The diffusional evolution of chemical composition in a solar model

We consider the basic physical processes resulting in a differential, microscopic redistribution of stellar matter, generally known as diffusion. The main effect of diffusion in the solar interior is a segregation of light and heavy elements in the gravitational field. As a result, the abundance of helium and heavy elements in the solar envelope is reduced, while it becomes enriched by hydrogen. We present estimates of the degree of settling for a sequence of evolutionary models via numerical solution of the generalized diffusion equation. The effect of the ion charge (in the approximation of full ionization) on the settling rate is studied in detail. Abundance variations are given for the centers of the models, as well as for the convective envelope of the modern Sun. We analyze the effects of the thermal and concentrational diffusion on the evolution of the chemical-composition profile. Quantitatively, the effect of thermal diffusion is not very large, but it leads to the appearance of new features in the hydrogen-abundance profile, namely, a discontinuity at the base of the convective zone. The effect of concentration diffusion is relatively small, and is appreciable only at the model center at late stages of the evolution, and also close to the base of the convective envelope. All the mechanisms studied are necessary components of a modern model for the internal structure and evolution of the Sun.     

Low-degree solar oscillation spectrum with wavelet decomposition

We present the technique and results of processing the observations of the solar oscillations with frequencies of 1.5–4.0 mHz. We used the time series obtained in the period 1990–1996 in the International IRIS project. The power spectrum averaged over the entire observing period was estimated from the spectra of each year preaveraged with five orthogonal tapers. The spectral profiles of the individual modes with degree l = 0 and orders n ? 12–26 were fitted using a wavelet decomposition with thresholding of the high-frequency decomposition levels. The smoothed power spectrum estimate has a considerably smaller variance, but also a lower density of reference points. The derived smoothed profiles were used to determine the eigenfrequencies by two methods: from the local peak and from the correlation between the neighboring peaks, which correspond to a nonparametric estimation procedure. For the radial modes (l = 0), there is good agreement with the independent parametric maximum likelihood frequency estimates.     

Detection of Collisional Asteroid Orbits Under Observable Nonlinearity in the Problem of Orbit Improvement

Solar System Research - A method has been developed for detecting collisional orbits of asteroids in the initial confidence region with a noticeable nonlinearity in the problem of improving their...     

Ferromanganese crusts from the Sea of Okhotsk

New data on the microstructures and the mineral and chemical compositions of ferromanganese crusts obtained from the western slope of the Kuril Island Arc in the Sea of Okhotsk during cruises of the R/V Vulkanolog are discussed. The study of the crusts using analytical electron microscopy methods revealed that their manganese phase is represented by vernadite, Fe-vernadite, todorokite, asbolane, and asbolane-buserite, while the iron phase consists of hematite, hydrohematite, ferroxyhite, and magnetite. The assemblage of lithic minerals includes apatite, quartz, epidote, and montmorillonite. According to the chemical analysis, most of the crusts contain a significant share of volcanogenic and hydrothermal material, which is evident from the elevated values of the Mn and Ti modules, the low concentrations of some trace elements, and the positive Eu anomaly in the rare earth elements composition.     

Ferromanganese nodules from the East Siberian Sea near Bennett Island

Ferromanganese nodules recovered from the bottom of the East Siberian Sea near Bennett Island are studied by coupled ultramicroscopic and ICP-MS methods. The majority of nodules are flattened dense formations 2.5 to 10 cm in cross section and circled by a thick rim, which is common in nodules from other Arctic basins. The major components of nodules are iron and manganese oxides in the form of ferruginous vernadite and magnetite, as well as accessory minerals, including apatite and titanomagnetite. The major and trace element compositions of nodules are comparable to Arctic nodules from other Arctic seas, but somewhat different compared to those from the Mendeleev Rise. A specific feature of these nodules is that they contain high amounts of mercury in all samples and a positive europium anomaly in one sample, along with gold; this may be related to the influence of endogenous gas-and-vapor exhalations.     

Trace elements in phosphorites from Kotelny Island (New Siberian Islands)

Doklady Earth Sciences - The first study of the full chemical composition of Triassic phosphorites from Kotelny Island and Jurassic–Cretaceous phosphorite from the Egorjevsk deposit showed...     

Phosphorus Cycle in the Ocean

The behavior of phosphorus is considered at major stages of the sedimentary cycle beginning with supply sources for its delivery into the ocean to precipitation and its sedimentation, localization and subsequent diagenetic redistribution in bottom sediments. River runoff represents the main phosphorus source in the ocean. It delivers annually about 1.5 Mt of dissolved phosphorus and more than 20 Mt of suspended phosphorus into the ocean. Up to 80% of the suspended phosphorus incorporated in the lithogenic material precipitates within submarine continental margins. Phosphorus dissolved in seawater repeatedly participates in biogeochemical processes owing to its assimilation by phytoplankton that annually consumes from 1.5 to 2.5 Gt of phosphorus. Dissolved phosphorus is incorporated in organic remains and precipitates from seawater by a biogenic mechanism, too. Only a part of phosphorus settled onto the bottom is buried in sediments. Due to reducing diagenetic processes, up to 30–40% of the primarily precipitated phosphorus diffuses from the upper layer of sediments into bottom water. Diffusion flux into the ocean significantly exceeds the supply of dissolved phosphorus from river runoff. The absolute mass phosphorus dispersed in sediments is several orders of magnitude greater than the mass concentrated in phosphorite deposits. However, the majority of phosphorite formation epochs coincide with the intensification of total phosphorus accumulation in marine sediments in conditions of humid climate, intense chemical weathering of rocks on continents, and considerable expansion of the oceanic shelf area.     

Structure and Composition of Ferromanganese–Phosphate Nodules from the Black Sea

Ferruginate shells and tubular worm burrows from the oxygenated zone of the Black Sea (Kalamit Bay and Danube River mouth) are studied using transmission and scanning electron microscopy combined with analyses of elemental composition. Iron and manganese hydroxide nodules considered here are enriched in phosphorus. They contain variable amounts of terrigenous and biogenic material derived from host sediments. The hydroxides are mainly characterized by colloform structure, whereas globular and crystalline structures are less common. The dominating iron phase is represented by ferroxyhite and protoferroxyhite, whereas the manganese phase is composed of Fe-free vernadite. Relative to sediments, concentrations of Mn, As, and Mo increase 12–18 times, while concentrations of Fe, P, Ni, and Co increase 5–7 times during the nodule formation.     

Transformation of Hydroxyapatite of Bone Phosphate from the Ocean Bottom during Fossilization

Samples of Recent–Miocene fish and marine mammal bones from the bottom of the Atlantic and Pacific oceans and Miocene Maikop deposits (Transcaspian region) are studied by the X-ray diffraction (XRD) technique combined with the chemical and energy-dispersive (EDX) analyses. Changes of lattice parameters and chemical composition of bioapatite during the fossilization and diagenesis suggest that the development of skeletal apatite proceeds from the dahllite- type hydroxyapatite to the francolite-type carbonate-fluorapatite. It is assumed that a jump-type transition from dahllite to francolite during the initial fossilization reflects the replacement of biogeochemical reactions in living organisms, which are subject to nonlinear laws of nonequilibrium thermodynamics, by physicochemical processes according to the linear equilibrium thermodynamics.