Analysis of dust events in 2008 and 2009 using the lidar network, surface observations and the CFORS model

The Asian dust events in 2008 (May 24–June 4 in 2008) and in 2009 (March 12–25, October 13–26, and December 15–28 in 2009) were analyzed with the lidar network observations, surface observations in China, Korea, Japan, and Mongolia, and with the chemical transport model CFORS. Transport of Asian dust and mixing of dust with air pollution aerosols were studied. The event of May 24 to June 4 in 2008 was a significant event unusually late in the spring dust season. The dust event of March 12–25, 2009 was an interesting example of elevated dust layer, and transport of dust from the elevated dust layer to the ground by the boundary layer activity was observed with the lidars and surface observations in Japan. The concentration of air pollution aerosols was relatively high during the dust event, and the results suggest that vertical structure as well as transport path is important for the mixing of dust and air pollution aerosols. The dust events in October and December 2009 were examples of dust events in autumn and winter. The online mode CFORS reproduced the observation data generally well, except for the event of May 24 to June 4 in 2008. The results of the fourdimensional variational assimilation of the lidar network data reproduced the dust concentration in Korea and Japan reasonably in that event.     

High-Mg diorites derived from sanukitic HMA magmas, Kyushu Island, southwest Japan arc: evidence from clinopyroxene and whole rock compositions

High-Mg diorites that have similar whole rock composition to high-Mg andesites (HMAs) should not be simply interpreted as rocks solidified from the HMA magmas, because the high-Mg diorites may be mafic cumulates derived from a different magma from the HMAs.

The HMAs contain unique clinopyroxenes with higher Mg# and Si than those of other sub-alkaline series igneous rocks. The Mg# and Si are controlled by the source magma composition rather than its crystallized conditions such as pressure and temperature. The chemical composition of clinopyroxenes would present important information for the investigation of the source of high-Mg diorites.

We considered the source of Early Cretaceous high-Mg diorites on Kyushu Island, southwest Japan arc, based on their clinopyroxene and whole rock compositions. The clinopyroxenes have similar chemical characteristics to those in HMAs rather than those in other sub-alkaline rocks. Moreover, the whole rock compositions are equivalent to the sanukitic HMA and do not show features of mafic cumulates. This indicates that the high-Mg diorites solidified from sanukitic HMA magmas. It is generally believed that the sanukitic HMA magmas involve the subduction of a young and/or hot oceanic slab was situated in their genesis. Therefore, the occurrence of the high-Mg diorites suggests that Kyushu was situated in the tectonic setting of young and/or hot slab subduction in the Early Cretaceous.     

1986 Values for Fifteen GSJ Rock Reference Samples, "Igneous Rock Series"

During the five-year period (April 1981 - March 1986), a series of fifteen rock reference samples, "Igneous rock series", has been prepared by the Geological Survey of Japan (GSJ). Based on the data available (published and communicated), consensus values for major, minor and trace elements have been derived; these values are presented for this second series of samples as well as for the first series of two samples, Granodiorite JG-1 and Basalt JB-1.     

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.     

Response of plant growth to surface water balance during a summer dry period in the Kazakhstan steppe

In drylands, water deficit is the primary factor limiting plant growth. In the present study, surface energy balance and plant growth (above‐ground and below‐ground biomass) were measured continuously during the 2002 growing season in semiarid grassland in the northern part of Kazakhstan, Central Asia. Although there was above normal total rainfall during the 2002 growing season (May–November; 244 mm over 183 days), there was a dry period during July and August. Evaporative water was effectively supplied by precipitation and surface soil moisture during the wet season (May and June), during which time above‐ground biomass increased. During the early stages of the dry period, mature plants were likely to tap deeper sources of soil moisture, representing stored snowmelt water. As the soil moisture content decreased during the summer dry period due to the high levels of evapotranspiration and lack of precipitation, the evaporative fraction and above‐ground biomass rapidly decreased, whereas the below‐ground biomass increased. These results suggest that in summer, soil moisture acts to store water, and that soil moisture is essential for plant growth as a direct source of water during the dry period in natural grasslands in the Kazakhstan steppe. Copyright © 2007 John Wiley & Sons, Ltd.     

Crustal strain observation for nine years with a laser strainmeter in Kobe, Japan

We carried out precise crustal strain observation using a laser strainmeter system at the Rokko-Takao station in Kobe, Japan from 1989 to 1997. The long-term strain record is characterized by remarkable annual changes of the order of 2–3×10⁻⁶ and linear strain accumulation of −4.4×10⁻⁷/year (in contraction). The annual strain changes are inversely proportional to temperature changes that precede the strain changes by about 1 month. The apparent annual strain changes were mainly caused by refractive-index changes in the light path due to the ambient temperature changes. After eliminating the annual temperature effect, linear strain accumulation is corrected to be −6.3−6.7×10⁻⁷/year. Residual strains show the oscillating behavior, in which the oscillating cycle seems to become shorter and shorter as time goes by. During the period, a destructive earthquake of M=7.2 occurred near the Kobe City on 17 January 1995. We investigated the oscillating behavior in secular variations of ground-strains by introducing the deterministic approach of earthquake prediction to search for the “critical point” of the occurrence of an earthquake in the extended power law equation. However, we could not obtain a unique solution to determine eight unknown parameters including the “critical point”. This may be mainly due to lack of data for 4 months from August to November in 1994 by the failure of the laser source before the occurrence of earthquake on 17 January 1995. After removing environmental effects and tidal components, we carefully re-examined strain changes in 7 days and 1 day before the occurrence of the earthquake, but we could not detect anomalous strain changes exceeding 1×10⁻⁸ before the earthquake.     

Styles of mesoscale brittle deformations associated with the Miocene folding of the Taishu Group,Tsushima, between the Japan Sea and East China Sea backarc basins

The Taishu Group is a folded, Eocene–Lower Miocene, thick sedimentary package exposed widely on Tsushima Island between the Japan Sea and East China Sea. This location makes the strata important to understand tectonics and paleo-environments in the Far East, but the timing of the folding is controversial. We studied the styles of brittle deformations of the strata. It was found that flextural-slip folds were dominant. Mesoscale faults were classified into two groups: NE–SW trending reverse faults and NW–SE trending strike-slip faults. Members of both the groups showed movements largely perpendicular to the fold axes. The latter group consisted of sinistral and dextral faults. Accordingly, we interpreted that they were transfer faults activated during the folding. Consequently, mesoscale faults and flexural-slip faults evidence the map-scale plane strain of the Taishu Group in the plane perpendicular to the NE-trending fold axes. There were few transpressional deformations in the group. This is inconsistent with the transpression hypothesis for explaining the simultaneous folding and Japan Sea opening. Another hypothesis in which the folds in Tsushima are regarded as an onshore part of the Taiwan-Shinji fold belt is inconsistent with the timing of folding suggested by mining geologists to be consistent with and contemporaneous with this deformation. On the other hand, we found that dolerite dikes and sills were involved in the folding. Therefore, we conclude that the folding began during the late Early Miocene time and climaxed during the ore mineralization at around 15 Ma. We suggest that the folding in Tsushima was the easternmost manifestation of the compressional regime around the Yellow Sea and East China Sea in the Early to early Middle Miocene, and that the compression was brought about by the arrival of the Philippine Sea plate to initiate buoyant subduction under Kyushu.     

Concentrations of Trace Elements in Carbonate Reference Materials Coral JCp-1 and Giant Clam JCt-1 by Inductively Coupled Plasma-Mass Spectrometry

Trace elements in the Geological Survey of Japan carbonate reference materials Coral JCp-1 and Giant Clam JCt-1 were determined by inductively coupled plasma-mass spectrometry after digestion with 2% v/v HNO₃. A standard addition method was adopted in this determination in order to neutralise the Ca matrix effect. In addition, Sc, Y, In and Bi were used as internal standards to control the matrix effect and correct instrumental drift. Of the eighteen elements measured in JCp-1, precisions for fourteen elements, including Cu, Cd and Ba, were better than 10% RSD and concentrations ranged from 0.002 μg g^-1 (Cs) to 8.02 μg g^-1 (Ba). The concentrations of measured trace elements in JCt-1, except for Cu, were lower than those in JCp-1. Precisions for all elements with concentrations higher than 0.04 μg g^-1 in JCt-1 were also better than 10% RSD and concentrations were found to be between 0.001 μg g^-1 (Cs) and 4.84 μg g^-1 (Ba). The concentrations of more than fifteen trace elements in the aragonite reference materials are reported here for the first time. Both reference materials are suitable for use in geochemical studies of environmental reconstruction based upon biogenic carbonate materials.     

Differential Fractionation of Rare Earth Elements in Oxidized and Reduced Granitic Rocks: Implication for Heavy Rare Earth Enriched Ion Adsorption Mineralization

Ion adsorption rare earth element (REE) deposits in southern China are the exclusive source of heavy REEs (HREEs) in the world, and this HREE‐enriched character of the deposits is inherited from the REE compositions of the underlying granitic rocks. Such HREE‐enriched rocks form from heavy fractionation of reduced granitic magmas. We explore why reduced granitic magmas are enriched in HREEs during the fractionation, based on the REE geochemistry of granitic rocks and abundance of REEs in their constituent minerals in the southwestern Japan arc of Cretaceous to Paleogene age. The compilation of the whole rock geochemistry and REE compositions of the granitic rocks of the Sanin (oxidized), Sanyo (reduced) and Ryoke (reduced) belts in the southwestern Japan arc indicates that: (i) light REEs (LREEs) decease with fractionation of the granitoids in the Sanin belt but this trend is not clear in the granitoids in the Sanyo belt and LREEs rather increase in the Ryoke granitoids; (ii) Eu decreases with fractionation in all the belts; and (iii) HREEs slightly, but steadily decrease in the Sanin belt but enrich significantly in the Sanyo and Ryoke belts with fractionation. Analytical results of REE concentrations by scanning electron microscope with energy dispersive X‐ray spectroscope and laser ablation‐inductively coupled plasma mass spectrometer in the constituent minerals in a granodiorite sample from the Sanin belt show a moderate concentration of REEs in hornblende (577 ppm) in addition to high concentrations in allanite (~20 %), britholite (~30 %), primary titanite (8922 ppm), apatite (4062 ppm), and zircon (1693 ppm). Because primary titanite and allanite are commonly present in the oxidized granitoids but not in the reduced ones, the REE depletion in the fractionated, oxidized granites is attributed to the crystallization of these minerals. In contrast, scarcity of these minerals in the reduced granitoids enriches REEs, in particular HREEs in the fractionated magmas, which finally precipitate REEs in the granites and pegmatites. Both positive, but different correlation ratios between the Nb and Dy concentrations in the granitoids of the Sanin and Sanyo‐Ryoke belts suggest that columbite–pyrochlore‐group and fergusonite‐group minerals are the major HREE host in the oxidized and reduced granites, respectively.     

Functional roles of interzonal migrating mesozooplankton in the western subarctic Pacific

Grazing experiments and production estimation based on life-history analysis of Neocalanus copepods (N. cristatus, N. plumchrus and N. flemingeri) were carried out in the Oyashio region to understand the carbon flows associated with the interzonal migrating copepods. These copepods, and also Eucalanus bungii, fed on nano- and micro-sized organisms non-selectively throughout the season. However, diatoms were the dominant food resource until May and organisms, such as ciliates were the major resource after May. Daily growth rate was estimated from the Ikeda–Motoda, Huntley–Lopez and Hirst–Sheader models. Since the growth rates were considered to be overestimates for the Huntley–Lopez model and underestimates for the other two models, we applied the weight-specific growth rates previously reported for these species in the Bering Shelf. Surface biomass of Neocalanus increased rapidly in June during the appearance of C5, and a successive increase of overwintering stock was evident in the deeper layer. The deep biomass decreased gradually from September to May during the dormant and reproduction period. N. cristatus has the largest annual mean biomass (2.3 gC m⁻²), followed by N. plumchrus (1.1) and N. flemingeri (0.4). Daily production rate of Neocalanus varied from 0.4 to 363.4 mgC m⁻² day⁻¹, to which N. cristatus was the largest contributor. Annual production was estimated as 11.5 gC m⁻² year⁻¹ for N. cristatus, 5.7 for N. plumchrus and 2.1 for N. flemingeri, yielding annual P/B ratio of 5 for each species. The annual production of Neocalanus accounted for 13.2% of the primary production in the Oyashio region. Their fecal pellets were estimated to account for 14.9% (0.7 gC m⁻² year⁻¹) of sinking flux of organic carbon at 1000-m depth. Moreover, their export flux by ontogenetic vertical migration, which is not measured by sediment trap observations, is estimated to be 91.5% (4.3 gC m⁻² year⁻¹) of carbon flux of sinking particles at 1000-m depth. These results suggest the important role of interzonal migrating copepods in the export flux of carbon.