Saturated Carbon Research Articles

Fabrication of corrosion-resistant and heat-resistant multi-walled carbon nanotubes/poly ether ether ketone/thermoplastic polyimide electromagnetic shielding foams based on double percolation structure

The corrosion-resistant and heat-resistant electromagnetic shielding foams were fabricated by multi-walled carbon nanotube/poly ether ether ketone/thermoplastic polyimide (MWCNTs/PEEK/TPI) composites with double percolation structure. MWCNTs/PEEK/TPI foams based on double percolation structure were obtained by introducing the cell into MWCNTs/PEEK/TPI composites using near-melting point saturated supercritical carbon dioxide (Sc-CO2) foaming technology. The appearance of cell structure further reduced the conductivity and the electromagnetic shielding percolation thresholds of MWCNTs/PEEK/TPI foam to 0.03989 vol% and 0.05552 vol% respectively, which were 89.58% and 91.33% lower than those of MWCNTs/PEEK/TPI composite. By contrast, it was found that the total electromagnetic shield value (SETotal) and specific total electromagnetic shield value (SSETotal) of 0.6313 vol%-MWCNTs/PEEK/TPI foam (0.1894 g/cm3) were 26.09% and 795.6% higher than that of 0.6404 vol%-MWCNTs/PEEK/TPI composite (1.3449 g/cm3). The introduction of the cell led to a transformation from reflective to absorptive electromagnetic shielding materials. The MWCNTs/PEEK/TPI foam could withstand various chemical corrosion and high temperature of 300 °C for a long time, which was suitable for extreme environmental service.

Carbonate compensation depth drives abyssal biogeography in the northeast Pacific.

Abyssal seafloor communities cover more than 60% of Earth's surface. Despite their great size, abyssal plains extend across modest environmental gradients compared to other marine ecosystems. However, little is known about the patterns and processes regulating biodiversity or potentially delimiting biogeographical boundaries at regional scales in the abyss. Improved macroecological understanding of remote abyssal environments is urgent as threats of widespread anthropogenic disturbance grow in the deep ocean. Here, we use a new, basin-scale dataset to show the existence of clear regional zonation in abyssal communities across the 5,000 km span of the Clarion-Clipperton Zone (northeast Pacific), an area targeted for deep-sea mining. We found two pronounced biogeographic provinces, deep and shallow-abyssal, separated by a transition zone between 4,300 and 4,800 m depth. Surprisingly, species richness was maintained across this boundary by phylum-level taxonomic replacements. These regional transitions are probably related to calcium carbonate saturation boundaries as taxa dependent on calcium carbonate structures, such as shelled molluscs, appear restricted to the shallower province. Our results suggest geochemical and climatic forcing on distributions of abyssal populations over large spatial scales and provide a potential paradigm for deep-sea macroecology, opening a new basis for regional-scale biodiversity research and conservation strategies in Earth's largest biome.

Some Features of the Process of Interaction of Iron with Methane at a Temperature of 900°C and a Pressure of 100 MPa

Using the original high-gas pressure unit (IHPV), experiments were conducted for the first time on the interaction of iron with methane at a temperature of 900°C and a pressure of 100 MPa. Complex methods (microprobe, Raman spectroscopy, chromatography, mass balance calculations) are used for a thorough analysis of fluid compositions and metallic phases formed in experiments. For the first time, experimental and theoretical quantitative data on the composition of the fluid and the composition of the fluid components dissolved in the metal were obtained. Unlike the previously studied Fe3C–H2 system, in experiments, when Fe reacts with methane, there is an active interaction of carbon formed due to the pyrolysis of methane with iron up to the synthesis of Fe3C carbide. The experiments have shown that increasing pressure inhibits significantly hydrogen yield during methane conversion on metallic iron. Carbon saturation of iron with the formation of Fe3C is not complete within the entire volume of the metal during 24 h runs at 900°С. Employing molybdenum containers facilitates CH4 decomposition.

Deglacial temperature and carbonate saturation state variability in the tropical Atlantic at Antarctic Intermediate Water Depths

Deglacial temperature and carbonate saturation state variability in the tropical Atlantic at Antarctic Intermediate Water Depths

Assessing carbon storage capacity and saturation across six central US grasslands using data–model integration

Abstract. Future global changes will impact carbon (C) fluxes and pools in most terrestrial ecosystems and the feedback of terrestrial carbon cycling to atmospheric CO2. Determining the vulnerability of C in ecosystems to future environmental change is thus vital for targeted land management and policy. The C capacity of an ecosystem is a function of its C inputs (e.g., net primary productivity – NPP) and how long C remains in the system before being respired back to the atmosphere. The proportion of C capacity currently stored by an ecosystem (i.e., its C saturation) provides information about the potential for long-term C pools to be altered by environmental and land management regimes. We estimated C capacity, C saturation, NPP, and ecosystem C residence time in six US grasslands spanning temperature and precipitation gradients by integrating high temporal resolution C pool and flux data with a process-based C model. As expected, NPP across grasslands was strongly correlated with mean annual precipitation (MAP), yet C residence time was not related to MAP or mean annual temperature (MAT). We link soil temperature, soil moisture, and inherent C turnover rates (potentially due to microbial function and tissue quality) as determinants of carbon residence time. Overall, we found that intermediates between extremes in moisture and temperature had low C saturation, indicating that C in these grasslands may trend upwards and be buffered against global change impacts. Hot and dry grasslands had greatest C saturation due to both small C inputs through NPP and high C turnover rates during soil moisture conditions favorable for microbial activity. Additionally, leaching of soil C during monsoon events may lead to C loss. C saturation was also high in tallgrass prairie due to frequent fire that reduced inputs of aboveground plant material. Accordingly, we suggest that both hot, dry ecosystems and those frequently disturbed should be subject to careful land management and policy decisions to prevent losses of C stored in these systems.

Study of CO2 absorption by low salinity aqueous solutions of specific salts in the absence and presence of carbonate rocks

Fossil-fuels combustion is currently the main driving force of industrialization; however, it has resulted in CO2 emission that challenges sustained socioeconomic growth. One way to reduce CO2 emissions is to sequester it into saline aquifers or depleted hydrocarbon reservoirs. In this study, CO2 absorption in different aqueous salt solutions is elucidated. CO2 absorption in different salines is also simulated using PHREEQC software to predict the concentration of different species formed by saline-CO2 interactions at equilibrium. Investigated parameters include concentration of different salts at low salinity condition, type of cations and anions, temperature, and carbonate rock on the CO2 absorption and storage in aqueous media at high pressures. Results revealed that both initial absorption rate and final absorbed amount of CO2 in aqueous salt solution decay in the order of MgSO4 > Na2SO4 > CaCl2 > MgCl2 > NaCl. For a given anion in the dissolved salt, the presence of divalent cations promotes CO2 absorption more than that of monovalent cations. Also, for equivalence cations the one with a higher charge density promotes CO2 absorption. It is also evident that for a given cation in the dissolved salt the associated anion which has a higher charge density hinders CO2 absorption more than that with a lower charge density. Similar pattern is maintained for CO2 absorption in saturated carbonate rock. PHREEQC simulations revealed that concentrations of precipitated carbonate salts in CO2-saturated Na2SO4 and NaCl brines are higher than those of the other brines. Moreover, increasing temperature increases concentration of precipitated carbonate salts in CO2-saturated MgSO4, CaCl2, and MgCl2 brines while it has an opposite effect on precipitated carbonate salts formed due to CO2 absorption in Na2SO4 and NaCl brines.

New insights into binary mixture toxicology: 2. Effects of reactive oxygen species generated by some carboxylic diesters on marine and freshwater organisms (VIII)

This paper presents the development of toxicity of some saturated and phthalate carboxylic diesters (CDE) quantified by experimentally measured (Mes) and calculated (C) values using the Hydractinia echinata (invertebrate) Toxicity Screening Test System (HeTSTS) and the Köln Model (KM) algorithm. The validity of the investigation model is confirmed by the results for three other aquatic organisms: the ciliate protozoan Tetrahymena pyriformis, the freshwater fish Pimephales promelas and the freshwater crustacean Daphnia magna test systems have shown that the evolution of effectiveness is similar, although the absolute values are different. CDE undergoes rapid, irreversible, selective and abiotic –OH– nucleophilic catalyzed monohydrolysis with the formation of the substrate amphiphilic carboxylate monoester (CME), saturated or phthalate and alcohol (AL) as a xenobiotic (SbX) binary mixture in stoichiometric proportion. The Mes represents the inverse of the logarithm of the diester concentration (molL-1), which determines the 50% reduction in metamorphosis of H. echinata from larva to polyp and is influenced by the saturated carbon atom (Cs) of the molecular substructure involved in monohydrolysis. According to the KM algorithm, Cs is the Elementary Specific Interaction Parameter (ESIP) with a specific and constant toxicity value – identical in different substances – depending on the nature of the organism that allows the calculation of toxicity predictions in C. AL is the fingerprint of the mixture (FP) because it influences the diffusion of CMEs through the cell membrane to cellular receptors (CRs). Generally, the Mes and C, are the predicted ECOSAR and calculated C* values form the Class Regulated Increased Toxicity (CRIT) and Class Regulated Decreased Toxicities (CRDT) series. The use of H. echinata in toxicity determinations is an alternative for the study of the relevant ecological impact of chemical oxidative stress on aquatic organisms and, consequently, on human health.

Iso-propyl caprylate and iso-propyl linolenate synthetic fluids as novel alternatives in deep-water drilling operations: Critical fluid properties and aerobic biodegradability assessments

Present drilling fluids for deep water wells have severe degenerative effect on the environment with high operational and disposal costs. Thus, making them less desirable in recent times. Ester synthetic drilling fluid provides a novel environmentally friendly alternative but conventional ester-based drilling fluids exhibit high viscosities in deep-water wells causing excessive equivalent circulating density (ECD) and increased risk of lost circulation owing to narrow mud density window. This study experimentally investigates the critical fluid properties and aerobic biodegradability potentials of two newly developed deep-water synthetic ester drilling fluids namely: iso-propyl caprylate (COIPE) and iso-propyl linolenate (LOIPE) synthetic fluids and their comparison with synthetic-paraffin (SP-SBF) and isomerized-olefin (IO-SBF) synthetic hydrocarbon fluids. The esters of iso-propyl caprylate and iso-propyl linolenate were produced from the isolation of ester mixtures that were obtained from the homogeneous catalytic transesterification of coconut and linseed plant oil biomass respectively. The COIPE was isolated from the coconut oil iso-propyl ester mixture by low-pressure fractional distillation technique. While fractional distillation and crystallization were used to isolate the LOIPE ester from the linseed oil iso-propyl ester mixture. Meanwhile, the aerobic biodegradation investigation was conducted by a modified oxygen consumption respirometry technique. The GC-MS analysis of the COIPE and LOIPE showed that the former contains essentially of lower saturated carbon compounds (C8). Whereas the latter contains higher molecular weight and unsaturated carbon compounds (C18+). The COIPE and LOIPE kinematic viscosity values are in good agreement with that of the reference synthetic hydrocarbon fluid samples (SP-SBF and IO-SBF). Although, the COIPE synthetic ester has lower viscosity value owing to the presence of shorter chain and saturated carbon atoms (C8 esters). Similarly, the linolenic oil iso-propyl ester has excellent cold flow characteristics for deep-water well drilling owing to lower values of cloud and pour points as a result of higher concentration of poly-unsaturated linolenic esters. The iso-propyl caprylate and the iso-propyl linolenate ester synthetic fluids are readily biodegradable in the sea water inoculum under aerobic condition. However, the iso-propyl caprylate is inherently biodegradable because its degradation level and that of the reference chemical sample were already above 60% during the 10-day window period. The SP-SBF and the IO-SBF synthetic fluids have lower aerobic biodegradation values because they contain little quantity of poly aromatic hydrocarbons as evident in their GC-MS profiles. Finally, esters and unsaturated synthetic-based fluid are more rapidly biodegradable than paraffinic synthetic fluids and the rate of biodegradation of organic compounds decreases as molecular weight increases

Organic alkalinity dynamics in Irish coastal waters: Case study Rogerstown Estuary

Total alkalinity (TA) is a popularly measured carbonate system parameter and is widely used in calculations of key carbonate system descriptors such as the calcium carbonate saturation state, an important indicator of ocean acidification. Organic alkalinity (OrgAlk) is recognised as a contributor to TA in coastal waters, with this having implications on the use of TA to calculate key carbonate chemistry descriptors. As titratable charge groups of OrgAlk can act as unknown acid-base species, the inclusion of the total concentration and apparent dissociation constants of OrgAlk in carbonate calculations involving TA is required to minimise uncertainty in computed speciation. Here we present an investigation of the prevalence and properties of OrgAlk as well as the impact of OrgAlk on carbonate chemistry calculations in a transitional waterbody. Water samples were collected during low and high tide over a 5-week period in Rogerstown Estuary, Dublin Ireland. TA and OrgAlk were measured using modified Global Ocean Acidification Observing Network (GOA-ON) titration apparatus in conjunction with OrgAlkCalc, an open-source Python based computational programme. pH was measured on the total scale using meta-cresol purple (mCP) as the indicator dye. Dissolved inorganic carbon (DIC), the partial pressure of CO2 (pCO2), in situ pH on the total scale (pHT) and the saturation state of aragonite (∆ΩA) were calculated using pH and both OrgAlk adjusted TA and measured TA as the input parameters. Optical analysis of DOM was conducted to compliment OrgAlk characterisations and to further elucidate OrgAlk sources and dynamics. OrgAlk charge groups concentrations ranged from 35,198 μmol·kg−1, with the highest concentrations observed in more marine waters. Two apparent charge groups were associated with OrgAlk, with pK values of 4.38 ± 0.27 and 6.95 ± 0.43. Differences between calculated carbonate system parameters when using OrgAlk adjusted TA and non-OrgAlk adjusted TA ranged from 88 to 254 μmol·kg−1 DIC, −98–67 μatm pCO2, −0.02–0.12 pHT and 0.02–0.64 ∆ΩA. Variability in the differences in calculated carbonate systems was largely a factor of OrgAlk charge group concentration and pK. This work highlights the importance of considering OrgAlk if using TA as an input parameter in carbonate system investigations of coastal waters.

Characterization and energy recovery from biomass wastes

The rise in energy demand, underutilization of resources, and the challenge of identifying suitable energy sources are critical issues, particularly in developing countries. Given these issues, this research aimed to characterize groundnut shell (GNS) and pinewood chips (PWC) biomass using thermal, combustion, FTIR, SEM, EDX and downdraft gasifier tests in order to assess the suitability of these biomass sources for gasification in Uganda. Results indicate that the volatile matter (VM) of GNS and PWC were 67.40 wt% and 71.88 wt%, respectively. Due to its higher VM, PWC vaporized before combustion, resulting in faster burning due to its high oxidation state compared to GNS. GNS had relatively high fixed carbon (FC), moisture content (MC), and ash contents were compared to PWC, resulting in higher amounts of char deposit during gasification. The calorific values obtained were ∼18.87 MJ/kg for GNS and ∼17.04 MJ/kg for PWC. The major decomposition peaks appeared between ≥348 °C to ≤640 °C for GNS and ≥316 °C to ≤620 °C for PWC, which led to an average weight loss of 61 % and 65.78 %, respectively. The morphological image of PWC shows the presence of granules, independent behavior and fibrous growth inside the carbon compared to GNS. Both samples formed conjugated structures due to isomerization, which stabilizes the bonds when the oxidation degradation between the double bonds occurs at the saturated carbon. GNS had a firepower of 5.07 kW at a burning rate of 17.338 g/min, which is ∼26.2 % higher than that of PWC. PWC had a lower energy consumption per unit time of 221.225 kJ/min than GNS, due to a test time reduction of ∼58 s and a lower energy density in the biomass fuel.

Formation of molar tooth structures in low sulfate Precambrian oceans

Molar tooth structures (MTS) comprise calcite microspar-filled voids in fine-grained shallow-water carbonate, and were commonly formed in the Mesoproterozoic and early Neoproterozoic. However, the origin of MTS and links between the temporal distribution of MTS and contemporaneous seawater chemistry remains poorly understood. Here we report elemental and isotopic data for MTS and host rocks from the Mesoproterozoic Gaoyuzhuang Formation (∼1,600–1,550 Ma), North China Craton. The results reveal similar C, S and Sr isotope signatures between MTS and host rocks, which are close to the isotopic compositions of contemporaneous global seawater, suggesting an early diagenetic, seawater-buffered origin for MTS. A small sulfur isotopic fractionation between seawater sulfate and pyrite (Δ34SCAS-Py) of 4.1 ± 1.5‰ in host rocks is consistent with previously reported data, providing support for sub-millimolar sulfate concentrations in Mesoproterozoic seawater. Our observations suggest that the widespread occurrence of MTS through the Mesoproterozoic to early Neoproterozoic was broadly linked to sulfate scarcity in the ocean. We further propose that in Proterozoic oceans with sub-millimolar seawater sulfate concentrations, where aerobic and anaerobic methane oxidation was likely inhibited, methane produced via methanogenesis may have been more prone to accumulate in sediments, creating voids during escape. The absence of MTS across periods of higher sulfate concentrations during the Palaeoproterozoic and after the mid-Neoproterozoic, suggests that elevated sulfate concentrations promoted consumption of methane via anaerobic methane oxidation, thus preventing methane accumulation and the formation of sediment voids. Rapid lithification of the substrate as a result of elevated carbonate saturation may have also hindered the formation of MTS during these intervals. The link between MTS and changes in both oceanic sulfate levels and benthic methane fluxes gives a new perspective on temporal fluctuations in Earth’s redox state through time.

Degradation kinetics of epoxidized soybean oil

AbstractThis work deals with the degradation kinetics of epoxidized soybean oil, whereas the weight loss of epoxidized soybean oil (ESO) cured with methyl tetrahydrophthalic anhydride (MTHPA) as hardener and 2,4,6‐tris (dimethylaminomethyl) phenol (DEH 35) as catalyst displayed two main regions in the thermogravimetry (TG) plots. Nevertheless, deconvolution of the weight loss plots presented three or more events depending on the composition and experimental parameters. Increase the MTHPA addition led to a decrease in the activation energy (AE) for curing which conducted to an increased AE during the degradation. Friedman's isoconversional model exhibits proper R2 for the curing kinetics, but lower R2 values for lower anhydride contents during the degradation kinetics analyses. Kissinger‐Akahira‐Sunose (KAS) and Ozawa‐Flynn‐Wall (OFW) models displayed the best R2 during the kinetics evaluation, whereas the degradation mechanisms fitted reasonably with Avrami‐Erofeev (An) and nth‐order autocatalytic (Cn) during the first and second weight loss regions. Microstructural analyzes and in‐depth investigations into the thermal degradation mechanism of ESO suggest two possible pathways, that is, production of carbonic groups through heterolytic scission, and formation of electrically stable groups with saturated carbon bonds.

Increased Biogenic Calcification and Burial Under Elevated pCO2 During the Miocene: A Model‐Data Comparison

AbstractOcean acidification due to anthropogenic CO2 emission reduces ocean pH and carbonate saturation, with the projection that marine calcifiers and associated ecosystems will be negatively affected in the future. On longer time scale, however, recent studies of deep‐sea carbonate sediments suggest significantly increased carbonate production and burial in the open ocean during the warm Middle Miocene. Here, we present new model simulations in comparison to published Miocene carbonate accumulation rates to show that global biogenic carbonate production in the pelagic environment was approximately doubled relative to present‐day values when elevated atmospheric pCO2 led to substantial global warming ∼13–15 million years ago. Our analysis also finds that although high carbonate production was associated with high dissolution in the deep‐sea, net pelagic carbonate burial was approximately 30%–45% higher than modern. At the steady state of the long‐term carbon cycle, this requires an equivalent increase in riverine carbonate alkalinity influx during the Middle Miocene, attributable to enhanced chemical weathering under a warmer climate. Elevated biogenic carbonate production resulted in a Miocene ocean that had carbon (dissolved inorganic carbon) and alkalinity (total alkalinity) inventories similar to modern values but was poorly buffered and less saturated in both the surface and the deep ocean relative to modern.

Fish muscle mercury concentration and bioaccumulation fluctuate year-round - Insights from cyprinid and percid fishes in a humic boreal lake

Boreal lakes demonstrate pronounced seasonality, where the warm open-water season and subsequent cold and ice-covered season dominate natural cycles. While fish muscle total mercury concentration (mg/kg) [THg] is well documented in open-water summer months, there is limited knowledge on the ice-covered winter and spring mercury dynamics in fish from various foraging and thermal guilds. This year-round study tested how seasonality influences [THg] and its bioaccumulation in three percids, perch (Perca fluviatilis), pikeperch (Sander lucioperca), ruffe (Gymnocephalus cernua), and three cyprinids, roach (Rutilus rutilus), bleak (Alburnus alburnus), and bream (Abramis brama) in deep boreal mesotrophic Lake Pääjärvi, southern Finland. Fish were sampled and [THg] was quantified in the dorsal muscle during four seasons in this humic lake. Bioaccumulation regression slopes (mean ± STD, 0.039 ± 0.030, range 0.013–0.114) between [THg] and fish length were steepest during and after spawning and shallowest during autumn and winter for all species. Fish [THg] was significantly higher in the winter-spring than summer-autumn in all percids, however, not in cyprinids. The lowest [THg] was observed in summer and autumn, likely due to recovery from spring spawning, somatic growth and lipid accumulation. Fish [THg] was best described by multiple regression models (R2adj: 52–76%) which included total length and varying combinations of seasonally changing environmental (water temperature, total carbon, total nitrogen, and oxygen saturation) and biotic factors (gonadosomatic index, and sex) in all species. The seasonal variation in [THg] and bioaccumulation slopes across multiple species suggests a need for standardized sampling seasons in long-term monitoring to avoid any seasonality bias. From the fisheries and fish consumption perspective in seasonally ice-covered lakes, monitoring of both winter-spring and summer-autumn would improve knowledge of [THg] variation in fish muscle.

Taphonomy and dissolution rates of the razor clam Ensis magnus shells: Current status and projected acidification scenarios

The analysis of the natural variability of seawater (Ta, Ωaragonite and pCO2) at Rodas Beach (NW Iberian Peninsula, Spain) revealed an increase of acidification. However, such pH change was not linked to any detrimental effect of the shell taphonomic characteristics of live razor clams harvested during distinct temporal series (length, thickness, organic content or strength). Temperature affected negatively shell strength and thickness, although the large correlation between the environmental variables would limit the individual characterization. Modelled trends in pH (and Ωaragonite) showed a significant decrease in the last 20 years, despite Ω > 1. Therefore, more recent shells are being secreted in a progressively less saturated carbonate environment and, consequently, more prone to suffer dissolution (and weakening) in projected climatic scenarios. When shells of harvested razor clams were exposed to projected climatic scenarios in the laboratory, dissolution rates were significantly greater for cold-acidic scenarios (more corrosive) as compared to warm-acidic. The median dissolution time (DT50) for shells under the cold-acidic scenario was reduced by half (15 years) when compared to the values observed for shells under current water chemistry conditions (30 years).Galician coastline, often characterised by pCO2-rich and cold waters due to upwelling system, would represent the most corrosive scenario for the shells according to the responses monitored in our survey which highlight future compromise for the ecosystem services supplied by these hard skeletons. Future climate scenarios might condition performance of bivalves but also more complex processes related to carbonate structures. Local biodiversity may be lowered which may reduce the possibility that many species find shelter and feeding grounds, diminishing the optimal substrate for other organisms as needed elements for optimal services in the ecosystems.

Fossil coccolith morphological attributes as a new proxy for deep ocean carbonate chemistry

Abstract. Understanding the variations in past ocean carbonate chemistry is critical to elucidating the role of the oceans in balancing the global carbon cycle. The fossil shells from marine calcifiers present in the sedimentary record are widely applied as past ocean carbon cycle proxies. However, the interpretation of these records can be challenging due to the complex physiological and ecological response to the carbonate system during an organisms' life cycle and the potential for preservation at the seafloor. Here we present a new dissolution proxy based on the morphological attributes of coccolithophores from the Noëlaerhabdaceae family (Emiliania huxleyi > 2 µm, and small Gephyrocapsa spp.). To evaluate the influences of coccolithophore calcification and coccolith preservation on fossil morphology, we measured morphological attributes, mass, length, thickness, and shape factor (ks) of coccoliths in a laboratory dissolution experiment and surface sediment samples from the South China Sea. The coccolith morphological data in surface sediments were also analyzed with environment settings, namely surface temperature, nutrients, pH, chlorophyll a concentration, and carbonate saturation of bottom water by a redundancy analysis. Statistical analysis indicates that carbonate saturation of the deep ocean explains the highest proportion of variation in the morphological data instead of the environmental variables of the surface ocean. Moreover, the dissolution trajectory in the ks vs. length of coccoliths is comparable between natural samples and laboratory dissolution experiments, emphasizing the importance of carbonate saturation on fossil coccolith morphology. However, the mean ks alone cannot fully explain the main variations observed in our work. We propose that the normalized ks variation (σ/ks), which is the ratio between the standard deviation of ks (σ) and the mean ks, could reflect different degrees of dissolution and size-selective dissolution, influenced by the assemblage composition. Applied together with the σ/ks ratio, the ks factor of fossil coccoliths in deep ocean sediments could be a potential proxy for a quantitative reconstruction of past carbonate dissolution dynamics.

Computational Modeling of the Feasibility of Substituted [1.1.1]Propellane Formation from Anionic Bridgehead Bromide Precursors

[1.1.1]Propellane, a compound whose structure includes two saturated carbons in which all four bonds are directed into a single hemisphere, is of theoretical interest, but has also seen recent practical applications. Mono-, di-, and trisubstituted derivatives of this propellane (by substitution of its CH2 bridges with O, S, NH, CF2, CO, SO, and SO2) remain unknown despite several computational studies that have suggested some may be stable. In this study, we show that, in several cases, substituted propellanes are spontaneously formed upon the attempted computational optimization of the geometries of anionic bridgehead bromide precursors using the ωB97X-D/aug-cc-pVDZ DFT method. Spontaneous formation suggests that these propellanes are at lower energy relative to the precursors and, therefore, are promising synthetic targets. The success or failure to spontaneously form the propellane is considered in relation to the length and strain energy of the central bridgehead-bridgehead bond, as well as the total strain energy of each propellane.

A Review of Combined Use of Biochar with Nitrogen Fertilizer as an Instrument for Improving Maize Yield and Soil Fertility

The decline of soil fertility is one of the major problems around the world for producing crops and ensuring food security. Therefore, the review's objective was to examine how biochar and inorganic nitrogen fertilizers affect soil physicochemical characteristics, as well as maize production and growth parameters. Similarly, biochar is a product of the thermochemical decomposition of biomass produced under limited oxygen. It has potential benefits in agriculture, such as improving soil fertility, water retention. The nutrient composition of biochar produced is determined by the type of feedstock used and the pyrolysis conditions. A study showed that adding biochar and nitrogen fertilizer decreased soil bulk density and enhanced water-holding capacity and soil chemical properties like pH, nitrogen, phosphorus, potassium, organic carbon, calcium, ECEC, and base saturation. Moreover, the review reported that the addition of N fertilizer and biochar greatly promoted crop N uptake and N content, which then increased leaf photosynthetic efficiency, dry matter accumulation, and grain yields. The findings discovered that when the rate of biochar and nitrogen increased, crop productivity and soil properties also increased significantly. It is concluded that applying biochar along with nitrogen fertilizer increased maize crop productivity as well as soil attributes more than applying biochar and nitrogen fertilizer separately. Therefore, farmers and agricultural experts should consider incorporating these practices into their land management strategies to improve overall agricultural sustainability.

Periodic flooding enhances the function of soil Fe/Al oxides in stabilizing particulate organic carbon in a water level drawdown zone

The stabilization of soil organic carbon is closely linked to edaphic properties and environmental variables. Despite this, the mechanism of soil organic carbon stabilization, as well as the primary factor controlling soil organic carbon in riparian ecosystems, remains unclear. To address this gap, our study investigated the impact of flooding regimes on soil organic carbon fractions and other chemical properties in the riparian zone, focusing on the dominant intrinsic factors controlling soil organic carbon content within the three soil types (Anthrosols, Luvisols, and Regosols). Our results demonstrated that flooding regimes significantly affect soil chemical properties in the riparian zone, with varying effects among the three soil types. Specifically, Regosols showed an increase in the particulate organic carbon with flooding intensity. Organic carbon fractions in Anthrosols and Luvisols are found to respond similarly to flooding regimes. The effects of soil chemical properties on organic carbon fractions varied across the three soil types. The variations in POCc, POCf, and MOC for Anthrosols were explained by path models by 43 %, 95 %, and 33 %, respectively. Similarly, for Luvisols, the path models accounted for 66 %, 90 %, and 29 % of the variations, whereas for Regosols, the variations were explained by 43 %, 93 %, and 21 %. Overall, for all tested soils combined, the path models explained 36 %, 89 %, and 12 %, respectively. Therefrom, under flooding regimes, soil oxides played a more significant role in stabilizing soil organic carbon for the three soil types than clay, silt, and cations. Specifically, in Anthrosols, Luvisols, and Regosols, the path coefficient for soil oxides was 0.90, 0.95, and 0.97, respectively, for POCf; while it was 0.30, 0.21, and 0.22 for POCc. In conclusion, we revealed that flooding regimes enhance the role of soil oxides in stabilizing organic carbon. Therefore, we recommend that soil oxides shall be included in organic carbon saturation models for riparian zones subjected to flooding regimes.

The role of irradiance in controlling coralline algal calcification

AbstractCoralline algae are an essential element of benthic ecosystems throughout the ocean's photic zone. Yet, the role of light in shaping the physiology of coralline algae from cold‐water, low‐light habitats is poorly understood. Here, we assess the calcification physiology of five cool temperate coralline algae in response to different irradiance levels over 3 months. We show that in contrast to current models focused on warmer water species, previously observed enhancement of calcification rates by photosynthesis is largely limited to lower irradiances, and that the removal of CO2 from the calcifying fluid is not the underlying mechanism of this enhancement. Instead, this most likely occurs via two processes: (1) increased ion pumping rates to elevate the calcium carbonate saturation state in the calcifying fluid; and (2) a higher daytime pH in the diffusion boundary layer that raises calcifying fluid pH. However, as irradiance increases, ion pumping becomes increasingly saturated limiting further enhancements. Our results also suggest the existence of two calcification strategies in coralline algae and indicate that magnesium incorporation is determined by the magnesium to calcium ratio in the calcifying fluid ([Mg]CF/[Ca]CF). This study adds to our mechanistic understanding of calcification in coralline algae and fills in much needed knowledge about the role of light in controlling their physiology.