Temporal and Spatial Variability of Phytoplankton Pigment Concentrations in the Japan Sea Derived from CZCS Images

Temporal and spatial variability of phytoplankton pigment concentrations in the Japan Sea are described, using monthly mean composite images of the Coastal Zone Color Scanner (CZCS). In order to describe the seasonal changes of pigment concentration from the results of the empirical orthogonal function (EOF) analysis, we selected four areas in the south Japan Sea. The pigment concentrations in these areas show remarkable seasonal variations. Two annual blooms appear in spring and fall. The spring bloom starts in the Japan Sea in February and March, when critical depth (CRD) becomes equal to mixed layer depth (MLD). The spring bloom in the southern areas (April) occurs one month in advance of that in the northern areas (May). This indicates that the pigment concentrations in the southern areas may increase rapidly in comparison with the northern areas since the water temperature increases faster in spring in the southern than in the northern areas. The fall bloom appears first in the southwest region, then in the southeast and northeast regions, finally appearing in the northwest region. Fall bloom appears in November and December when MLD becomes equal to CRD. The fall bloom can be explained by deepening of MLD in the Japan Sea. The pigment concentrations in winter are higher than those in summer. The low pigment concentrations dominate in summer.     

Spatio-temporal streamflow generation in a small,steep headwater catchment in western Japan

Headwaters contribute a substantial part of the flow in river networks. However, spatial variations of streamflow generation processes in steep headwaters have not been well studied. In this study, we examined the spatio-temporal variation of streamflow generation processes in a steep 2.98-ha headwater catchment. The time when baseflow of the upstream section exceeded that downstream was coincident with the time when the riparian groundwater switched from downwelling to upwelling. This suggests that upwelling of the riparian groundwater increased considerably in the upstream section during the wet period, producing a shift in the relative size of baseflow between the upstream and downstream sections. The timing of fluctuations among hillslope soil moisture, hillslope groundwater and streamflow reveals that the hillslope contributed to storm flow, but this contribution was limited to the wet period. Overall, these results suggest that streamflow generation has strong spatial variations, even in small, steep headwater catchments.

EDITOR A. Castellarin ASSOCIATE EDITOR X. Chen     

Canopy conductance in a two‐storey Siberian boreal larch forest,Russia

A larch forest in eastern Siberia was characterized by the presence of two distinct storeys, the overstorey with a small leaf area index (LAI) and a dense understorey with a relatively large LAI. To understand the roles of the overstorey and understorey in forest–atmosphere water exchange, canopy conductance (G_c), a critical parameter used in determining the energy and mass exchange, was calculated on the basis of latent heat flux above the overstorey and understorey, measured separately. Results showed that G_c for the overstorey (G_co) and understorey (G_cu) experienced different seasonal fluctuations. G_co was smaller than G_cu during periods of leaf expansion and leaf fall and showed an increasing trend until 1 month after the onset of leaf expansion. In contrast, a sharp decrease in G_co was observed immediately before onset of leaf fall. Furthermore, G_co was slightly larger than G_cu during the fully foliated period. A simple model using solar radiation and vapour pressure deficit (D) as inputs successfully reproduced the G_c in fully foliated periods with acceptable accuracy. Furthermore, both the understorey and overstorey in this study have a large reference G_c (G_c at D = 1 KPa) than their counterparts of other boreal forests and would not be able to sustain a constant leaf–soil water potential difference as D increases. We speculated that this confers the forest with an advantage allowing it to be able to sustain carbon assimilation during large D days and thus provides for the survival of the ecosystem during the short growing season at this site. Copyright © 2014 John Wiley & Sons, Ltd.     

Distribution of Changjiang Diluted Water detected by satellite chlorophyll-a and its interannual variation during 1998–2007

Sea-viewing Wide Field-of-view Sensor (SeaWiFS) chlorophyll-a distribution in summer in the East China Sea during 1998–2007 was analyzed. Statistical analysis with K-means clustering technique allowed us to define the proper satellite chlorophyll-a concentration indicating the Changjiang Diluted Water (CDW). The spatial distributions of the higher satellite chlorophyll-a concentrations (>0.48 mg m⁻³) corresponded well with the distributions of lower salinity CDW (<30–32) every year. Interannual variation of the CDW area, indicated by the high satellite chlorophyll-a, correlated with the interannual variation of the Changjiang summer freshwater discharge. The correlation analysis indicated that the CDW spread eastward in the East China Sea with a time lag of 1 to 2 months after the discharge.     

Hydrogeological and ground-water resource analysis using a geotechnical database

An application of a geotechnical database system for primary evaluation of ground-water resources in a sedimentary basin is proposed. The database consists of 1200 borehole logs including geologic columns,in situ test results, ground-water level, water quality data, and resistivity logs. The Kumamoto plain, situated in southwest Japan, is chosen as a study area. The evaluation process consists of two steps: (1) modeling of shapes of water-bearing strata, and (2) modeling of distribution of physical quantity which has some relationship with the porosity of those strata. In step (1), the shapes of upper and/or lower surface of the pyroclastic flow deposits and the andesitic lava were determined, whereas the three-dimensional distribution model of resistivity was constructed from resistivity logging data obtained from 100 boreholes and using the proposed interpolation method in the step (2). An empirical equation between the porosity and the resistivity of the lava was also identified. The integration of two types of model and the empirical equation contributed to an estimate of the total volume of the ground-water under the study area.     

Rb-Sr dating for the Jiaodong gneiss of the Su-Lu ultra-high pressure province, eastern China

Abstract Gneiss samples were collected from the Shandong Peninsula, eastern China, in order to carry out Rb-Sr dating using whole rock powder and biotite mineral separates. Middle Proterozoic whole rock age (1808 ± 71 Ma) and Middle to Late Proterozoic biotite ages (1312 and 729 Ma) were obtained for country gneisses in the northwestern part of the peninsula. Late Proterozoic whole rock age (707 ± 61 Ma) and Mesozoic biotite ages (172 and 222 Ma) were obtained for orthogneisses in the southeastern part of the peninsula. These new age data, as well as recent petrological results and published radiometric data, support the subdivision of the Shandong Peninsula into two geological districts: (i) a northwestern area of Proterozoic age represented by a low- and middle-pressure metamorphic sequence belonging to the Sino-Korean craton; and (ii) a southeastern area of Late Proterozoic and Mesozoic age accompanied by ultra-high pressure eclogite.     

Modeling of spring bloom in the western subarctic Pacific (off Japan) with observed vertical density structure

Effects of vertical stability on spring blooms of phytoplankton were investigated for the western subarctic Pacific ocean using a one-dimensional (depth) ecosystem model. In the model, vertical stability was expressed by diffusion constants calculated from observed density distribution. Dynamics of phytoplankton in blooms was calculated by the model using the vertical diffusion. Then, the calculated results were compared with the Coastal Zone Color Scanner (CZCS) data. The comparison shows that the shallow surface mixed layer causes early start days of spring blooms at inshore (northern) stations. In addition, spring blooms continue long at inshore (northern) stations since a water column has weak stability. This is because weak stability of a water column causes large nutrient supply from a deep layer and large diffusive transport of phytoplankton biomass from the subsurface maximum.     

Batch fractionation model for the evolution of volcanic rocks in an island arc: an example from Central Japan

Analyses of fifty-one rock samples from three stratovolcanoes in Central Japan revealed that K and Rb contents vary in a saw-toothed fashion with the growth of these volcanoes. Peaks and valleys of the saw-toothed variation pattern of Rb (and also K) increase at first and then gradually converge on constant values. This variation trend is also shown by the Rb/Sr ratio. The convergent Rb/Sr ratio (0.23–0.24) at the peaks coincides with recent estimates of the average value for continental crust. These geochemical features are well explained by the batch fractionation model. In this model, the magma reservoir lying at the top of the mantle is periodically supplied with a batch of parental magma, while the magma in it undergoes continuous crystallization and the cumulate is continuously removed by the divergent movement of the mantle. This model, working under physical conditions in the crust-mantle structure of an island arc, not only accounts for the above geochemical features, but also gives insight into the genesis of the calc-alkaline rock series and of the continental crust.