Accelerated continental-scale snowmelt and ecohydrological impacts in the four largest Siberian river basins in response to spring warming     

Kazuyoshi Suzuki  Tetsuya Hiyama  Koji Matsuo  Kazuhito Ichii  Yoshihiro Iijima  Dai Yamazaki 《水文研究》2020,34(19):3867-3881

River runoff from the four largest Siberian river basins (the Ob, Yenisei, Lena, and Kolyma) considerably contributes to freshwater flux into the Arctic Ocean from the Eurasian continent. However, the effects of variation in snow cover fraction on the ecohydrological variations in these basins are not well understood. In this study, we analysed the spatiotemporal variability of the maximum snow cover fraction (SCF_max) in the four Siberian river basins. We compared the SCF_max from 2000 to 2016 with data in terms of monthly temperature and precipitation, night-time surface temperatures, the terrestrial water storage anomaly (TWSA), the normalised difference vegetation index (NDVI), and river runoff. Our results exhibit a decreasing trend in the April SCF_max values since 2000, largely in response to warming air temperatures in April. We identified snowmelt water as the dominant control on the observed increase in the runoff contribution in May across all four Siberian river basins. In addition, we detected that the interannual river runoff was predominantly controlled by interannual variations in the TWSA. The NDVI in June was strongly controlled by the timing of the snowmelt along with the surface air temperature and TWSA in June. The rate of increase in the freshwater flux from the four Siberian rivers decreased from 2000 to 2016, exhibiting large interannual variations corresponding to interannual variations in the TWSA. However, we identified a clear increase trend in the freshwater flux of ~4 km³/year when analysing the long-term 39-year historical record (1978–2016). Our results suggest that continued global warming will accelerate the transition towards the earlier timing of snowmelt and spring freshwater flux into the Arctic Ocean. Our findings also highlight the effects of earlier snowmelt on ecohydrological changes in the Northern Hemisphere.  相似文献   

The role of crabs (Macrophthalmus japonicus) burrows on organic carbon cycle in estuarine tidal flat,Japan     

Sosuke Otani  Yasunori Kozuki  Ryoichi Yamanaka  Hiromitsu Sasaoka  Tetsu Ishiyama  Yoshihito Okitsu  Hajime Sakai  Yoji Fujiki 《Estuarine, Coastal and Shelf Science》2010,86(3):434-440

The objective of this study is to elucidate the burrow structure and to clarify the role of burrows in material cycle in the tidal flat. In our work, we focused on the dominant species in muddy tidal flat, crab Macrophthalmus japonicus.Burrow structure of Macrophthalmus japonicus was investigated on a Katsuura river tidal flat in Tokushima prefecture, Japan, using in situ resin casting. Sampling was conducted in August 2006, and a total of 48 burrow casts were obtained. Burrows consisted mainly of J-shaped structures (98%) while the rest belonged to U-shaped structures (2%). The maximum measured burrow volume was 120 cm³ and wall surface area was 224 cm², while maximum burrow length and depth were 23.2 cm and 16.5 cm, respectively. Burrow volume and surface area were strongly correlated with carapace width of M. japonicus. Investigation of the individual number of M. japonicus in 13 quadrats (50 × 50 × 20 cm) was conducted using 2 mm sieve. The number of M. japonicus was 15–31 ind./m². Using cohort analysis we estimated that surface area of burrows was 0.07–0.15 m²/m².CO₂ emission rate was measured at the surface sediment during the period from June to December 2008. Results varied from 13.8 ± 2.2 to 49.4 ± 3.2 mg CO₂/m²/h, and organic carbon decomposition was 3.8 ± 0.6–13.5 ± 0.9 mg C/m²/h. This leads the increase of organic carbon decomposition by 1.1 times, because of the expansion of the tidal flat surface area by burrowing activity. Organic carbon decomposition in burrow walls therefore contributed to organic matter decomposition in the tidal flat. These results indicated that in situ activities of Macrophthalmus japonicus significantly influence the material cycle and it is important to consider the existence of burrow in order to understand the fluxes of materials and to evaluate the purification function of the tidal flat.  相似文献   

Seasonal and inter-annual changes of volume density of martian CO₂ snow from time-variable elevation and gravity     

Koji Matsuo 《Icarus》2009,202(1):90-578

The martian atmosphere seasonally exchanges CO₂ with the surface by repeating condensation and sublimation, causing seasonal growth and decay of the polar CO₂ snowcaps. These processes leave two kinds of geodetic signatures, i.e. seasonal changes of the martian gravity field and of surface elevation of the snow-covered regions. Here we study gradual increase of the volume density of the martian snow due to compaction, by combining these two data sets during 1999-2001 covering three martian winters. We found that light fresh snow of slowly becomes denser reaching or more immediately before it thaws. The maximum snow density varies slightly from year to year, and between hemispheres. In the second southern winter, the density became as high as . This might have been caused by a dust storm activity, e.g. increased mixing of silicate particles and/or enhancement of sintering.  相似文献   

Aerodynamic Parameters of Regular Arrays of Rectangular Blocks with Various Geometries   总被引：8，自引：8，他引：0  

Aya Hagishima  Jun Tanimoto  Koji Nagayama  Sho Meno 《Boundary-Layer Meteorology》2009,132(2):315-337

The aerodynamic effects of various configurations of an urban array were investigated in a wind-tunnel experiment. Three aerodynamic parameters characterising arrays—the drag coefficient (C _d ), roughness length (z _o) and displacement height (d)—are used for analysis. C _d is based on the direct measurement of the total surface shear using a floating element, and the other two parameters are estimated by logarithmic fitting of the measured wind profile and predetermined total drag force. The configurations of 63 arrays used for measurement were designed to estimate the effects of layout, wind direction and the height variability of the blocks on these parameters for various roughness packing densities. The results are summarised as follows: (1) The estimated C _d and z _o of the staggered arrays peak against the plan area index (λ _p ) and frontal area index (λ _f ), in contrast with values for the square arrays, which are less sensitive to λ _p and λ _f . In addition, the square arrays with a wind direction of 45° have a considerably larger C _d , and the wind direction increases z _o/H by up to a factor of 2. (2) The effect of the non-uniformity of roughness height on z _o is more remarkable when λ _f exceeds 20%, and the discrepancy in z _o is particularly remarkable and exceeds 200%. (3) The effect of the layout of tall blocks on C _d is stronger than that of short blocks. These results indicate that the effects of both wind direction and the non-uniformity of the heights of buildings on urban aerodynamic parameters vary greatly with λ _p and λ _f ; hence, these effects should be taken into account by considering the roughness packing density.  相似文献   

Erratum to: Estimation of Heat Flux through the Eastern Bering Strait     

Kohei Mizobata  Koji Shimada  Sei-ichi Saitoh  Jia Wang 《Journal of Oceanography》2010,66(6):885-885

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A trial for monitoring temporal variation of seismic velocity using an ACROSS system   总被引：4，自引：0，他引：4  

Koshun Yamaoka  Takahiro Kunitomo  Koji Miyakawa  Kazunori Kobayashi  Mineo Kumazawa 《Island Arc》2001,10(3-4):336-347

Abstract The temporal variation of seismic velocity near the Nojima Fault, which ruptured during the 1995 Kobe earthquake (Hyogo-ken Nanbu earthquake), was detected using an accurately controlled routine-operated seismic source (ACROSS). The source generates elastic waves by a centrifugal force of an eccentric mass rotating around an axis. The mass is driven with an AC servomotor whose angular position is accurately controlled with reference to a very accurate global positioning system (GPS) clock. The error of the mass' position is less than 0.002 radian and does not accumulate. As a result, the source generates sinusoidal waves of very narrow spectral peaks enabling their detection with an excellent signal-to-noise ratio. Although the stability of the rotation is quite excellent, a large daily variation was found, which seems to be caused by changes in atmospheric temperature. The daily variation was 10% in amplitude and 0.1 radian in phase of the signal observed at the 800 m borehole seismometer. A significant variation was found to be due to that of coupling between the rotational source and the foundation made of reinforced concrete in which the source was situated. In order to make a correction on the signal of the 800 m borehole seismometer, the vibration of the foundation was measured and modeled assuming a rigid body movement. The correction successfully reduced the daily variation by approximately 90%, resulting in a variation of 1% in amplitude and 0.01 radian in phase. The phase variation of 0.01 radian corresponds to 100 μs and less than 0.1% in velocity over 1000 m between the source and the receiver.  相似文献   

The precambrian evolution of South America     

Umberto G. Cordani  Gilberto Amaral  Koji Kawashita 《International Journal of Earth Sciences》1973,62(2):309-317

Zusammenfassung Mit Hilfe von ca. 1500 radiometrischen Zeitmessungen wird eine Synthese der prÄkambrischen Entwicklung Südamerikas aufgestellt. In Abb. 1 wird versucht, die Lage der spÄtprÄkambrischen orogenen Gürtel sowie ihre Plattformen darzustellen.Der grö\te alte Kern des Kontinents umfa\t den Guyana-Schild, das Basement des Amazonas-Sedimentbeckens und den Guaporé-Kraton im Süden, einen Raum von ungefÄhr 4,5 Mio. qkm. Die meisten Gesteine wurden von dem transamazonischen orogenen Zyklus erfa\t, dessen radiometrisches Alter etwa 2000 M. J. betrÄgt. Der etwa gleichaltrige SÃo-Francisco-Kraton in Ostbrasilien umfa\t ungefÄhr 1 Mio. qkm. Kleinere Kerne, die ebenfalls die Ereignisse des transamazonischen Zyklus' widerspiegeln, wurden nahe der Atlantikküste, östlich der Mündung des Amazonasflusses (SÃo-Luis-Kraton-Gebiet) und in der Umgebung des La-Plata-Flusses (Rio de la Plata-Kraton-Gebiet) gefunden.Die Kratone sind getrennt durch metamorphe Gürtel, die zum brasilianischen orogenen Zyklus spÄtprÄkambrischen Alters gehören. Der Caririan-Gürtel und die Sergipe-Geosynklinale liegen in der Nordostecke von Brasilien, und der Ribeira-Gürtel erstreckt sich entlang der Atlantikküste im Süden. Zwei symmetrische geosynklinale Einheiten wurden im zentralen Teil des Kontinents erkannt: der Brasilia- und der Paraguay-Araguaia-Gürtel.In den brasilianischen orogenen Gürteln treten an vielen Stellen transamazonische oder sogar Ältere Serien auf, Anzeichen für aufgearbeitetes altes Basement. Dies scheint zu zeigen, da\ die Sialkruste des südamerikanischen Kontinents vor 2000 M. J. schon eine rÄumliche Ausdehnung von mehr als 10 Mio. qkm hatte.

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A general synthesis of the precambrian evolution of South America has been made with the aid of about 1500 radiometric age determinations. In Fig. 1, the position of the late precambrian orogenic belts, as well as their platforms, is tentatively outlined.The largest ancient core of the continent includes the Guyana Shield, the basement of the Amazon sedimentary basin, and the Guaporé craton, to the south, covering an area of about 4.5 million square kilometers. Most of the rocks were affected by the Trans-Amazonian orogenic cycle, whose radiometric ages are close to 2000 m. y. The SÃo Francisco craton of similar age outcrops over an area of about one million square kilometers, in eastern Brazil. Smaller ancient nucleii, also reflecting the events of the Tranz-Amazonian cycle, were found near the Atlantic coast, east of the mouth of the Amazon river (SÃo Luis cratonic area), and surrounding the La Plata river (Rio de la Plata cratonic area).The old cratonic areas are separated from each other by metamorphic belts which belong to the Brazilian orogenic cycle of late precambrian age. The Caririan belt, and the Sergipe geosyncline, occur at the northeastern corner of Brazil, and the Ribeira belt along the Atlantic coast, to the south. Two symmetrical geosynclinal units were recognized in the central part of the continent: the Brasilia and the Paraguay-Araguaia belts.Within the areas of the Brazilian orogenic belts, in many places Trans-Amazonian or even older ages occur, indicating remobilized ancient basement. This seems to demonstrate that the sialic crust of the South American continent, 2000 m. y. ago, already exhibited an areal extent of more than 10 million square kilometers.

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Résumé Une synthèse générale de l'évolution précambrienne de l'Amérique du Sud a été faite à l'aide de 1500 déterminations d'âge radiométrique. La fig. 1 présente un essai sur la répartition des zones orogéniques du Précambrien supérieur et de leurs platesformes.Le noyau ancien du continent, qui est le plus vaste, comprend le bouclier de la Guyane, le socle du bassin sédimentaire de l'Amazone et le Craton de Guaporé, au Sud, couvrant une aire d'environ 4,5 millions de Km². La plupart des roches ont été affectées par le cycle orogénique Trans-Amazonien dont l'âge radiométrique est d'environ 2000 millions. Le craton de SÃo Francisco d'âge semblable, affleure sur une étendue d'environ 1 million de Km², dans l'Est du Brésil. Des noyaux anciens plus petits, affectés également par le cycle Trans-Amazonien, ont été trouvés près de la cÔte Atlantique, à l'Est de l'embouchure de l'Amazone (région cratonique de SÃo Luis), et aux environs du fleuve la Plata (région cratonique du Rio de la Plata).Les régions cratoniques anciennes sont séparées les unes des autres par des zones métamorphiques appartenant au cycle orogénique brésilien, d'âge Précambrien supérieur. La zone caririenne et le géosynclinal de Sergipe affleurent dans l'extrémité NE du Brésil, et la zone de Ribeira, le long de la cÔte Atlantique au S. Deux unités géosynclinales symétriques ont été reconnues dans la partie centrale du continent: les zones de Brasilia et de Paraguay-Araguaia.Dans les régions occupées par les ceintures orogéniques Brésiliennes, il existe en beaucoup d'endroits des roches d'âge Trans-Amazonien et mÊme plus ancien, indices d'un socle ancien remobilisé. Ceci semble démontrer que la croûte sialique du continent Sud Américain montrait déjà, il y a environ 2000 millions d'années, une étendue de plus de 10 millions de Km².

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1500 . . 1 , , . , Guaporé , . . 4,5 . , 2000 . Sao Francisco 1 . . , , , ( Sao Luis) la Plata ( (Rio de la Plata). , . Caririan Sergipe , Paraiba . : Brasilia Paraguay-Araguaia. , . , , , - , 10 . 2000 .

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Discovery of an ancient tsunami deposit in coastal sequences of southwest Japan: Verification of a large historic tsunami   总被引：1，自引：0，他引：1  

Koji  Minoura Takashi  Nakata 《Island Arc》1994,3(1):66-72

Abstract A tsunamigenic sand layer is present in coastal sequences of the Masuda Plain, southwest Japan. The radiometric age of the layer has been estimated at 930 ± 80 years BP. It is proposed that the deposit is the product of a large historic tsunami believed to have occurred in the Japan Sea on 16 June 1026 AD.  相似文献   

Timing of remanent magnetization acquisition in red beds: A case study from a syn-folding sedimentary basin     

Koji Uno  Kuniyuki Furukawa 《Tectonophysics》2005,406(1-2):67-80

We propose to explain the origin of the double trend in seismicity of the Macas swarm in the Subandean Cordillera of Cutucú (Ecuador) and characterize the corresponding active deformation of that region. For that purpose, seismological and geological data have been used, with the deployment of a temporary seismological array, with geological field observations and image processing. We found that some earthquakes are aligned on a well known NNE–SSW trend corresponding to the orientation of the nodal planes of the reverse focal mechanism of the M_w=7.0 1995 Macas earthquake as for its aftershocks. Nevertheless, many smaller events are aligned on an unexpected NNW–SSE trend inside the Cutucú Cordillera. We interpret these two orientations of the Macas swarm as linked to Subandean basement thrusts inherited from the inversion tectonics of a NNE–SSW trending Triassic–Jurassic rift, which has been uplifted and partly extruded in the Cutucú Cordillera. The present partitioning of this part of the Subandean deformation is controlled by pre-existing NNE–SSW to NNW–SSE Triassic–Jurassic normal faults that have been subsequently compressed–transpressed and reactivated into reverse faults. Major boundary faults of the rift were NNE–SSW oriented and correspond now to some main Subandean thrusts as confirms the focal mechanism of the 1995 main shock located on the eastern border (Morona frontal thrust) and the orientation of its aftershocks. In the Cutucú Cordillera, the double orientation of present swarm can be interpreted as the result of accommodation of deformation along NNW–SSE pre-existing faults inside the inverted rift system, linked to the motion of the Morona frontal NNE–SSW thrust.  相似文献   

Isotopic Evaluation on the Genesis of the Kanamaru Pegmatite Deposit, Niigata Prefecture, Japan     

Shunso Ishihara    Koji Hamano  Asami Ikegami 《Resource Geology》1998,48(1):1-6

Abstract: The Kanamaru pegmatite is one of the two largest pegmatite deposits in Japan and is rich in K–feldspar, which is maximum microcline. The mica minerals and microcline from this ore deposit were studied for K-Ar ages and δ¹⁸O ratios. Biotite gives K-Ar age of 78. 5 Ma, but microcline is much younger in age of 66. 0 and 58. 3 Ma. Oxygen isotopic equilibrium temperature of the biotite-quartz pair is 625°C. Using closure temperature of the K-Ar system for biotite and microcline, cooling rate of the pegmatite is calculated to be 88°C/m. y. at the beginning but 12°C/m. y. in the later period of the cooling history. The microcline is slightly depleted in ¹⁸O, yielding apparent equilibrium temperatures of 230°C and 155°C on quartz-microcline pairs. It is suggested that the fluid phase, magmatic and partly meteoric in origin, contained in the solidifying pegmatite, was interacted with the original orthoclase and converted it to microcline during the subsolidus stage.  相似文献