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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 505 records · Page 28
All sourcesNASA NTRSDOE OSTI
DOE OSTI2013

Development of Zeolite Nonwoven for the Adsorption of Radioactive Cesium - 13288

The zeolite nonwoven fabric produced by TDS (Totally Dry System) process has some advantages such as the control of zeolite content, flexibility, strength and water-resistant property depending on the purpose. Hence the zeolite nonwoven fabric is expected for the application in various fields of the decontamination of Cs-contaminated water. In this study, Cs adsorption properties of zeolite nonwoven fabrics were examined by batch experiments, and the radiation stability, thermal stability and chemical durability were evaluated. As for batch adsorption properties, relatively large uptake rate of Cs{sup +} was obtained; the uptake equilibrium attained within 20 min and the uptake (%) was above 95%. The differences in zeolite content had no effects on the Cs{sup +} uptake (%). The uptake (%) of Cs{sup +} in seawater was slightly lowered compared to that in the presence of HNO{sub 3}. The uptake (%) of Cs{sup +} in seawater was estimated to be above 90% after 2 h-shaking, indicating the considerable enhancement of uptake rate compared to the conventional granular zeolites. The uptake (%) of Cs{sup +} for the zeolite high content type was estimated to be above 99% by using {sup 137}Cs tracer. As for the comparison of sealing treatment, the uptake (%) for the zeolite sheet treated with edge sealing was larger than that with rapping treatment. The uptake (%) for the zeolite sheet (zeolite high content type) was estimated to be about 95%, which is independent of sealing treatment and NaOH concentration. As for the stability, the surface morphology and the structure of zeolite sheet were not altered by the treatment with acid and alkaline solutions under the experimental conditions. The zeolite sheets were also stable after {sup 60}Co-γ ray irradiation up to 7.01x10{sup 6} R. On the other hand, color change for both fiber and zeolite and the shrinkage of the fiber were observed after heat treatment at 150 deg. C for 2 h. Thus the considerable enhancement of adsorption properties was observed by using zeolite nonwoven fabrics compared to the conventional granular zeolites. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2016

Reevaluation of Actinide(IV)-Humic Complexation in the WIPP Performance Assessment - 16547

The legacy humic colloid model for tetravalent actinides (Th(IV), U(IV), Np(IV), and Pu(IV)) in the performance assessment (PA) of the Waste Isolation Pilot Plant (WIPP) is highly conservative. The model structure is feasible, but substantial reductions are needed for two constants, PHUMSIM and PHUMCIM. These constants are proportionality constants representing the equilibrium aqueous concentration ratio of humic-bound An(IV) to non-colloidal An(IV) for the Salado and Castile formations. In the WIPP PA model, both constants are set at 6.3 based on observed colloidal partitioning of Th(IV) in seawater. This value greatly enhances the mobile An(IV) concentration in the WIPP PA. Actual humic partitioning of An(IV) in WIPP brines is expected to be significantly lower than in seawater because the pH of WIPP brines (∼9) is higher, concentrations of competing cations (e.g., Mg{sup 2+}) are higher, and concentrations of aqueous humic substances may be lower. In this work, the results of recent studies of Th(IV)-humic and Ca{sup 2+}-humic complexation are used to simulate competitive humic complexation under WIPP conditions. The PHUMSIM and PHUMCIM values calculated for these simulations are in the range of 0.0013-0.0016 and 0.0047-0.0056, respectively. These values reduce humic-bound An(IV) to less than 1% of aqueous non-colloidal concentrations and would reduce mobile An(IV) concentrations in the WIPP PA by as much as 85%. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2019

Study on Characterization of Colloidal Silica Grout for Rock Excavation Under Saline Groundwater - 19332

A rock excavation grouting technology has been recently studied as significant technology for reducing the ingress of water into the deep repository. However, it has not been studied for applying to the coastal region, where it is discussed to be a more suitable region for the geological disposal in Japan. The latest material called colloidal silica grout (CSG) is good for sealing narrow fractures but is known to be sensitive to the salinity of groundwater because of its gelling property with salt accelerator. Although the gelling of CSG can be controlled by adding an acidic pH adjuster, the methodology for delivering the appropriate grout is not well established for such conditions of saline groundwater. Therefore, this research project was established to enhance the existing rock grouting technology for deep repositories. Initially, a grouting workshop was held with Nordic authorities in order to understand the state of the art and identify the most significant challenges to developing a generic mixing method for injecting CSG under seawater. Based on laboratory tests, we developed a feasible mixing methodology that prevents the rapid reaction with the salty water, which shows that CSG is not negatively impacted by salty mixing water or submerged by saline water. Combining the latest grouting techniques from Japan and the Nordic countries creates an optimal grouting methodology for use under seawater. Using this hybrid approach, the CSG can find wide-scale use as an agent for grouting narrow rock fractures filled with saline or fossil water in order to decrease the ingress of water in the disposal facilities. The reduction of the water ingress will enhance the safety of the repository, reduce water discharge, and diminish the long-term cost of water treatment. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2016

Additive effects of acidification and mineralogy on calcium isotopes in Triassic/Jurassic boundary limestones

The end-Triassic mass extinction coincided with a negative δ 13 C excursion, consistent with release of 13 C-depleted CO 2 from the Central Atlantic Magmatic Province. However, the amount of carbon released and its effects on ocean chemistry are poorly constrained. The co upled nature of the carbon and calcium cycles allows calcium isotopes to be used for constraining carbon cycle dynamics and vice versa. We present a high-resolution calcium isotope (δ 44/40 Ca) record from 100 m of marine limestone spanning the Triassic/Jurassic boundary in two stratigraphic sections from northern Italy. Immediately above the extinction horizon and the associated negative excursion in δ 13 C, δ 44/40 Ca decreases by ca. 0.8‰ in 20 m of section and then recovers to preexcursion values. Coupled numerical models of the geological carbon and calcium cycles demonstrate that this δ 44/40 Ca excursion is too large to be explained by changes to seawater δ 44/40 Ca alone, regardless of CO 2 injection volume and duration. Less than 20% of the δ 44/40 Ca excursion can be attributed to acidification. The remaining 80% likely reflects a higher proportion of aragonite in the original sediment, based largely on high concentrations of Sr in the samples. Our study demonstrates that coupled models of the carbon and calcium cycles have the potential to help distinguish contributions of primary seawater isotopic changes from local or diagenetic effects on the δ 44/40 Ca of carbonate sediments. Finally, differentiating between these effects is critical for constraining the impact of ocean acidification during the end-Triassic mass extinction, as well as for interpreting other environmental events in the geologic past.

58 GEOSCIENCES↗
DOE OSTI2024

Design and Synthesis of PtPdNiCoMn High‐Entropy Alloy Electrocatalyst for Enhanced Alkaline Hydrogen Evolution Reaction: A Theoretically Supported Predictive Design Approach

Electrocatalytic hydrogen generation requires a multifunctional electrocatalyst with abundant active sites to drive multielectron transfer reactions. High entropy alloys (HEA) are five or more-elements with high configurational entropy are considered unique materials for next-generation electrocatalysts. Here, in this work, based on new screening guidelines for catalyst selections that combine density-functional theory calculated Gibbs formation-enthalpy with bond length and electronegativity variance, a novel HEA electrocatalyst consisting of five elements, namely, Pt, Pd, Ni, Co, and Mn has been designed. By simple room temperature electrodeposition, the designed catalyst is prepared and its hydrogen evolution reaction (HER) is explored and validated through experimental and theoretical approaches. The HEA demonstrated a superior HER activity with an overpotential of 22.6 mV at -10 mA cm -2 which outperforms Pt/C commercial catalyst. No evident degradation of the material is detected even after 100 hours of continuous operation under high current density. Moreover, the HEA has shown exceptional performance in harsh electrolyte conditions such as in simulated seawater and actual seawater. Remarkably, the density-functional theory calculated Gibbs formation-enthalpy is small (≈0 eV) compared to Pt/C placing the new HEA near the apex of Trasatti's model of Volcano plot, which is also suggestive of superior HER activity.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Spatial Engineering Direct Cooperativity between Binding Sites for Uranium Sequestration

Preorganization is a basic design principle used by nature that allows for synergistic pathways to be expressed. Herein, a full account of the conceptual and experimental development from randomly distributed functionalities to a convergent arrangement that facilitates cooperative binding is given, thus conferring exceptional affinity toward the analyte of interest. The resulting material with chelating groups populated adjacently in a spatially locked manner displays up to two orders of magnitude improvement compared to a random and isolated manner using uranium sequestration as a model application. This adsorbent shows exceptional extraction efficiencies, capable of reducing the uranium concentration from 5 ppm to less than 1 ppb within 10 min, even though the system is permeated with high concentrations of competing ions. The efficiency is further supported by its ability to extract uranium from seawater with an uptake capability of 5.01 mg g -1 , placing it among the highest-capacity seawater uranium extraction materials described to date. The concept presented here uncovers a new paradigm in the design of efficient sorbent materials by manipulating the spatial distribution to amplify the cooperation of functions.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2017

Efficient collection and preparation of methane from low concentration waters for natural abundance radiocarbon analysis

Freshwater and marine environments constitute the largest global reservoirs of the greenhouse gas methane (CH 4 ) and natural abundance radiocarbon measurements ( 14 C-CH 4 ) can allow for high confidence interpretations about CH 4 dynamics operating in these environments. Collecting sufficient amounts of CH 4 sample for a standard, high precision 14 C-accelerator mass spectrometry (AMS) analysis (~ 200 μg carbon (C)) was previously unfeasible when sampling from low CH 4 concentration waters, such as much of the surface ocean (~ 2 nM), which would require collecting the CH 4 from 8500 L of seawater. The method described here involves pumping 20,000–40,000 L of seawater up from depth through a dissolved gas extraction system, which enables the collection of a sample composed of 100s of L of gas in less than 4 h on station. The large volume extracted gas sample is compressed into a 1.7 L cylinder for transport from the ship to the home laboratory. The home laboratory preparation of each sample to a CH 4 -derived carbon dioxide aliquot for 14 C-AMS analysis is carried out in 3 h on a flow-through vacuum line that simultaneously prepares aliquots for stable isotope analyses (δ 13 C-CH 4 and δ 2 H-CH 4 ). The total process blank of the method is small (5.0 μg CH 4 -C) and composes 1.2% of the average collected and prepared sample (424 ± 163 μg, from a recent campaign; n = 16). Finally, the 14 C-CH 4 blanks prepared on the vacuum line have acceptably low 14 C content (0.23 ± 0.07 percent Modern Carbon (pMC); n = 7) relative to the 14 C-dead (0 pMC) CH 4 from which they are prepared.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2021

Integrating Solar Energy, Desalination, and Electrolysis

Solar electricity enables the advancement and deployment of technologies that are strongly influenced by clean energy availability and cost. The economics of both desalination and hydrogen production from water electrolysis are dominated by the cost of energy, and the availability of inexpensive solar energy creates markets and offers incentives to the desalination and electrolyzer industries. In this report the production of high-purity water and hydrogen from seawater is focused on. Current electrolyzers require deionized water so they need to be coupled with desalination units. It is shown that such coupling is cost effective in hydrogen generation, and it also offers benefits to thermal desalination, which can utilize waste heat from electrolysis. Furthermore, such coupling can be optimized when electrolyzers operate at high current density, using low-cost solar and/or wind electricity, as such operation increases both hydrogen production and heat generation. Results of technoeconomic modeling of polymer electrolyte membrane electrolyzers define thresholds of electricity pricing, current density, and operating temperature that make clean electrolytic hydrogen cost competitive with hydrogen from steam methane reforming (SMR). By using 2020 hourly electricity pricing in California and Texas, it is estimated that hydrogen can be produced from seawater in coupled desalination-electrolyzer systems at prices near $2 kg -1 H 2 , reaching cost parity with hydrogen produced from SMR.

14 SOLAR ENERGY↗
DOE OSTI2018

Environmental Constraints that Limit Methanogenesis

Methanogens are active in many different ecosystems, including habitats with biologically-derived organic matter as substrates such as aquatic sediments, wetlands, agricultural or natural soils subject to inundation, sewage digesters, and the anoxic portions of animal digestive tracts. Methanogens are also present in habitats with geochemically-supplied substrates such as hot springs, hydrothermal vents, volcanically-influenced habitats, and, potentially, the deep crustal subsurface. Methanogens as a group tolerate a broad range of physicochemical conditions, including temperatures from -2 to 122°C, pH values of 3.0 to 10.2, salinities up to halite saturation, and pressures of at least 75 MPa. Globally, variations in methane emissions can be explained to a large degree by variations in temperature and water availability. The distribution and activity of methanogens are constrained by ecological interactions that can be stimulatory or competitive, and by physicochemical factors that act at the biochemical or bioenergetic levels. In addition to the constraints placed on methanogens by physicochemical extremes, methanogen distribution and activity are constrained by the availability of energy and nutrients, the presence of inhibitory molecules (most notably oxygen), and the seawater anion, sulfate, due to competitive ecological interactions. Although methanogen tolerances to individual extremes are documented in culture, and the corresponding biochemical adaptations are understood to varying degrees, the natural environment frequently presents combinations of extreme conditions and energy limitations that may limit methanogen distribution to less than the optimally tolerated range of a single parameter. Little is understood about the compound effects of such extremes, nor the commonalities among them that will ultimately form the basis for predictive models of environmental methanogen population distribution. Future work that targets these questions, through a combination of culture work, “omic” analyses, in situ studies, and conceptual and quantitative models, will be needed to better understand the physiological ecology of methanogens.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2019

Chemistry of the consumption and excretion of the bumphead parrotfish ( Bolbometopon muricatum ), a coral reef mega-consumer

Bolbometopon muricatum are ecologically unique mega-consumers in coral reef ecosystems. They primarily divide their dietary intake between living scleractinian corals and coral rock, a substrate richly colonized by non-coral biota. Here we examine how the chemical, structural, and energetic content of these two main classes of forage material may influence B. muricatum feeding behavior and selectivity. We then also examine nutrient content, pH, and alkalinity of the carbonate-rich feces of B. muricatum as a step toward understanding how B. muricatum defecation could affect reef nutrient dynamics and localized seawater chemistry. Our results suggest that by most measures, coral rock constitutes a richer food source than living corals, exhibiting higher levels of eight biologically relevant elements, and containing approximately three times greater caloric value than living corals. Additionally, the two forage types also presented distinct mineralogy, with the coral rock resembling a Mg-enriched carbonate phase in contrast to the primarily aragonitic live corals. Despite the fact that individual B. muricatum excrete tons of macerated coral annually, the low measured concentrations of N and P in feces suggest that this excretion may have relatively minor effects of reef macronutrient budgets. We also observed negligible local-scale impacts of B. muricatum feces on seawater pH and alkalinity. The approaches applied here integrate perspectives from marine biogeochemistry, materials science, and ecology. Altogether, these results provide preliminary insight into how reef chemistry could shape foraging of this dominant and vulnerable coral reef consumer and how it, in turn, might affect the chemistry of these reefs.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2018

Effect of Localized Corrosion on Fatigue–Crack Growth in 2524-T3 and 2198-T851 Aluminum Alloys Used as Aircraft Materials

Corrosion and fatigue of aluminum alloys are major issues for the in-service life assessment of aircraft structures and for the management of aging air fleets. The aim of this work was to evaluate the effect of localized corrosion on fatigue crack growth (FCG) resistance of the AA2198-T851 Al-Li alloy (Solution Heat Treated, Cold Worked, and Artificially Aged), comparing it with the FCG resistance of AA2524-T3 (Solution Heat Treated and Cold Worked), considering the effect of seawater fog environment. Before fatigue tests, the corrosion behavior of 2198-T851 and 2524-T3 aluminum alloys was verified using open circuit potential and potentiodynamic polarization techniques. Fatigue in air and corrosion fatigue tests were performed applying a stress ratio (R) of 0.1, 15 Hz (air) and 0.1 Hz (seawater fog) frequencies, using a sinusoidal waveform in all cases. The results showed that the localized characteristics of the 2198-T851 and 2524-T3 aluminum alloys are essentially related to the existence of intermetallic compounds, which, due to their different nature, may be cathodic or anodic in relation to the aluminum matrix. The corrosive medium has affected the FCG rate of both aluminum alloys, in a quite similar way. Graphical Abstract: .

36 MATERIALS SCIENCE↗
DOE OSTI2025

Structure-dependent mechanisms for plastic degradation in the marine environment

The visible and invisible accumulation of waste plastic in our oceans is a consequence of rapidly increasing inputs and very slow degradation rates. In general, this combination of effects results in long residence times. Nevertheless, the abiological degradation rate of a specific synthetic plastic varies widely, depending on its structural characteristics at the molecular, mesoscopic, and macroscopic levels. This chapter summarizes factors that determine these rates of degradation, and describes their principal mechanisms, for several of the major types of waste plastic found in the oceans. Mechanical forces cause cracking and flaking that break macroplastics into microplastics and even smaller fragments with increasing surface-to-volume ratios. Chemical degradation rates increase with surface area, influenced by intrinsic variations in crystallinity and the presence of additives, as well as extrinsic factors such as temperature, pH, and UV light intensity. Since polyolefin-based plastics are less dense than seawater and lack hydrolysable bonds in their polymer backbones, they accumulate close to the surface of the ocean where photo-oxidation is the principal cause of C–C bond cleavage in the polymer backbone. In contrast, polyesters and polyamides are denser than seawater and they sink, experiencing less exposure to solar irradiation. However, they can also degrade by slow hydrolysis of the C–O or C–N bonds intrinsic to the polymer structures.

Maciulis, Nicholas A.↗
DOE OSTI2020

Tree growth, transpiration, and water-use efficiency between shoreline and upland red maple (Acer rubrum) trees in a coastal forest

Coastal shoreline forests are vulnerable to seawater exposure, the impacts of which will increase due to sea-level rise, but the longterm adaption strategies and vulnerability of coastal forests are not well understood. We used whole-tree transpiration, leaf water potential, tree-ring width, and tree-ring d13C (a proxy for intrinsic water use efficiency, iWUE) to examine the long-term adaption strategies of red maple (Acer rubrum) trees at the coastal interface (i.e., shoreline) and nearby upland in Maryland, USA. Red maple trees that grew along the shoreline and were exposed to slightly saline water (up to two PSU) had higher transpiration rates than those growing in the nearby upland forest during a wet year, but these differences disappeared during a normal precipitation year. Shoreline trees grew more slowly than upland trees over the last four decades, but these growth differences have disappeared in the last six years. Shoreline and upland trees had similar variation in iWUE, indicating that higher transpiration rates of the seawater exposed trees did not translate into differences in water use efficiency. There were no differences in predawn and midday water potential between upland and shoreline trees, suggesting no water stress occurs in shoreline trees. These findings indicate that urrent soil salinity is below the threshold to constrain coastal red maple physiological activities.

Wang, Wenzhi↗
DOE OSTI2023

Experimental investigation of a reverse osmosis desalination system directly powered by wave energy

Powering desalination processes with renewable energy is a promising solution to address the global issue of water shortage with minimum carbon footprint and environmental impact. Here, we experimentally investigate a sustainable reverse osmosis (RO) desalination system directly powered by wave energy. In this system, seawater is pressurized and pumped to a RO desalination module via a piston pump directly driven by an oscillating surge wave energy converter (OSWEC). An accumulator is adopted on the feed inlet to mitigate the pressure fluctuations under time-varying ocean conditions. Meanwhile, a needle valve on the brine outlet is used to adjust the system pressure and water recovery. A 1:10 scaled model was designed, fabricated, and tested in a wave tank based on the Froude scaling law. Further, the optimal specific water productivity (SWP) obtained in the tank tests with 3.5 g/L feed salinity was 2.23m 3 /kWh, indicating a full-scale specific water productivity of 0.22m 3 /kWh for 35g/L seawater salinity. The influence of needle valve tuning on the specific water productivity was experimentally investigated and analyzed. Under a specific operational condition, tuning this valve improved specific water productivity by about 17% and reduced the system pressure by 24%, thereby avoiding extreme pressure and improving the system’s capability. This pilot study demonstrates that ocean wave energy is a promising source to sustainably power reverse osmosis desalination and provide freshwater water for coastal regions.

16 TIDAL AND WAVE POWER↗
DOE OSTI2024

Plastic additives in the ocean: Use of a comprehensive dataset for meta-analysis and method development

In excess of 13,000 chemicals are added to plastics (‘additives’) to improve performance, durability, and production of plastic products. They are categorized into numerous chemical classes including flame retardants, light stabilizers, antioxidants, and plasticizers. While research on plastic additives in the marine environment has increased over the past decade, there is a lack of methodological standardization. To direct future measurement of plastic additives, we compiled a first-of-its-kind dataset of literature assessing plastic additives in marine environments, delineated by sample type (plastic debris, seawater, sediment, biota). Using this dataset, we performed a meta-analysis to summarize the state of the science. Currently, our dataset includes 217 publications published between 1978 and May 2023. The majority of publications analyzed plastic additives in biota collected from Europe and Asia. Analyses concentrated on plasticizers, brominated flame retardants, and bisphenols. Common sample preparation techniques included Solvent - Agitation extraction for plastic, sediment, and biota samples, and Solid Phase Extraction for seawater samples with dichloromethane and solvent mixtures including dichloromethane as the organic extraction solvent. Finally, most analyses were performed utilizing gas chromatography/mass spectrometry. There are a variety of data gaps illuminated by this meta-analysis, most notably the small number of compounds that have been targeted for detection compared to the large number of additives used in plastic production. The provided dataset facilitates future investigation of trends in plastic additive concentration data in the marine environment (allowing for comparison to toxicity thresholds) and acts as a starting point for optimizing and harmonizing plastic additive analytical methods.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Energy requirements of the switchable polarity solvent forward osmosis (SPS-FO) water purification process

A model was developed to estimate the process energy requirements of a switchable polarity solvent forward osmosis (SPS FO) system for water purification from aqueous NaCl feed solution concentrations ranging from 0.5 to 4.0 molal at an operational scale of 480 m3/day (feed stream). The model indicates recovering approximately 90% of the water from a feed solution with NaCl concentration similar to seawater using SPS FO would have total equivalent energy requirements between 2.4 and 4.3 kWh per m 3 of purified water product. The process is predicted to be competitive with current costs for disposal/treatment of produced water from oil and gas drilling operations. As a result, once scaled up the SPS FO process may be a thermally driven desalination process that can compete with the cost of seawater reverse osmosis.

15 GEOTHERMAL ENERGY↗
DOE OSTI2022

Performance of reverse osmosis membrane with large feed pressure fluctuations from a wave-driven desalination system

Wave-driven desalination systems are proposed water treatment systems that involve reverse osmosis of seawater powered directly by wave motion. Such a configuration would result in drastic feed pressure fluctuations. For a technology conventionally operated with a constant feed condition, the effect of these variable pressures on membrane integrity and performance is unknown. Here, experiments were conducted with spiral wound membranes coupled to a system capable of producing feed pressure fluctuations of more than 400 psi. Feed composition included 5, 20, and 35 g/L NaCl, and a synthetic seawater at normal and 1.5x concentration. The variable feed conditions included sine-like pressure waves swings of 200-500 and 500-900 psi with frequencies of 1.25, 7.5, and 12 waves/min, and a model-generated random waveform. Between each wave experiment we performed membrane integrity tests at 650 psi and 25 g/L NaCl feed, which showed a 7.4% drop in the membrane's water permeability coefficient, an 18.4% flux decline, and more than 99% salt rejection over 1770 h of cumulative experimental time. Analysis of permeate samples showed high salt rejection. In general, variable feed pressure had no significant deleterious effect on membrane integrity or performance.

16 TIDAL AND WAVE POWER↗
DOE OSTI2020

Brachiopod δ 34 S CAS microanalyses indicate a dynamic, climate-influenced Permo-Carboniferous sulfur cycle

Early isotopic studies of sulfate in carbonate minerals (carbonate associated sulfate; CAS) suggested that carbonates can provide a reliable, well-dated archive of the marine sulfur cycle through time. However, subsequent research has shown that diagenetic alteration can impose highly heterogeneous CAS sulfur isotopic compositions (δ 34 S CAS ) among different carbonate phases within sediments. Such alteration necessitates targeted sampling of well-preserved, primary carbonate phases. Here, we present a new record of Carboniferous and Early Permian brachiopod δ 34 S CAS generated from over 130 measurements of microsampled brachiopod shells. Our record refines existing brachiopod δ 34 S CAS records and confirms a large, ~6.5‰ δ 34 S CAS decrease in the Early Carboniferous. Importantly, the record also features a novel 3–5‰ increase in δ 34 S CAS near the Serpukhovian-Bashkirian boundary (323.4 Ma) that coincides with carbonate δ 13 C and δ 18 O increases. Variability in δ 34 S CAS is minor both within (≤0.3‰) and among (≤2‰) individual co-depositional brachiopod specimens. A taxon-specific δ 34 S CAS offset is present one species (Composita subtilita) that also exhibits a δ 13 C offset, supporting the existence of biological “vital effects” on δ 34 S CAS . Geologic evidence and mathematical modeling of the Permo-Carboniferous carbon and sulfur cycles suggest that changes in the burial ratio of organic carbon to pyrite sulfur (R C:S ) are insufficient to explain the observed mid-Carboniferous δ 34 S CAS record. We find that changes in the 34 S depletion of pyrite relative to seawater sulfate ( 34 ε) or in the δ 34 S of the input to the ocean (δ 34 S in ) are also needed. Large additions of O 2 from organic carbon burial during the Permo-Carboniferous cannot be entirely compensated for with sulfur cycle changes; lower than modern late Visean pO 2 and/or additional O 2 sinks are needed to keep pO 2 at plausible levels. Based on the geologic context surrounding our record's mid-Carboniferous δ 34 S CAS increase, we advocate for simultaneous changes in pyrite burial, 34 ε, and δ 34 S in , driven by sea level or tectonically induced changes in environments of sulfur burial, as a viable mechanism to produce rapid seawater δ 34 S changes.

54 ENVIRONMENTAL SCIENCES↗