Search results for "Calcium carbonate"
showing 10 items of 175 documents
Calcifying phytoplankton standing stocks in the North Pacific from the R/V Kilo Moana cruise KM1712
2022
This dataset compiles the CaCO3 standing stocks of living coccolithophores (mg/m³), of detached coccoliths (mg/m³) and the integrated CaCO3 standing stocks of coccolithophores (mg/m²). The samples were collected in the North Pacific between Hawaii and the Gulf of Alaska during the R/V Kilo Moana cruise KM1712 in August 2017, with rosette Niskin bottles equiped with CTD (Sea-Bird SBE 9) at different depths throughout the photic zone including the deep chlorophyll maximum. To estimate the CaCO3 contribution by coccolithophore assemblages in each sample, we carried out the transformation of coccospheres in number of coccoliths, following the estimates by Yang and Wei (2003), and then we adopte…
Integrated annual calcium carbonate production of planktic calcifiers in the North Pacific from the R/V Kilo Moana cruise KM1712
2022
This dataset compiles the estimates of annual CaCO3 production, including the upper and lower limits of the estimates, for the 4 planktic calcifying groups considered in the study, the pteropods (mg/m²/yr), the heteropods (mg/m²/yr), the foraminifers (mg/m²/yr) and the coccolithophores (mg/m²/yr). The estimates derived from the living standing stocks of these 4 groups of organisms collected in the North Pacific between Hawaii and the Gulf of Alaska during the R/V Kilo Moana cruise KM1712 in August 2017. R code was used to calculate the integrated annual CaCO3 production for the different organisms, including the upper and lower limits (Gray, 2022).
Monitoring the whiting phenomenon in Lake La Cruz (Cuenca, Spain)
2020
[EN] In the present study, a five-year follow-up was performed by remote sensing of the calcium carbonate precipitation in La Gitana karstic lake also known as La Cruz (located on the province of Cuenca, Spain). The important role that calcium carbonate precipitation plays in the ecology of the lake is well known for its influence on the vertical migrations of phytoplankton, the concentration of bioavailable phosphorus and, therefore, the eutrophication and quality of the waters. Whiting take place between the months of July and August, and it can be studied at this time through its optical properties, with the main objective of offering updated data on a phenomenon traditionally studied an…
The influence of water and of alkali promotor on the carbon number distribution of fischer-tropsch products formed over iron catalysts
1987
The carbon number distribution of Fischer-Tropsch products formed over an alkalized precipitated iron catalyst has been studied as a function of the water vapor pressure of the synthesis gas. The carbon number distribution of formed hydrocarbons is characterized by a bimodal Schulz-Flory distribution of growth probabilities P1 ≈ 0.6 and P2 ≈ 0.87 attributed to unpromoted and promoted (alkalized) sites on the catalyst surface. Promoted sites are more stable with respect to oxidation (deactivation) by water than unpromoted sites. The growth probability of unpromoted sites decreases with increasing ratio P/P — Studies using Mossbauer spectroscopy have shown that iron foils treated with water c…
Snapshots of calcium carbonate formation – a step by step analysis
2017
Abstract Recent advances in our understanding of CaCO3 nucleation from solution have provoked new and challenging questions. We have studied CaCO3 formation using precipitation by carbonate ester hydrolysis which ensures precipitation from a strictly homogeneous solution state and allows “titrating” carbonate to a solution with a given Ca2+ concentration on a timescale suited for kinetic studies. Nucleation and crystallization were traced by combining dynamic light scattering (DLS) and transmission electron microscopy (TEM). DLS served as in situ technique to identify the nucleation time, to monitor particle size evolution, to discriminate different precipitation mechanisms and to validate …
Cr(VI)/Cr(III) and As(V)/As(III) Ratio Assessments in Jordanian Spent Oil Shale Produced by Aerobic Combustion and Anaerobic Pyrolysis
2011
With the increase in the awareness of the public in the environmental impact of oil shale utilization, it is of interest to reveal the mobility of potentially toxic trace elements in spent oil shale. Therefore, the Cr and As oxidation state in a representative Jordanian oil shale sample from the El-Lajjoun area were investigated upon different lab-scale furnace treatments. The anaerobic pyrolysis was performed in a retort flushed by nitrogen gas at temperatures in between 600 and 800 °C (pyrolytic oil shale, POS). The aerobic combustion was simply performed in porcelain cups heated in a muffle furnace for 4 h at temperatures in between 700 and 1000 °C (burned oil shale, BOS). The high loss-…
Biomineralisations in crustaceans: storage strategies
2004
Abstract Crustaceans are a remarkable group of animals because of their ability to elaborate cyclically two kinds of calcified biomineralisations: an unstretchable exoskeleton (or cuticle) and also, for many species, depending of the way of life of the considered animal, transitory calcium deposits. They are in consequence subjected to a cyclic life and notably, to a periodical balance between two sources of calcium, exogenous and/or endogenous. The storage structures, essentially composed of calcium carbonate precipitated within a proteinaceous organic matrix, are very diversified. The calcium carbonate of the cuticle of most of the species is under a crystalline state and/or an amorphous …
Anisotropic lattice distortions in biogenic calcite induced by intra-crystalline organic molecules.
2006
9 pages; International audience; We have performed precise structural measurements on five different calcitic seashells by high-resolution X-ray powder diffraction on a synchrotron beam line and by laboratory single crystal X-ray diffraction. The unit cell parameters a and c of biogenic calcite were found to be systematically larger than those measured in the non-biogenic calcite. The maximum lattice distortion (about 2.10(-3)) was detected along the c-axis. Under heat treatment above 200 degrees C, a pronounced lattice relaxation was observed, which allowed us to conclude that anisotropic lattice swelling in biogenic calcite is induced by organic macromolecules incorporated within the sing…
Ab Initio Structure Determination of Vaterite by Automated Electron Diffraction
2012
tion that is fundamental for understanding material properties. Still, a number of compounds have eluded such kinds of analysis because they are nanocrystalline, highly disordered, with strong pseudosymmetries or available only in small amounts in polyphasic or polymorphic systems. These materials are crystallographically intractable with conventional Xray or synchrotron radiation diffraction techniques. Single nanoparticles can be visualized by high-resolution transmission electron microscopy (HR-TEM) up to sub�ngstrom resolution, [2] but obtaining 3D information is still a difficult task, especially for highly beam-sensitive materials and crystal structures with long cell parameters. Elec…
Calcification is not the Achilles'heel of cold-water corals in an acidifying ocean
2015
Ocean acidification is thought to be a major threat to coral reefs: laboratory evidence and CO2 seep research has shown adverse effects on many coral species, although a few are resilient. There are concerns that cold-water corals are even more vulnerable as they live in areas where aragonite saturation (Omega ara) is lower than in the tropics and is falling rapidly due to CO2 emissions. Here, we provide laboratory evidence that net (gross calcification minus dissolution) and gross calcification rates of three common cold-water corals, Caryophyllia smithii, Dendrophyllia cornigera, and Desmophyllum dianthus, are not affected by pCO2 levels expected for 2100 (pCO2 1058 µatm, Omega ara 1.29),…