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81.
ZHANG Shuo FANG Xin ZHANG Junbo YIN Fang ZHANG Hu WU Lizhen KITAZAWA Daisuke 《中国海洋大学学报(英文版)》2020,19(1):232-240
Filter-feeding shellfish are common benthos and significantly affect the biogeochemical cycle in the shallow coastal ecosystems.Ark clam Scapharca subcrenata is one of the widely cultured bivalve species in many coastal areas owing to its tremendous economic value.However,there is little information regarding the effects of the bioturbation of S.subcrenata on the fluxes of nutrient exchange in the sediment-water interface(SWI).In this regard,S.subcrenata was sampled during October 2016 to determine the effects of its bioturbation activity on the nutrient exchange flux of the SWI.The results showed that the biological activity of S.subcrenata could increase the diffusion depth and the rate of the nutrients exchange in the sediments.The bioturbation of S.subcrenata could allow the nutrients to permeate into the surface sediments at 6-10cm and increase the release rate of nutrients at the SWI.The releasing fluxes of DIN and PO43−-P in the culture area were found to be around three times higher than that in the non-cultured region.The culture of S.subcrenata has been proved to be an important contributor to nutrient exchange across the SWI in the farming area of Haizhou Bay.Nutrients exchange in the SWI contributes a part of 86%DIN,71%PO43−-P and 18%SiO32−-Si for the aquaculture farm. 相似文献
82.
Mineral chemistry and petrogenesis of chromitites from the Khoy ophiolite complex,Northwestern Iran: Implications for aggregation of two ophiolites 下载免费PDF全文
Fatemeh Zaeimnia Ali Kananian Shoji Arai Mirsaleh Mirmohammadi Ali Imamalipour Mohamed Zaki Khedr Makoto Miura Khadidja Abbou‐Kebir 《Island Arc》2017,26(6)
The Khoy ophiolitic complex in Northwestern Iran is a part of the Tethyan ophiolite belt, and is divided into two sections: the Eastern ophiolite in Qeshlaq and Kalavanes (Jurassic–Cretaceous) and the Western ophiolite in Barajouk, Chuchak and Hessar (Late Cretaceous). Our chromitites can be clearly classified into two groups: high‐Al chromitites (Cr# = 0.38–0.44) from the Eastern ophiolite, and high‐Cr chromitites (Cr# = 0.54–0.72) from the Western ophiolite. The chromian spinels in high‐Al chromitite include primary mineral inclusions mainly as Na‐bearing diopside and pargasite with subordinate rutile and their formation was probably related to reaction between a MORB (mid‐ocean‐ridge basalt)‐like melt with depleted harzburgite, possibly in a back‐arc setting. Their host harzburgites contain clinopyroxene with higher contents of Al2O3, Na2O, Cr2O3, and TiO2 relative to Western harzburgites and are possibly residue after moderate partial melting (~15 %) whereas the Western harzburgite is residue after high partial melting (~25 %). The chromian spinel in the Western Khoy chromitites contains inclusions such as clinopyroxene, olivine and platinum group mineral‐bearing sulfides. These Western chromitites were possibly formed at two stages during arc growth and are divided into the moderately high‐Cr# chromitites (Barajouk and Hessar) and the high‐Cr# chromitites (Chuchak A and C). The former crystallized from island‐arc‐tholeiite (IAT) melts during reaction with the host depleted harzburgites, whereas the latter crystallized from boninitic melts (second stage melt) during reaction with highly depleted harzburgite in a supra‐subduction‐zone environment. Based on the mineral chemistry of chromian spinels, pyroxenes, and mineral inclusions, the chromitites and the host peridotites from the Eastern and Western Khoy ophiolites were formed in a back‐arc basin and arc‐related setting, respectively. The Khoy ophiolitic complex is a tectonic aggregate of the two different ophiolites formed in two different tectonic settings at different ages. 相似文献
83.
84.
Assessing the role of forests in mitigating eutrophication downstream of pasture during spring snowmelt 下载免费PDF全文
Masaaki Chiwa Sachiko Inoue Naoaki Tashiro Daisuke Ohgi Yoshitoshi Uehara Hideaki Shibata Atsushi Kume 《水文研究》2015,29(4):615-623
Little research has examined whether forests reduce stream water eutrophication in agricultural areas during spring snowmelt periods. This study evaluated the role of forests in ameliorating deteriorated stream water quality in agricultural areas, including pasture, during snowmelt periods. Temporal variation in stream water quality at a mixed land‐use basin (565 ha: pasture 13%, forestry 87%), northern Japan, was monitored for 7 years. Synoptic stream water sampling was also conducted at 16 sites across a wide range of forest and agricultural areas in a basin (18.3 km2) in spring, summer and fall. Atmospheric nitrogen (N) and phosphorus (P) deposition were measured for 4 years. The results showed that concentration pulses of nitrate, organic N and total P in stream water were observed when discharge increased during spring snowmelt. Their concentrations were high when silicate concentrations were low, suggesting surface water exported from pasture largely contributed to stream water pollution during snowmelt. Atmospheric N and P deposition (4.1 kg N ha?1 y?1; 0.09 kg P ha?1 y?1, respectively) was too low to affect the background concentrations of N and P in streams from forested areas. Reduction of eutrophication caused by nutrients from pasture was mainly due to dilution by water containing low concentrations of N and P exported from forested areas, whereas in‐stream reduction was not a dominant process. Results indicate that forests have a limited capacity to reduce the concentration pulses of N and P in stream water during snowmelt in this study basin. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
85.
The processes underlying the development of the Kuroshio large meanders that occurred in 1986 and 1989 are investigated using
a satellite SST data set and hydrographic data. In both processes visible on the satellite SST images, a round-shaped, lower
SST region with a diameter of about 200 km is found to the east of the Kuroshio small “trigger” meander (Solomon, 1978) until
the region became extinguished near theEnshu Nada. The lower SST region can be interpreted as an anti cyclonic eddy, mainly because of the existence of a warm water mass in
the subsurface layer of this region. The warm water mass is characterized by a constant temperature of 18–19°C, the maximum
thickness of which is about 400 m. The satellite images show that the eddy is closely related to the Kuroshio path transforming
into a shape like the letter “S”. This means that the eddy plays an important role in the development of the Kuroshio large
meander since this, too, tends to follow an “S”-shaped path. Added to this, the subsurface layer structure of the eddy is
similar to that of the warm water mass offShikoku. This similarity, together with the eddy behavior visible on the satellite SST images, implies that the examined eddy corresponds
to the warm water mass offShikoku. In other words, the warm water mass offShikoku can be advected near to theEnshu Nada when the Kuroshio large meander occurs. 相似文献
86.
We analyzed noble gases in nine individual chondrules, an assemblage of small chondrules, and four whole‐rock samples of the Allende CV3 chondrite. Major elements were also determined for five chondrules. The cosmic ray exposure ages are calculated from cosmogenic 3He to be 5.17 ± 0.38 and 5.15 ± 0.25 Myr for the averages of the chondrules and whole rocks, respectively, showing no significant pre‐exposure evidence for the studied chondrules. Large amounts of 36Ar, 80,82Kr, and 128Xe produced by neutron capture are observed in most samples; the abundances of these nuclides are correlated among the samples. The epithermal neutron flux and neutron slowing down density are calculated based on [80Kr]n, from which a sample depth of about 30 cm can be calculated. The measured chondrules contain variable amounts of radiogenic 129Xe. The abundance ratios of radiogenic 129Xe to neutron capture–produced 128Xe are rather constant among the studied chondrules; four chondrules give more precise ratios at the high‐temperature fractions, ranging from 1920 ± 80 to 2280 ± 140, which corresponds to a time difference of 3.9 ± 2.4 Myr. It is noticeable that most chondrules also contain 244Pu‐derived fission Xe. The average 244Pu/238U ratio for nine chondrules is 0.0069 ± 0.0018, which agrees well with the preferred ratio reported for chondrites. 相似文献
87.
88.
Yuki Shibazaki Eiji Ohtani Hiroshi Fukui Takeshi Sakai Seiji Kamada Daisuke Ishikawa Satoshi Tsutsui Alfred Q.R. Baron Naoya Nishitani Naohisa Hirao Kenichi Takemura 《Earth and Planetary Science Letters》2012
We have determined the density evolution of the sound velocity of dhcp-FeHx (x ≈ 1) up to 70 GPa at room temperature, by inelastic X-ray scattering and by X-ray diffraction. We find that the variation of VP with density is different for the ferromagnetic and nonmagnetic dhcp-FeHx, and that only nonmagnetic dhcp-FeHx follows Birch's law. Combining our results with Birch's law for iron and assuming an ideal two-component mixing model, we obtain an upper bound of the hydrogen content in the Earth's inner core, 0.23(6) wt.% H, corresponding to FeH0.13(3). The iron alloy with 0.23(6) wt.% H can satisfy the density, and compressional and shear sound velocities of the PREM inner core, assuming that there are no other light elements in the inner core. 相似文献
89.
Surface-correlated noble gases in lunar soils are primarily implanted SW (solar wind) noble gases. However, they also include apparently orphan radiogenic 40Ar, 129Xe, and 244Pu-derived fission Xe in excess of plausible primordial solar origin. These orphan radiogenic components are usually assigned a lunar origin, in a scenario in which radiogenic noble gases produced in the lunar interior were degassed into the transient atmosphere and then re-implanted to the lunar surface together with SW. There are some quantitative difficulties with this scenario, however, and it requires special constraints on the degassing history of the Moon that have not emerged from more general thermal history models. We therefore urge consideration of alternative hypotheses. As a possible source for the orphan radiogenic noble gases, we have examined planetary pollution of the Sun, as suggested by studies of extrasolar planetary systems (e.g., Murray et al., 2001, Astrophys. J. 555, 801-815; Israelian et al., 2001, Nature 411, 163-166). Pollution of the Sun by 2M⊕ (two Earth mass) planetary materials (Murray et al., 2001, Astrophys. J. 555, 801-815) is likely not significant for Ar but could be important to account for orphan Xe in the Moon. 相似文献
90.
N. Sugiura K. Hashizume Y. Miura K. Kiyota S. Zashu 《Meteoritics & planetary science》1995,30(6):646-653
Abstract— The isotopic disequilibrium of N molecules in meteorites was examined. For a large data-set, consisting of mass compositions of N molecules extracted at 1200 °C by stepped combustion of chondrites and eucrites, we find that a cosmogenic-N-enriched component and a normal air-like N component are isotopically disequilibrated with each other. The isotopic composition of the cosmogenic-N-enriched component seems to be variable, although the cause for the variation is not clear. The abundance of indigenous atomic N in silicate minerals seems to be small. Indigenous N in meteoritic silicates, if present, may be present in the form of N molecules. 相似文献