Aragonite Layers Research Articles

Effect of reduced pH on physiology and shell integrity of juvenile Haliotis iris (pāua) from New Zealand.

The New Zealand pāua or black footed abalone, Haliotis iris, is one of many mollusc species at potential risk from ocean acidification and warming. To investigate possible impacts, juvenile pāua (~24 mm shell length) were grown for 4 months in seawater pH/pCO2 conditions projected for 2100. End of century seawater projections (pHT 7.66/pCO2 ~1,000 μatm) were contrasted with local ambient conditions (pHT 8.00/pCO2 ~400 μatm) at two typical temperatures (13 and 15 °C). We used a combination of methods (morphometric, scanning electron microscopy, X-ray diffraction) to investigate effects on juvenile survival and growth, as well as shell mineralogy and integrity. Lowered pH did not affect survival, growth rate or condition, but animals grew significantly faster at the higher temperature. Juvenile pāua were able to biomineralise their inner nacreous aragonite layer and their outer prismatic calcite layer under end-of-century pH conditions, at both temperatures, and carbonate composition was not affected. There was some thickening of the nacre layer in the newly deposited shell with reduced pH and also at the higher temperature. Most obvious was post-depositional alteration of the shell under lowered pH: the prismatic calcite layer was thinner, and there was greater etching of the external shell surface; this dissolution was greater at the higher temperature. These results demonstrate the importance of even a small (2 °C) difference in temperature on growth and shell characteristics, and on modifying the effects at lowered pH. Projected CO2-related changes may affect shell quality of this iconic New Zealand mollusc through etching (dissolution) and thinning, with potential implications for resilience to physical stresses such as predation and wave action.

Mineral composition and structural features of jewelry ammonites from mine OJSC «Mikhailovcement», Ryazan region

Система комплексной поддержки и сопровождения научного журнала Elpub позволяет запустить двуязычный сайт журнала со встроенной системой электронной редакции в соответствии с лучшими издательскими практиками, а так же предусматривает техническую и методическую поддержку со стороны специалистов НЭИКОН.

Adsorption/Absorption of Lithium Affecting the Growth Morphology of Aragonite. The Two-Dimensional Epitaxy of Li2CO3 (Zabuyelite) on the {001} Form of Aragonite (CaCO3)

Growing aragonite crystals from aqueous solution in the presence of Li+ ions increases the morphological importance of the {001} pinacoid, both in single and twinned crystals. Owing to the structural similarities between the basal d002 layers of aragonite and the d00.6 layers of calcite and having re-collected the habit modification induced by lithium on calcite crystals nucleated and grown from aqueous solution, an interpretation is given of experimental results on the basis of the adsorption/absorption mechanism of dh0l slices of Li2CO3 (mineral zabuyelite), in the {001} growth sectors of aragonite. Detailed analysis on the coincidence lattices and the evaluation of the specific interface energies allow us to determine that two-dimensional epitaxy occurs between the adsorbed d202 slices of zabuyelite and the outmost 001 layers of the growing aragonite.

Fabrication and characterization of nacre-inspired alumina-epoxy composites

Abstract Nacre consisting of aragonite layers and organic layers exhibits extraordinary strong and tough properties due to its hierarchical structure. Generally, nacre-like structure can be produced by freeze casting technique. However the waviness of aragonite layers of nacre is still not replicated in the existing freeze-cast materials. Here, a novel method is proposed to create the waviness in freeze-cast lamellar alumina scaffolds through a heat-treatment process of their green-bodies whose side-faces are glued to Teflon plates. The heat-treatment temperatures of 60 °C, 120 °C and 180 °C are used in the heat-treatment process, respectively. Lamellar composites with nacre-like waviness are obtained through infiltrating the alumina scaffolds with epoxy. The waviness heights and mechanical properties of the alumina-epoxy composites show a strong dependence on the heat-treatment temperature. When the heat-treatment temperature is 120 °C, the alumina-epoxy composites exhibit the optimal waviness heights and better comprehensive mechanical properties: relatively high flexural strength, flexural modulus, toughness and ultimate strain.

From pristine aragonite to blocky calcite: Exceptional preservation and diagenesis of cephalopod nacre in porous Cretaceous limestones.

Aragonite (along with calcite) is one of the most common polymorphs of the crystalline calcium carbonate that forms the skeletal structures of organisms, but it has relatively low preservation potential. Under ambient conditions and in the presence of water, aragonite transforms into calcite, the stable polymorph. Aragonite is also more soluble therefore, in water-permeable siliceous limestones (opokas) that are typical of Upper Cretaceous deposits of Poland and Ukraine, the primary aragonitic skeletons are either entirely dissolved and found as moulds and casts or transformed into secondary calcite, whereas the primary calcitic shells remain well preserved. Contrary to the common notion of the lack of aragonite in such porous carbonate deposits, we show that relics of aragonite can be preserved as a nacreous lining on cephalopod moulds or as thin, lenticular structures entrapped in neomorphic calcite. Based on the observed intermediate steps of aragonite alteration, we propose an extended model of nacre diagenesis. Among the originally aragonitic biota, only nautilids and ammonites have retained relics of pristine skeletons. Such selective preservation of only some aragonitic structures (nacre but not the prismatic aragonitic layers) points to the role of microstructural and biochemical differences between cephalopod shell layers that may set a threshold for the dissolution, dissolution/precipitation or preservation of original biomineral structures.

Connecting pattern to process: Growth of spiral shell sculpture in the gastropod Nucella ostrina (Muricidae: Ocenebrinae).

Shell morphology is a well-suited and underused system to examine the development of novel forms. The three-dimensional structure produced (the shell) is separate from the largely two-dimensional tissue that secretes it (the mantle), allowing us to disentangle the pattern from the process. Despite knowing a great deal about the mechanics of shell secretion (process), and the variety of shell shapes that exist (pattern), no effort has been made to understand how the mantle changes to produce different shell shapes. We investigated this question in the dimorphic snail Nucella ostrina, which exhibits both smooth and ribbed shells to determine how ribs are formed by the mantle. Rib thickenings are produced only in the outer calcitic shell layer and secreted by the distal Outer Mantle Epithelium (OME) with increased acid phosphatase activity. The evenly thick inner aragonitic layers are secreted by the proximal OME which expresses acid phosphatase. Here we show that locally thicker ribs in N. ostrina are produced by changing the dimensions of the distal OME: elongation in the direction of growth and increased cell height. This should increase the amount of shell material secreted, producing locally thicker shell (ribs). Preliminary evidence suggests this mechanism may be widespread in gastropods.

Riddle of the Nautilus: Specific Structural Features of Its Shell

The shells of the chambered nautilus (Nautilus pompilius) are studied by X-ray structure analysis (XRD) and electron microscopy (SEM and TEM). The shell structure is examined in a nanometer scale using XRD and synchrotron-based small angle X-ray scattering (SAXS). The mineral composition of shells includes 98–99 wt % aragonite, ~1 wt % organic substance (conchiolin), 1 wt % strontianite, and 0.5 wt % calcite. Trace elements comprise Na, Mg, Al, K, Si, Fe, P, S, Zn, Sr, Ba, and Cl. The laminated layers are composed of aragonite crystals with a width of 5–10 μm and a thickness of 0.5–1 μm; the prismatic layers, with a length of 7–12 μm long and a width of 1–3 μm. According to XRD and SAXS assays, the aragonite layers are formed of flawless monocrystals lacking any internal structuring. The shell conchiolin is a polymer formed of a system of parallel fibers folded with a step of approximately 100 nm without longitudinal structuring. Presumably, the unique structure of the nautilus shells has determined the existence of Nautiloidea over 500 Ma and their preservation as fossils for over 100 Ma.

Calculation of Reflection Spectrum with Actual Layer Thickness Profile in Nacre of Akoya Pearl Oyster

Pearls have beautiful color and luster which are caused by the interference of light within a multilayer in nacre. The nacre is composed of submicron aragonite layers and nanoscale organic sheets of chitin. The value of a pearl is determined by its size, color, and luster. To improve the quality of cultured pearls, we investigate reflection properties and layer thickness profiles in pieces of nacre of Akoya pearl oyster. SEM images show us how large the thickness variation of the nacre of Akoya oyster is. We discuss the reflection properties of the pieces of nacre to connect the relation between the reflection spectra and the thickness profiles obtained by SEM observation.

Functional Prioritization and Hydrogel Regulation Phenomena Created by a Combinatorial Pearl-Associated Two-Protein Biomineralization Model System.

In the nacre or aragonitic layer of an oyster pearl, there exists a 12-member proteome that regulates both the early stages of nucleation and nanoscale-to-mesoscale assembly of nacre tablets and calcitic crystals from mineral nanoparticle precursors. Several approaches to understanding protein-associated mechanisms of pearl nacre formation have been developed, yet we still lack insight into how protein ensembles or proteomes manage nucleation and crystal growth. To provide additional insights, we have created a proportionally defined combinatorial model consisting of two pearl nacre-associated proteins, PFMG1 and PFMG2 (shell oyster pearl nacre, Pinctada fucata) whose individual in vitro mineralization functionalities are distinct from one another. Using scanning electron microscopy, atomic force microscopy, Ca(II) potentiometric titrations, and quartz crystal microbalance with dissipation monitoring quantitative analyses, we find that at 1:1 molar ratios, rPFMG2 and rPFMG1 co-aggregate in specific molecular ratios to form hybrid hydrogels that affect both the early and later stages of in vitro calcium carbonate nucleation. Within these hybrid hydrogels, rPFMG2 plays a role in defining protein co-aggregation and hydrogel dimension, whereas rPFMG1 defines participation in nonclassical nucleation processes; both proteins exhibit synergy with regard to surface and subsurface modifications to existing crystals. The interactions between both proteins are enhanced by Ca(II) ions and may involve Ca(II)-induced conformational events within the EF-hand rPFMG1 protein, as well as putative interactions between the EF-hand domain of rPFMG1 and the calponin-like domain of rPFMG2. Thus, the pearl-associated PFMG1 and PFMG2 proteins interact and exhibit mineralization functionalities in specific ways, which may be relevant for pearl formation.

Paleoenvironmental reconstruction of a saline lake in the Tertiary: Evidence from aragonite laminae in the northern Tibet Plateau

The origin of aragonite has long been debated because it is precipitated and preserved under specific conditions. Aragonite laminae, first found from Eocene to Miocene strata in the western Qaidam Basin, northern Tibet Plateau, contain much information on paleolake signatures. Mineralogical and geochemical analyses were conducted on alternating yellowish and grayish aragonite layers. The yellowish layers are mainly composed of aragonite crystals, while the grayish layers contain less aragonite and fewer organic remnants that accumulate among debris with sporadic framboidal pyrite. The δ13C values of yellowish layers are remarkably positive by approximately 4.01‰ (VPDB), and the δ18O values are slightly negative compared with base data of the Qaidam Basin. Considering the 12CO2 absorption of algal blooms, positive excursions of δ13C shown in aragonite indicate high 13C values in depositional water. Therefore, a seasonal algal-influenced inorganic origin is proposed to explain the formation of aragonite laminae. During warm seasons, Mg/Ca ratios are elevated because of evaporation effects. The algal blooms decrease the CO2 content, leading to high pH values. These conditions promote the rapid crystal growth of aragonite instead of other carbonate minerals. Slightly negative δ18O values in yellowish layers are interpreted as the result of intense inflow during warm seasons, which leads to less precipitation of organic matter and debris. The grayish layers in cold seasons are the opposite. From the Eocene to Oligocene, the progressively decreasing δ18O values of aragonite reflect global cooling during this time. A conspicuously positive step in δ18O values indicates an arid environment coinciding with the uplift of the Himalaya, from the Oligocene to Lower Miocene. The results from this study show that understanding of aragonite in the Qaidam Basin is essential to reconstruct the high-resolution paleoenvironment and to reveal the Tertiary evolution of paleoclimates in the northern Tibet Plateau.

Calcareous electrochemical precipitation, a new method to trap nickel in seawater

There are few efficient, rapid and cheap methods to remove toxic metals from contaminated waters. Here we hypothesised that cathodic protection, an existing method used to control the corrosion of metallic structures, may trap toxic metals. Indeed, in seawater, the application of a cathodic current on a metallic structure induces the precipitation of limestone (CaCO3) and magnesium dihydroxyde (Mg(OH)2), thus forming a calcareous deposit on the metal surface. We therefore presumed that such calcareous deposit may trap metals dissolved in waters. Actually calcareous deposit formation has never been studied in the presence of dissolved metallic contaminants such as nickel. Here we tested ionic nickel (Ni2+) precipitation in calcareous deposit with a galvanized steel electrode by spiking artificial seawater with a NiCl2 salt during 7 days of applied current. We analysed deposit surface and cross section by µ-Raman spectroscopy and scanning electron microscopy (SEM) with X-ray microanalysis. Ni concentration in the deposit was quantified by inductively coupled plasma analysis, after deposit dissolution in 60% HNO3. Results show that in 7 days up to 24% of nickel can be trapped in the calcareous deposit. Scanning electron microscopy reveals that Ni is trapped under a pure CaCO3 layer of aragonite. Raman spectra show that nickel is incorporated as nickel dihydroxyde (Ni(OH)2), as evidence by vibration bands at 446 and 510 cm−1. Overall our findings disclose a new and efficient method, calcareous electrochemical precipitation, which has potential applications to remove toxic metals from contaminated waters.

Biomimetic synthesis of oriented aragonite crystals and nacre-like composite material by controlling the fluid type

Shape-controlled biomineralization and self-assembly of highly ordered aragonite architectures were achieved under laminar flow on a fresh natural nacre substrate at 35°C. In this paper, a film of tightly packed needles of c-axis oriented aragonite was obtained under the circumstance of laminar-flow. The mass transfer rate and growth time of crystals play important roles in the formation of aragonite crystals with different forms and sizes. In order to fabricate an artificial nacreous structure, polyacrylic acid (PAA) was used as an organic film in coating the aragonite layer. Then, the aragonite layer and PAA film were alternately assembled. The structures and morphologies of the products were characterized by X-ray diffractometry, scanning electron microscopy and FTIR spectroscopy. The results indicate that the layer-by-layer aragonite structure has potential applications in biomimetic synthesis materials.

Synergistic Biomineralization Phenomena Created by a Combinatorial Nacre Protein Model System.

In the nacre or aragonite layer of the mollusk shell, proteomes that regulate both the early stages of nucleation and nano-to-mesoscale assembly of nacre tablets from mineral nanoparticle precursors exist. Several approaches have been developed to understand protein-associated mechanisms of nacre formation, yet we still lack insight into how protein ensembles or proteomes manage nucleation and crystal growth. To provide additional insights, we have created a proportionally defined combinatorial model consisting of two nacre-associated proteins, C-RING AP7 (shell nacre, Haliotis rufescens) and pseudo-EF hand PFMG1 (oyster pearl nacre, Pinctada fucata), whose individual in vitro mineralization functionalities are well-documented and distinct from one another. Using scanning electron microscopy, flow cell scanning transmission electron microscopy, atomic force microscopy, Ca(II) potentiometric titrations, and quartz crystal microbalance with dissipation monitoring quantitative analyses, we find that both nacre proteins are functionally active within the same mineralization environments and, at 1:1 molar ratios, synergistically create calcium carbonate mesoscale structures with ordered intracrystalline nanoporosities, extensively prolong nucleation times, and introduce an additional nucleation event. Further, these two proteins jointly create nanoscale protein aggregates or phases that under mineralization conditions further assemble into protein-mineral polymer-induced liquid precursor-like phases with enhanced ACC stabilization capabilities, and there is evidence of intermolecular interactions between AP7 and PFMG1 under these conditions. Thus, a combinatorial model system consisting of more than one defined biomineralization protein dramatically changes the outcome of the in vitro biomineralization process.

Heterogeneous distribution of dye-labelled biomineralizaiton proteins in calcite crystals.

Biominerals are highly ordered crystals mediated by organic matters especially proteins in organisms. However, how specific proteins are distributed inside biominerals are not well understood. In the present study, we use fluorescein isothiocyanate (FITC) to label extracted proteins from the shells of bivalve Pinctada fucata. By confocal laser scanning microscopy (CLSM), we observe a heterogeneous distribution of dye-labelled proteins inside synthetic calcite at the microscale. Proteins from the prismatic calcite layers accumulate at the edge of crystals while proteins from the nacreous aragonite layers accumulate at the center of crystals. Raman and X-ray powder diffraction show that both the proteins cannot alter the crystal phase. Scanning electron microscope demonstrates both proteins are able to affect the crystal morphology. This study may provide a direct approach for the visualization of protein distributions in crystals by small-molecule dye-labelled proteins as the additives in the crystallization process and improve our understanding of intracrystalline proteins distribution in biogenic calcites.

Outer organic layer and internal repair mechanism protects pteropod Limacina helicina from ocean acidification

Scarred shells of polar pteropod Limacina helicina collected from the Greenland Sea in June 2012 reveal a history of damage, most likely failed predation, in earlier life stages. Evidence of shell fracture and subsequent re-growth is commonly observed in specimens recovered from the sub-Arctic and further afield. However, at one site within sea–ice on the Greenland shelf, shells that had been subject to mechanical damage were also found to exhibit considerable dissolution. It was evident that shell dissolution was localised to areas where the organic, periostracal sheet that covers the outer shell had been damaged at some earlier stage during the animal’s life. Where the periostracum remained intact, the shell appeared pristine with no sign of dissolution. Specimens which appeared to be pristine following collection were incubated for four days. Scarring of shells that received periostracal damage during collection only became evident in specimens that were incubated in waters undersaturated with respect to aragonite, ΩAr≤1. While the waters from which the damaged specimens were collected at the Greenland Sea sea–ice margin were not ΩAr≤1, the water column did exhibit the lowest ΩAr values observed in the Greenland and Barents Seas, and was likely to have approached ΩAr≤1 during the winter months. We demonstrate that L. helicina shells are only susceptible to dissolution where both the periostracum has been breached and the aragonite beneath the breach is exposed to waters of ΩAr≤1. Exposure of multiple layers of aragonite in areas of deep dissolution indicate that, as with many molluscs, L. helicina is able to patch up dissolution damage to the shell by secreting additional aragonite internally and maintain their shell. We conclude that, unless breached, the periostracum provides an effective shield for pteropod shells against dissolution in waters ΩAr≤1, and when dissolution does occur the animal has an effective means of self-repair. We suggest that future studies of pteropod shell condition are undertaken on specimens from which the periostracum has not been removed in preparation.

Controlled in Vivo Nacre Formation in Flat Pearls with Hydroxyapatite Bioceramic Nuclei

We carried out in vivo experiments of cultured flat pearl production using disc-like hydroxyapatite (HAp) bioceramics as a nucleus, with and without electric polarization treatment, and evaluated the effects of electric polarization and the quality of HAp materials on flat pearl formation. The thickness of the lamellar structures of the nacreous aragonite layers increased when polarized HAp pellets, instead of nonpolarized HAp pellets, as the nucleus, were used as the nuclei, while the thickness of the columnar structures of the prismatic calcite layers decreased. These phenomena were observed remarkably on the negative potential surface of the polarized HAp pellet. The electric polarization treatment promoted the formation rate of the nacreous lamella structure. It was speculated that electric polarization may control the physiological actions of mantle tissue and regulate the formation of the prismatic calcite and nacreous aragonite layers. The polarization treatment leads to an interference color with ...

Effects of sample storage and shell orientation on LA-ICPMS trace element measurements on deep-sea mussels

Geochemical markers are being increasingly applied to fundamental questions in population and community ecology in marine habitats because they allow inferences on individuals dispersal, but vital effects, small sample size and instrumental limitation are still challenging particularly in deep-sea studies. Here we use shells of the deep-sea bivalve Idas modiolaeformis to assess potential effects of sample storage, mineralogy, and valve orientation on LA-ICPMS measurements. Trace element concentrations of 24Mg, 43Ca, 88Sr, 137Ba, 208Pb, and 238U are not affected by the two most commonly used storage methods of biologic deep-sea samples (frozen at –20°C and fixed in 95% ethanol); thus combined analysis of differently preserved specimens is possible when the number of individuals is insufficient and distinct sample fixation is needed for multiple purposes. Valve orientation had a strong impact on quantification of trace elements in the calcitic but not in the aragonitic layer of adult shells. Hence, to enable comparisons between adult shells and entirely aragonitic embryonic shells, a reference map of site-specific signatures can potentially be generated using the aragonitic layer of the adult shells. Understanding ontogenetic changes and environmental effects in trace element incorporation is critical before geochemical fingerprinting can be used as a tool for larval dispersal studies in the deep-sea.

Natural Deposit Coatings on Steel during Cathodic Protection and Hydrogen Ingress

The calcareous coating formed during cathodic protection (CP) in seawater is known to reduce the current demand by hindering the transport of species required to support the cathodic reactions and, thereby, improve the economic performance of CP systems. There is, however, uncertainty as to whether the coating reduces hydrogen uptake or indeed enhances it. To ascertain this, two sets of samples were polarized at −1.1 V (standard calomel electrode, SCE) in 3.5% w/v NaCl and synthetic seawater (ASTM D1141) at 20 °C and the diffusible hydrogen content measured over a period of 530 h. Under such conditions reports suggest a deposit with two distinct layers, comprising an initial brucite layer followed by an aragonite layer. Contrary to other findings, a fine initial layer containing Ca and Mg followed by a brucite layer was deposited with a few specks of Ca-containing zones in synthetic seawater. The hydrogen uptake was found to occur within the initial 100 h of exposure in synthetic seawater whilst it continued without the benefit of a deposit coating, i.e., in 3.5 wt % NaCl solution.

Ocean acidification and temperature increase impact mussel shell shape and thickness: problematic for protection?

Ocean acidification threatens organisms that produce calcium carbonate shells by potentially generating an under-saturated carbonate environment. Resultant reduced calcification and growth, and subsequent dissolution of exoskeletons, would raise concerns over the ability of the shell to provide protection for the marine organism under ocean acidification and increased temperatures. We examined the impact of combined ocean acidification and temperature increase on shell formation of the economically important edible mussel Mytilus edulis. Shell growth and thickness along with a shell thickness index and shape analysis were determined. The ability of M.edulis to produce a functional protective shell after 9months of experimental culture under ocean acidification and increasing temperatures (380, 550, 750, 1000μatm pCO 2, and 750, 1000μatm pCO 2+2°C) was assessed. Mussel shells grown under ocean acidification conditions displayed significant reductions in shell aragonite thickness, shell thickness index, and changes to shell shape (750, 1000μatm pCO 2) compared to those shells grown under ambient conditions (380μatm pCO 2). Ocean acidification resulted in rounder, flatter mussel shells with thinner aragonite layers likely to be more vulnerable to fracture under changing environments and predation. The changes in shape presented here could present a compensatory mechanism to enhance protection against predators and changing environments under ocean acidification when mussels are unable to grow thicker shells. Here, we present the first assessment of mussel shell shape to determine implications for functional protection under ocean acidification.

Selective colors reflection from stratified aragonite calcium carbonate plates of mollusk shells.

An interaction between the incident light and the structural architecture within the shell of Asian green mussel (Perna viridis) induces observable pearlescent colors. In this paper, we investigate the influence of the structural architecture on the expressed colors. After a removal of the organic binder, small flakes from crushed shells show vivid rainbow reflection under an optical microscope. An individual flake expresses vivid color under a bright-field illumination while become transparent under a dark-field illumination. The expressed colors of the aragonite flakes are directly associated with its structural architecture. The flakes with aragonite thickness of 256, 310, and 353 nm, respectively, appear blue, green, and red under an optical microscope. The spectral simulation corroborates the experimentally observed optical effects as the flakes with thicker aragonite layers selectively reflected color with longer wavelengths. Flakes with multiple aragonite thicknesses expressed multi-color as the upper aragonite layers allow reflected colors from the lower layers to be observed.