Speciation of dissolved metals associated with organic matter in coastal seawaters

By combined use of chloroform extraction and Amberlite XAD-2 resin chromatography, metal-organic compounds dissolved in coastal seawaters of Harima Sound, the Seto Inland Sea, were separated into three groups: hydrophobic, hydrophilic neutral and basic, and hydrophilic acidic. The hydrophobic metal-organic compounds, which are associated with organic matter with molecular weight less than 300, accounted for only a small fraction of the metal-organic compounds; 6 % for Cu and an insignificant fraction for Fe, Mn and Zn. The hydrophilic metal-organic compounds with molecular weights between 100 and 1,500 were major components of the metal-organic compounds. The metals associated with the organic matter on average accounted for 12 % of the Fe, 11 % of the Mn, 7 % of the Zn and 23 % of the Cu of the reactive dissolved metals.     

Benthic Front and the Yamato Basin Bottom Water in the Japan Sea

Hydrographic observations have revealed detailed structure of the Bottom Water in the Japan Sea. The Yamato Basin Bottom Water (YBBW) exhibits higher temperatures and lower dissolved oxygen concentrations than those found in the Japan Basin Bottom Water (JBBW). Both Bottom Waters meet around the boundary region between the Yamato and the Japan Basins, forming a clear benthic front. The structure of the benthic front suggests an estuary-like water exchange between both Basins, with the inflow from the Japan Basin passing under the outflow from the Yamato Basin. It is inferred from the property distributions that the JBBW flowing into the Yamato Basin is entrained by the cyclonic circulation in the basin, and modified to become the YBBW. Vertical diffusion and thermal balance in the YBBW are examined using a box model. The results show that the effect of geothermal heating has about 70% of the magnitude of the vertical thermal diffusion and both terms cancel the advection term of the cold JBBW from the Japan Basin. The box model also estimates the turnover time and vertical diffusivity for the YBBW as 9.1 years and 3.4 × 10⁻³ m²s^{− 1}, respectively.     

High resolution velocity analysis of ocean bottom seismometer data by theτ-p method

A method of high resolution seismic velocity analysis for ocean bottom seismometer (OBS) records is applied to the study of the shallow oceanic crust, especially sedimentary and basement layers. This method is based on the direct-p mapping and the-sum inversion. We use data obtained from a 1989 airgun-OBS experiment in the northern Yamato Basin, Japan Sea and derive P- and S-wave velocity functions that can be compared with the seismic reflection profiles. Using split-spread profile records, we obtain interface dips and true interval velocities from the OBS data. These results show good agreement with the reflection profile records, the acoustic velocities of core samples, and sonic log profiles. We also present a method for estimating errors in the derived velocity functions by calculating covariance of the derived layers' thicknesses. The estimated depth errors are about 150 m at shallow depths, which is close to the seismic wavelength used. The high resolution of this method relies on accurate determination of shot positions by GPS, spatially dense seismic observations, and the use of unsaturated reflected waves arriving after the direct water wave that are observed on low-gain component records.     

CFC Indicating Renewal of the Japan Sea Deep Water in Winter 2000–2001

The distributions of CFC (chlorofluorocarbon) in the water column was determined twice in 2000 and 2001 in the northwestern Japan Sea. In 2000 the CFC-11 concentration decreased almost exponentially with depth from 6 pmol/kg at a few hundred m deep to 0.3 pmol/kg or less at the bottom of about 3400 m depth at three stations (40–41°N, 132–133°E) about 300 km off Vladivostok. In 2001 the CFC-11 concentration increased sharply up to 2 pmol/kg in the bottom water, while it did not increase at a station (42.0°N, 136.5°E) about 450 km away to the northeast. This is due to the renewal of the bottom water which is replaced by the surface water flowing down along the continental slope, as suggested by Tsunogai et al. (1999), who proposed the continental shelf pump. Furthermore, an increase in the CFC-11 concentration was observed throughout the entire water column above 3000 m depth, although the proportion of the increase was about 20%, which was one order of magnitude smaller than that in the bottom water. The increase in inventory is almost four times larger than that in the bottom water below 3000 m depth which is equivalent to about 1/6 of the total inventory found in 2000. The increase also means that 3% of the deep water was replaced by the recent surface water, or, if the turnover occurs every year, that the turnover time of the deep water to be about 30 years. This revised version was published online in July 2006 with corrections to the Cover Date.     

Evolutionary tracks of the terrestrial planets

On the basis of the model proposed by Matsui and Abe, we will show that two major factors — distance from the Sun and the efficiency of retention of accretional energy — control the early evolution of the terrestrial planets. A diagram of accretional energy versus the optical depth of a proto-atmosphere provides a means to follow the evolutionary track of surface temperature of the terrestrial planets and an explanation for why the third planet in our solar system is an aqua-planet.     

Tidal alignments as a contaminant of redshift space distortions

We investigate the effect of orientation-dependent selection effects on galaxy clustering in redshift space. It is found that if galaxies are aligned by large-scale tidal fields, then these selection effects give rise to a dependence of the observed galaxy density on the local tidal field, in addition to the well-known dependences on the matter density and radial velocity gradient. This alters the galaxy power spectrum in a way that is different for Fourier modes parallel to and perpendicular to the line of sight. These tidal galaxy alignments can thus mimic redshift space distortions (RSD), and thus result in a bias in the measurement of the velocity power spectrum. If galaxy orientations are affected only by the local tidal field, then the tidal alignment effect has exactly the same scale and angular dependence as the RSDs in the linear regime, so it cannot be projected out or removed by masking small scales in the analysis. We consider several toy models of tidal alignments and orientation-dependent selection, normalize their free parameter (an amplitude) to recent observations, and find that they could bias the velocity amplitude   f ( z ) G ( z )  by 5–10 per cent in some models, although most models give much smaller contamination. We conclude that tidal alignments may be a significant systematic error in RSD measurements that aim to test general relativity via the growth of large-scale structure. We briefly discuss possible mitigation strategies.     

Degassing history and carbon cycle of the Earth: From an impact-induced steam atmosphere to the present atmosphere

The recent theoretical studies on the formation and evolution of the atmosphere and oceans of the Earth are reviewed. Impact degassing during accretion of the Earth would probably generate an impact-induced steam atmosphere on the proto-Earth. At the end of accretion, the steam atmosphere became unstable and condensed to form the proto-ocean with almost the present mass of ocean. The steam atmosphere would have thus evolved to the proto-CO₂ atmosphere during the earliest history of the Earth because CO in the proto-atmosphere may be photochemically converted to CO₂. However, CO₂ in the proto-atmosphere has decreased with time through the global carbon cycle which may have stabilized the terrestrial environment against an increase in the solar luminosity. The continental growth during Hadean and Archean would therefore have a significant influence on the carbon cycle and the surface temperature. It is also suggested that the continental growth is a necessary condition for the terrestrial environment to evolve to the present state. Both the impact degassing and the subsequent continuous degassing are suggested to have played a major role in the formation and evolution of the atmosphere and ocean. In particular, most of N₂ may have been produced by the impact degassing during accretion, and the contribution of the subsequent continuous degassing is at most 10% for N₂. As a consequence, after the CO₂ level decreased to less than 1 bar, the atmosphere may have been at about 1 bar and composed mainly of N₂ for most of the subsequent history of the Earth.     

Fault system of the 2004 Mid Niigata Prefecture Earthquake and its aftershocks

Data recorded by a seismic network deployed the day after the 2004 Mid Niigata Prefecture Earthquake (M6.8) in central Japan are used to determine the major source faults responsible for the mainshock and major aftershocks. Using this high-resolution seismic data, three major source faults are identified: two parallel faults dipping steeply to the west located 5 km apart, and the other dipping eastward and oriented perpendicular to the west-dipping faults. The analysis also reveals that the lateral variation in seismic velocity observed at the surface extends to a depth of 15 km, encompassing the source area of the mainshock. This strong heterogeneity of the crust, related to the complex geological and tectonic evolution of the area, is considered to be responsible for the prominent aftershock activity following the 2004 Niigata event.