Calcium isotopes distribution

The temperature dependence of equilibrium isotope exchange in the calcite-water system has been intensively studied since Urey (1947) first suggested that the paleotemperature of the ancient oceans could be estimated by the 0-isotope distribution between seawater and the calcium carbonate precipitated from it. Urey et al. (1951) argued that O-isotope equilibrium between seawater and CaC03 was likely and support for this idea has come from the close agreement between the CaC03-H20 isotopic fractionation observed in natural systems and those derived from both thermodynamic calculations and laboratory experiments (e.g. Epstein et al., 1951, 1953 Emiliani, 1955 O Neil et al., 1969 O Neil et al., 1975). 

In all experiments an enrichment of the heavy isotope Ca is found in the aqueous phase. Within the limits of error, the experiments No. 1-5 (Table 6) show no dependence on the type of the isomer or on the concentration of the crown ether. The application of DjO instead of H2O also has no influence on the e-value. Experiments where dibenzo[18]crown-6 was used have shown the same trend of enrichment as was found with dicyclohexano[l8]crown-6. However, the measurements were not precise enough to calculate the e-values from this data. For the complete characterization of the discussed extraction systems, one has to know the dependence of the calcium complex distribution of the calcium concentration in the aqueous phase. This dependence is given in Table 7 for dicyclohexano[18]crown-6. 

The application of the described extraction systems for a practical enrichment of calcium isotopes is not too attractive because Ca instead of the more important Ca is enriched in the chloroform phase. A mass balance can show that no usable enrichment of Ca is obtained in the aqueous phase because of the high distribution ratio of calcium ions between the aqueous solution and chloroform (see Chap. 2.4). 

In contrast to the investigations with calcium where Ca, which is not the preferable calcium isotope for application purposes, is enriched in the chloroform phase (see Chap. 4.2.2), Li which is of importance for the production of tritium is enriched in that phase. Certainly, corresponding to the disadvantageous distribution coefficient (see Table 10) a small amount of enriched Li is only obtainable within one equilibrium stage. Therefore, a cascade experiment as described in Chap. 2.5.2 must be applied. 

The investigated extraction systems with lithium and calcium have shown that the lighter isotopes are always enriched in the organic phase where the cyclic polyether is present. This is advantageous for the production of Li but not for the production of the heavy calcium isotopes. The different distribution of the element between the two phases, which one needs for as high as possible isotopic fractionations in one phase, causes a practical isotopic separation only in the organic phase (see Chap. 2.4). In most of the chromatographic experiments with cyclic polyethers, the heavier isotopes were enriched in the first fractions of the elution band. Here, it is of minor... 

G. zu Putlitz, Nuclear Charge Distribution of Eight Ca - Nuclei by Laser Spectroscopy, Z. Phys. A294 319 (1980) M. Arnold, E. Bergmann, P. Bopp, C. Dorsch, J. Kowalski, T. Stehlin, F. Trager, G. zu Putlitz, Hyperfine structure and nuclear moments of odd calcium isotopes by laser and radiofrequency spectroscopy, Hyperfine Inter. 9 159 (1981) C.W.P. Palmer, P.E.G. 

B.A. Brown, S.E. Massen, P.E. Hodgson, The charge distributions of the oxygen and calcium isotopes, Phys. Lett. 85B 167... 

Of all of the machines used for microanalysis LAMMA seems to be the most problematic. A laser beam is used to disintegrate a spot in the sample, and the material emitted is then analyzed in a mass spectrometer. It has similar lateral resolution to PIXE, and like SIMS can be used to distinguish between isotopes of the same element. It has, however, proved very difficult to quantify, and is destructive to the specimen. One recent investigation (13) ofthe distribution of stable isotopes of calcium, magnesium, and potassium in Norway spruce used three microprobes EDAX at 0.3 pm lateral resolution isotope specific point analysis, using LAMMA at 1.5 pm lateral resolution and isotope specific imaging using SIMS at 1-3 pm lateral resolution. 

The use of Cd/Ca measurements in the tests of benthic foraminifera for deep-water nutrient reconstructions was developed in parallel with the carbon isotope method. Cadmium concentrations in seawater follow a nutrient-like distribution, while calcium concentrations simply reflect variations in salinity. The benthic foraminifera incorporate the cadmium and calcium into their shells in proportion to their presence in seawater, which allows for the reconstruction of deep-water cadmium (and thus macronutrient) distributions. 

The residence time of calcium, —1 Myr versus the mixing rates of ocean of —1,000 yr, means that its isotopes are distributed homogeneously in... 

The results of the described experiments are summarized in Table 8 where the totally extracted amounts of calcium and cryptand are also listed. Additionally, a blank result is given which was obtained under the same conditions, however without a cryptand compound. The e-values were calculated under the assumption that during the passage of the chloroform droplets through the aqueous solution a distribution equilibrium has developed. Only under this condition the measured isotope ratio of calcium in the distillating flask is equal to that of one extraction equilibrium stage. Because of the fact that the establishment of the equilibrium is not completely... 

In these experiments the calcium distribution ratio between the Dowex 50 resin and the solution was established to be about ten by using the corresponding amounts of exchanger and CaCL salt. With such a distribution ratio, the isotopic fractionation effect is almost completely shifted into the solution, whereas the initial isotope ratio is present in the resin phase (see Chap. 2,4). Under this condition and under... 

Silicate glasses are conventionally regarded as silicate frameworks in which cations are distributed at random. However, Gaskell et al. (5), using neutron scattering with isotopic substitutions of Ca in a calcium silicate... 

We start with another set of isotope signatures. The rate of erosion in the distant past can be estimated by measuring the ratio of strontium isotopes in marine carbonates. Two stable isotopes of strontium — strontium-86 and strontium-87 — differ in their distribution between the Earth s crust and the mantle underneath it. The mantle is rich in strontium-86, whereas the crust is more richly endowed with strontium-87. The major source of strontium-86 in the oceans is the igneous rock basalt. This rock is extruded continuously from the mantle at the mid-ocean ridges, from where it spreads slowly across the ocean floor before diving back into the mantle beneath the ocean trenches. A little strontium dissolves from the basalt into seawater. The speed of dissolution is more or less constant. The gradual build-up of dissolved strontium-86 in the oceans is balanced by a steady uptake of strontium by marine carbonates, such as limestone (calcium carbonate). This is because strontium can displace its sister element, calcium, in the crystalline structure of limestone. As each of these processes takes place at a steady rate, we would not expect the relative amount of strontium-86 in limestone to fluctuate a great deal. In fact it varies quite a lot. Strontium-87 is to blame. 

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