Sea surface temperature record off central Japan since the Last Glacial Maximum using planktonic foraminiferal Mg/Ca thermometry

We conducted paired measurements of the Mg/Ca ratio and δ¹⁸O of planktonic foraminifera, Globigerina bulloides, from a sediment core (MD01‐2420) off central Japan in the northwest Pacific, to reconstruct current movements since the Last Glacial Maximum (LGM). These methods make it possible to determine the magnitude and timing of the sea surface temperature (SST) changes and to reconstruct the variations of the past seawater δ¹⁸O (δ¹⁸Ow) off central Japan. The amplitude of Mg/Ca‐based SST changes between the Holocene and the LGM was about 10°C. The strong resemblance of the SSTs estimated from both methods, Mg/Ca‐based and δ¹⁸O‐based, suggests that the SST changes were caused primarily by latitudinal displacement of the Kuroshio–Oyashio currents and no distinct change in the carbonate dissolution of the core. The southward migration of the water mass was 5–6° in latitude at the LGM. The values for regional δ¹⁸Ow changes, which were obtained by subtracting the ice volume contribution from the calculated δ¹⁸Ow, describe the millennial‐scale water mass migration over the last 30 kyr. Copyright © 2005 John Wiley & Sons, Ltd.     

Noble gases in Muong Nong‐type tektites and their implications

Abstract— We have the elemental abundances and isotopic compositions of noble gases in Muong Nong‐type tektites from the Australasian strewn field by crushing and by total fusion of the samples. We found that the abundances of the heavy noble gases are significantly enriched in Muong Nong‐type tektites compared to those in normal splash‐form tektites from the same strewn field. Neon enrichments were also observed in the Muong Nong‐type tektites, but the Ne/Ar ratios were lower than those in splash‐form tektites because of the higher Ar contents in the former. The absolute concentrations of the heavy noble gases in Muong Nong‐type tektites are similar to those in impact glasses. The isotopic ratios of the noble gases in Muong Nong‐type tektites are mostly identical to those in air, except for the presence of radiogenic ⁴⁰Ar. The obtained K‐Ar ages for Muong Nong‐type tektites were about 0.7 Myr, similar to ages of other Australasian tektites. The crushing experiments suggest that the noble gases in the Muong Nong‐type tektites reside mostly in vesicles, although Xe was largely affected by adsorbed atmosphere after crushing. We used the partial pressure of the heavy noble gases in vesicles to estimate the barometric pressure in the vesicles of the Muong Nong‐type tektites. Likely, Muong Nong‐type tektites solidified at the altitude (between the surface and a maximum height of 8–30 km) lower than that for splash‐form tektites.     

Near-infrared imaging observations of the southern massive star-forming region G333.6−0.2

We present near-infrared broad-band JHK ' images of the southern massive star-forming region G333.6−0.2. The slope of the K -luminosity function towards the region  (0.24 ± 0.01)  is considered to be equivalent to that expected for main-sequence stars in the solar neighbourhood. Point sources with their ( H − K ) colour greater than 1 are more likely to be located in extended emission and it is suggested that these objects are physically associated with the H  ii region.     

Distribution of noble gases in Chinese tektites: Implication for neon solubility in natural glasses

Abstract— Five indochinites from Hainan Island and the Leizhou Peninsula, China were analyzed for noble gas abundances and isotopic ratios. These splash‐form tektites show vesiculation ranging from 0.4 vol% to 8 vol%, as determined by digital image analysis (software SXM®) on thin section photographs. To study the distribution of noble gases in vesicles and in glass, the gases were extracted by heating and by crushing, respectively, on 2 aliquots of the same sample. The results show that 5 to 53% of the total measured ²⁰Ne resides in vesicles. The calculated concentration of neon dissolved in the glass is higher (0.7‐1 times 10^?7 cm³STP/g) than that expected from solubility equilibrium (1 times 10^?8 cm³STP/g), assuming solubility data from MORB glasses. The neon concentration of splash‐form tektites, those analyzed in this work and those from other strewn‐fields worldwide, is correlated with the SiO₂ content of glass and with the nonbridging oxygen per tetrahedral cation in the melt (hereafter NBO/T ratio), the latter being an index of the free‐volume in the silica network where neon could be dissolved. These correlations suggest that the glass structure of tektite has a larger free‐volume available for dissolving noble gases than MORB glasses.     

Infrared polarimetry of the southern massive star-forming region G333.6−0.2

We present     spectropolarimetry, and 12- and 2-μm imaging polarimetry of the southern massive star-forming region G333.6−0.2. Spectro-polarimetry measurements show that the polarization observed towards the nebula contains a mixture of both absorptive and emissive polarizations. Model fitting to the spectra indicates that the temperature of the mid-infrared emitting dust grains is generally ∼200 K and the optical depth of the absorbing dust at 9.7 μm is ∼1.5. Fits are also made to the polarimetry spectra, which show a reasonably constant peak absorptive polarization (∼3.4 per cent at 43°) across the face of the H  ii region. This absorptive polarization position angle is consistent with that found by the 2-μm imaging polarimetry     and is most likely due to the Galactic magnetic field local to G333.6−0.2. When the absorptive polarization is subtracted from the 12-μm polarization image, the emissive polarization pattern that is intrinsic to the star-forming region is revealed. A probable magnetic field configuration implied by the intrinsic polarization suggests star formation initially influenced by the Galactic magnetic field which is eventually perturbed by the star formation process.     

Single-crystal X-ray diffraction and spectroscopic studies on humboldtine and lindbergite: weak Jahn–Teller effect of Fe<Superscript>2+</Superscript> ion

The single-crystal of humboldtine [Fe²⁺(C₂O₄) · 2H₂O] was first synthesized and the crystal structure has been refined. Single-crystal X-ray diffraction data were collected using an imaging-plate diffractometer system and graphite-monochromatized MoKα radiation. The crystal structure of humboldtine was refined to an agreement index (R1) of 3.22% calculated for 595 unique observed reflections. The mineral crystallizes in the monoclinic system, space group C2/c, with unit cell dimensions of a = 12.011 (11), b = 5.557 (5), c = 9.920 (9) Å, β = 128.53 (3)?, V = 518.0 (8) Å³, and Z = 4. In this crystal structure, the alternation of oxalate anions [(C₂O₄)^2?] and Fe²⁺ ions forms one-dimensional chain structure parallel to [010]; water molecules (H₂O)⁰ create hydrogen bonds to link the chains, where (H₂O)⁰ is essentially part of the crystal structure. The water molecules with the two lone electron pairs (LEPs) on their oxygen atom are tied obliquely to the chains, because the one lone electron pair is considered to participate in the chemical bonds with Fe²⁺ ions. Humboldtine including hydrogen bonds is isotypic with lindbergite [Mn²⁺(C₂O₄) · 2H₂O]. The donor–acceptor separations of the hydrogen bonds in humboldtine are slightly shorter than those in lindbergite, which suggests that the hydrogen bonds in the former are stronger than those in the latter. The infrared and Raman spectra of single-crystals of humboldtine and lindbergite confirmed the differences in hydrogen-bond geometry. In addition, Fe²⁺–O stretching band of humboldtine was split and broadened in the observed Raman spectrum, owing to the Jahn–Teller effect of Fe²⁺ ion. These interpretations were also discussed in terms of bond-valence theory.     

Quartz and polymineral luminescence dating of Japanese loess over the last 0.6 Ma: Comparison with an independent chronology

There are only a few luminescence dating studies of loess sediments in Japan, but interleaved with these deposits are many well-described tephras of known age based on ¹⁴C and fission track analysis; these independent age controls provide an opportunity to test the reliability of loess luminescence ages. This study provides such a comparison at two sites in central Honshu, the largest island in the Japanese archipelago. Samples were collected from sequences of interleaved volcanic tephra and loess deposited on a Middle Pleistocene river terrace in the Niigata Prefecture and on an Early to Middle Pleistocene dissected fluvial surface at in the Tochigi Prefecture, Honshu. Equivalent doses (D_e) were estimated from fine grains (4–11 μm) using both polymineral IR-OSL and (post-IR) blue-OSL, and quartz blue-OSL. The blue-stimulated luminescence signals could be represented by up to three exponentially decaying components; only the most light sensitive of these components was used in the final D_e estimation. Almost all the estimates of D_e from polymineral IR-OSL are smaller than those from polymineral (post-IR) blue-OSL and quartz blue-OSL, whereas the latter two are in good agreement. The blue-light stimulated luminescence ages using the most light sensitive component are shown to be in good agreement with the independent control, up to 500 ka. Although the IR-OSL signals underestimate the known age, a simple laboratory fading test is found empirically to correct for this underestimation. We conclude that the most rapidly blue-stimulated luminescence signals from quartz extracted from our loess samples give reliable ages, and that future loess dating studies should concentrate on these signals.