in the deep ocean.
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Dataset: Cruise Event Log - HRS1415Event Log from R/V Hugh R. Sharp cruise HRS1415 in the Chesapeake Bay and coastal Atlantic Ocean in August 2014 For a complete list of measurements, refer to the full dataset description in the... more
Dataset: Cruise Event Log - HRS1415Event Log from R/V Hugh R. Sharp cruise HRS1415 in the Chesapeake Bay and coastal Atlantic Ocean in August 2014 For a complete list of measurements, refer to the full dataset description in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: https://www.bco-dmo.org/dataset/717994NSF Division of Ocean Sciences (NSF OCE) OCE-115538
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Nanomaterials in the Earth system Nanomaterials have been part of the Earth system for billions of years, but human activities are changing the nature and amounts of these materials. Hochella Jr. et al. review sources and impacts of... more
Nanomaterials in the Earth system Nanomaterials have been part of the Earth system for billions of years, but human activities are changing the nature and amounts of these materials. Hochella Jr. et al. review sources and impacts of natural nanomaterials, which are not created directly through human actions; incidental nanomaterials, which form unintentionally during human activities; and engineered nanomaterials, which are created for specific applications. Knowledge of the properties of all three types as they cycle through the Earth system is essential for understanding and mitigating their long-term impacts on the environment and human health. Science , this issue p. eaau8299
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The combined effects of anthropogenic and biological CO2 inputs may lead to more rapid acidification in coastal waters compared to the open ocean. It is less clear, however, how redox reactions would contribute to acidification. Here we... more
The combined effects of anthropogenic and biological CO2 inputs may lead to more rapid acidification in coastal waters compared to the open ocean. It is less clear, however, how redox reactions would contribute to acidification. Here we report estuarine acidification dynamics based on oxygen, hydrogen sulfide (H2S), pH, dissolved inorganic carbon and total alkalinity data from the Chesapeake Bay, where anthropogenic nutrient inputs have led to eutrophication, hypoxia and anoxia, and low pH. We show that a pH minimum occurs in mid-depths where acids are generated as a result of H2S oxidation in waters mixed upward from the anoxic depths. Our analyses also suggest a large synergistic effect from river-ocean mixing, global and local atmospheric CO2 uptake, and CO2 and acid production from respiration and other redox reactions. Together they lead to a poor acid buffering capacity, severe acidification and increased carbonate mineral dissolution in the USA's largest estuary.The poten...
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Western Pacific hydrothermal vents will soon be subjected to deep‐sea mining and peripheral sites are considered the most practical targets. The limited information on community dynamics and temporal change in these communities makes it... more
Western Pacific hydrothermal vents will soon be subjected to deep‐sea mining and peripheral sites are considered the most practical targets. The limited information on community dynamics and temporal change in these communities makes it difficult to anticipate the impact of mining activities and recovery trajectories. We studied community composition of peripheral communities along a cline in hydrothermal chemistry on the Eastern Lau Spreading Center and Valu Fa Ridge (ELSC‐VFR) and also studied patterns of temporal change. Peripheral communities located in the northern vent fields of the ELSC‐VFR are significantly different from those in the southern vent fields. Higher abundances of zoanthids and anemones were found in northern peripheral sites and the symbiont‐containing mussel Bathymodiolus brevior, brisingid seastars and polynoids were only present in the northern peripheral sites. By contrast, certain faunal groups were seen only in the southern peripheral sites, such as lolli...
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Recent advances in understanding the chemistry of iron sulfides in sedimentary environments are beginning to shed more light on the processes involved in the global sulfur cycle. Pyrite may be formed via at least three routes including... more
Recent advances in understanding the chemistry of iron sulfides in sedimentary environments are beginning to shed more light on the processes involved in the global sulfur cycle. Pyrite may be formed via at least three routes including the reaction of precursor sulfides with polysulfides, the progressive solid-state oxidation of precursor iron sulfides and the oxidation of iron sulfides by hydrogen sulfide. The kinetics and mechanism of the polysulfide pathway are established and those of the H2S oxidation pathway are being investigated. Preliminary considerations suggest that the relative rates of the three pathways are H2S oxidation > polysulfide pathway much greater than solid-state oxidation. The kinetics and mechanisms of iron(II) monosulfide formation suggest the involvement of iron bisulfide complexes in the pathway and iron bisulfide complexes have now been identified by voltammetry and their stabililty constants measured. The framboidal texture commonly displayed by sedimentary pyrite appears to be an extreme example of mosaicity in crystal growth. Framboidal pyrite is produced through the H2S oxidation reaction. Frontier molecular orbital calculations are beginning to provide theoretical underpinning of the reaction mechanisms. Recent progress in understanding iron sulfide chemistry is leading to questions regarding the degree of involvement of precursor iron sulfides in the formation of pyrite in sediments. Spin-offs from the work are addressing problems relating to the involvement of iron sulfides in the origin of life, the nature of metastability, the mechanism of precipitation reactions and the use of iron sulfides in advanced materials.
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ABSTRACT Manganese dioxide (MnO2) has been suspected of being the active agent for the observed enhancement of crevice and galvanic corrosion rates involving passive metal cathodes in the presence of natural marine biofilms. To... more
ABSTRACT Manganese dioxide (MnO2) has been suspected of being the active agent for the observed enhancement of crevice and galvanic corrosion rates involving passive metal cathodes in the presence of natural marine biofilms. To investigate the viability of this mechanism, polymeric MnO2 was precipitated onto UNS N08367 stainless steel, which was then polarized potentiostatically at -550 mV us saturated calomel electrode (SCE) in natural seawater under various conditions to measure the effect of MnO2 on current capacity. The same alloy was also polarized with natural biofilms on the surface for comparison. The data showed that MnO2 was capable of increasing both the open-circuit potential of the coupon and the current that can be drawn from it, even in the absence of biofilms. The observed effect of MnO2 on current density was greater than could be accounted for by reduction of all the MnO2 deposited. Comparison of the total charge passed during polarization with the amount of MnO2 deposited indicated that each Mn+2 ion was being reoxidized 2 to 5 times during the polarization process by a combination of dissolved oxygen and disproportionation of a soluble Mn+3 intermediate to MnO2 and Mn+2. The current supplied by MnO2 coatings under air-saturated conditions was similar to that provided by coupons with natural biofilms. However, the rapid regeneration of current capacity demonstrated by natural biofilms could only be matched by the MnO2 coatings under oxygen-saturated conditions. This indicated that both chemical and biological reoxidation probably take place in natural biofilms. Results were consistent with the idea that MnO2 recycling (perhaps augmented by iron and nitrogen cycling) within natural biofilms is sufficient to account for observed long-term galvanic and crevice corrosion rates.
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Research Interests: Zoology, Oceanography, Chemistry, Biology, Volcano, and 5 moreHydrothermal Vent, Shellfish, Mussel, Sulfide, and East Pacific Rise
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The oxidation of organosulfur compounds requires the transfer of oxygen atoms and is important in decontamination of chemical warfare agents, desulfurization of fossil fuel for high quality, deodorization of wastewater and sludge, and... more
The oxidation of organosulfur compounds requires the transfer of oxygen atoms and is important in decontamination of chemical warfare agents, desulfurization of fossil fuel for high quality, deodorization of wastewater and sludge, and remediation of industrial effluents. The kinetics of the oxidation of organosulfur compounds (sulfur-containing amino acids, aliphatic and aromatic thiols, and mercaptans) by the environmentally-friendly oxidant, ferrate(VI) FeO(4)(2-), was quantitatively examined in this study using a kinetic model considering possible reactions among the species of ferrate(VI) and organosulfur compounds. The ratios of ferrate(VI) to the various organosulfur compounds for the one oxygen-atom transfer were 0.50 and 0.67 for Fe(II) and Fe(III) as final products, respectively. The second-order rate constants for the oxidation of organosulfur compounds by protonated ferrate(VI) HFeO(4)(-) ion were correlated with thermodynamic 1-e(-) and 2-e(-) reduction potentials in order to understand the mechanisms of the reactions. The oxidation of the compounds involved a 1-e(-) transfer step from Fe(VI) to Fe(V), followed by 2-e(-) transfer to Fe(III) as the reduced product (Fe(VI)→Fe(V)→Fe(III)). The 2-e(-) transfer steps resulted in the formation of Fe(II) (Fe(VI)→Fe(IV)→Fe(II)). Conclusions drawn from the correlations are consistent with the experimentally determined stoichiometries and products of the reactions. The calculated half-lives for the oxidation were in the range of ms to s at a dose of 10mg K(2)FeO(4)L(-1) and hence ferrate(VI) has a great potential in treating organosulfur compounds present in water and wastewater.