Seasonal change in CO2 and H2O exchange between grassland and atmosphere     

N. Saigusa  S. Liu  T. Oikawa  T. Watanabe 《Annales Geophysicae》1996,14(3):342-350

The seasonal change in CO₂ flux over an artificial grassland was analyzed from the ecological and meteorological point of view. This grassland contains C₃ and C₄ plants; the three dominant species belonging to the Gramineae; Festuca elatior (C₃) dominated in early spring, and Imperata cylindrica (C₄) and Andropogon virginicus (C₄) grew during early summer and became dominant in mid-summer. CO₂ flux was measured by the gradient method, and the routinely observed data for the surface-heat budget were used to analyze the CO₂ and H₂O exchange between the grassland and atmosphere. From August to October in 1993, CO₂ flux was reduced to around half under the same solar-radiation conditions, while H₂O flux decreased 20% during the same period. The monthly values of water use efficiency, i.e., ratio of CO₂ flux to H₂O flux decreased from 5.8 to 3.3 mg CO₂/g H₂O from August to October, the Bowen ratio increased from 0.20 to 0.30, and the ratio of the bulk latent heat transfer coefficient C_E to the sensible heat transfer coefficient C_H was maintained around 0.40-0.50. The increase in the Bowen ratio was explained by the decrease in air temperature from 22.3 °C in August to 16.6 °C in October without considering biological effects such as stomatal closure on the individual leaves. The nearly constant C_E/C_H ratios suggested that the contribution ratio of canopy resistance to aerodynamic resistance did not change markedly, although the meteorological conditions changed seasonally. The decrease in the water use efficiency, however, suggested that the photosynthetic rate decreased for individual leaves from August to October under the same radiation conditions. Diurnal variations of CO₂ exchange were simulated by the multi-layer canopy model taking into account the differences in the stomatal conductance and photosynthetic pathway between C₃ and C₄ plants. The results suggested that C₄ plants played a major role in the CO₂ exchange in August, the contribution of C₄ plants decreased in September, and daily variations of CO₂ exchange were mainly due to C₃ plants in October. The results also suggested that the decrease in the net canopy CO₂ exchange from August to October was induced partly by the decrease of net photosynthesis on the individual leaves in both C₄ and C₃ plants, which could be due to aging of the leaves.  相似文献   

Geochemical behaviour of iron and manganese ions in the Ningyo-Toge uranium deposit district, southwest Japan     

Koji Watanabe 《Chemical Geology》1987,60(1-4):299-307

The Ningyo-Toge uranium deposit is one of the typical sedimentary uranium deposits in Japan. In general, during weathering, U is removed from the basal granite through underground water. The underground water in this area is rich in U, and has a comparatively high concentration of Fe and Mn.

In this area, three types of Fe minerals can be recognized in different modes of occurrence: (1) in the oxide zone brownish Fe-hydroxide mineral with ferric ion, i.e. goethite (-FeOOH); (2) in the reduced zone of the mine gallery pale-blue Fe-hydroxide mineral with some ferrous ion, i.e. lepidocrocite (γ-FeOOH); and (3) Fe-sulphate minerals such as melanterite (FeSO₄·7H₂O), etc. Some uranyl sulphate minerals, uranopilite and zippeite, are closely associated with these Fe-sulphate minerals. Under weakly alkaline conditions of the oxidizing environment, Mn-hydroxide (MnOOH) coexists with goethite as alternative thin laminae with shale, or coprecipitates resembling a marine Mn nodule, in the size of 0.5 cm in diameter. Radioactive anomalies have been recognized frequently for these Mn sediments due to absorption of Ra by the sediments.  相似文献   

Fine-grained aggregates in L3 chondrites     

Seiko Watanabe  Masao Kitamura  Nobuo Morimoto 《Earth and Planetary Science Letters》1987,86(2-4)

The textures and chemical compositions of the constituent minerals of the fine-grained aggregates (FGA's) of L3 chondrites were studied by the backscattered electron image technique, electron probe microanalysis, and transmission electron microscopy. Plagioclase and glass in the interstices between fine grains of olivine and pyroxene indicate that the FGA's once partly melted. Compositional zoning and decomposition texture of pyroxenes are similar to those observed in chondrules, indicating a common cooling history of the FGA's and chondrules. Therefore, the mechanism that caused melting of the FGA's is considered to be the same as for chondrules. Bulk compositions of the FGA's are within the range of those of chondrules, so some chondrules probably were produced by complete melting of the same precursor materials as those of the FGA's. The precursor materials must have included fine olivine and other grains that probably are condensates.  相似文献   

Interpretation of the soft X-ray spectra from Hinotori     

K. Tanaka  N. Nitta  K. Akita  T. Watanabe 《Solar physics》1983,86(1-2):91-100

We present analyses of the soft X-ray iron line spectra of flares obtained from the Bragg Spectrometer on Hinotori. We first present a case of strong K emission at the impulsive phase of the hard X-ray burst, and assess net K emission due to the electron impact by eliminating the fluorescence contribution. Second we discuss on the differences in the electron temperatures and emission measures derived respectively from FeXXVI and FeXXV spectra. A pilot two-temperatures model which can explain the two spectra is presented. Finally, we compare the temporal relations between the soft X-ray and hard X-ray intensities and show two extreme classes of flares, one characterized by the efficient formation of a hot thermal plasma above 30 million degree, and the other characterized by the spiky hard X-ray component. Energetical relation of the thermal plasma to the electron beam is discussed for the two classes.  相似文献   

Direct measurement of conjugate photoelectrons and predawn 630 nm airglow     

G.G. Shepherd  J.F. Pieau  T. Ogawa  T. Tohmatsu  K. Oyama  Y. Watanabe 《Planetary and Space Science》1978,26(3):211-217

A sounding rocket was flown during the predawn on 17 January, 1976 from Uchinoura, Japan, to measure directly the behaviour of the conjugate photoelectrons at magnetically low latitudes. On board the rocket were an electron energy analyzer, 630 nm airglow photometer, and plasma probes to measure electron density and temperature. The incoming flux of the photoelectrons was measured in the altitude range between 210 and 340 km. The differential flux at the top of the atmosphere was determined to be $\text{F = (1.3 ± 0.4) × 10}{}^{11}\text{exp}\text{[?}\text{E(}\text{eV}\text{)}\text{12}\text{]}$ electron · m^?2 · sr^?1 · s^?1 in the energy range 10 ? E ? 50 eV. The emission rate of the 630 nm airglow was observed in the altitude range between 90 and 360 km. The apparent emission rate observed at 80 km was 32 ± 5 R. From a theoretical calculation of the optical excitation rate using the observed electron flux data along with a model distribution of atomic oxygen, it was estimated that more than 65% of the emission could be produced by direct impact of the photoelectrons with atomic oxygen in the thermosphere between 200 and 360 km. Using the observed electron density and the model distribution of oxygen molecules the residual of the emission was ascribed to the excitation of O(¹D) through dissociative recombination, $\text{O}{}_2{}^{\mathrm{+}}\text{+}\text{e}\text{→}\text{O}{}^1\text{+}\text{O}{}^7$. The direct collisional excitation by ambient electrons is estimated to be negligibly small at the level of observed electron temperature.  相似文献   

区域最小人均耕地面积与耕地资源调控   总被引：199，自引：7，他引：199  

蔡运龙  傅泽强  戴尔阜 《地理学报》2002,12(2):127-134

耕地资源对农业和国民经济可持续发展起着不可替代的基础性作用。中国人均耕地资源短缺，快速工业化、城市化进程对耕地的占用使耕地资源更趋紧张。目前的市场机制必然驱动耕地资源不断向获利更多的用途转移，最终会危急食物安全。因此，创新耕地资源利用与保护的调控机制已迫切之至。基于中国耕地资源流失原因及态势的分析，提出了最小人均耕地面积和耕地压力指数概念，并以此为基础提出了构建耕地资源利用和管理调控机制的思路。实际数据分析结果表明，以最小人均耕地面积和耕地压力指数作为耕地保护的基本标准，能因地制宜地兼顾食物安全和经济发展对土地的需求，具有显著的科学性和可操作性。  相似文献   

Characteristics of an atypical large-meander path of the Kuroshio current south of Japan formed in September 2017     

Nagano  Akira  Yamashita  Yusuke  Hasegawa  Takuya  Ariyoshi  Keisuke  Matsumoto  Hiroyuki  Shinohara  Masanao 《Marine Geophysical Researches》2019,40(4):525-539

Since September 2017, the Kuroshio has taken a large-meander (LM) path in the region south of Japan. We examined characteristics of the 2017–present LM path in comparison with previous LM paths, using tide gauge, altimetric sea surface height, and bottom pressure data. The 2017–present LM path was formed from a path passing through a channel south of Hachijo-jima Island, while a typical LM path originated from a path through a channel north of Miyake-jima Island. The meander trough of this atypical path was found to be shifted far to the east and to vary on a timescale of months. These characteristics are different from those of a typical LM path but they are similar to those of the 1981–1984 LM path. Therefore, we identified two types of LM path; a stable and unstable LM paths. The 2017–present unstable type large meander has a zonal scale greater than that of the 2004–2005 stable type large meander and protrudes from the eastern boundary of the Shikoku Basin, i.e., Izu-Ogasawara Ridge. No significant bottom pressure depression was observed, associated with the formation of the 2017–present LM path, indicating that baroclinic instability was not important in the formation of this LM path. Due to no significant bottom steering, even during the 2017–present LM period, a mesoscale current path disturbance occurred southeast of Kyushu, propagated eastward, and amplified the offshore displacement of the Kuroshio.

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Circulation patterns in the lower Arctic Ocean derived from geochemical data     

Motoyoshi Ikeda  Shinichi S. Tanaka  Yutaka W. Watanabe 《Journal of Oceanography》2018,74(5):453-470

Climatological water-mass structures were identified in the Arctic Ocean using the geochemical dataset in the Hydrochemical Atlas of the Arctic Ocean (HAAC) as well as data on a geochemically conserved parameter, PO₄*, based on phosphate and dissolved oxygen. In the upper ocean above a depth of 500 m, the HAAC was found to reliably depict the boundary between Pacific-Origin Water (P-Water) and Atlantic-Origin Water (A-Water), which is aligned 135°E–45°W near the surface but rotates counterclockwise with depth. Thus, the Arctic and Atlantic oceans exchange high-silicate P-Water and low-silicate A-Water. The PO₄* field in the lower ocean below a depth of 1500 m was analyzed statistically, and the results indicated that the Eurasian Basin receives low-PO₄* Nordic Seas Deep Water, which flows along the bottom from the Greenland Sea. The routes from the upper ocean to the lower ocean were determined. Only the southern portion of the Canada Basin, which receives water from the Chukchi and Beaufort Seas, has high PO₄* levels; the rest of the Amerasian Basin receives low-PO₄* water from the Laptev Sea and/or the Barents Sea. The Eurasian Basin receives moderate levels of PO₄* from the Fram Strait and from the intermediate layer. The intermediate-layer water gradually travels up from the lower ocean and returns to the Atlantic, entraining the subsurface portion. It is likely that high-PO₄* water occasionally flows down from the upper ocean along Greenland, making the Eurasian Basin heterogeneous.  相似文献   

Overview of NOPACCS (Northwest Pacific Carbon Cycle Study)     

Hiroyuki Tsubota  Joji Ishizaka  Akira Nishimura  Yutaka W. Watanabe 《Journal of Oceanography》1999,55(6):645-653

The Northwest Pacific Carbon Cycle Study (NOPACCS) was a program aimed at investigating the carbon cycle of the North Pacific Ocean, which can be thought of as a large reservoir of carbon dioxide. NOPACCS was also aimed at estimating the North Pacific's capacity as a carbon sink. Project design, scientific results, and data availability, and subsequent projects resulting from this project are also described in this review. Studies of the upper ocean processes focused on the latitudinal differences in the fugacity of carbon dioxide; and on the detail of plankton community structures. Intermediate water was studied in relation to the formation of North Pacific Intermediate Water and the amount of accumulated anthropogenic carbon. The sedimentation process, past carbon cycle and coral reefs were also studied during the project. A preliminary, overall view of the carbon cycle of the North Pacific was drawn from the results of the project and compared to global values.  相似文献   

U–Pb zircon geochronology of the North Pole Dome adamellite in the eastern Pilbara Craton          下载免费PDF全文

Hisashi Asanuma  Yusuke Sawaki  Shuhei Sakata  Hideyuki Obayashi  Kazue Suzuki  Kouki Kitajima  Takafumi Hirata  Shigenori Maruyama 《Island Arc》2018,27(4)

Supracrustal rocks around the North Pole Dome area, Western Australia, provide valuable information regarding early records of the evolution of crustal processes, surface environments, and biosphere. Owing to the occurrence of the oldest known microfossils, the successions at the North Pole Dome area have attracted interest from many researchers. The Paleoarchean successions (Warrawoona Group) mainly comprise mafic‐ultramafic greenstones with intercalated cherts and felsic lavas. Age constraints on the sediments have been mainly based on zircon U–Pb geochronology. However, many zircon grains have suffered from metamictization and contain anomalously high contents of common Pb, which makes interpretation of the U–Pb data complicated. In order to provide more convincing chronological constraints, an U–Pb Concordia age is widely accepted as the best estimate. Most zircons separated from two adamellites also suffered from severe metamictization. In our analyses, less metamictized domains were selected using a pre‐ablation technique in conjunction with elemental mapping, and then their U–Pb isotopic compositions were determined with a laser ablation inductively coupled plasma mass spectrometry. Most analyzed domains contained certain amounts of common Pb (²⁰⁴Pb/²⁰⁶Pb > 0.000 1), whereas three and five U–Pb data points with less common Pb (²⁰⁴Pb/²⁰⁶Pb < 0.000 1) were obtained. These U–Pb datasets yielded U–Pb Concordia ages of ca 3 445 Ma and 3 454 Ma, respectively. These ages represent the timing of the adamellite intrusion, and constrain the minimum depositional age of the Warrawoona Group. In addition, a single xenocrystic zircon grain showed a ²⁰⁷Pb/²⁰⁶Pb age of ca 3 545 Ma, supporting the idea that the sialic basement of the Pilbara Craton existed prior to 3 500 Ma. The in situ U–Pb zircon dating combined with the pre‐ablation technique has the potentials to identify non‐metamictized parts and to yield precise and accurate geochronological data even from partially metamictized zircons.  相似文献