Perturbations by the oblateness of the Earth and by the planets in the motion of the Moon

Perturbations in the motion of the Moon are computed for the effect by the oblateness of the Earth and for the indirect effect of planets. Based on Delaunay's analytical solution of the main problem, the computations are performed by a method of Fourier series operation. The effect of the oblateness of the Earth is obtained to the second order, partly adopting an analytical evaluation. Both in longitude and latitude are found a few terms whose coefficient differs from the current lunar ephemeris based on Brown's theory by about 0.01. While, concerning the indirect effect of planets, several periodic terms in the current ephemeris seem to have errors reaching 0.05.As for the secular variations of and due to the figure of the Earth and the indirect effect of planets, the newly-computed values agree within 1/cy with Brown's results reduced to the same values of the parameters. Further, the accelerations in the mean longitude, and caused by the secular changes in the eccentricity of the Earth's orbite and in the obliquity of the ecliptic are obtained. The comparison with Brown shows an agreement within 0.3/cy² for the former cause and 0.02/cy² for the latter. An error is found in the argument of the principal term for the perturbations due to the ecliptic motion in the current ephemeris.Proceedings of the Conference on Analytical Methods and Ephemerides: Theory and Observations of the Moon and Planets. Facultés universitaires Notre Dame de la Paix, Namur, Belgium, 28–31 July, 1980.     

Incorporation of U,Pb and Rare Earth Elements in Calcite through Crystallisation from Amorphous Calcium Carbonate: Simple Preparation of Reference Materials for Microanalysis

Uncertainty for elemental and isotopic measurements in calcite by LA‐ICP‐MS is largely controlled by the homogeneity of the reference materials (RMs) used for calibration and validation. In order to produce calcite RMs with homogeneous elemental and isotopic compositions, we incorporated elements including U, Pb and rare earth elements into calcite through heat‐ and pressure‐induced crystallisation from amorphous calcium carbonate that was precipitated from element‐doped reagent solution. X‐ray absorption spectra showed that U was present as U(VI) in the synthesised calcite, probably with a different local structure from that of aqueous uranyl ions. The uptake rate of U by our calcite was higher in comparison with synthetic calcite of previous studies. Variations of element mass fractions in the calcite were better than 12% 2RSD, mostly within 7%. The ²⁰⁷Pb/²⁰⁶Pb ratio in the calcite showed < 1% variations, while the ²³⁸U/²⁰⁶Pb ratio showed 3–24% variations depending on element mass fractions. Using the synthetic calcite as primary RMs, we could date a natural calcite RM, WC‐1, with analytical uncertainty as low as < 3%. The method presented can be useful to produce calcite with controlled and homogeneous element mass fractions and is a promising alternative to natural calcite RMs for U‐Pb geochronology.     

Supercooled drizzle formed by condensation–coalescence in the mid-winter season of the Canadian Arctic

Supercooled drizzle (freezing drizzle) was observed at Inuvik, N.W.T., Canada (68°22′N, 133°42′W) on December 20, 21 and 27, 1995. Meteorological conditions in which the supercooled drizzle could form under low temperatures (colder than −20°C) in the mid-winter season of the Canadian Arctic were examined from the sounding data and data measured by a passive microwave radiometer at ground level. The following results were obtained. (1) Supercooled drizzle fell to the ground with ice pellets and frozen drops on snow crystals. (2) The maximum size of supercooled drizzle particles increased as the depth of cloud layer saturated with respect to water increased. (3) Because a layer of air temperature higher than 0°C was not detected from the sounding data at Inuvik, melting of snow particles was impossible. It was concluded, therefore, that supercooled drizzle was formed by the condensation–coalescence process below freezing temperature.     

Incessant excitation of the Earth's free oscillations: global comparison of superconducting gravimeter records

Records of superconducting gravimeters (SGs) at Canberra (Australia), Esashi (Japan), Metsähovi (Finland) and Syowa Stations (Antarctica) were analyzed to search for further evidence of background free oscillations of the Earth. Spectrograms for 1-year period and averaged power spectra for seismically quiet periods were obtained for each of the stations. Anomalous features of the oscillations observed at Syowa Station, such as an apparent seasonal variation and a high intensity at frequencies between 3 and 4 mHz, were absent at the other SG stations. Among the SG stations used in this study, the background free oscillations were detected most consistently and distinctly at Canberra, where the noise level was comparable to that at the IDA quietest station, while that at Syowa Station was close to the critical limit for detecting the oscillations. The background free oscillations provide a good reference to evaluate the noise level in the milliHertz band.     

Effect of human activity on Lake Saroma (Japan) during the past 150 years: Evidence by variation of diatom assemblages

Diatom assemblages of the surface and in core sediment samples from Lake Saroma (Japan) were examined for the purpose of evaluating anthropogenic effect on the coastal environmental changes. Before the first inlet excavation, the lake's water quality and ecology were controlled by water exchange with the Okhotsk Sea as well as lake-level variation. However, large-scale ecological modification occurred, mainly due to artificial excavation and shellfish industrial farms. A distinct record of the succession of the dominant diatom taxa was preserved in core sediments. Low-oxygen water was prevalent in the lake in 1929, before the first inlet excavation. Immediately after the first inlet excavation, the low-oxygen water in the western basin of the lake began to disappear, in a trend that became increasing transparent, which has been attributed to an increasing rate of water exchange. However, the lacustrine environment of bottom sediments resumes deterioration 20 years after since the first artificial excavation: the resultant deposition of river-mouth materials into the deep basin caused eutrophication and environmental disturbance of the lake bottom. At the same time, the eutrophication of surface water became intensified with the onset of intense scallop culturing beginning in 1966. Increasing organic loads deposited onto the bottom layer in the form of excreta from the scallop nursery led to more oxygen deficiency and the elution of nitrogen and phosphorus from the sediment, which again brought about eutrophication of the surface layer. Such environmental change was reflected in a decrease of benthic diatom taxa and an increase of planktonic taxa, trends which have continued until today. Particularly, the numbers of diatom assemblage have been decreasing all over the lake during the last 10 years, which suggests that Lake Saroma's present-day deterioration and eutrophication will continue or become even worse.     

Fate of carbonates within oceanic plates subducted to the lower mantle, and a possible mechanism of diamond formation

We report on high-pressure and high-temperature experiments involving carbonates and silicates at 30–80 GPa and 1,600–3,200 K, corresponding to depths within the Earth of approximately 800–2,200 km. The experiments are intended to represent the decomposition process of carbonates contained within oceanic plates subducted into the lower mantle. In basaltic composition, CaCO₃ (calcite and aragonite), the major carbonate phase in marine sediments, is altered into MgCO₃ (magnesite) via reactions with Mg-bearing silicates under conditions that are 200–300°C colder than the mantle geotherm. With increasing temperature and pressure, the magnesite decomposes into an assemblage of CO₂ + perovskite via reactions with SiO₂. Magnesite is not the only host phase for subducted carbon—solid CO₂ also carries carbon in the lower mantle. Furthermore, CO₂ itself breaks down to diamond and oxygen under geotherm conditions over 70 GPa, which might imply a possible mechanism for diamond formation in the lower mantle.     

Iron–bentonite interactions in the Kawasaki bentonite deposit,Zao area,Japan

Greenish veins occurring in brecciated bentonite were found in the Kawasaki bentonite deposit of the Zao region in Miyagi Prefecture, Japan. Their occurrence possibly indicates the interaction of bentonite with Fe-rich hydrothermal solutions. In order to prove the hypothesis and understand the long-term mineralogical and petrographic evolution of bentonite during such interactions, the greenish veins and the surrounding altered bentonite were analyzed using X-ray fluorescence (XRF), scanning electron microscopy (SEM), X-ray diffraction (XRD), electron probe micro-analysis (EPMA), scanning transmission electron microscopy with energy dispersed spectroscopy (STEM-EDS) and micro X-ray absorption near-edge structure (XANES). The greenish veins resulting from hydrothermal solution are composed of mixed-layer minerals consisting of smectite and glauconite (glaucony), pyrite and opal. The occurrences indicate that glaucony and pyrite formed almost simultaneously from hydrothermal solution prior to opal precipitation. The mineral assemblages of the greenish veins and their surroundings indicate that the hydrothermal activity had most likely taken place at a temperature of less than 100 °C and that the pH and Eh conditions of the reacted solution were neutral to alkaline pH and reducing. The unaltered bentonite is composed mainly of Al smectite and opal. These minerals coexist as a mixture within the resolution level of the microprobe analyses. On the other hand, the bentonite in contact with the greenish veins consists of discrete opal grains and dioctahedral Al smectite containing Fe and was altered mineralogically and petrographically by the hydrothermal activity. Both the clay minerals and the opal were formed by dissolution and subsequent precipitation from the interaction of the original bentonite with the hydrothermal solution.     

Postglacial anthropogenic fires related to cultural changes in central Japan,inferred from sedimentary charcoal records spanning glacial–interglacial cycles

We examined long-term charcoal records spanning the glacial–interglacial cycles that are evident in two cores collected from Lake Biwa in central Japan. We found that the records of the two cores have a similar long-term variation pattern of charcoal concentrations and abundant large charcoal fragments in postglacial sediments, which indicates that frequent fires occurred near the shores of Lake Biwa during the postglacial period. Analogous natural conditions in the early postglacial period and the early part of the last interglacial period strongly suggest that the frequent fires that occurred only during the postglacial period were anthropogenic. A comparison between the charcoal records of Lake Biwa sediments and the cultural changes and human populations in this district suggests that anthropogenic fires in this district were influenced by the lifestyle and culture of each era rather than by the populations. Humans tended to use more fire at the start of the settlement during the early Neolithic era in this region, in spite of the small population size.     

Rotation of the elastic Earth: the role of the angular-velocity-dependence of the elasticity-caused perturbation

We calculate the so-called convective term, which shows up in the expression for the angular velocity of the elastic Earth, within the Andoyer formalism. The term emerges due to the fact that the elasticity-caused perturbation depends not only on the instantaneous orientation of the Earth but also on its instantaneous angular velocity. We demonstrate that this term makes a considerable contribution into the overall angular velocity. At the same time the convective term turns out to be automatically included into the correction to the nutation series due to the elasticity, if the series is defined by the perturbation of the figure axis (and not of the rotational axis) in accordance with the current IAU resolution. Hence it is not necessary to take the effect of the convective term into consideration in the perturbation of the elastic Earth as far as the nutation is related to the motion of the figure axis.     

Experimental study of reaction between perovskite and molten iron to 146 GPa and implications for chemically distinct buoyant layer at the top of the core

Partitioning of oxygen and silicon between molten iron and (Mg,Fe)SiO₃ perovskite was investigated by a combination of laser-heated diamond-anvil cell (LHDAC) and analytical transmission electron microscope (TEM) to 146 GPa and 3,500 K. The chemical compositions of co-existing quenched molten iron and perovskite were determined quantitatively with energy-dispersive X-ray spectrometry (EDS) and electron energy loss spectroscopy (EELS). The results demonstrate that the quenched liquid iron in contact with perovskite contained substantial amounts of oxygen and silicon at such high pressure and temperature (P–T). The chemical equilibrium between perovskite, ferropericlase, and molten iron at the P–T conditions of the core–mantle boundary (CMB) was calculated in Mg–Fe–Si–O system from these experimental results and previous data on partitioning of oxygen between molten iron and ferropericlase. We found that molten iron should include oxygen and silicon more than required to account for the core density deficit (<10%) when co-existing with both perovskite and ferropericlase at the CMB. This suggests that the very bottom of the mantle may consist of either one of perovskite or ferropericlase. Alternatively, it is also possible that the bulk outer core liquid is not in direct contact with the mantle. Seismological observations of a small P-wave velocity reduction in the topmost core suggest the presence of chemically-distinct buoyant liquid layer. Such layer physically separates the mantle from the bulk outer core liquid, hindering the chemical reaction between them.