Continuous measurement of methane flux over a larch forest using a relaxed eddy accumulation method   总被引：1，自引：0，他引：1  

Masahito Ueyama  Ken Hamotani  Wataru Nishimura  Yoshiyuki Takahashi  Nobuko Saigusa  Reiko Ide 《Theoretical and Applied Climatology》2012,109(3-4):461-472

We measured the methane flux of a forest canopy throughout a year using a relaxed eddy accumulation (REA) method. This sampling system was carefully validated against heat and CO₂ fluxes measured by the eddy covariance method. Although the sampling system was robust, there were large uncertainties in the measured methane fluxes because of the limited precision of the methane gas analyzer. Based on the spectral characteristics of signals from the methane analyzer and the diurnal variations in the standard deviation of the vertical wind velocity, we found the daytime and nighttime precision of half-hourly methane flux measurements to be approximately 1.2 and 0.7?μg?CH₄?m^?2?s^?1, respectively. Additional uncertainties caused by the dilution effect were estimated to affect the accuracy by as much as 0.21?μg?CH₄?m^?2?s^?1 on a half-hourly basis. Diurnal and seasonal variations were observed in the measured fluxes. The biological emission from plant leaves was not observed in our studies, and thus could be negligible at the canopy-scale exchange. The annual methane sink was 835?±?175?mg?CH₄?m^?2?year^?1 (8.35?kg?CH₄?ha^?1?year^?1), which was comparable to the flux range of 379–2,478?mg?CH₄?m^?2?year^?1 previously measured in other Japanese forest soils. This study indicated that the REA method could be a promising technique to measure canopy scale methane fluxes over forests, but further improvement of precision of the analyzer will be required.  相似文献   

A review of fossil rhinoceroses from the Neogene of Myanmar with description of new specimens from the Irrawaddy Sediments   总被引：1，自引：0，他引：1  

Zin-Maung-Maung-Thein  Masanaru Takai  Takehisa Tsubamoto  Naoko Egi  Thaung-Htike  Takeshi Nishimura  Maung-Maung  Zaw-Win 《Journal of Asian Earth Sciences》2010,37(2):11

Four genera and one indeterminate genus (total eight species) of fossil rhinoceroses (Mammalia; Perissodactyla; Rhinocerotidae) are recognized from the Neogene of central Myanmar. In the early Miocene, most area of central Myanmar were under the shallow marine condition, and no rhinocerotid remain has been documented yet. During the middle to late Miocene, the rhinocerotid remains are commonly found and are represented by “Diceratherium” naricum, Brachypotherium perimense, Brachypotherium fatehjangense and an indeterminate rhinocerotid. In the latest Miocene, these archaic rhinoceroses became extinct. In the late Neogene, the extant genera, Rhinoceros (late Miocene to Pleistocene) and Dicerorhinus (Plio-Pleistocene) first appeared in Myanmar. They appear to have dispersed to the Island Southeast Asia from the continental Asia during the early Pleistocene to middle Pleistocene when the eustatic sea level became low remarkably.  相似文献   

Crustal structure of northern Spitsbergen along the deep seismic transect between the Molloy Deep and Nordaustlandet   总被引：1，自引：0，他引：1  

Wojciech Czuba  Oliver Ritzmann  Yuichi Nishimura  Marek Grad  Rolf Mjelde  Aleksander Guterch  Wilfried Jokat 《Geophysical Journal International》2005,161(2):347-364

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Strong inhomogeneity beneath Quaternary volcanoes revealed from the peak delay analysis of S-wave seismograms of microearthquakes in northeastern Japan     

Tsutomu Takahashi  Haruo Sato  Takeshi Nishimura  Kazushige Obara 《Geophysical Journal International》2007,168(1):90-99

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The balloon observations of small cosmic X-ray bursts     

Y. Ogawara  M. Matsuoka  S. Miyamoto  N. Muranaka  J. Nishimura  M. Oda 《Astrophysics and Space Science》1976,42(1):211-216

In the record of the balloon observation which was performed on 27 September, 1970, a transient burst of X-rays was found. This event is concluded to be a cosmic gamma-ray burst of a smaller size or of a larger distance compared to the Vela bursts observed over the X-ray energy range. The energy spectrum is consistent with that of some of the Vela bursts. The time profile of the event is qualitatively similar to the 27 April, 1972 event studied by Apollo 16. The detection of small bursts over the X-ray energy range by the balloon observation during a period of the order of 10 to 100 h is not surprising considering a probable frequency-size distribution of the burst.Paper presented at the COSPAR Symposium on Fast Transients in X- and Gamma-Rays, held at Varna, Bulgaria, 29–31 May, 1975.  相似文献   

5β-isomers of stanols and stanones as potential markers of sedimentary organic quality and depositional paleoenvironments     

Mitsugu Nishimura 《Geochimica et cosmochimica acta》1982,46(3):423-432

Organic molecules originating only from the in situ diagenesis of biogenic molecules are ideal geochemical fossils which may provide information essential for the characterization and reconstruction of depositional environments and subsequent chemical reactions during diagenesis. It is proposed herein that this is the case for the 5β-isomers of stanols and stanones produced during stenol hydrogenation in young aquatic sediments, if shown to be essentially free of any major anthropogenic pollution (particularly, sewage). In order to clarify the environmental factors controlling the production of the 5β-steroidal isomers from stenols in recent aquatic sediments, attempts were made to relate the occurrence of 5β-stanols to various environmental parameters. Positive correlations between elevated concentrations of 5β-stanols and the degree of autochthonous contribution to sedimentary organic matter were consistently found in various surface aquatic sediments from a wide variety of depositional environments and also in older sediments extending even to the late Pleistocene. According to this finding, it was concluded that the primary factor controlling the conversion of stenols to 5β-stanols through 5β-stanones in anaerobic aquatic sediments is probably the relative contribution of autochthonous organic matter suitable for microbial metabolism (i.e. metabolizable organic matter) to the sediments. Consequently, it is proposed that the 5β-isomers of stanols and stanones, at least in immature aquatic (marine and non-marine) sediments, can serve as primary markers for defining the quality of sedimentary organic matter (viz. the relative contribution of metabolizable organic materials to sedimentary organic matter) and as indicators for the types and rates of microbiological activities responsible for early diagenesis of organic matter in anaerobic sediments. It is also suggested that the combination of the 5β-steroidal isomers with organic source parameters will allow these compounds to assist in indicating oxic or anoxic depositional environments.  相似文献   

Paleomagnetic evidence for clockwise rotation of the northern arm of Sulawesi,Indonesia     

Yo-ichiro Otofuji  Sadao Sasajima  Susumu Nishimura  Agus Dharma  Fred Hehuwat 《Earth and Planetary Science Letters》1981,54(2):272-280

Paleomagnetic results from the northern arm of Sulawesi show that the arm has been subjected to a clockwise rotation of more than 90° and that its rotational motion began no later than the middle Miocene. The mean direction showing a normal polarity at the Eocene to the early Miocene isD = 98.0° andI = 6.9°. A declination value ofD = 50.1° obtained from Miocene rocks indicates a transition stage of the rotational motion. The datum from Plio-Pleistocene volcanics isD = ?4.6° andI = ?9.3°. This suggests that the rotational motion terminated before the initiation of volcanic activity during the Plio-Pleistocene.  相似文献   

Crustal structure and transform margin development south of Svalbard based on ocean bottom seismometer data     

Asbjrn Johan Breivik  Rolf Mjelde  Paul Grogan  Hideki Shimamura  Yoshio Murai  Yuichi Nishimura 《Tectonophysics》2003,369(1-2):37-70

The Barents Sea is located in the northwestern corner of the Eurasian continent, where the crustal terrain was assembled in the Caledonian orogeny during Late Ordovician and Silurian times. The western Barents Sea margin developed primarily as a transform margin during the early Tertiary. In the northwestern part south of Svalbard, multichannel reflection seismic lines have poor resolution below the Permian sequence, and the early post-orogenic development is not well known here. In 1998, an ocean bottom seismometer (OBS) survey was collected southwest to southeast of the Svalbard archipelago. One profile was shot across the continental transform margin south of Svalbard, which is presented here. P-wave modeling of the OBS profile indicates a Caledonian suture in the continental basement south of Svalbard, also proposed previously based on a deep seismic reflection line coincident with the OBS profile. The suture zone is associated with a small crustal root and westward dipping mantle reflectivity, and it marks a boundary between two different crystalline basement terrains. The western terrain has low (6.2–6.45 km s⁻¹) P-wave velocities, while the eastern has higher (6.3–6.9 km s⁻¹) velocities. Gravity modeling agrees with this, as an increased density is needed in the eastern block. The S-wave data predict a quartz-rich lithology compatible with felsic gneiss to granite within and west of the suture zone, and an intermediate lithological composition to the east. A geological model assuming westward dipping Caledonian subduction and collision can explain the missing lower crust in the western block by subduction erosion of the lower crust, as well as the observed structuring. Due to the transform margin setting, the tectonic thinning of the continental block during opening of the Norwegian-Greenland Sea is restricted to the outer 35 km of the continental block, and the continent–ocean boundary (COB) can be located to within 5 km in our data. Distinct from the outer high commonly observed on transform margins, the upper part of the continental crust at the margin is dominated by two large, rotated down-faulted blocks with throws of 2–3 km on each fault, apparently formed during the transform margin development. Analysis of the gravity field shows that these faults probably merge to one single fault to the south of our profile, and that the downfaulting dominates the whole margin segment from Spitsbergen to Bjørnøya. South of Bjørnøya, the faulting leaves the continental margin to terminate as a graben 75 km south of the island. Adjacent to the continental margin, there is no clear oceanic layer 2 seismic signature. However, the top basement velocity of 6.55 km s⁻¹ is significantly lower than the high (7 km s⁻¹) velocity reported earlier from expanding spread profiles (ESPs), and we interpret the velocity structure of the oceanic crust to be a result of a development induced by the 7–8-km-thick sedimentary overburden.  相似文献   

Benzo(a)pyrene in the sediment of Osaka Bay and Keihin Canal and its estimated sources     

Yasushi Kawakami  Hajime Nishimura 《Journal of Oceanography》1976,32(4):175-181

Benzo(a)pyrene (BP) in the sediment of Osaka Bay were determined. High concentration was found at two stations near the mouth of Shin-Yodo and off Kobe respectively (0.98g g^–1 dry mud basis, 1.1g g^–1). The concentration decreases regularly from the mouth of the river further into the bay. The other supplemental determination was carried on the sediment and the seawater of Keihin Canal. Notable BP concentration of 89g g^–1 was observed in the sediment beneath the effluent outlet of a gasworks. The BP in the sediment near the ironworks was also considerable, while the BP was relatively less in the sediment beneath the effluent outlet of refineries. These data suggest that coke plants working in gasworks or ironworks may be the larger sources of BP than refineries. The results of Osaka Bay coincide with this hypothesis.Cadmium, lead, copper, zinc, nickel, ignition loss and fine sand content were measured from the same sediment samples of Osaka Bay. Cd, Pb, Cu and ignition loss showed the regular distributions which resemble to BP and accordingly, good correlations with BP. No significant correlations were found between BP and Ni, Zn and fine sand content which showed no regular distributions.  相似文献   

Calcium in the Antarctic Ocean     

Shizuo Tsunogai  Tadashige Yamazaki  Masakichi Nishimura 《Journal of Oceanography》1971,27(5):191-196

Calcium in sea water was determined of the samples taken from the Antarctic and Indian Oceans. Surface water commonly contains less calcium relative to chlorinity than does deep water. The tendency, however, is very faint in the Antarctic Ocean. In the surface waters, the Ca/Cl ratio is lower in the tropical and subtropical waters and the ratio well correlates with phosphate. The Ca/P ratio is calculated as 37 in atomic ratio. These may indicate that calcium is uptaken by organisms to make skeletal parts from surface water which is supersaturated with respect to calcite or aragonite. On the other hand, no definite correlationship between calcium and phosphate is found in subsurface water. This fact suggests that the regeneration process of calcium from organic debris is different from that of phosphate. The increase-rate of calcium in the abyssal water is estimated to be 0.18g at./(1 yr), which is due to the dissolution of calcium carbonate. The rate is about a half of total carbonate increase in the water.  相似文献