Comparison of sinking particles in the upper 200 m between subarctic station K2 and subtropical station S1 based on drifting sediment trap experiments

Drifting sediment trap experiments were conducted during various seasons to elucidate the characteristics of particles sinking through the upper 200 m of the water column in the western Pacific at subarctic station K2 and subtropical station S1. The sinking particle flux increased when primary productivity was high at each station, during June–July at K2 and during February at S1. Biogenic opal (Opal) and CaCO₃ were the major components of the fluxes at K2 and S1, respectively. Contrary to the expectation of a high flux at the eutrophic station K2 and low flux at the oligotrophic station S1, the annual average organic carbon fluxes at 100 m were comparable at both stations: 62.7 mg C m^?2 day^?1 at K2 and 56.1 mg C m^?2 day^?1 at S1. The similarity of the fluxes was perhaps a reflection of the unexpectedly high primary production at S1. At K2, the organic carbon export ratio (organic carbon flux/primary productivity) was significantly and negatively correlated with primary production and tended to decrease with depth. The magnitude of the rate of attenuation of the organic carbon flux with depth was larger at S1 than at K2. This rate of attenuation tended to decrease and increase with primary production at K2 and S1, respectively. The explanation for these patterns may be that the flux of labile organic carbon at relatively shallow depths decreased with increasing primary production at K2, and zooplankton grazing pressure increased with increasing primary productivity at S1.     

Time evolution of hydraulic and electrokinetic parameters around the Nojima fault, Japan, estimated by an electrokinetic method

The Nojima Fault Zone Probe was designed to study the properties and healing processes of the Nojima fault, which is the surface fault rupture of the Hyogo-ken Nanbu earthquake (M7.2) of 1995 (1995 Kobe earthquake). In this project, water injection experiments were conducted in a borehole of 1800 m depth at the Nojima fault. We set up electrodes around the borehole and observed self-potential variations to investigate the magnitude of electrokinetic and hydraulic parameters around the Nojima fault zone. In the 1997 experiment, self-potential variations were in the range of a few to about 20 mV across 320–450 m electrode dipoles with hydraulic pressure variations from 3.5 to 4 MPa. In the 2000 experiment, self-potential variations were in the range of a few to about 85 mV across 160–260 m electrode dipoles with the hydraulic pressure variations from 3 to 4.5 MPa. In the 2003 experiment, self-potential variations were in the range of a few to about 30 mV across 20–80 m electrode dipoles with hydraulic pressure of 4 MPa. These observed self-potential variations were explained well with an electrokinetic effect due to the underground flow of the injected water. From the observed results, we estimated that the ratio of hydraulic parameters (permeability, porosity, and tortuosity) to electrokinetic parameters (zeta potential and dielectric constant) decreased approximately 40% during eight years after the earthquake. This result suggests that the healing process around the fault zone progress.     

Seismic detectability of anomalous structure at the top of the Earth’s outer core with broadband array analysis of SmKS phases

I have examined precisely the differential travel times and waveforms of SmKS seismic phases propagating under the southern Indian Ocean obtained from African broadband seismic arrays. The SmKS phases analyzed in this study travel in the mantle with weak heterogeneity confirmed by a global tomographic study for the distance range of 115-135°. The SmKS differential times were obtained from a vespagram (a stack intensity on a time-slowness diagram), and comparison with the vespagram created from synthetic waveforms with PREM gives the travel-time residual for each event-array pair. Although the residuals of S3KS-S2KS times exhibit apparently a systematic dependence on epicentral distance, this is likely due to small-scale heterogeneity beneath the Oceania where is covered by the SmKS ray entering points at the CMB. Waveform modeling was applied to a record section with a small travel-time residual that suggests a small effect from the mantle heterogeneity on the data set, I found that a low-velocity zone in the outermost 50 km in the core rather than PREM can explain an additional arrival detected just after the S3KS phase. This result is still inconclusive because of the small number of data and non-uniqueness of the model and ambiguity due to mantle structure. However, accumulation of the precise measurement described in this study may help the reduction of uncertainty and trade-offs.     

Geochemical and isotopic studies of aeolian sediments in China

The Sr and Nd isotopic, rare earth element (REE) and major element compositions, together with mineral and grain‐size proportions, are reported for aeolian loess deposits and desert sands from several Chinese localities. The study was carried out in order to examine regional variations in the isotopic and geochemical features of these aeolian sediments, and to constrain the provenance of Chinese loess. Samples include loesses from the Tarim and Junggar basins and desert sands from the Taklimakan desert in north‐west China, loess from the Ordos area and desert sands from the Tengger and Mu‐us deserts in north‐central China, as well as loess and desert sands from the Naiman area, north‐east China. REE distributions show minimal variation among the Chinese loess deposits, whereas those for the desert sands show regional variations. New isotopic data document a latitudinal variation in Sr and Nd isotopic features for the loesses and desert sands. The Naiman and Junggar loesses have distinctly lower ⁸⁷Sr/⁸⁶Sr ratios and higher ε_Nd(0) values than the loesses from the Tarim Basin, the Ordos area and the Loess Plateau. Among the desert sands, the Naiman samples have higher ε_Nd(0) values than the Taklimakan, Tengger and Mu‐us samples. Isotopic data suggest that loesses of the Loess Plateau were supplied from the Tarim Basin loesses and Taklimakan Desert sand, and that the Naiman loesses were supplied from the Junggar Basin loesses. The latitudinal variation in the loesses and desert sands may be partly explained by isotopic variations reported previously for moraines from the Tianshan and west Kunlun Mountains, which are possible sources for the loesses and desert sands. These inferences on the provenance of the loesses and desert sands are consistent with the dust transport pattern over East Asia.     

Noble gases in submarine pillow basalt glasses from the Lau Basin: Detection of a solar component in backarc basin basalts

Noble gas elemental and isotopic abundances have been analysed in eight samples of youthful basaltic glass dredged from three different locations within the Lau Backarc Basin: (1) the King's Triple Junction, (2) the Central Lau Spreading Centre at 18°S and (3) the Eastern Lau Spreading Centre at 19°S. Samples from the Lau central and eastern spreading centres have MORB-like helium isotopic ratios of approximately 1.2 × 10⁻⁵ (8.5 R/R_A). In contrast, the samples from the King's Triple Junction yield helium isotopic ratios averaging 9.4 (±0.8) × 10⁻⁶ (6.7 ± 0.6 R/R_A), systematically lower than the MORB-like value, which may be reflecting the addition of radiogenic ⁴He released from the descending slab. Neon isotopic ratios are enriched in ²⁰Ne and ²¹Ne with respect to atmospheric ratios by as much as 23% and 62% respectively. These observations further confirm that non-atmospheric neon is a common characteristic of samples derived from the mantle. The helium and neon isotopic signatures in the samples can be explained by mixing of a primordial solar component, radiogenic and nucleogenic components produced by radioactive processes inside the Earth, and an atmospheric component. This reconnaissance survey of noble gases in a backarc basin indicates that current volcanism is dominated by magmas from the mantle wedge, a source similar to that from which MORBs are derived. The heavier noble gases (argon, krypton and xenon), however, show more atmosphere-like compositions, either indicating strong interaction of the magmas with the atmosphere or the presence of a recycled component derived from the underlying subducting slab.     

Variability in the Relative Penetration of Ultraviolet Radiation to Photosynthetically Available Radiation in Temperate Coastal Waters, Japan

UVR and PAR wavelengths are attenuated to different extents within the water column, causing variations in spectral composition with depth. The present investigation (a) describes the variability of UVR and PAR penetration at a station in the temperate coastal waters of Sagami Bay and determines (b) the characteristics of relative UVR penetration to the euphotic zone. Examination of the seasonal irradiance profile measurements indicated eight measurements displaying two distinct attenuation coefficients (K _d) for specific UVR wavelengths and PAR. The two attenuation coefficients observed from specific wavelengths in the water column may be caused not only by chlorophyll pigments, but also by dissolved organic material in the upper layer. The 1% depth of surface UVR at 305, 320, 340, and 380 nm averaged 10.8 ± 5.7, 14.9 ± 9.5, 19.8 ± 12.1, and 30.4 ± 17.6 m, respectively. The depth of euphotic layer displayed less variability averaging 62 ± 15 m throughout the entire study. Relative UVR penetration within the euphotic zone averaged 17.8 ± 8.1, 22.9 ± 10, 30.5 ± 13.8, and 46 ± 46.9% for 305, 320, 340, and 380 nm, respectively. A large variation of the relative transmission of UVR within the euphotic zone was found although the spectral composition was relatively stable in the air throughout the study.     

Permeability measurements of natural and experimental volcanic materials with a simple permeameter: Toward an understanding of magmatic degassing processes

Permeability measurement of quenched volcanic porous materials is an important approach to understand permeability development and degassing of vesicular silicic magmas. In this study, we developed a gas permeameter to measure permeability of natural samples and experimental products. The permeameter has broad measurement ranges of pressure difference (10¹–10⁵ Pa) and gas-flow rate (10^− 9–10^− 5 m³/s). These ranges enable us to measure viscous permeability in the range of 10^− 17–10^− 9 m² for 1 centimeter-scale samples, using the Forchheimer equation, which includes the inertial effect of gas flow permeating through the samples. In addition, we improved the procedure for performing permeability measurements of mm-sized products of decompression experiments. Although a previous study reported the first permeability data for vesicular silicic glass products of decompression experiments, we found an overestimation in their permeability data due to problems in sample preparation, especially for very low permeability samples. Our improved measurements give lower permeability values than those of Takeuchi et al. (2005)(Takeuchi, S., Nakashima, S., Tomiya, A., Shinohara, H., 2005. Experimental constraints on the low gas permeability of vesicular magma during decompression. Geophys. Res. Lett., 32, L10312 doi:10.1029/2005GL022491).     

Does heavy oil pollution induce bacterial diseases in Japanese flounder Paralichthys olivaceus?

As basic research for the effect of heavy oil on the fish immune system, in this study, the number of leukocyte was counted in Japanese flounder Paralichthys olivaceus, after exposure to heavy oil at a concentration of 30 g/8 L for 3 days. To compare the numbers of bacteria in the skin mucus between oil-exposed and control fish, viable bacteria were enumerated by counting colony forming unit (CFU). Compared with 5.79 ± 1.88 × 10⁷ leukocytes/mL in the controls, the exposed fish demonstrated higher counts, averaging 1.45 ± 0.45 × 10⁸ cells/mL. The bacterial numbers of control fish were 4.27 ± 3.68 × 10⁴ CFU/g, whereas they were 4.58 ± 1.63 × 10⁵ CFU/g in the exposed fish. The results suggest that immune suppression of the fish occurred due to heavy oil stressor, and bacteria could invade in the mucus, resulting in the increasing leukocyte number to prevent infectious disease.     

A New Solar Imaging System for Observing High-Speed Eruptions: <Emphasis Type="Italic">Solar Dynamics Doppler Imager</Emphasis> (SDDI)

A new solar imaging system was installed at Hida Observatory to observe the dynamics of flares and filament eruptions. The system (Solar Dynamics Doppler Imager; SDDI) takes full-disk solar images with a field of view of \(2520~\mbox{arcsec} \times 2520~\mbox{arcsec}\) at multiple wavelengths around the \(\mathrm{H}\alpha\) line at 6562 Å. Regular operation was started in May 2016, in which images at 73 wavelength positions spanning from \(\mathrm{H}\alpha -9~\mathring{\mathrm{A}}\) to \(\mathrm{H}\alpha +9~\mathring{\mathrm{A}}\) are obtained every 15 seconds. The large dynamic range of the line-of-sight velocity measurements (\({\pm}\,400~\mbox{km}\,\mbox{s}^{-1}\)) allows us to determine the real motions of erupting filaments in 3D space. It is expected that SDDI provides unprecedented datasets to study the relation between the kinematics of filament eruptions and coronal mass ejections (CME), and to contribute to the real-time prediction of the occurrence of CMEs that cause a significant impact on the space environment of the Earth.