Latitudinal and downcore (0–750 ka) changes in n-alkane chain lengths in the eastern equatorial Pacific

The n-alkane C₃₁/(C₂₉ + C₃₁) ratios from surface sediments in the eastern equatorial Pacific (EEP) exhibit higher values to the north and lower values to the south across the southern edge (2–4°N) of the Intertropical Convergence Zone (ITCZ). Since plants tend to synthesize longer chain length n-alkanes in response to elevated temperature and/or aridity, the higher C₃₁/(C₂₉ + C₃₁) ratios at northern sites suggest a higher contribution of vegetation under hot and/or dry conditions. This is consistent with the observation that northern sites receive higher levels of plant waxes transported by northeasterly trade winds from northern South America, where hot and dry conditions prevail. Furthermore, from a sediment core covering the past 750 ka (core HY04; 4°N, 95°W) we found that C₃₁/(C₂₉ + C₃₁) ratios exhibit a long-term decrease from MIS (marine oxygen isotope stage) 17 to 13. During this period, the zonal SST (sea-surface temperature) gradient in the equatorial Pacific increased, suggesting an increase in Walker circulation. Such intensified Walker circulation may have enhanced moisture advection from the equatorial Atlantic warm pool to the adjacent northern South America, causing arid regions in northern South America to contract, which may explain long-term decrease in n-alkane chain lengths.     

Surface microtopography of metamorphic white micas

Gold decoration and platinum-carbon-shadowing techniques of electron microscopy have been applied to study the surface microtopographs of noncleavage (001) faces of porphyroblastic white micas and sericite crystals collected from the chlorite, biotite, and garnet zones in the Shiragayama area in the Sanbagawa metamorphic terrain, Shikoku, Japan. Two different types of surface microtopograph have been observed; parallel step system and saw-tooth step system. The former is interpreted as representing the surface microtopographs formed either by growth or under near equilibrium conditions, the latter either by dissolution or under rigorous kinetic conditions. The former has been observed on porphyroblastic white micas occurring in the middle portion of each metamorphic zone and on all sericite crystals, the latter on most sericites and on porphyroblastic white micas occurring along the boundaries of the neighboring metamorphic zones. It is suggested that the observed variations in the surface microtopographic characteristics are due to Ostwald ripening during a kind of sintering process in which interstitial water plays an essential role, and that the drastic changes along the metamorphic zone boundaries are due to dehydration reactions. Retrogressive metamorphism is considered to have an almost negligible effect, if any, upon the surface microtopographs.     

Plagioclase zoning in the setogawa ash-flow sheet of the Nohi rhyolite complex,central Japan

Single whole crystals of calcic augite from M. Etna, Sicily, which display both sector and oscillatory zoning, have been serially sectioned and the form of the sectors mapped out. The principal intersectorial chemical variation is shown to be that of Ti and Al by as much as 39% (cation %) change in each, and the least variation, that of Ca (showing a 0.77 to 3.20% change). For each of three isochronous surfaces the ratio of Ti∶Al is shown to be individually constant no matter what the sector and this is thought to indicate near equilibrium conditions at the crystal/liquid interface. In addition to sector zoning these crystals display two types of concentric banding, having dimensions of about 0.25 mm, 20 μm. The 20 μm banding is shown to be both optically and chemically oscillated. Relative diffusion rates of cationic species in the melt, and growth rates of crystal faces are thought to play an important role in the formation of the oscillations, and the sector zoning.     

Fine-grained aggregates in L3 chondrites

The textures and chemical compositions of the constituent minerals of the fine-grained aggregates (FGA's) of L3 chondrites were studied by the backscattered electron image technique, electron probe microanalysis, and transmission electron microscopy. Plagioclase and glass in the interstices between fine grains of olivine and pyroxene indicate that the FGA's once partly melted. Compositional zoning and decomposition texture of pyroxenes are similar to those observed in chondrules, indicating a common cooling history of the FGA's and chondrules. Therefore, the mechanism that caused melting of the FGA's is considered to be the same as for chondrules. Bulk compositions of the FGA's are within the range of those of chondrules, so some chondrules probably were produced by complete melting of the same precursor materials as those of the FGA's. The precursor materials must have included fine olivine and other grains that probably are condensates.     

Petrological study of Nasu-Chausudake Volcano (ca. 16 ka to Present), northeastern Japan

Chausudake Volcano is representative of the active volcanoes in northeastern Japan, and has a record of many historical eruptions. Because its 16-ky eruptive history is well documented, Chausudake is well-suited for examining the temporal change of magma chamber processes and for assessing potential hazards. The activity of the Chausudake Volcano can be divided into six magmatic units (CH1-CH6). Most of its products have similar characteristics, but those from unit CH1 show wider variation. Most rocks are andesite and have plagioclase, clinopyroxene, orthopyroxene, and Fe-Ti oxides as phenocrysts, with or without olivine or quartz. Mafic inclusions, which are observed in most products, are basaltic andesites that have various combinations of the same phenocryst species. Petrographic features observed in host rocks and mafic inclusions, such as disequilibrium phenocrysts and resorbed textures, suggest magma mixing/co-mingling. Whole rock compositions of both host rocks and mafic inclusions show linear trends in variation diagrams, which suggest that the rocks are derived from the mixing/co-mingling between mafic and felsic end members. Bulk silica content of the mafic end-member magma is estimated to be ca. 52%, and contains Mg-rich olivine and An-rich plagioclase. The temperature of this end member is estimated to have been higher than 1,100 °C. Bulk silica content of the felsic end-member magma is estimated to be ~66%, and contains Mg-poor pyroxenes, An-poor plagioclase, and quartz phenocrysts, with a temperature of between 800 and 900 °C. Trace element compositions show that the end members have different origins, but have changed little over the entire 16-ky of activity. The mafic end-member magmas might come from a lower-crustal homogeneous, large magma chamber, whereas the felsic end-member magmas may be partial melts of crustal materials produced by the heat of the mafic end member. Felsic end-member magma may have accumulated in the middle crust before CH1 activity. The mixing ratio of the felsic to mafic end members was 0.5:0.5 to 0.4:0.6 for the CH1 unit, and ca. 0.4:0.6 for the other units. Considering that ca. 75% of the total volume of the eruptive products form the first unit, its wider compositional variation is attributed to more heterogeneous mixing ratios.     

The Brightness Temperature of the Quiet Solar Chromosphere at 2.6 mm

The absolute brightness temperature of the Sun at millimeter wavelengths is an important diagnostic of the solar chromosphere. Because the Sun is so bright, measurement of this property usually involves the operation of telescopes under extreme conditions and requires a rigorous performance assessment of the telescope. In this study, we establish solar observation and calibration techniques at 2.6 mm wavelength for the Nobeyama 45 m telescope and accurately derive the absolute solar brightness temperature. We tune the superconductor–insulator–superconductor (SIS) receiver by inducing different bias voltages onto the SIS mixer to prevent saturation. Then, we examine the linearity of the receiver system by comparing outputs derived from different tuning conditions. Furthermore, we measure the lunar filled beam efficiency of the telescope using the New Moon, and then derive the absolute brightness temperature of the Sun. The derived solar brightness temperature is \(7700 \pm 310~\mbox{K}\) at 115 GHz. The telescope beam pattern is modeled as a summation of three Gaussian functions and derived using the solar limb. The real shape of the Sun is determined via deconvolution of the beam pattern from the observed map. Such well-calibrated single-dish observations are important for high-resolution chromospheric studies because they provide the absolute temperature scale that is lacking from interferometer observations.     

一种特殊类型硅质岩——浮石状燧石

一种较为少见的特殊硅质岩产于南京及巢湖地区的下二叠统孤峰组地层中。它的显著特征是岩石中存在大量菱形和不规则状孔隙,孔隙周边和孔隙间主要由微晶石英组成。通过对该岩石的成分和结构等特征的研究,认为它是一种交代碳酸盐岩成因的硅质岩,并定名为浮石状燧石。     

Microbiological and Chemical Studies in the Seas of Hiuchi and Bingo—II

The distribution of inorganic nitrogen compounds and the metabolic rates of these compounds by microorganisms as a whole were investigated in the Seas of Hiuchi and Bingo. The results obtained are as follows:

1. Of inorganic nitrogen compounds, the contents in sea water, those in bottom muds, the uptake or liberation rates of microorganisms as a whole in sea water, and the liberation rates from bottom muds to sea water are 0.2～4.0 μg at. N/l, 3～60 μg at.N/100 g, 0.01～0.5 μg at.N//lhr, and 0.3～1.9 μg at.N/100 cm²/hr, respectively, and these contents or rates of ammonia usually are the largest of these inorganic nitrogen compounds.
2. From the above-mentioned results and the others, it is suggested that the nitrogen in the seas circulates mainly in sea water itself and the course of nitrogen cycle, which passes through bottom muds, is not so important, and further that, of the cycle of inorganic nitrogen compounds, the main course is the course which ammonia is liberated from organic nitrogen compounds and it is immediately uptaked by microorganisms, and the course which it is oxidized to nitrate and the others are not so important.