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Contribution of slab-fluid in arc magmas beneath the Japan arcs 总被引：5，自引：0，他引：5
Identifying the amount and composition of slab-derived fluid and its spatial variation is key to quantifying fluid processes in subduction zones. Based on the isotopic systematics of arc lavas, we found regional variations over the Japan arcs in terms of the amount and composition of slab-derived fluid added to the melting source region. The average amounts of slab-derived fluid differ among the arcs: 2.6 wt.% for Central Japan, 0.69 wt.% for Ryukyu, 0.17 wt.% for NE Japan, and 0.12 wt.% for both Kurile and Izu–Bonin. These differences may be attributed to the arc setting (oceanic or continental) and the geometry of the slabs. Contribution of sediment involved in the slab-derived fluid is dominant in NE Japan compared to the Izu–Bonin and Central Japan arcs. This could be attributed to mechanical features such as fractures near the subducting plate surface, in addition to the arc setting and the slab geometry. Therefore, the amount and composition of slab-derived fluid are thought to be controlled not only by the thermal conditions, but also by the tectonic and mechanical features around the subduction zone. On top of the variability of slab-derived fluid, the mantle wedge shows the regional variation in terms of proportion of the Pacific-type and Indian-type MORB-source mantle components, which also contributes to the compositional variations of arc magmas. 相似文献
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Dynamics of microphytobenthic biomass in a coastal area of western Seto Inland Sea, Japan 总被引：2，自引：0，他引：2
Hitomi Yamaguchi Shigeru Montani Hiroaki Tsutsumi Ken-ichiro Hamada Naoko Ueda Kuninao Tada 《Estuarine, Coastal and Shelf Science》2007,75(4):423-432
This study focused on the causes of the variation in microphytobenthic biomass and the effects of this variation on macrobenthic animals in the western Seto Inland Sea, Japan, where the importance of microphytobenthos as the primary food source for benthic animals has been recently reported. We investigated the microphytobenthic biomass together with light attenuation of seawater, phytoplanktonic biomass, macrobenthic density and biomass at eight stations (water depth = 5–15 m) during four cruises in 1999–2000. The increased light attenuation coefficient of the water column associated with increased concentration of the phytoplanktonic Chl-a caused a decrease in light flux that reached the seafloor. The biomass of the microphytobenthos within the upper 1 cm of the sediment, 1.9–46.5 mg Chl-a m−2, was inversely correlated with the phytoplanktonic biomass in the overlying water column, 10.9–65.0 mg Chl-a m−2. Thus, interception of light by phytoplankton is considered to be a main cause of the variation in the microphytobenthic biomass. The microphytobenthos biomass showed a significant positive correlation with the macrobenthic density (78–9369 ind. m−2) and biomass (0.4–78.8 gWW m−2). It appears that the increase in oxygen production by the microphytobenthos allowed macrobenthic animals to become more abundant, as a consequence of oxygenation of the organically enriched muddy sediments (14.5 ± 2.69 mg TOC g−1). This study suggests that the variation in the microphytobenthic biomass is influenced by the phytoplanktonic biomass due to shading effect, and the balance between these two functional groups might affect the variability in the macrobenthic density and biomass. 相似文献
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In order to examine the seasonal and spatial distributions of benthic animals in the intertidal mudflat of the southern Yellow River Delta,field investigations were carried out in 2007 and 2008 and multiple methods were applied.Results showed that,the biomass of macro benthos ranged at 0.75-1151.00 g wet m~(-2) and averaged at 156.31 g wet m~(-2),in which Mactra veneriformis accounted for 75.6%-93.4% of the total macro benthic biomass.More than 90% of macro benthos inhabited in the middle and low tide lines,and higher biomass occurred in early summer and lower in winter.Statistical analysis showed that:1)M.veneriformis growth was primarily favored at higher temperature and lower salinity;2)after long time interaction,benthic bivalve grazers led to patching distributions of Chlorophyll a(Chl a);3)macro benthic biomass positively related with Chl a when the concentration of Chl a was low,but they were negatively related when Chl a concentration was high;and 4)furthermore,the biomass of benthic bivalves peaked in the sediment with median grain size about 0.55 mm,but decreased gradually in coarse or fine sediments.The secondary productivity ranged at 0.37-283.68 g m~(-2)yr~(-1) and averaged at 47.88 g m~(-2) yr~(-1),in which 69.7% was contributed by M.veneriformis It was estimated that primary production was transformed to secondary production at a rate of 6.87%approximately,which implies that there is a local sustainability of high bivalve production. 相似文献
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Abstract— The howardite‐eucrite‐diogenite (HED) clan is a group of meteorites that probably originate from the asteroid Vesta. Some of them are complex breccias that contain impact glasses whose compositions mirror that of their source regions. Some K‐rich impact glasses (up to 2 wt% K2O) suggest that in addition to basalts and ultramafic cumulates, K‐rich rocks are exposed on Vesta's surface. One K‐rich glass (up to 6 wt% K2O), with a felsic composition, provides the first evidence of highly differentiated K‐rich rocks on a large asteroid. They can be compared to the rare lunar granites and suggest that magmas generated in a large asteroid are more diverse than previously thought. 相似文献
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A one-dimensional, steady-state model has been developed to understand the factors controlling vertical distributions of nutrients
such as nitrate and phosphate in the western North Pacific water columns. The model includes simple physics and some biogeochemical
processes. Nutrients are supplied by upwelling of nutrient-rich deep waters with a constant upwelling velocity and nutrient
regeneration due to decomposition of sinking particulate matter; the latter is expressed by an exponential-type export flux.
Nutrients are consumed in the water column due to uptake by marine organisms, represented by a first-order substrate kinetics.
The consumption rate constant is given as an exponential function of depth. The model has been applied to a data set of WOCE
(World Ocean Circulation Experiment) P9 one-time measurements observed in the western North Pacific. The calculated curves
fit well to observed vertical nutrient profiles from 100 m depth to over 2,500 m depth at 35 stations from 19°N to 33°30′
N along 137°E with correlation factors of greater than 0.998. A modified model, including a correction term representing a
depth-dependent upwelling velocity, can reproduce observed vertical nutrient profiles at 32 stations from 5°N to 18°30′ N
along 137°E with correlation factors greater than 0.993. The results support the hypothesis that most of the vertical nutrient
profiles in the western North Pacific are controlled by particle export flux, consumption rate, remineralization rate and
upwelling velocity.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
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Determinations of Chlorophyll a (Chl a) in eutrophic coastal marine waters were compared using N, N-dimethylformamide (DMF) and 90% acetone techniques. Measured
Chl a concentrations ranged from 0.89 to 10.65 μg l−1 for 90% acetone extracts and from 0.97 to 12.92 μg l−1 for DMF extracts, respectively, for 24 surface water samples from the Harima-nada, Seto Inland Sea, Japan. Chl a concentrations using DMF as a solvent were consistently higher than those found using 90% acetone (p < 0.001, n= 24). Chl a is thus likely to be underestimated (by 13%) when 90% acetone is used for eutrophic waters.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
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Takashi Midorikawa Sonoki Iwano Kazuhiro Saito Hiroyuki Takano Hitomi Kamiya Masao Ishii Hisayuki Y. Inoue 《Journal of Oceanography》2003,59(6):871-882
We observed the partial pressure of oceanic CO2, pCO2
sea, and related surface properties in the westernmost region of the subarctic North Pacific, seasonally from 1998 to 2001. The
pCO2
sea in the Oyashio region showed a large decrease from winter to spring. In winter, pCO2
sea was higher than 400 μatm in the Oyashio region and this region was a source of atmospheric CO2. In spring, pCO2
sea decreased to extremely low values, less than 200 μatm (minimum, 139 μatm in 2001), around the Oyashio region with low surface
salinity and this region turned out to be a strong sink. The spatial variations of pCO2
sea were especially large in spring in this region. The typical Oyashio water with minimal mixing with subtropical warm water
was extracted based on the criterion of potential alkalinity. The contribution of main oceanic processes to the changes in
pCO2
sea from winter to spring was estimated from the changes in the concentrations of dissolved inorganic carbon and nutrients, total
alkalinity, temperature and salinity observed in surface waters in respective years. These quantifications indicated that
photosynthesis made the largest contribution to the observed pCO2
sea decreases in all years and its magnitude was variable year by year. These year-to-year differences in spring biological contribution
could be linked to those in the development of the density stratification due to the decrease in surface salinity. Thus, the
changes in the surface physical structure could induce those in pCO2
sea in the Oyashio region in spring. Furthermore, it is suggested that the direction and magnitude of the air-sea CO2 flux during this season could be controlled significantly by the onset time of the spring bloom.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献