Depositional age of the Himenoura Group on the Amakusa‐Kamishima area,Kyushu, southwest Japan: Using zircon U–Pb dating of the acidic tuffs

The Upper Cretaceous Himenoura Group in the Amakusa‐Kamishima Island area, southwest Japan is subdivided into the Hinoshima and Amura Formations. In order to determine the numerical depositional age of the formations, zircon U–Pb ages were investigated using laser ablation inductively coupled plasma mass spectrometry (LA–ICP–MS) for acidic tuff samples from the lower part of the Hinoshima Formation and the upper part of the Amura Formation. Although the two samples contain some accidental zircons, the samples have a definite youngest age cluster and their weighted mean ages are 85.4 ± 1.3 and 81.5 ± 1.1 Ma, respectively (errors are 95 % confidence interval). These age data indicate that the Himenoura Group in the Amakusa‐Kamishima Island area was deposited mainly in the early Santonian to early Campanian which is consistent with biostratigraphic ages. Additionally, zircon age distributions of the two tuff samples from the upper part of the Hinoshima Formation do not show a distinct youngest peak of eruption age but characteristics of detrital zircons suggestive of maximum depositional age of the host sediments. These results demonstrate that the mean age of the youngest zircon age cluster of a tuff sample does not always indicate depositional age of the tuff, and statistical evaluation of age data is effective to determine depositional age of a tuff bed using zircon U–Pb ages.     

Regionality and seasonality of submesoscale and mesoscale turbulence in the North Pacific Ocean

The kinetic energy (KE) seasonality has been revealed by satellite altimeters in many oceanic regions. Question about the mechanisms that trigger this seasonality is still challenging. We address this question through the comparison of two numerical simulations. The first one, with a 1/10° horizontal grid spacing, 54 vertical levels, represents dynamics of physical scales larger than 50 km. The second one, with a 1/30° grid spacing, 100 vertical levels, takes into account the dynamics of physical scales down to 16 km. Comparison clearly emphasizes in the whole North Pacific Ocean, not only a significant KE increase by a factor up to three, but also the emergence of seasonal variability when the scale range 16–50 km (called submesoscales in this study) is taken into account. But the mechanisms explaining these KE changes display strong regional contrasts. In high KE regions, such the Kuroshio Extension and the western and eastern subtropics, frontal mixed-layer instabilities appear to be the main mechanism for the emergence of submesoscales in winter. Subsequent inverse kinetic energy cascade leads to the KE seasonality of larger scales. In other regions, in particular in subarctic regions, results suggest that the KE seasonality is principally produced by larger-scale instabilities with typical scales of 100 km and not so much by smaller-scale mixed-layer instabilities. Using arguments from geostrophic turbulence, the submesoscale impact in these regions is assumed to strengthen mesoscale eddies that become more coherent and not quickly dissipated, leading to a KE increase.     

Temporal dynamics of dissolved organic carbon (DOC) produced in a microcosm with red tide forming algae <Emphasis Type="Italic">Chattonella marina</Emphasis> and its associated bacteria

Acute and severe hypoxia associated with harmful algal bloom has become one of the major causes for the environmental deterioration of coastal areas. Although it is generally thought that a large part of the dissolved oxygen consumption at a bloom site is initiated by heterotrophic bacteria that attack organic matter derived from dead or dying algal cells, precise microbial processes leading to the hypoxia are yet to be examined. Here we show temporal dynamics of extracellular dissolved organic carbon (DOC) of the red tide forming raphidophyte Chattonella marina and bacterial populations associating with the algae under laboratory conditions. During the growth of non-axenic strains of C. marina, we monitored abundance of algae, associated bacteria, and DOC in the culture media. Bacterial cell abundance increased in response to the increase in DOC both at the beginning and the late log phase of the algal growth. Flow cytometric analysis revealed that transient increase in the percentage of respiratory-active bacterial cells also coincided with the timing of the increase in bacterial abundance and DOC. These results strongly suggest that DOC released from growing C. marina fuels respiration and growth of planktonic bacteria surrounding the algae. This has implications for the role of DOC released from C. marina bloom before the collapse in mediating interactions between neighboring algae and bacterial assemblage which may eventually lead to algal bloom-associated hypoxia.     

Determination of cation distribution in (Co,Ni,Zn)2SiO4 olivine by synchrotron X-ray diffraction

 The cation distribution of Co, Ni, and Zn between the M1 and M2 sites of a synthetic olivine was determined with a single-crystal diffraction method. The crystal data are (Co_0.377Ni_0.396Zn_0.227)₂SiO₄, M _r  = 212.692, orthorhombic, Pbnm, a = 475.64(3), b = 1022.83(8), and c = 596.96(6) pm, V = 0.2904(1) nm³, Z = 4, D _x  = 4.864 g cm⁻³, and F(0 0 0) = 408.62. Lattice, positional, and thermal parameters were determined with MoKα radiation; R = 0.025 for 1487 symmetry-independent reflections with F > 4σ(F). The site occupancies of Co, Ni, and Zn were determined with synchrotron radiation employing the anomalous dispersion effect of Co and Ni. The synchrotron radiation data include two sets of intensity data collected at 161.57 and 149.81 pm, which are about 1 pm longer than Co and Ni absorption edges, respectively. The R value was 0.022 for Co K edge data with 174 independent reflections, and 0.034 for Ni K edge data with 169 reflections. The occupancies are 0.334Co + 0.539Ni + 0.127Zn in the M1 sites, and 0.420Co + 0.253Ni + 0.327Zn in the M2 sites. The compilation of the cation distributions in olivines shows that the distributions depend on ionic radii and electronegativities of constituent cations, and that the partition coefficient can be estimated from the equation: ln [(A/B)_M1/(A/B)_M2] = −0.272 (IR _A -IR _B ) + 3.65 (EN _A −EN _B ), where IR (pm) and EN are ionic radius and electronegativity, respectively. Received: 8 April 1999 / Revised, accepted: 7 September 1999     

Vertical coupling and dynamical source for the intraseasonal variability in the deep Kuroshio Extension

Ocean Dynamics - In the power spectrum, the upper and deep parts of the Kuroshio Extension have distinctly different peaks. The former peaks around 200 days, while the latter is mainly at the...     

Surface morphological features of boulders on Asteroid 25143 Itokawa

On the sub-kilometer S-type asteroid, 25143 Itokawa, some boulders on rough terrains seem to be exposed without any powdery material covering. Based on surface morphological features, there are two major types of boulders: one has rounded edges and corners (rounded boulders), while the other has angular edges and corners (angular boulders). The surface features of the rounded boulders suggest that they have hardness heterogeneity and that some may be breccias. The angular boulders appear to be more resistant to impact disruption than the rounded ones, which may be due to a difference in lithology. The major constituents of Itokawa may be LL chondrite-like brecciated lithology (rounded boulders) along with a remarkable number of boulders suggesting that lithology is atypical among LL chondrites (angular boulders). Some of both types of boulders contain intersecting and stepped planar foliations. Comparison with meteorite ALH76009 suggests that the planar foliations may be marks where rocks were torn apart. As lithified breccias cannot be formed on present-day sub-kilometer-sized Itokawa, it is reasonable that boulders with various lithologies on Itokawa were formed on its large ancestor(s). The rubble-pile structure of Itokawa suggested by its low density (∼1.9 g/cm³) indicates that boulders on Itokawa are reassembled fragments formed by catastrophic disruption of large ancestor(s).     

Visible and near-infrared spectral survey of Martian meteorites stored at the National Institute of Polar Research

Martian meteorite chip samples stored at the National Institute of Polar Research (NIPR) have been studied by a visible and near-infrared (VNIR) spectrometer. Measured spots are about 3 × 2 mm in size, which are clearly marked on photographs of the meteorite chips. Rock types and approximate mineral compositions of studied meteorites have been identified or obtained through this spectral survey with no sample preparation required. This study demonstrates that this kind of spectral survey is effective in classifying and describing Marian meteorites, and that such a VNIR spectrometer on a Mars rover would be useful for identifying these kinds of unaltered Mars rocks. Further studies which utilize a smaller spot size are desired for improving the accuracy of identifying the clasts and mineral phases in the rocks.     

Hydrochemical characteristics of throughfall and stemflow in a Moso‐bamboo (Phyllostachys pubescens) forest

To investigate the impacts of the invasion by bamboo on fluxes of nutrients and pollutants, the nutrient/pollutant fluxes and canopy interactions, including neutralization of acidity, leaching and uptake of nitrogen (N), were characterized in conjunction with rainfall partitioning in a Moso‐bamboo (Phyllostachys pubescens) forest. Measurements of precipitation volume, pH, major ions, and silicate (SiO₂) in rainfall, throughfall and stemflow were collected weekly in a Moso‐bamboo forest located in Munakata City, Western Japan for 1 year. Results showed that rainfall partitioning into stemflow was larger than that for other types of forest, which may be due to the properties of Moso‐bamboo forest structure, such as a straight and smooth culm. Inorganic N (NO₃⁻ + NH₄⁺) and S (SO₄²⁻) fluxes of throughfall and stemflow were approximately 1·6 and 1·3 times higher than that of rainfall, respectively. Contribution of stemflow flux to inorganic N and S fluxes to the forest floor was high. This could be due to lower uptake of inorganic N through culm and a higher rainfall partitioning into stemflow than that for other types of forest. The Moso‐bamboo canopy neutralized rainfall acidity, reducing the fluxes of potentially acidifying compounds via throughfall and stemflow. Canopy leaching of K⁺ was distinctly higher than that of Mg²⁺ and Ca²⁺ and could be related to the high mobility of K⁺ in plant tissues. Cl⁻ and SiO₂ were readily leached as for K⁺. The impact of the invasion by bamboo on nutrient cycling was discussed. Copyright © 2010 John Wiley & Sons, Ltd.     

Spatial variations in throughfall in a Moso bamboo forest: sampling design for the estimates of stand‐scale throughfall

We investigated the spatial and seasonal variations in throughfall (Tf) in relation to spatial and seasonal variations in canopy structure and gross rainfall (Rf) and assessed the impacts of the variations in Tf on stand‐scale Tf estimates. We observed the canopy structure expressed as the leaf area index (LAI) once a month and Tf once a week in 25 grids placed in a Moso bamboo (Phyllostachys pubescens) forest for 1 year. The mean LAI and spatial variation in LAI did have some seasonal variations. The spatial variations in Tf reduced with increasing Rf, and the relationship between the spatial variation and the Rf held throughout the year. These results indicate that the seasonal change in LAI had little impact on spatial variations in Tf, and that Rf is a critical factor determining the spatial variations in Tf at the study site. We evaluated potential errors in stand‐scale Tf estimates on the basis of measured Tf data using Monte Carlo sampling. The results showed that the error decreases greatly with increasing sample size when the sample size was less than ～8, whereas it was near stable when the sample size was 8 or more, regardless of Rf. A sample size of eight results in less than 10% error for Tf estimates based on Student's t‐value analysis and would be satisfactory for interception loss estimates when considering errors included in Rf data. Copyright © 2009 John Wiley & Sons, Ltd.