Search

ABSTRACT Aim Location Taxa Methods Results Main Conclusions Significance To test if temperature significantly influences the global biogeographic distribution of marine epifaunal bivalves via their skeletal mineralogy.Global.Marine, epifaunal bivalves.The skeletal mineralogy of 45,789 epifaunal bivalve occurrences from 669 species from the Ocean Biodiversity Information System (OBIS) was related to sea surface temperatures from Bio‐ORACLE. Binomial regression was used to assess the influence of temperature and seasonality on the distribution of aragonitic and calcite‐secreting bivalve occurrences, aggregated in equal‐area grid cells.The proportion of aragonitic bivalve occurrences significantly increases with mean annual temperature in our global analysis and most marine biogeographic realms. A greater prevalence of calcite‐secreting bivalves in seasonal climates could be shown at low mean annual temperatures at the global scale but not within biogeographic realms.The global biogeographic distribution of epifaunal bivalves is significantly influenced by water temperature via their skeletal mineralogy. The mechanism driving this pattern is best explained by the temperature modulation of the effect of Mg2+ on calcite growth. Although this Mg2+ effect predicts an advantage for aragonite secretion at higher temperatures, poleward migration in response to higher temperature extremes will expose tropical taxa to cooler temperatures in the cold season, which may impede aragonite secretion in taxa not adapted to these climates.Our results suggest that skeletal mineralogy is likely to influence ocean warming‐induced migration patterns. [ABSTRACT FROM AUTHOR]

Aragonite is a metastable mineral, which is easily transformed into calcite, and generally difficult to preserve in the stratum. However, large amounts of aragonites were found in the Paleogene shale of the Jiyang Depression. The characteristics and preservation mechanisms of these aragonites were analyzed through a series of analytical methods, including cathodoluminescence, field-emission scanning electron microscopy (FESEM), laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), microarea carbon and oxygen isotopes, Sr isotopes, and dissolution simulation experiments under high temperature and high pressure. The research results show that: ①Aragonite in the Paleogene shale of the Jiyang Depression is related to algal microbial fossils, primarily composed of coccoliths and characterized by two emission peaks at 420 nm and 480 nm in cathodoluminescence; ②The primary factor allowing biological aragonite to be preserved is the immaturity of the organic matter and the deficiency of abundant organic acids necessary for its dissolution or transformation, which is confirmed by the evidence of organic matter maturity and simulation experiments of organic acid dissolution on aragonite under high-temperature and high-pressure conditions. Additional factors that may aid in the preservation of aragonite are the ideal sedimentation conditions, the defense of organic coating, and the enclosed environment with tiny pores, low porosity, and low permeability; ③These aragonite-rich shales, characterized by coccolithophores, provide a solid evidence for seawater intrusion into terrestrial lake basin, and have a significant implication for the source and storage of shale oil. [ABSTRACT FROM AUTHOR]

The two most abundant CaCO3 polymorphs, calcite and aragonite, are universally recognized for the richness of their morphology to which different twins make relevant contributions. The epitaxial transformation calcite ↔ aragonite has long been debated. While the twinning has been thoroughly treated, the homo‐epitaxy occurring within each of these minerals has, inexplicably, been overlooked to date, both experimentally and theoretically. Twinning can be deceptive to the point where it can be mistaken for homo‐epitaxy, thus making the proposed growth mechanism in the crystal aggregate wrong. Within the present work, the first aim is a theoretical investigation of the homo‐epitaxies among the three {10.4}‐cleavage, {01.2}‐steep and {01.8}‐flat rhombohedra of calcite. Accordingly, the specific adhesion energies were calculated between facing crystal forms, unequivocally showing that the {01.2}/{01.8} homo‐epitaxy competes with the generation of both {01.2} and {01.8} contact twins. Secondly, the calculation of the specific adhesion energy was extended to consider homo‐epitaxy for the {10.4} rhombohedron. The two‐dimensional geometric lattice coincidence has been tried for the {00.1} pinacoidal form as well. [ABSTRACT FROM AUTHOR]

Active and relic marine methane‐seep sites are widely distributed globally and are distinguished by distinctive geology, biogeochemistry, and ecosystems. The discovery of methane‐seep sites in the Krishna‐Godavari (K‐G) basin has created exciting new opportunities for methane‐seep research in the Bay of Bengal. In this study, we document the occurrence of authigenic carbonates, including micro‐crystalline aragonite crust (arg‐crusts) admixed with chemosynthetic shells and high‐magnesium carbonate tubular structures (HMC‐tube), from the methane‐seep site SSD‐045/4 in the K‐G basin. The δ13C values of HMC‐tubes (−54.5 to −46.2‰) and arg‐crusts (−57.6 to −34.8‰) indicate biogenic methane as the likely carbon source. Enhanced porewater alkalinity driving carbonate precipitation may be attributed to microbial‐mediated SO₄2−‐AOM processes. Additionally, δ13C values (−35.2 ± 8‰) of the residual organic matter within the carbonates suggest a contribution of methanotrophic bacterial biomass. The δ18Ocarb values of HMC and aragonite indicate methane hydrate degassing and crystallization pathways, respectively. Pelloid‐filled burrows suggest the reworking of shallow HMC deposit by burrowing organisms, whereas the polyphase cementations (aragonite and HMC) within burrows indicate early and burial diagenetic pathways. The wide range in ΣLREE/ΣHREE ratios and Ceanom values in arg‐crusts reflect micro‐spatial variations in redox conditions, likely due to cementation occurring in both open and closed diagenetic systems. In contrast, more constrained Ceanom values and ΣLREE/ΣHREE ratios in HMC tubes suggest persistent sulfidic conditions. Overall, these findings provide insights into the pathways of carbonate formation at the K‐G basin methane‐seep site, highlighting the complex interplay of microbial processes, fluid dynamics, and diagenetic alterations. Plain Language Summary: Methane cold‐seeps are regions on the seabed where methane (CH4) gas oozes out across the sediment‐water interface into the water column. Both active and inactive seepage sites are known across the oceans. Active methane seep sites expel significant quantities of methane into the seawater which influences the oceanic methane budget as well as the carbon cycle. In contrast, the preserved authigenic carbonate deposits and chemosynthetic fauna at the relic seep sites are archives of past seepage activities. The seep ecosystem comprises a variety of chemosynthetic and non‐chemosynthetic organisms, whereas the geological features include mounds, mud volcanoes, carbonate crusts, chimneys, etc. formed due to methane expulsion processes. Here, we investigate the origin of calcium carbonate structures formed in a cold seep region off the east coast of India. The carbonate structures include tubular‐shaped high magnesian carbonates (HMC) and crusts composed of aragonite minerals. These tubes and crusts archive biological and geological processes, including past variations in methane effusion and diffusion through the sediment. Tubular structures are formed by gas flow through the sediments as chimneys and by burrowing activities of benthic organisms. On the other hand, the aragonite crusts are formed where methane flow is high across the seabed. Key Points: Relics of methanogenic high magnesian calcite tubes and aragonite crust recovered from cold seep site K‐G basin east coast of IndiaHMC precipitation is confined to sulfidic conditions in contrast to a wider redox range for aragonite precipitationReworking of unconsolidated HMC produced the pelloid rich tubular structures, whereas aragonite crust formed at high CH4 flow conditions [ABSTRACT FROM AUTHOR]

Phreatic overgrowths on speleothems (POS) are unique precipitates that are found in a small number of coastal caves around the world, like those in the Mallorca Island. Their growth is directly related to the water level of the brackish lakes connected to the sea characteristic of these caves and, therefore, they can be very reliable indicators of past sea levels. The study presented here characterizes and classifies an important number of POS samples collected in the coastal caves of Mallorca. The characterization includes not only the observations made on 117 handheld samples and on 102 thin sections from POS, but also the study of their mineralogy and their location in the caves. This study has provided the basis for a systematization of all these characteristics, some of which are reported here for the first time in POS samples. The results indicate that (1) most of the POS precipitate on stalactites, (2) calcite POS show branched internal and external texture and their most common crystal fabric is mosaic calcite and (3) aragonite POS show globular external texture and fan‐shaped internal texture, and their principal crystal fabric is needle‐like. All the aragonitic samples have been found above or at the same heights as the current sea level, which indicates that they have probably formed during warmer climates. The calcite POS have been found at heights above and below the present sea level and are interpreted as to have formed during cold and rainy periods. The systematization proposed in this paper could be applied and checked in other POS worldwide. Additionally, the combination of these results with the information obtained from studies on the present precipitation of these phreatic speleothems in some Mallorca caves has provided an insight on their formation conditions which will enlarge the utility of these speleothems as palaeoenvironmental indicators. [ABSTRACT FROM AUTHOR]

CaCl2 solution and Ca(OH)2 slurry, both prepared from marble waste (MARWAS), were carbonated with CO2 gas in the presence of cetyltrimethylammonium bromide (CTAB), sodium dodecyl sulfate (SDS), Teepol-610s, Triton X-100, and Tween-80 as the surface modifiers in a semi-batch foam-bed reactor (FBR) to synthesize ultrafine or submicron precipitated calcium carbonate (PCC) particles with enhanced hydrophobicity. Nano/ultrafine PCC particles with and without surfactant were also synthesized in a semi-batch stirrer reactor (SR) using CaCl2 solutions made from MARWAS and NH4HCO3 as the carbonating agent by single or simultaneous application of ultrasonication (US) and surfactant, respectively. The products were characterized by SEM, TEM, XRD, FTIR, and drop-shape analyzer. In the presence of SDS in the FBR, distinct and smaller hydrophobic (water contact angle of 103.3°) vaterite particles (426 nm) could be produced using CaCl2 solution than those with the Ca(OH)2 slurry. However, in the SR, methanol was more effective than the aqueous solvent in synthesizing needle-like aragonite nanoparticles (215.6 nm with L/D = 8.55) from CaCl2 solution without any use of US or surfactant. Handmade papers were manufactured using ground MARWAS powder, modified- and unmodified-PCC. The physical, mechanical, and optical properties of these filler-loaded papers were determined. The use of surface-modified and unmodified PCC was superior to the commercial PCC in increasing filler retention, burst strength, tear strength, brightness, and opacity of the paper handsheets. Even the direct use of MARWAS powder was more effective than ground calcium carbonate in enhancing the optical properties with a slight decrease in the mechanical strength. Utilization of marble waste into papermaking [ABSTRACT FROM AUTHOR]

Rationale: Stable carbon and oxygen isotope data of biogenic and abiogenic aragonite are of fundamental relevance in paleoclimate research. Wet‐chemical analysis of such materials requires well‐homogenized, fine‐grained powder. In the present study, the effect of different grinding/milling methods on sample homogeneity and the potential risk of unintentional calcite formation and isotope shift were evaluated. Methods: Shells of Arctica islandica and aragonite sputnik crystals were pulverized using a set of commonly used methods, including a hand‐held drill, a vibromill operated at various settings (with and without liquid nitrogen cooling, changes in ball diameters, frequencies, and processing durations), and an agate mortar and pestle. Stable isotope values were measured using an isotope ratio mass spectrometer operated in continuous flow mode. Identification of mineral phases was obtained by powder X‐ray diffraction (PXRD), Raman spectroscopy, and attenuated total reflectance‐Fourier transform infrared (ATR‐FTIR) spectroscopy. Calcite content was quantified by PXRD Rietveld refinement. Results: Samples showed substantial homogeneity, in particular after vibromilling (duration 3–10 min). More vigorous grinding resulted in larger fractions of calcite (0.5–4.2 wt%) and a concomitant δ18O and δ13C decrease, specifically in bivalve shells. The only method for producing pure aragonite powder was by pounding the aragonite sputniks manually with an agate mortar and pestle. Conclusions: None of the studied, commonly used machine‐based pulverization methods produced pure aragonite powder from samples consisting originally of aragonite. These findings have significant implications for light‐stable isotope‐based paleoclimate reconstructions. Except for abiogenic aragonite powder produced by pounding in an agate mortar, paleotemperatures would be overestimated. [ABSTRACT FROM AUTHOR]

The linkage between the variation of the seawater Mg budget and the long-term carbon cycle can be elucidated by seawater Mg isotope composition (δ26Mg). However, obtaining primary seawater δ26Mg signatures from marine archives is challenging due to the widespread alteration of diagenesis. Aragonite, a common primary marine carbonate, can effectively record seawater δ26Mg but is prone to alteration and transformation into calcite during early diagenesis. Therefore, a comprehensive understanding of Mg isotope behavior during the aragonite–calcite transition is essential to enhance the applicability of aragonite δ26Mg. In this study, we investigate the variation of aragonite δ26Mg during diagenesis with a limited supply of Mg by conducting a series of well-controlled aragonite–calcite transition experiments in a closed system. The experimental conditions encompass temperatures of 60 and 90 °C, the presence of Ca and Na in the solution, varying Na concentrations, as well as the presence of calcite seed. Results demonstrate that the significant decrease of bulk carbonate δ26Mg is accompanied by a substantial amount of Mg released into the solution during the aragonite–calcite transition, and the amount of released Mg is controlled by fluid chemistry via altering Mg partitioning in calcite. Furthermore, Mg isotope fractionation during calcite precipitation is influenced by temperature, ionic strength, and the presence of calcite seed, while kinetics played a negligible role in our experiments. Combined with previous experiments, the temperature-dependent Mg isotope fractionation during calcite precipitation in unseeded experiments is Δ26Mg cal-sol = (−0.13 ± 0.06) × 106/T2 – (0.47 ± 0.68). This fractionation is systematically higher than that of seeded experiments by 0.3–0.6 ‰ from 15 to 90 °C and can mainly be attributed to differences in surface free energy between homogeneous and heterogeneous calcite nucleation. These findings offer fundamental understandings of the Mg isotope behavior during the aragonite–calcite transformation, providing useful insights for interpreting the variation of δ26Mg in experimental and natural carbonates and facilitating ancient seawater δ26Mg reconstruction. [ABSTRACT FROM AUTHOR]

Calcium carbonate (CaCO 3) minerals serve as a major sink to retain metal ions through mineral-water interfacial reactions in which the capacity and long-term stability of contaminant uptake are influenced by coupled dissolution and precipitation reactions of both primary and secondary carbonate minerals (i.e., mineral replacement). Notably, recent studies of calcite reactivity in acidic solutions containing high levels of metal ions demonstrated complex behavior under conditions of sustained disequilibrium. We explored the reactivity of three CaCO 3 polymorphs (calcite, aragonite, and vaterite) with acidic Zn2+-containing aqueous solutions using a suite of imaging techniques including optical and scanning electron microscopies, synchrotron-based micro X-ray fluorescence, and transmission X-ray microscopy. Zn uptake by calcite occurred through a two-step process: the formation of a thin layer of the zinc precipitate on the substrate surface followed by the growth of fibrous and radiating hydrozincite particles from the layer. In contrast, Zn uptake by aragonite occurred by mineral replacement where the secondary Zn carbonate phase preserved the external morphology of the original crystal (i.e., a pseudomorph). The replacement of vaterite by hydrozincite occurred within the confined space beneath the porous shell of vaterite, signifying that the primary mechanism driving Zn carbonate precipitation was chemical exchange through the pores. When multiple CaCO 3 polymorphs coexisted, the replacement of aragonite and vaterite occurred preferentially over that of calcite. These results demonstrate the distinct morphological and mineralogical controls over the reactivities of calcium carbonate minerals with Zn2+ under acidic conditions. [ABSTRACT FROM AUTHOR]

In recent years, fluorescent imaging has emerged as an active area of interest in medical imaging. Fluorescent imaging plays a critical role in molecular imaging. Evidence suggests its use in providing a detailed structural outlook and genetic and cellular operatives of the body procedures on a molecular plane. Imaging agents are identified to be related to risks such as not biologically disintegration and great poisonousness. Researchers have shown a keen attentiveness to the growth of targeted multifunctional agents in oncology and near-infrared (NIR) fluorescence imaging. This study assessed fluorescent imaging and bio-cellular acceptance of the gold (NIR) conjugated cockle shell-derived calcium carbonate nanoparticles Au-CsCaCO3NPs. The synthesized Au-CsCaCO3NPs were characterized by Transmission electron microscopy (TEM) for size and morphology, Zeta potential, and UV-Vis spectrophotometer. Biocompatibility of Au-CsCaCO3NPs in cultured human breast carcinoma cells MCF-7 and mouse embryonic fibroblast cells NIH3T3 was evaluated using bioassays like Lactate Dehydrogenase LDH and Reactive Oxygen Species ROS for toxic examination. Cellular morphology and uptake were studied by fluorescence and confocal microscopy. The outcomes proved that MCF-7 treated Au-CsCaCO3NP cells observed more cell deaths than NIH3T3 treated Au-CsCaCO3NP cells. Additionally, the cells were capable of assuming nanoparticles within their cellular compartments. In conclusion, gold-near infrared dye conjugated cockle shell calcium carbonate nanoparticles Au-CsCaCO3NPs were easily synthesized, biocompatible, and environmentally friendly. It is safe to state that the Au-CsCaCO3NPs could be used for imaging and could present opportunities for progressing cancer imaging.

Natural aragonite was used as a support for different percentages (5%, 10% and 20%) of nano-Ni which obtained from nickel nitrate and reduced by hydrazine hydrate. It was demonstrated that the 20% catalyst has higher activity compared to other nickel percentages for the reduction of p-nitrophenol to p-aminophenol. The reduction process was performed in alkaline medium (NaOH) by using hydrazine hydrate as a source of hydrogen. The catalysts were characterised by using XRD, SEM, FT-IR and XRF. In order to discuss the kinetics of reduction process, the effect of the catalysts load and p-nitrophenol concentration on the initial reduction rate were studied. The value of rate constant, reaction order and the activation energy were estimated. Moreover, thermodynamic functions at different temperatures were obtained. The proposed reaction mechanism was postulated. [ABSTRACT FROM AUTHOR]

Purpose: There is limited comparative evidence on patient outcomes following cartilage repair in various knee compartments. The aim of this study was to compare clinical and imaging outcomes after treating cartilage defects in femoral condyles and trochlea with either an aragonite-based scaffold or surgical standard of care (SSoC, i.e., debridement/microfractures) in a large multicentre randomized controlled trial. Methods: 247 patients with up to three knee joint surface lesions (ICRS grade IIIa or above) in the femoral condyles, trochlea or both ("mixed"), were enrolled and randomized to surgery with either a cell-free aragonite scaffold or SSoC. Patients were followed for up to 48 months by analysing subjective scores (KOOS and IKDC), radiological outcomes (defect filling on MRI), as well as treatment failure rates and adverse events. A differential analysis of outcomes for condylar, trochlear and mixed lesions was performed. Results: The scaffold group significantly outperformed the SSoC group regardless of lesion location with statistically significantly better KOOS Overall scores at 24 months (all p ≤ 0.0009) and 48 months (all p ≤ 0.02). Similar results were observed for KOOS subscales and IKDC scores. For KOOS responder rates, superiority of the implant group was demonstrated at 24, 36, and 48 months (all p ≤ 0.004). Higher defect filling on MRI for implants was observed for all locations. Lower treatment failure rates for the implant were observed in condylar and mixed lesions. Conclusion: The aragonite-based scaffold was safe and effective regardless of the defect location, providing superior clinical and radiological outcomes compared to SSoC up to four years follow-up. Level of evidence: I – Randomized controlled trial. [ABSTRACT FROM AUTHOR]

The article provides new data on the structure of the Laptev Sea flank of the Gakkel Ridge. The intensive supply of clastic material from the Laptev Sea shelf leads to the development of a thick alluvial fan at the continental rise, which determines the structure of the bottom topography. In the northwestern direction, the influence of the fan decreases and tectonics becomes the main relief-forming factor. The bathymetric survey traced the asymmetrical rift valley of the Gakkel Ridge, the western flank of which is complicated by terraces. The presence of fault structures, bottom subsidence, extensive sediment supply, and the widespread development of subaqueous slump processes indicate the high neotectonic activity of the Laptev Sea flank of the Gakkel Ridge. For the first time in this region, numerous carbonate rocks have been discovered, the authigenic cement of which is represented by magnesian calcite or aragonite with an admixture of terrigenous material. The palynological and micropaleontological analysis of the carbonate rocks indicates the Quaternary formation of authigenic carbonate cement. An important role in the formation of authigenic carbonates was played by diagenetic solutions coming from the sedimentary cover together with methane and oxidation products of gases and organic matter. The authigenic carbonates were precipitated mainly in an isotopic equilibrium with bottom water at a temperature of about 0°C. The negative correlation between 87Sr/86Sr and δ13C indicates the presence of at least two different sources of carbonate-forming solutions. [ABSTRACT FROM AUTHOR]

Abstract The export of neritic material from the top of carbonate platforms is a key process in the construction of their slopes. However, our knowledge of the supply pattern of materials from platforms is dominantly based on platforms lying in the euphotic zone during the present sea‐level highstand. This is a somewhat biased perspective as through geological time not all platforms were euphotic. The Saya de Malha Bank in the Mascarene Plateau is an example of a modern mesophotic carbonate platform, and as such, its flooding and export patterns differ from those of euphotic ones. Using cores collected on the western slope of the Saya de Malha Bank, the export patterns of the platform since the last glacial maximum were explored. Material on the platform edge is winnowed and transported to the slope by multiple possible processes. The material on the platform is a combination of high and low magnesium calcite as well as high and low strontium aragonite, integrating pelagic and neritic sources. The ratio of these constituents varies over time with changes in the platform production capability as it was flooded and drowned during the Holocene transgression. The material from the platform is transported in both confined flows, mainly during lowstands, and unconfined flows, mainly during late transgression and early highstand. In the present state of the highstand, supply may have diminished, leading to erosion of the canyon shoulders.

Mollusk shells protect the animals that form and inhabit them. They are composites of minerals and organics, with diverse mesostructures, including nacre, prismatic calcite, crossed‐lamellar aragonite, and foliated calcite. Twins, that is, crystals mirror symmetric with respect to their coherent interface, occurring as formation or deformation twins, are observed in all mollusk shell mesostructures but never within calcite prisms. Here, nanotwins and microwins within single calcite prisms are observed in different shells. Using Polarization‐dependent Imaging Contrast (PIC) mapping with 20–60 nm resolution, twins are observed to be 0.2–3 µm thick layers of differently oriented and colored crystals with respect to the main prism crystal. Multiple twins are interspersed with the prism crystal, parallel to one another, and similarly oriented. When comparing images of calcite prisms and twins obtained by PIC mapping and by Electron Back‐Scattered Diffraction (EBSD), the images correspond precisely. All twins are e‐twin types, with 127° angular distance between c‐axes. E‐twins are the most common deformation twins in geologic calcite, as also observed here in Carrara marble. Location of all twins near the outer surface of all shells and e‐twin type both suggest that twins within calcite prisms in mollusk shells result from deformation twinning. [ABSTRACT FROM AUTHOR]

Shells are primarily composed of calcite and aragonite, making the inclusion of micronized shells as bio-based fillers in organic coatings a potential means to enhance the mechanical properties of the layers. A water-based coating was reinforced with 5 wt.% Acanthocardia tuberculata powder, 5 wt.% Mytilus galloprovincialis powder, and 5 wt.% of an LDPE/ceramic/nanoceramic composite. An improvement in abrasion resistance was achieved using micronized seashells, as demonstrated by the Taber test (evaluating both weight loss and thickness reduction). Additionally, Buchholz hardness improved with powders derived from Mytilus galloprovincialis. No significant differences were observed among the samples in terms of color and gloss after 200 h of UV-B exposure. However, the delamination length from the scratch after 168 h of exposure in a salt spray chamber indicated that the addition of particles to the polymeric matrix resulted in premature degradation, likely due to the formation of preferential paths for water penetration from the scratch. This hypothesis was supported by electrochemical impedance spectroscopy measurements, which revealed a decrease in total impedance at 0.01 Hz shortly after immersion in a 3.5% NaCl solution. In conclusion, the particle size and shape of the micronized shells improved abrasion resistance without altering color and gloss but led to a decrease in the coating's isolation properties. [ABSTRACT FROM AUTHOR]

Coral skeletal B/Ca (effectively B/CO 3 2–), in combination with boron isotopic composition (δ11B), has been used to reconstruct the dissolved inorganic carbon chemistry of coral calcification media and to explore the biomineralisation process and its response to ocean acidification. This approach assumes that B(OH) 4 −, the B species incorporated into aragonite, competes with dissolved inorganic carbon species for inclusion in the mineral lattice. In this study we precipitated aragonite from seawater in vitro under conditions that simulate the compositions of the calcification media used to build tropical coral skeletons. To deconvolve the effects of pH and [CO 3 2–] on boron incorporation we conducted multiple experiments at constant [CO 3 2–] but variable pH and at constant pH but variable [CO 3 2–], both in the absence and presence of common coral skeletal amino acids. Large changes in solution [CO 3 2–], from < 400 to >1000 µmol kg−1, or in precipitation rate, have no significant effect on aragonite B/Ca at pH total of 8.20 and 8.41. A significant inverse relationship is observed between solution [CO 3 2–] and aragonite B/Ca at pH total = 8.59. Aragonite B/Ca is positively correlated with seawater pH across precipitations conducted at multiple pH but this relationship is driven by the effect of pH on the abundance of B(OH) 4 – in seawater. Glutamic acid and glycine enhance the incorporation of B in aragonite but aspartic acid has no measurable effect. Normalising aragonite B/Ca to solution [B(OH) 4 –] creates K D B(OH)4− which do not vary significantly between pH treatments. This implies that B(OH) 4 – and CO 3 2– do not compete with each other for inclusion in the aragonite lattice at pH total 8.20 and 8.41. Only at high pH (8.59), when [B(OH) 4 –] is high, do we observe evidence to suggest that the 2 anions compete to be incorporated into the lattice. These high pH conditions represent the uppermost limits reliably measured in the calcification media of tropical corals cultured under present day conditions, suggesting that skeletal B/Ca may not reflect the calcification media dissolved inorganic carbon chemistry in all modern day corals. [ABSTRACT FROM AUTHOR]

Low-Mg calcite, precipitating from meteoric fluids, is a common mineral that forms in a variety of near-surface diagenetic environments. However, recent studies, based on a combination of analyses of δ18O and Δ 47 values, have suggested that this mineral might form in disequilibrium and consequently yield kinetic bias in Δ 47 -derived temperatures and fluid δ18O values. Here, we use dual clumped isotope proxies (Δ 47 and Δ 48) to investigate the influence of kinetic isotope effects within different meteoric diagenetic zones of Holocene and Pleistocene carbonates from the southern Florida and the Dominican Republic. In the Miami Oolite, the primary aragonite ooids and secondary low-Mg calcite cements in the bulk sample were separated from each other and their isotopic compositions (δ13C, δ18O, Δ 47 and Δ 48 values) were measured. The Δ 47 and Δ 48 values of the separated aragonite are consistent with the modern ooid sediments and in approximate equilibrium with the surface seawater. In contrast, the low-Mg calcite cement shows the higher Δ 48 and lower Δ 47 values, than expected, with the disequilibrium arising as a result of CO 2 degassing in the vadose zone. Such deviations of Δ 47 and Δ 48 values are also observed in low-Mg calcite vadose cements in the Dominican Republic. While low-Mg calcites formed in the lower freshwater phreatic zone in the Dominican Republic have the Δ 47 - and Δ 48 -derived temperatures close to expected, the same mineral forming near the water-table and upper phreatic zone shows much higher Δ 48 -derived temperatures (up to ∼ 90 °C). The possible origin of such elevated temperatures can be attributed to non-equilibrium processes caused by changes in pH and pCO 2 , mediated by microbial sulfate reduction. Such differential kinetic behavior of Δ 48 values between vadose and phreatic zones could be used as a proxy marker for the presence and the location of a water-table. This study demonstrates the great potential of dual clumped isotopes in the investigation of meteoric diagenesis and will help understand the alteration of ancient sequences and the interpretation of stable C isotope trends that they contain. [ABSTRACT FROM AUTHOR]

Multiple geochemical proxies (e.g., trace elements, δ18O and δ13C) and precise 230Th ages in speleothems are crucial for conducting robust paleoclimatic reconstructions, but the impact of diagenesis on these proxies and 230Th ages is not well-established. In this study, we investigate the petrography and geochemical composition of six aragonite-calcite stalagmites from Shennong Cave in southeastern China to analyze the transformation from aragonite to calcite (primary versus secondary) and its effects on geochemical proxies and 230Th ages. No aragonite relics are observed in columnar calcite in four aragonite-calcite stalagmites (SN55, SN49, SN104 and SNB1), although traces of aragonite exist between the calcite crystals or grow parallel at the aragonite-calcite borders. This is different from the obvious aragonite relics preserved in secondary mosaic calcite in the other two aragonite-calcite stalagmites (SN3 and SN15). Both mosaic and columnar calcite show various changes in geochemical proxies and 230Th ages compared with primary aragonite. The trend in the geochemical proxies analyzed (trace elements, δ18O and δ13C) of columnar calcite remains consistent with those of aragonite, despite significant differences in their absolute values within the overlapping periods. These differences are due to the different fractionation coefficients of isotopes and trace elements in aragonite and calcite formed under the same solution conditions rather than late diagenesis. The 230Th ages of columnar calcite are similar to those of primary aragonite, and the values of subsamples from the same calcite layer are consistent. In contrast, the trace elements and δ13C values of mosaic calcite are similar to those of primary aragonite, while its 230Th age significantly differs from that of primary aragonite, exhibiting no consistent patterns. Therefore, these geochemical characteristics of columnar calcite are significantly different from secondary mosaic calcite, indicating that the columnar calcite in these four aragonite-calcite stalagmites is primary. A comparison of trace elements and δ13C records between aragonite-calcite and pure aragonite stalagmites during the overlapping period further confirms that these columnar calcites are primary. Their geochemical proxies can be used for paleoclimate reconstruction after careful evaluation, and the transformation from aragonite to columnar calcite is caused by increased precipitation. However, due to age and geochemical proxies change, secondary mosaic calcite is unsuitable for paleoclimate reconstruction, unlike columnar calcite. This study provides competent evidence to identify whether calcite in aragonite-calcite stalagmites is primary versus secondary and whether it can be used for paleoclimatic reconstruction. [ABSTRACT FROM AUTHOR]

Aim: Quantify the contribution of environmental factors (water temperature, salinity and depth) and evolutionary history to varied skeletal mineralogy in calcifying marine organisms. Location: Global Ocean. Time period: Present. Major taxa studied: Order: Cheilostomatida; Phylum: Bryozoa. Methods: We employed X‐ray diffraction (XRD) to analyse the skeletal mineral composition of 872 individual colonies, representing 437 bryozoan species, in terms of calcite/aragonite ratios. We integrated these data with equivalent published data, thus reaching 981 species, and applied linear models (LMs), generalized linear models (GLMs) and phylogenetic generalized least squares models (PGLSs) to investigate the influences of temperature, salinity, depth and phylogenetic history on the mineralogy of nearly 1000 cheilostome bryozoan species. Results: Cheilostome bryozoans vary considerably in their skeletal mineral composition: in our dataset 65% of the species possess purely calcite skeletons, 15% exclusively employ aragonite and 20% exhibit mixed (i.e. calcite and aragonite) mineralogies. Temperature is the predominant measured environmental factor influencing bryozoan skeletal mineralogy, accounting for 20% of its variability across species, when phylogenetic relatedness is unaccounted for. Bryozoans in lower latitudes, characterized by higher seawater temperatures, have higher aragonite concentrations. By accounting for phylogenetic structure using a subset of 87 species for which we have topological information, 40% of the observed mineralogical variability could be attributed to present‐day temperature. In contrast, depth and salinity played minor roles, explaining less than 1% of the mineralogical variation each. Main conclusions: This study emphasizes the influence of evolutionary history on the mineralogical variability of calcifying organisms, even when it can be shown that a single environmental factor (temperature) explains a substantial amount of this variability. When confronted with changing temperature, calcifiers such as bryozoans are likely to respond in diverse ways, depending on the species, given their phylogenetic relatedness and the external conditions they meet. [ABSTRACT FROM AUTHOR]

Recent observations of crystallization by thermal chemical vapor deposition systems indicate that the classical mechanism of nucleation and growth is followed. Information on aragonite nanocrystal growth and formation on substrate have been lacking due to the lack of reports on diffusional growth that can observe calcium carbonate nucleation processes in thin film formation. This report is important due to the additive‐free method able to grow stable single‐phase nanocrystals without the presence of other phases, amorphous or impurities. This work demonstrates homogeneous nucleation occurred in gas phase reaction in a constant flow of carbon dioxide gas (100 sccm) with optimally 0.5 M calcium chloride precursor in atmospheric pressure at 400 °C resulting in a calculated crystallite size of 27.8 nm. X‐ray diffraction and energy dispersive spectrometer confirm the presence of calcium carbonate nanocrystal, whereas its structural changes are observed by its micrograph from field emission scanning electron microscope. The aim is to convey its importance in gaining control of aragonite nanocrystal morphology and structural properties, and thus generate nanocrystals with controlled phase. This work may contribute to development of more sensitive and crucial applications of calcium carbonate nanocrystal thin film such as in biosensors and biomedical. [ABSTRACT FROM AUTHOR]

Introduction: Ayurvedic marine drugs derived from mollusc shells and coral are regularly used by Ayurvedic physicians to treat several disease conditions like acid peptic disease, irritable bowel syndrome, osteoporosis, etc. However, standard operating procedures for manufacturing these drugs and their complete characterization have not been published in the Ayurvedic Formulary and Ayurvedic Pharmacopeia of India to date. Methods: Present study describes the traditional manufacturing process and thorough characterization using classical and advanced analytical tools. The raw materials characters, in-process parameters, and finished product specifications have been elaborated to develop monographs. Especially, the identity and purity of raw coral and pearl were checked by Raman Spectroscopy and Energy Dispersive X-ray Fluorescence analysis. Results: In the finished product analysis, the X-Ray Diffraction study revealed that incineration after trituration with Aloe barbadensis leaf pulp or rose water converted the aragonite phase of calcium carbonate into calcite phase in mother pearl, cowry, and pearl while the calcite form of raw coral was retained. The prominent bands around 1390, 870, and 712 cm−1 detected by Fourier Transform-Infrared Spectroscopy and mass loss between 39–44% (w/w) revealed by thermogravimetric analysis confirmed the carbonate form of these calcium-based drugs. The finished products were very fine grayish-white powders constituted by irregularly shaped nano-micro particulate calcium carbonate exhibiting particle size between 600 nm (D10 value) to 1.2 µm (D90 value). Conclusion: The quality control and assurance achieved in this study may be further utilized by the pharmaceutical industries to manufacture quality marine drugs and conduct efficacy studies. [ABSTRACT FROM AUTHOR]

This study investigated the effect of a magnetic field on the crystal deposition of treated seawater to determine the mechanism of calcium carbonate deposition on the quartz surface. Several samples of standard seawater (43 g/L) were circulated through a permanent magnetic field of 0.16 T at a fixed temperature, pH, and flow rate. Scaling experiments showed that magnetic treatment of seawater enhanced the precipitation of calcium carbonate and that two superposed phases were deposited. A first layer formed with crystals of aragonite covering the whole surface of the quartz, and then a second phase of calcite was deposited. In the untreated solutions, only homogeneous agglomerates of aragonite were deposited. [ABSTRACT FROM AUTHOR]

Aragonite, a metastable crystal form of calcium carbonate, exhibits the highest density and hardness among all species. Diversified forms of aragonite composites can be produced through different preparation processes, forming a relatively complete system in various application fields. Their properties and applications are determined by their multiple levels of structures and shapes. However, research information for aragonite‐related fields is currently lacking integration and clarification. This review provides a comprehensive overview on the preparation methods, properties, and potential applications of three main aragonite‐based materials: aragonite particles, nacre‐inspired mineralized aragonite composites (NMACs), and shell‐derived aragonite nanoparticles (SANPs). The formation mechanisms and versatile applications of these materials are thoroughly surveyed based on their initial precursor, reaction conditions, product forms including filler of aragonite whiskers synthesized by carbonation reaction; functional materials of NMACs fabricated by amorphous calcium carbonate‐organic matter (ACC‐OM) mediated process; biomedical materials of SANPs derived from aragonite cockle shells. Overall, this review aims to provide assistance for customized production of aragonite‐based materials as well as new research directions for both pure aragonites and its composites. [ABSTRACT FROM AUTHOR]

A significant proportion of marine calcium carbonate sediments are comprised of metastable minerals that are susceptible to diagenetic alterations during burial. These reactions can reset the geochemical signature of sediments and pore fluids and influence elemental cycling in the ocean. However, the timing and mechanisms by which these reactions take place are poorly constrained. This study uses cores drilled on the slope of the Great Bahama Bank to provide quantitative constraints on important diagenetic reactions; namely respiration-driven dissolution, authigenic carbonate mineral formation, and conversion of aragonite to low Mg calcite (LMC). We perform detailed mineralogical characterization using newly acquired, high resolution X-ray diffraction (XRD) data and over 1000 reanalyzed XRD scans, characterize sediments texturally and elementally using electron microprobe data, calculate pore fluid saturation state with respect to aragonite using a Pitzer ion interaction approach, and use pore fluid chemistry and experimental distribution coefficients to predict authigenic carbonate compositions. These data suggest that aerobic organic matter oxidation, enabled by the advection of oxygenated seawater throughout the upper ∼ 30 m interval of sediment, causes undersaturation and thus dissolution of biogenic high Mg calcite (HMC) and aragonite. Deeper, anaerobic organic matter oxidation takes over and causes supersaturation, promoting authigenic precipitation in the form of HMC, which in turn decreases pore fluid Mg/Ca and promotes aragonite conversion to LMC. One novel aspect of this study is the identification of three types of calcites using the newly acquired XRD and electron microprobe data. Based on their unique crystallographic characteristics and chemical compositions, these types of calcites are interpreted to represent pelagic biogenic LMC, bank-derived biogenic HMC, and authigenic HMC precipitated from pore fluids. Notably, the composition of the authigenic calcite matches that predicted to precipitate from pore fluids using an empirical Mg partition coefficient in calcite. Calcites that form authigenically and from aragonite via replacement are suggested to recrystallize with burial as evidenced by the decrease in Mg content and micro-strain. This process-based geochemical framework assigns diagenetic processes to a specific depth window within the sediment column and paves the way for a mechanistic understanding of carbonate diagenesis, one that is rooted in thermodynamic and kinetic bases. [ABSTRACT FROM AUTHOR]

Powdered biogenic calcium carbonate from butter clams shows variations in its tendency to convert from aragonite to calcite when suspended in water, depending on whether the suspension has additional calcite or not. Our investigations treat these biogenic samples as complex hierarchical materials, considering both their mineral and organic components. We assess the mineral composition from Attenuated Total Reflection Fourier Transform Infrared spectroscopy peak shifts, as well as quantitative assessments of lattice constant refinements (powder X-ray diffraction). To isolate the mineral portions, we compare results from samples where the periostracum is removed mechanically and samples that are heated to temperatures that are sufficient to remove organic material but well below the temperature for thermal phase conversion from aragonite to calcite. The results show that the total organic content does not play a significant role in the aqueous mineral phase conversion. These results have potential implications for understanding carbonate mineral interactions in ocean sediments. [ABSTRACT FROM AUTHOR]

In the last few years, an increasing interest has developed regarding the application of different techniques for the identification of pollutants inside the tissues deriving from patients affected by benign or neoplastic diseases. Particular attention was paid to neoplasia linked to particular exposures, e.g., heavy metals, carbon dusts, silica, asbestos. As regards the last pollutant, a wide body of scientific literature has been collected, considering the severe effects caused by mineral fibers on human health. Optical and electronic microscopies were widely applied to identify the fibers in respiratory and extra-respiratory organs to detect the minerals and to link their presence to an exposure source and to understand their role in cancer development. The main advantage of electron microscopy lies in the possibility of coupling the microscopes with energy dispersive spectrometers and also collecting data on the elemental composition of various inorganic phases. In term of sample preparation and time of analysis, the most utilized microscope technique is Scanning Electron Microscopy with an annexed energy dispersive spectrometer (SEM/EDS), allowing for the morphological and chemical characterization of the observed particles/fibers. Moreover, this technique is envisaged by Italian Law for asbestos identification in air and bulk samples. On the other hand, this technique does not allow a reliable identification of the mineral phase in the case of polymorphs with the same chemical formula but different crystal structures. In this work, the coupling of a spectroscopical technique—micro-Raman spectroscopy—to SEM/EDS is proposed for a sure phase identification of particles, showing EDS spectra with ambiguous phase identification, observed in samples of tissues from patients affected by colorectal cancer and living in an asbestos-polluted area. In these tissues, different particles with EDS spectra that do not allow a sure identification of the phase—in particular calcium-rich particles and titanium oxides—were successively analyzed by micro-Raman spectroscopy. Thanks to this last technique, it was possible to ascribe the mineral phases associated to these particles to "aragonite" (a calcium carbonate polymorph) and to "anatase" (a Ti dioxide polymorph). [ABSTRACT FROM AUTHOR]

Chamid bivalves are marine organisms that live in high-energy environments and are cemented to hard substrates. To avoid shell damage, the organisms form thick, densely ornamented shells. Shell material consists of aragonite, and the ornamentation may be either aragonitic or calcitic. The latter can be developed as scaly spines, rows of blades, or comarginal, radial arched lamellae. We investigated biological crystal morphology and mode of assembly of Chama arcana and Chama gryphoides shells. Structural characteristics were obtained from electron backscatter diffraction (EBSD) measurements, complemented with laser confocal and BSE imaging. We found a wide range of crystal morphologies and sizes, ranging from irregularly shaped calcite and/or aragonite prisms to tiny and thin aragonite laths. We observed four different modes of crystal assembly patterns: 1. strongly interlocked dendritic calcite units forming the ornamentation blades; 2. aragonite laths arranged to lamellae forming the outer shell layer, the layer adjacent to the calcite; 3. aragonite laths arranged into blocks comprising inner shell layers or aragonitic ornamentations; and 4. shell portions consisting of aragonite prisms, structured in size and crystal orientation, at muscle attachment sites. These four different types of crystal arrangements were observed for the shells of the investigated chamid species; however, they had slightly different strengths of structuring and slight variations in crystal organisation. Additionally, we observed unique microstructural features in Chama shells: We report ornamentation crystals resembling idiomorphic calcite and novel, twinned entities found at the changeover between the aragonitic layers. We highlight and discuss these differences and anomalies in this contribution. [ABSTRACT FROM AUTHOR]

The interaction between multi‐component rare earth element (REE) aqueous solutions and carbonate grains (dolomite, aragonite, and calcite) are studied at hydrothermal conditions (21–210 °C). The effect of ionic radii of five REEs (La, Ce, Pr, Nd, Dy) on solid formation are analyzed using two solution types: equal REE concentrations and concentrations normalized to Post Archean Australian Shale Standard (PAAS). The interaction replaces the host Ca–Mg carbonate grains with a series of REE minerals (lanthanite → kozoite → bastnäsite → cerianite). At 165 °C, equal concentration solutions promote kozoite crystallization, maintaining similar REE ratios in solids and solution. PAAS solutions result in zoned REE‐bearing crystals with heterogeneous elemental distributions and discreet REE phases (e.g., cerianite). Chemical signatures indicate metastable REE‐bearing phases transforming into more stable polymorphs, along with symplectite textures formed by adjacent phase reactions. Overall, experiments highlight the dependence of polymorph selection, crystallization pathway, mineral formation kinetics, and chemical texture on REE concentrations, ionic radii, temperature, time, and host grain solubility. [ABSTRACT FROM AUTHOR]

Etheria elliptica is a freshwater oyster that produces an adhesive that hardens underwater, allowing them to attach to other oysters, rocks, wood, and other natural substrates, producing complex oyster bed communities. Despite the importance of the adhesive in oyster bed formation, little is known about its chemical composition, structure, or mechanical properties. Through a combination of scanning electron microscopy (SEM), x‐ray photoemission electron microscopy (X‐PEEM), infrared (IR) spectroscopy, microhardness testing, and nanoindentation, it is found that the oyster adhesive consists entirely of aragonite nanoparticles that clump together into crystallites of varied shape, size, and orientation. The crystallite clumping density varies from the exterior of the adhesive to the interior, with the adhesive closest to the prismatic layer generally being denser. With this variation in density comes a variation in material properties with the exterior adhesive layer being softer and more flexible and the interior adhesive layer being harder and less elastic, or more similar to the prismatic and nacre shell structures produced by the E. elliptica. The resultant material exhibits varied materials properties, despite similar mineral composition. [ABSTRACT FROM AUTHOR]

All-in-one injection strategy has been developed recently as an efficient method in microbially induced carbonate precipitation (MICP). In this method, engineers try to delay the beginning of precipitation and consequently distribute reagents homogeneously on a soil mass. In this article, a series of experiments have been carried out to modify all-in-one solution strategy and promote its uniformity. Primarily, the concentration of all-in-one solutions was optimized and the result showed that all-in-one solution with a 2 M concentration of urea/calcium chloride was completely consumed. The short columns treated by one-time one-pore volume (PV) injection of 2 M all-in-one solution provided approximately 450 kPa in UCS test. In the second step, magnesium substitution for calcium was investigated to improve the strength and homogeneity of biocementation. This substitution raised the UCS by approximately 70%, and 800 kPa was acquired. XRD analysis confirmed that Mg2+ changes the mineralogy of precipitation from vaterite to aragonite. Hence, the higher strength of columns treated with the magnesium-substituted solutions is attributed to the higher hardness of aragonite crystals than that of vaterite. Finally, the bacterial transport of all-in-one solutions showed that magnesium substitution for 20% of calcium cations, enhances its potential to provide a homogeneous biocement on large-scale projects. [ABSTRACT FROM AUTHOR]

Observations from the California Current System (CalCS) indicate that the long‐term trend in ocean acidification (OA) and the naturally occurring corrosive conditions for the CaCO3 mineral aragonite (saturation state Ω < 1) have a damaging effect on shelled pteropods, a keystone group of calcifying organisms in the CalCS. Concern is heightened by recent findings suggesting that shell formation and developmental progress are already impacted when Ω falls below 1.5. Here, we quantify the impact of low Ω conditions on pteropods using an individual‐based model (IBM) with life‐stage‐specific mortality, growth, and behavior in a high‐resolution regional hindcast simulation of the CalCS between 1984 and 2019. Special attention is paid to attributing this impact to different processes that lead to such low Ω conditions, namely natural variability, long‐term trend, and extreme events. We find that much of the observed damage in the CalCS, and specifically >70% of the shell CaCO3 loss, is due to the pteropods' exposure to naturally occurring low Ω conditions as a result of their diel vertical migration (DVM). Over the hindcast period, their exposure to damaging waters (Ω < 1.5) increases from 9% to 49%, doubling their shell CaCO3 loss, and increasing their mortality by ~40%. Most of this increased exposure is due to the shoaling of low Ω waters driven by the long‐term trend in OA. Extreme OA events amplify this increase by ~40%. Our approach can quantify the health of pteropod populations under shifting environmental conditions, and attribute changes in fitness or population structure to changes in the stressor landscape across hierarchical time scales. [ABSTRACT FROM AUTHOR]

Climate change accelerated by anthropogenic activities has led to the shrinkage and eventually disappearance of salt lakes all over the world. Gradual desiccation of Lake Urmia (LU) in northwestern Iran, as one example of desiccating lakes, has led to the exposure of the lakebed sediment with enormous dust emission potential in some parts. Sand sheets of western LU are identified as one of the major contributors to aerosols in this region. Yet, dust blown from this area is not well characterized. The aims of the current study were, therefore, to comprehensively investigate the origin of dust from sand sheets; the characteristics of dust and temporal variability of the aerosol and to test the effectiveness of the application of sodium alginate (SA) on soil crusting and stabilization. Soil samples were collected from the two prevailing soil types from sand sheets in August 2020. Dust samples were also collected during four time periods: July and August (the beginning of the dry season); October and November (the beginning of the wet season). Using SA with varying concentrations and different methods of application, the effectiveness of the induced crusts was investigated. Authigenic aragonite minerals with elongated needle shapes were found to be the major constituent of the soil and dust samples. Temporal variability of the dust characteristics and their elemental correlation to dust sources revealed that while dust source 1 (DS 1) with higher clay, salt, and silt contents contribute more to the dust composition from July to August (R 2 > 0.75 for DS 1 versus R 2 > 0.58 for DS 2), dust source 2 (DS 2) with less salinity and higher sand content becomes the major contributor to dust composition from October to November (R 2 > 0.91 for DS 2 versus R 2 > 0.75 for DS 1). Results of stabilizing both DS 1 and DS 2 showed that SA-induced crusts on DS 1 are more stable than DS 2 due to the presence of higher clay, silt, salt, organic matter, and lower aragonite minerals. SA-induced crusts by a compaction method significantly performed better than a spray of SA on either dry (DSp) or soil at its optimum water content (WSp) at all concentrations. Nevertheless, spray methods are more feasible at the field scale and in both DSp and WSp methods, SA 0.5 improved the crust thickness. Scanning electron microscope-energy dispersive X-ray spectroscopy (SEM-EDX) along with thermogravimetric analysis (TGA) confirmed the remaining SA on the soil surface three months after its application indicating the effective performance of the SA solution in sand sheets stabilization. Hence, its application at the field scale could possibly reduce aerosol release and transport to surrounding areas. [Display omitted] • The contribution of the Sa-sheet playa surface to dust composition is investigated. • Aragonite is the prevailing constituent of the soil and dust samples in the form of ooids. • Salt accumulation on dust source 1, reduces wind erosion towards the end of dry season. • PM 10 concentration in Urmia City was affected by dust blown from Sa-sheets. • Sodium alginate solution well improved the pressure resistance of the induced crusts on both dust sources. [ABSTRACT FROM AUTHOR]

The formation of calcium carbonate scale in pipes and devices in water supply networks poses serious problems. Electromagnetic treatment (EMT) is a technology that can prevent the formation of these scales without the need to add chemical reagents, reducing maintenance costs in the installations. In this work, the types of crystals commonly found in water distribution systems are studied, with emphasis on the different techniques that allow their characterization (TGA, XRD, SEM), and the effects that EMT produces on their morphology. Laboratory trials have been carried out with synthetic water prepared from a calcium carbonate solution to study the crystals obtained at different temperatures, with and without EMT. High temperatures cause the production of aragonite instead of the stable form (calcite), as was observed in the samples from the heater resistors. In contrast, in the samples taken in lower temperature zones, a majority presence of calcite was observed. These results have been corroborated with a laboratory-scale evaporation trial, obtaining an increase in the aragonite/calcite ratio with increasing temperature and with the treatment applied, generating crystalline phases that exceed 70% aragonite (needle shape). It is highlighted that the EMT limits the reversion of aragonite to calcite and decreases the formation of scale. [ABSTRACT FROM AUTHOR]

The export of neritic material from the top of carbonate platforms is a key process in the construction of their slopes. However, our knowledge of the supply pattern of materials from platforms is dominantly based on platforms lying in the euphotic zone during the present sea‐level highstand. This is a somewhat biased perspective as through geological time not all platforms were euphotic. The Saya de Malha Bank in the Mascarene Plateau is an example of a modern mesophotic carbonate platform, and as such, its flooding and export patterns differ from those of euphotic ones. Using cores collected on the western slope of the Saya de Malha Bank, the export patterns of the platform since the last glacial maximum were explored. Material on the platform edge is winnowed and transported to the slope by multiple possible processes. The material on the platform is a combination of high and low magnesium calcite as well as high and low strontium aragonite, integrating pelagic and neritic sources. The ratio of these constituents varies over time with changes in the platform production capability as it was flooded and drowned during the Holocene transgression. The material from the platform is transported in both confined flows, mainly during lowstands, and unconfined flows, mainly during late transgression and early highstand. In the present state of the highstand, supply may have diminished, leading to erosion of the canyon shoulders. [ABSTRACT FROM AUTHOR]

Arctic rivers carry not only large amounts of freshwater but also biogeochemical materials into the ocean and play important roles in Arctic ocean acidification (OA). This study quantitatively evaluated the effects of riverine biogeochemical fluxes (R‐BGC; carbon and nutrients) on the Arctic marine carbonate system and OA using multi‐decadal experiments (1979–2018) with a pan‐Arctic sea ice–ocean model. Improved initial and lateral boundary conditions of carbonate properties, observation‐based riverine biogeochemical data, and land model‐based interannually varying riverine freshwater discharge were adopted to enable more realistic experiments. The model simulated negative trends in aragonite saturation state (Ω) and pH in most regions of Arctic Ocean regardless of R‐BGC. The increased riverine freshwater promoted more OA through the higher dilution effect. Compared to the experiment with riverine discharge of only freshwater, the inclusion of R‐BGC caused positive anomalies in Ω and pH (by ∼0.14 and ∼0.03 in central basins, and by ∼0.15 and ∼0.06 in shelf seas, respectively). In the central basins, these anomalies were caused mostly by carbon (total alkalinity and dissolved inorganic carbon) of the R‐BGC. In the shelf seas, nutrient (nitrate and silicate) fluxes also contributed ∼14% and ∼32% of the anomalies owing to the enhanced primary production and a corresponding reduction in seawater pCO2. R‐BGC mitigated OA (ΔΩ = −1.53 × 10−3 year−1 and ΔpH = −0.56 × 10−3 year−1) in regions where riverine freshwater was accumulated (i.e., the Canada Basin, Chukchi Cap, Eurasian Basin, and East Siberian Sea). This study stressed the importance of including R‐BGC for OA model projection. Plain Language Summary: Ocean acidification (OA) is caused primarily by atmospheric CO2 absorption at the sea surface. In the Arctic Ocean, riverine biogeochemical inputs (R‐BGC; carbon and nutrients carried by riverine water), in addition to freshwater discharge, affect OA. This study quantified the effects of R‐BGC on OA using a couple of model simulations for 1979–2018. Advancing from previous studies, this study conducted more realistic experiments by using improved initial and lateral boundary conditions of carbonate properties, observation‐based riverine biogeochemical data, and the land model‐based interannually varying riverine freshwater discharge data. R‐BGC impacts on OA were found mainly in the surface waters of the Arctic, especially in coastal regions close to the river mouths. During 1989–2018, negative trends in carbonate saturation state and pH (both indicating OA) were simulated regardless of R‐BGC in most regions of Arctic Ocean. Compared to a simulation with riverine input of only freshwater, R‐BGC mitigated the simulated OA in the regions with increased riverine freshwater content. This study stressed the importance of R‐BGC for model‐based OA estimation and future projections. It will improve the understanding of OA under climate change and aid in informing marine ecosystem‐based management. Key Points: Simulations with only riverine freshwater overestimate Arctic ocean acidification and negative trends in aragonite saturation state and pHAddition of riverine biogeochemical fluxes, especially total alkalinity and dissolved inorganic carbon, can reduce this overestimationRiverine nutrient fluxes can also reduce ∼14% and ∼32% of the overestimation in aragonite saturation state and pH in shelf seas [ABSTRACT FROM AUTHOR]

Abstract Active and relic marine methane‐seep sites are widely distributed globally and are distinguished by distinctive geology, biogeochemistry, and ecosystems. The discovery of methane‐seep sites in the Krishna‐Godavari (K‐G) basin has created exciting new opportunities for methane‐seep research in the Bay of Bengal. In this study, we document the occurrence of authigenic carbonates, including micro‐crystalline aragonite crust (arg‐crusts) admixed with chemosynthetic shells and high‐magnesium carbonate tubular structures (HMC‐tube), from the methane‐seep site SSD‐045/4 in the K‐G basin. The δ13C values of HMC‐tubes (−54.5 to −46.2‰) and arg‐crusts (−57.6 to −34.8‰) indicate biogenic methane as the likely carbon source. Enhanced porewater alkalinity driving carbonate precipitation may be attributed to microbial‐mediated SO₄2−‐AOM processes. Additionally, δ13C values (−35.2 ± 8‰) of the residual organic matter within the carbonates suggest a contribution of methanotrophic bacterial biomass. The δ18Ocarb values of HMC and aragonite indicate methane hydrate degassing and crystallization pathways, respectively. Pelloid‐filled burrows suggest the reworking of shallow HMC deposit by burrowing organisms, whereas the polyphase cementations (aragonite and HMC) within burrows indicate early and burial diagenetic pathways. The wide range in ΣLREE/ΣHREE ratios and Ceanom values in arg‐crusts reflect micro‐spatial variations in redox conditions, likely due to cementation occurring in both open and closed diagenetic systems. In contrast, more constrained Ceanom values and ΣLREE/ΣHREE ratios in HMC tubes suggest persistent sulfidic conditions. Overall, these findings provide insights into the pathways of carbonate formation at the K‐G basin methane‐seep site, highlighting the complex interplay of microbial processes, fluid dynamics, and diagenetic alterations.

The present study focuses on the adsorption efficacy of solid-state synthesized calcium silicate for removing congo red dye. Three different sources were used as calcium precursors; one was calcium carbonate, and the other two were natural waste sources, aragonite (P. globosa) and calcite (Eggshells). Structural analysis and functional groups of the samples were carried out by X-ray diffractometer (XRD), and a Fourier Transform Infrared Spectrometer (FTIR). Various well-known models/equations models such as the Liner Straight Line method of Scherrer’s equation (LSLMSE), Sahadat-Scherrer Model (SSM), Monshi-Scherrer model (MSM), Williamson-Hall model (WHM), Size-Strain plot method (SSP), and Halder-Wagner Model (HWM) were applied to compute the crystallite size of the synthesized calcium silicates; the estimated crystallite size range was 8–77 nm. The adsorption efficacy of the synthesized E-CaSiO3, S-CaSiO3, and C-CaSiO3 was assessed under various provisos for eradicating Congo red dye from wastewater. Computed results revealed that the dye removal percentages were approximately 100 % at 120 min and 200 rpm for 0.2 g E-CaSiO3. The point of zero charge evaluation showed that the pH of the adsorbents during maximum dye removal was 7 and was less than the value of pHpzc. Thermodynamics studies confirmed that the adsorption process was spontaneous. The method of adsorption of dye by the adsorbent was more clearly comprehended by Langmuir, Freundlich, and Temkin adsorption isotherm. 151.28 mg/g was the maximum adsorption capacity for S- CaSiO3 depending on the Langmuir isotherm model’s linear form (R2 = 0.924).

Aplacophoran molluscs are shell-less and have a worm-like body which is covered by biomineralized sclerites. We investigated sclerite crystallography and the sclerite mosaic of the Solenogastres species Dorymenia sarsii, Anamenia gorgonophila, and Simrothiella margaritacea with electron-backscattered-diffraction (EBSD), laser-confocal-microscopy and FE-SEM imaging. The soft tissue of the molluscs is covered by spicule-shaped, aragonitic sclerites. These are sub-parallel to the soft body of the organism. We find, for all three species, that individual sclerites are untwinned aragonite single crystals. For individual sclerites, aragonite c-axis is parallel to the morphological, long axis of the sclerite. Aragonite a- and b-axes are perpendicular to sclerite aragonite c-axis. For the scleritomes of the investigated species we find different sclerite and aragonite crystal arrangement patterns. For the A. gorgonophila scleritome, sclerite assembly is disordered such that sclerites with their morphological, long axis (always the aragonite c-axis) are pointing in many different directions, being, more or less, tangential to cuticle surface. For D. sarsii, the sclerite axes (equal to aragonite c-axes) show a stronger tendency to parallel arrangement, while for S. margaritacea, sclerite and aragonite organization is strongly structured into sequential rows of orthogonally alternating sclerite directions. The different arrangements are well reflected in the structured orientational distributions of aragonite a-, b-, c-axes across the EBSD-mapped parts of the scleritomes. We discuss that morphological and crystallographic preferred orientation (texture) is not generated by competitive growth selection (the crystals are not in contact), but is determined by templating on organic matter of the sclerite-secreting epithelial cells and associated papillae. [ABSTRACT FROM AUTHOR]

Ocean acidification is likely to impact all stages of the ocean carbonate pump, i.e. the production, export, dissolution and burial of biogenic CaCO3. However, the associated feedback on anthropogenic carbon uptake and ocean acidification has received little attention. It has previously been shown that Earth system model (ESM) carbonate pump parameterizations can affect and drive biases in the representation of ocean alkalinity, which is critical to the uptake of atmospheric carbon and provides buffering capacity towards associated acidification. In the sixth phase of the Coupled Model Intercomparison Project (CMIP6), we show divergent responses of CaCO3 export at 100 m this century, with anomalies by 2100 ranging from - 74 % to +23 % under a high-emission scenario. The greatest export declines are projected by ESMs that consider pelagic CaCO3 production to depend on the local calcite/aragonite saturation state. Despite the potential effects of other processes on alkalinity, there is a robust negative correlation between anomalies in CaCO3 export and salinity-normalized surface alkalinity across the CMIP6 ensemble. Motivated by this relationship and the uncertainty in CaCO3 export projections across ESMs, we perform idealized simulations with an ocean biogeochemical model and confirm a limited impact of carbonate pump anomalies on 21st century ocean carbon uptake and acidification. However, we highlight a potentially abrupt shift, between 2100 and 2300, in the dissolution of CaCO3 from deep to subsurface waters when the global-scale mean calcite saturation state reaches about 1.23 at 500 m (likely when atmospheric CO2 reaches 900–1100 ppm). During this shift, upper ocean acidification due to anthropogenic carbon uptake induces deep ocean acidification driven by a substantial reduction in CaCO3 deep dissolution following its decreased export at depth. Although the effect of a diminished carbonate pump on global ocean carbon uptake and surface ocean acidification remains limited until 2300, it can have a large impact on regional air–sea carbon fluxes, particularly in the Southern Ocean. [ABSTRACT FROM AUTHOR]

The Sr/Ca and 87Sr/86Sr ratios are used as natural indicators (geomarkers) in fish to reveal migratory patterns, due to significant relationships between these ratios measured in the water and in the fish calcified structures (otoliths, bones). The aim of this study was to assess the potential use of the Limnoperna fortunei shell as a proxy for monitoring the spatial and temporal variability of Sr/Ca and 87Sr/86Sr in water. These ratios were compared in water samples and bivalve shells proceeding from eight sites of four hydrogeological regions of the La Plata Basin (Argentina and Uruguay), collected in two hydrological periods (winter and summer) in order to depict the pattern of geographical and temporal variability and to evaluate the relationship between both matrices. Significant positive linear relationships were found between shell edge and water for 87Sr/86Sr (R2 = 0.96–0.97, p < 0.005) and Sr/Ca (R2 = 0.83–0.86, p < 0.05) in summer and winter. Slopes did not differ significantly from 1 (p > 0.05) for 87Sr/86Sr, while they differed from 1 for Sr/Ca in both seasons (p < 0.05), indicating that the elemental ratio would be influenced by endogenous/exogenous factors. No significant seasonal differences were found for both natural tags (p > 0.05), except for the lower Uruguay River (87Sr/86Sr) and outer estuary (Sr/Ca). These results indicate that the L. fortunei shell could be a valuable tool for monitoring spatio-temporal variations in water 87Sr/86Sr. Shell Sr/Ca shows high potential utility as a geomarker in freshwater, but additional assessments are needed to understand the impact of temperature and growth on this ratio. [ABSTRACT FROM AUTHOR]

This study centers on a novel approach of high flexural strength rankinite (3CaO·2SiO2, abbreviated as C3S2) cement benefiting from in-situ formation of aragonite whisker (AW) during carbonation curing. The manufacturing parameters including MgCl2 concentration and reaction temperature play key influence on formation of AW. The results showed that high temperature favored AW formation and AW with length-diameter ratio of 15 ∼ 30 could be generated with concentration of Mg2+/Ca2+ molar ratio of 0.1 at 70 °C. Under this condition, the flexural strength of the C3S2 cement reached 7.5, and 15.6 MPa after 3d and 28d and the corresponding compressive strengths were 30.2 and 71.1 MPa, respectively. The results also showed that 40.9% of CO2 by mass was consolidated in rankinite paste after 48 h, suggesting a promising prospect for calcium silicate-containing waste residue and cement to capture CO2 and simultaneously manufacturing high-performance materia. [ABSTRACT FROM AUTHOR]

Stable isotope, trace element, and cathodoluminescence analyses were performed on gastropods and matrix from rock cores of the Middle to Upper McMurray Formation (Lower Cretaceous/Aptian, Northwestern Alberta, Canada) to characterize the extent to which pristine material remained from which depositional environmental conditions could be estimated. Aragonitic gastropod shells retain their original depositional chemistry, and along with other closely associated authigenic carbonate components, indicate that the Middle to Upper McMurray Formation was deposited in a freshwater environment that was part of a continent-scale river system. [ABSTRACT FROM AUTHOR]

A simple and effective method to eliminate the organic component from mussel shells is presented. It is based on the use of hot hydrogen peroxide. Mollusc shells are composite materials made of a calcium carbonate matrix with different polymorphs and numerous biomacromolecules. The described method was used on mussel shells, but it is generalisable and allows the complete removal of these organic components, without altering the inorganic part. Specimens were kept in a H2O2 40% bath for few hours at 70 °C. The organic layers found on the faces of the shells were peeled away in this way, and biomacromolecules were degraded and removed. Their fragments are soluble in aqueous solution. This easily permits the chemical-physical characterisation and the study of the microstructure. The quality of calcite and aragonite microcrystals of biogenic origin is very high, superior to that of materials of geological or synthetic origin. This may suggest various industrial applications for them. Calcium carbonate is a useful precursor for cements and other building materials, and the one obtained in this way is of excellent quality and high purity. [ABSTRACT FROM AUTHOR]

The geochemistry of tropical coral skeletons is widely used in paleoclimate reconstructions. However, sub‐aerially exposed corals may be affected by diagenesis, altering the aragonite skeleton through partial dissolution, or infilling of secondary minerals like calcite. We analyzed the impact of intra‐skeletal calcite on the geochemistry (δ18O, Sr/Ca, Mg/Ca, Li/Mg, Li/Ca, U/Ca, B/Ca, Ba/Ca, and Mn/Ca) of a sub‐aerially exposed Porites sp. coral. Each micro‐milled coral sample was split into two aliquots for geochemistry and X‐ray diffraction (XRD) analysis to quantify the direct impact of calcite on geochemistry. We modified the sample loading technique for XRD to detect low calcite levels (1%–2%; total uncertainty = 0.33%, 2σ) in small samples (∼7.5 mg). Calcite content ranged from 0% to 12.5%, with higher percentages coinciding with larger geochemical offsets. Sr/Ca, Li/Mg, Li/Ca, and δ18O‐derived sea‐surface temperature (SST) anomalies per 1% calcite were +0.43°C, +0.24°C, +0.11°C, and +0.008°C, respectively. A 3.6% calcite produces a Sr/Ca‐SST signal commensurate with local SST seasonality (∼1.5°C), which we propose as the cut‐off level for screening calcite diagenesis in paleo‐temperature reconstructions. Inclusion of intra‐skeletal calcite decreases B/Ca, Ba/Ca, and U/Ca values, and increases Mg/Ca values, and can therefore impact reconstructions of paleoclimate and the carbonate chemistry of the semi‐isolated calcifying fluid in corals. This study emphasizes the importance of quantifying fine‐scale calcite diagenesis to identify coral preservation levels and assure robust paleoclimate reconstructions. Key Points: The modified sample loading technique adopted for X‐ray diffraction significantly reduced the uncertainty of calcite measurement down to 0.33%Temperature reconstructions based on Sr/Ca, Li/Mg, and Li/Ca are significantly affected by low levels of intra‐skeletal calcite (1%–2%)Impact of low levels of intra‐skeletal calcite on δ18O, Ba/Ca, Mn/Ca, and U/Ca is not significant [ABSTRACT FROM AUTHOR]

The Eocene Geiseltal Konservat-Lagerstätte (Germany) is famous for reports of three dimensionally preserved soft tissues with sub-cellular detail. The proposed mode of preservation, direct replication in silica, is not known in other fossils and has not been verified using modern approaches. Here, we investigated the taphonomy of the Geiseltal anurans using diverse microbeam imaging and chemical analytical techniques. Our analyses confirm the preservation of soft tissues in all body regions but fail to yield evidence for silicified soft tissues. Instead, the anuran soft tissues are preserved as two layers that differ in microstructure and composition. Layer 1 comprises sulfur-rich carbonaceous microbodies interpreted as melanosomes. Layer 2 comprises the mid-dermal Eberth–Katschenko layer, preserved in calcium phosphate. In addition, patches of original aragonite crystals define the former position of the endolymphatic sac. The primary modes of soft tissue preservation are therefore sulfurization of melanosomes and phosphatization of more labile soft tissues, i.e., skin. This is consistent with the taphonomy of vertebrates in many other Konservat-Lagerstätten. These findings emphasize an emerging model for pervasive preservation of vertebrate soft tissues via melanosome films, particularly in stagnation-type deposits, with phosphatization of more labile tissues where tissue biochemistry is favorable. [ABSTRACT FROM AUTHOR]

CO2 capture and storage in geological reservoirs have the potential to significantly mitigate the effects of anthropogenic gas emissions on global climate. Here, we report the results of the first laboratory experiments of CO2 injection in continental flood basalts of South America. The results show that the analyzed basalts have a mineral assemblage, texture and composition that efficiently allows a fast carbonate precipitation that starts 72 h after injection. Based on the availability of calcium, chemical monitoring indicates an estimated CO2 storage of ~ 75%. The carbonate precipitation led to the precipitation of aragonite (75.9%), dolomite (19.6%), and calcite (4.6%). [ABSTRACT FROM AUTHOR]

Serpulids are the only polychaetes in which all species secrete calcium carbonate tubes. Some serpulid lineages, such as species in the genus Spirobranchus, possess a second kind of hard-calcified part—the operculum. The tube and operculum microstructure and mineralogy are highly variable among serpulid species, but this type of information is still scarce for some species. Furthermore, comparing the microstructure and mineralogical composition of species from warm and temperate waters helps to determine which are more susceptible to the effects of climate change. Therefore, the aim of this study is to determine and describe the microstructure and mineralogical composition of the tubes and opercula of three Spirobranchus species from warm and temperate waters of the Mexican Pacific. The microstructures of the two hard structures were analyzed with a scanning microscope and complemented by X-ray computed nanotomography; the mineralogy was determined by X-ray diffractometry. The tubes of the three species had two layers—inner and outer—and five microstructures were found in the tubes. Numerous pores cover the operculum of all three species and have an irregularly oriented prismatic (IOP) structure. The tubes of the three species were bimineralic but had different percentages of calcite and aragonite, whereas the opercula were only composed of aragonite. Given the mineralogical characteristics of S. spinosus and because its distribution is only in temperate waters, we may conclude it could probably be the main species negatively affected according to the climate change scenarios predicted for the end of this century. [ABSTRACT FROM AUTHOR]

An exploratory machine learning (ML) classification model that seeks to examine CaCO3 polymorph selection is presented. The ML model can distinguish if a given peptide sequence binds with calcite or aragonite, polymorphs of CaCO3. The classifier, which was created using SVM and amino acid chemical composition as the input descriptors, yielded satisfactory performance in the classification task, as characterized by AUC = 0.736 and F1 = 0.800 in the test set. Model optimization revealed that tiny, aliphatic, aromatic, acidic, and basic residues are essential descriptors for discriminating aragonite biomineralization peptides from calcite. The presented model offers valuable insights on the significant chemical attributes of biomineralization peptides involved in polymorph binding preference. This can deepen our understanding about the biomineralization phenomenon and may be deployed in the future for the creation biomimetic materials. [ABSTRACT FROM AUTHOR]

Along with its impact on calcifying plankton, ocean acidification also affects benthic biogeochemistry and organisms. Compared to the overlying water, fluid composition in sediments is altered through the effect of the mineralization of organic matter, which can further lower both pH and the carbonate saturation state. This can potentially be counteracted by the addition of carbonate minerals to the sediment surface. To explore the biogeochemical effects of mineral additions to coastal sediments, we experimentally quantified carbonate mineral dissolution kinetics, and then integrated this data into a reactive transport model that represents early diagenetic cycling of C, O, N, S and Fe, and traces total alkalinity, pH and saturation state of CaCO3. Model simulations were carried out to delineate the impact of mineral type and amount added, porewater mixing and organic matter mineralization rates on sediment alkalinity and its flux to the overlying water. Model results showed that the added minerals undergo initial rapid dissolution and generate saturated conditions. Aragonite dissolution led to higher alkalinity concentrations than calcite. Simulations of carbonate mineral additions to sediment environments with low rates of organic matter mineralization exhibited a significant increase in mineral saturation state compared to sediments with high CO2 production rates, highlighting the environment-specific extent of the buffering effect. Our work indicates that carbonate additions have the potential to effectively buffer surficial sediments over multiple years, yielding biogeochemical conditions that counteract the detrimental effect of OA conditions on larval recruitment, and potentially increase benthic alkalinity fluxes to support marine carbon dioxide removal (mCDR) in the overlying water. [ABSTRACT FROM AUTHOR]