High thallium content in Kuroko-type ore

Tl, Ga and Ge contents of Kuroko and other types of ore deposits were analysed semiquantitatively and quantitatively. The results show that Tl content is extremely high in Kuroko-type deposits compared to other types of mineralization. The T1 content is especially high in yellow ore and pyrite crystals; thus this element is considered to be incorporated in pyrite.     

Changes in microbial community composition in the leaf litter of successional communities after volcanic eruptions of Mount Usu,northern Japan

Changes in the fungal and bacterial biomass and community structure in litter after the volcanic eruptions of Mount Usu, northern Japan were investigated using a chronosequence approach, which is widely used for analyzing vegetation succession. The vegetation changed from bare ground(10 years after the eruptions) with little plant cover and poor soil to monotonic grassland dominated by Polygonum sachalinense with undeveloped soil(33 years) and then to deciduous broad-leaved forest dominated by Populus maximowiczii with diverse species composition and well-developed soil(100 years). At three chronosequential sites, we evaluated the compositions of phospholipid fatty acids(PLFAs), carbon(C) and nitrogen(N) contents and the isotope ratios of C(δ13C) and N(δ15N) in the litter of two dominant species, Polygonum sachalinense and Populus maximowiczii. The C/N ratio, δ13C and δ15N in the litter of these two species were higher in the forest than that in the bare ground and grassland. The PLFAs gradually increased from the bare ground to the forest, showing that microbial biomass increased with the development of the soil and/or vegetation. The fungi-to-bacteria ratio of PLFA was constant at 5.3 ± 1.4 in all three sites, suggesting that fungi were predominant. A canonical correspondence analysis suggested that the PLFA composition was related tothe successional ages and the developing soil properties(P 0.05, ANOSIM). The chronosequential analysis effectively detected the successional changes in both microbial and plant communities.     

Factors regulating the distribution of elements in marine sediments predicted by a simulation model

The contents of oxyanionic elements (V, Se and Mo) and cationic transition metals (Mn, Fe, Co, Ni, Cu and Zn) in sediments from near-shore to deep-sea environments were measured to clarify factors regulating the distribution of these elements in marine sediments. For cationic transition metals of which contents increase from near-shore to deep-sea environments, the chemical composition of pelagic clays is modeled by a mixture of aluminosilicates having the chemical composition of average shale and Fe–Mn oxides having the chemical composition of associated manganese nodules. The content of V is fairly constant in sediments from near-shore to deep-sea areas. The mixture model of average shale and manganese nodules holds also for V, although most of the V is located in the aluminosilicate lattices. The content of Se in the near-shore sediments is higher and that in the deep-sea sediments is lower than that in average shale. The high content in the near-shore sediments is interpreted as the addition of biogenic materials to aluminosilicates with average shale composition and the low content in deep-sea sediments is explained by oxidative release of Se from aluminosilicates. The content of Mo in sediments increases from near-shore to deep-sea environments. The general distribution of Mo in marine sediments is expressed by the mixture model. An anomalously high content of Mo in a near-shore sediment is attributed to adsorption of molybdate on manganese oxides.     

Estimating the Kuroshio Axis South of Japan Using Combination of Satellite Altimetry and Drifting Buoys

By tracking the locally strongest part of the sea-surface velocity field, which was obtained by integrating data of satellite altimeters and surface drifting buoys, we extracted the Kuroshio axis south of Japan every 10 days from October 1992 to December 2000. The obtained axes clearly express the effect of the bottom topography; three modes were observed when the Kuroshio ran over the Izu Ridge. The axis was very stable to the south of ‘Tosa-bae,’ off the Kii Channel. Mean current speed at the Kuroshio axis gradually increased from 0.65 m/s south of Kyushu to 1.45 m/s off Enshu-nada. This revised version was published online in July 2006 with corrections to the Cover Date.     

Interannual variability of the Kuroshio transport passing through the 137°E meridian in an OGCM related to the North Pacific windstress

The interannual variability of the Kuroshio volume transport passing through the 137°E meridian south of Japan was simulated with an ocean general circulation model (OGCM). The time series of the Kuroshio volume transport over the 1000 m depth in the OGCM is well reproduced by the one-dimensional quasi-geostrophic (QG) vorticity equation with a windstress forcing. In our analysis of the OGCM and QG results, we found that peaks and troughs of the time series of the Kuroshio volume transport with 2–3 yr time-scale were induced by windstress curl, both local and immediately eastward, whereas longer time-scale variability was also induced by windstress curl near the dateline.     

The content and the oxidation state of arsenic and antimony in coastal water of Japan

The content and the oxidation state of arsenic and antimony in coastal seawater were determined coupled with chemical separation and neutron activation method. The contents of arsenic and antimony in coastal seawater were estimated to be 1.56–2.73g As/l, 0.25–0.57g Sb/l. Most parts of these elements exist as soluble ionic species, passing through 0.45 pore-size membrane filter, and at surface, 80–97% of arsenic occurs as arsenate and 70–94 % of antimony may occurs as antimonate. The vertical distribution of arsenite and arsenate is almost constant from the surface to 1,200 m depth. However the distribution of Sb(III) and Sb(V) is much more complicated with depth.     

Mixed layer depth front and subduction of low potential vorticity water in an idealized ocean GCM

It is known that there is a front-like structure at the mixed layer depth (MLD) distribution in the subtropical gyre, which is called the MLD front, and is associated with the formation region of mode water. In the present article, the generation mechanism of the MLD front is studied using an idealized ocean general circulation model with no seasonal forcing. First, it is shown that the MLD front occurs along a curve where u _g ·∇T _s = 0 is satisfied (u _g is the upper ocean geostrophic velocity vector, T _s is the sea surface temperature and ∇ is the horizontal gradient operator). In other words, the front is the boundary between the subduction region (u _g ·∇T _s > 0) and the region where subduction does not occur (u _g ·∇T _s < 0). Second, we have investigated subduction of low potential vorticity water at the MLD front, which has been pointed out by past studies. Since u _g ·∇T _s = 0 at the MLD front, the water particles do not cross the outcrop at the MLD front. The water that is subducted at the MLD front has come from the deep mixed layer region where the sea surface temperature is higher than that at the MLD front. The temperature of the water in the deep mixed layer region decreases as it is advected eastward, attains its minimum at the MLD front where u _g ·∇T _s = 0, and then subducts under the warmer surface layer. Since the deep mixed layer water subducts beneath a thin stratified surface layer, maintaining its thickness, the mixed layer depth changes abruptly at the subduction location.     

Volume transport of the Soya Warm Current revealed by bottom-mounted ADCP and ocean-radar measurement

The vertical structure of the Soya Warm Current (SWC) was observed by a bottom-mounted acoustic Doppler current profiler (ADCP) in the region of the SWC axis near the Soya Strait during a 1-year period from May 2004. The ADCP data revealed a marked seasonal variability in the vertical structure, with positive (negative) vertical shear in summer and fall (winter and spring). The volume transport of the SWC is estimated on the basis of both the vertical structure observed by the ADCP and horizontal structure observed by the ocean radars near the strait. The transport estimates have a minimum in winter and a maximum in fall, with the yearly-averaged values in the range of 0.94–1.04 Sv (1 Sv = 10⁶ m³ s⁻¹). These lie within a reasonable range in comparison to those through other straits in the Japan Sea.     

Recovery of surface albedo and plant cover after wildfire in a Picea mariana forest in interior Alaska

Albedo influences vegetation structure, permafrost thawing, etc., in particular, after wildfires in Picea mariana forests in Alaska, USA, while albedo changes with plant succession. To understand interactions between albedo and ecosystem recovery after wildfire, surface albedo was measured in the spring and summer of 2005 at Poker Flat, interior Alaska, where P. mariana forest was dominant. The ground surface was mostly covered with Sphagnum moss before the 2004 wildfire, and was variously burned by the fire. The measured wavelengths ranged from 0.3 to 3.0 μm. We measured four independent variables, incidence, plant cover on the forest floor, cover of burned ground surface, canopy openness and incidence, to examine the determinants on surface albedo. Multiple regression analysis showed that total plant cover positively and mostly determines albedo, indicating that plant recovery is prerequisite to return high albedo. When the ground surface was damaged by fire, changes in albedo were mostly derived from decrease in reflectance wavelengths between 0.7 and 1.4 μm. The fluctuations of reflectance wavelengths did not differ greatly between damaged-moss and burned surfaces. We must mention the dynamics of Sphagnum to understand various environmental changes including surface albedo.