Observations of current and mixing around the shelf break in Pribilof Canyon in the Bering Sea     

T. Tanaka  I. Yasuda  H. Onishi  H. Ueno  M. Masujima 《Journal of Oceanography》2015,71(1):1-17

  相似文献   

http://www.sciencedirect.com/science/article/pii/S1674987114000917     

Miyuki Tahata  Yusuke Sawaki  Yuichiro Ueno  Manabu Nishizawa  Naohiro Yoshida  Toshikazu Ebisuzaki  Tsuyoshi Komiya  Shigenori Maruyama 《地学前缘(英文版)》2015,6(1):121-136

Important ecological changes of the Earth(oxidization of the atmosphere and the ocean) increase in nutrient supply due to the break-up of the super continent(Rodinia) and the appearance of multi-cellular organisms(macroscopic algae and metazoan) took place in the Ediacaran period,priming the Cambrian explosion.The strong perturbations in carbon cycles in the ocean are recorded as excursions in carbonate and organic carbon isotope ratio(δ~(13)C_(carb) and δ~(13)C_(org)) from the Ediacaran through early Cambrian periods.The Ediacaran-early Cambrian sediment records of δ~(13)C_(carb) and δ~(13)C_(org),obtained from the drill-core samples in Three Gorges in South China,are compared with the results of numerical simulation of a simple one-zone model of the carbon cycle of the ocean,which has two reservoirs(i.e.,dissolved organic carbon(DOC) and dissolved inorganic carbon(DIC).The fluxes from the reservoirs are assumed to be proportional to the mass of the carbon reservoirs.We constructed a model,referred to here as the Best Fit Model(BFM),which reproduce δ~(13)C_(carb) and δ~(13)C_(org) records in the Ediacaran-early Cambrian period noted above.BFM reveals that the Shuram excursion is related to three major changes in the carbon cycle or the global ecological system of the Earth:(1) an increase in the coefficient of remineralization by a factor of ca.100,possibly corresponding to a change in the dominant metabolism from anaerobic respiration to aerobic respiration,(2) an increase of carbon fractionation index from 25‰ to 33‰,possibly corresponding to the change in the primary producer from rock-living cyanobacteria to free-living macro algae,and(3) an increase in the coefficient of the organic carbon burial by a factor of ca.100,possibly corresponding to the onset of a biological pump driven by the flourishing metazoan and zooplankton.The former two changes took place at the start of the Shuram excursion,while the third occurred at the end of the Shuram excursion.The other two excursions are explained by the tentative decrease in primary production due to cold periods,which correspond to the Gaskiers(ca.580 Ma) and Bikonor(ca.542 Ma) glaciations.  相似文献   

Impact of Alaskan Stream eddies on chlorophyll distribution in the North Pacific   总被引：1，自引：0，他引：1  

Hiromichi Ueno  William R. Crawford  Hiroji Onishi 《Journal of Oceanography》2010,66(3):319-328

The impact of the Alaskan Stream (AS) eddies on the chlorophyll a (chl-a) distribution in the central subarctic North Pacific was investigated through analysis of chl-a and altimetry data from satellite observations. Altimetry observations provided the locations of mesoscale eddies in time and space within the maps of chlorophyll distributions. The climatological chl-a distributions averaged in the area and time showing presence of AS eddies suggested that AS eddies contributed significantly to the chl-a distribution in the deep-sea region of the subarctic North Pacific. The chl-a distribution was closely related to the AS eddies regardless of whether the eddy was located in or detached from the AS. A combination of two or three AS eddies sometimes formed high chl-a concentration belts that injected chlorophyll and coastal nutrient-rich waters southward from the Aleutian Islands far into the deep-sea region of the subarctic North Pacific. These results indicate that chl-a distribution in the central subarctic North Pacific was strongly impacted by AS eddies.  相似文献   

Lopingian (Late Permian) foraminiferal faunal succession of a Paleo-Tethyan mid-oceanic carbonate buildup: Shifodong Formation in the Changning–Menglian Belt, West Yunnan, Southwest China     

Katsumi  Ueno  Satoe  Tsutsumi 《Island Arc》2009,18(1):69-93

This paper deals with a Lopingian (Late Permian) foraminiferal faunal succession of the Shifodong Formation in the Changning–Menglian Belt, West Yunnan, Southwest China, which has been geologically interpreted as one of the closed remnants in East Asia of the Paleo‐Tethys Ocean. The Shifodong Formation is the uppermost stratigraphic unit in thick Carboniferous–Permian carbonates of the belt. These carbonates rest upon bases consisting of oceanic island basalt and are widely accepted as having a Paleo‐Tethyan mid‐oceanic (seamount‐ or oceanic plateau‐top) origin. Sixteen taxa of fusuline foraminifers and 37 taxa of smaller (non‐fusuline) foraminifers are recognized from the type section of the Shifodong Formation located in the Gengma area of the northern part of the Changning–Menglian Belt. Based on their stratigraphic distribution, three fusuline zones can be established in this section: they are, in ascending order, the Codonofusiella cf. C. kwangsiana Zone, Palaeofusulina minima Zone, and Palaeofusulina sinensis Zone. These three biozones are respectively referable to the Wuchiapingian, early Changhsingian, and late Changhsingian, of which the Wuchiapingian is first recognized in this study in the Changning–Menglian mid‐oceanic carbonates. The present study clearly demonstrates that the foraminiferal fauna in a Paleo‐Tethyan pelagic shallow‐marine environment still maintained high faunal diversity throughout the almost entire Lopingian, although the very latest Permian fauna in the upper part of the Palaeofusulina sinensis Zone of the Shifodong section records a sudden decrease in both faunal diversity and abundance. Moreover, the Shifodong faunas are comparable in diversity with those observed in circum‐Tethyan shelves such as South China. The present Paleo‐Tethyan mid‐oceanic foraminiferal faunas are definitely more diversified than coeval mid‐oceanic Panthalassan faunas, which are typically represented by those from the Kamura Limestone in a Jurassic accretionary complex of Southwest Japan. It is suggestive that the Paleo‐Tethyan mid‐oceanic buildups presumably supplied a peculiarly hospitable habitat for foraminiferal faunal development in a pelagic paleo‐equatorial condition.  相似文献   

Effects of deforestation and weather on diurnal frost heave processes on the steep mountain slopes in south central Japan          下载免费PDF全文

Kenichi Ueno  Kousei Kurobe  Fumitoshi Imaizumi  Ryoko Nishii 《地球表面变化过程与地形》2015,40(15):2013-2025

Freezing and thawing processes play an important role for the gravitational transport of surface materials on steep mountain slopes in Japan. The effects of deforestation on frost heave activity were observed through the 2012/2013 winter season in Ikawa University Forest, a southern mountainous area in central Japan (1180–1310 m above sea level). During periods without snow cover, needle ice development prevailed at a clear‐cut site, and the downslope sediment movement of upper soil was 10 to 15 cm through the winter season. At a non‐cut site, rise and fall in the ground surface level prevailed on a weekly scale, with no evident downslope movements at the surface; ice lens formation in the soil layer is assumed. Abrupt changes in the radiation budget, such as the strengthening of nighttime radiative cooling and increases in daytime direct insolation, induced frequent development/deformation of needle ice at the clear‐cut site. In snow‐free periods, the day‐to‐day variability in needle ice growth length and in nighttime averaged net radiation showed significant correlations; cloudy weather with warmer and moist air intrusion associated with synoptic disturbances prevented the occurrence of needle ice. Namely, day‐to‐day weather changes directly affected the mass movement of the upper soil after deforestation. Shallow snow cover occurred discontinuously through the winter and is likely an important factor in keeping the soil moisture sufficiently high in the upper soil layer for initiating needle ice during snow‐free periods. We also discuss contributions of coastal extratropical cyclone activities providing both snow cover and cloudy weather in the southern mountain areas of central Japan to the intra‐seasonal variability in frost heave and its indirect effect on soil creep and landslides on the deforested steep slopes. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

Determination of Sr/Sr mass-dependent isotopic fractionation and radiogenic isotope variation of Sr/Sr in the Neoproterozoic Doushantuo Formation     

Takeshi Ohno  Tsuyoshi Komiya  Yuichiro Ueno  Takafumi Hirata  Shigenori Maruyama 《Gondwana Research》2008,14(1-2):126

We measured both mass-dependent isotope fractionation of δ⁸⁸Sr (⁸⁸Sr/⁸⁶Sr) and radiogenic isotopic variation of Sr (⁸⁷Sr/⁸⁶Sr) for the Neoproterozoic Doushantuo Formation that deposited as a cap carbonate immediately above the Marinoan-related Nantuo Tillite. The δ⁸⁸Sr and ⁸⁷Sr/⁸⁶Sr compositions showed three remarkable characteristics: (1) high radiogenic ⁸⁷Sr/⁸⁶Sr values and gradual decrease in the ⁸⁷Sr/⁸⁶Sr ratios, (2) anomalously low δ⁸⁸Sr values at the lower part cap carbonate, and (3) a clear correlation between ⁸⁷Sr/⁸⁶Sr and δ⁸⁸Sr values. These isotopic signatures can be explained by assuming an extreme greenhouse condition after the Marinoan glaciation. Surface seawater, mixed with a large amount of freshwater from continental crusts with high ⁸⁷Sr/⁸⁶Sr and lighter δ⁸⁸Sr ratios, was formed during the extreme global warming after the glacial event. High atmospheric CO₂ content caused sudden precipitation of cap carbonate from the surface seawater with high ⁸⁷Sr/⁸⁶Sr and lighter δ⁸⁸Sr ratios. Subsequently, the mixing of the underlying seawater, with unradiogenic Sr isotope compositions and normal δ⁸⁸Sr ratios, probably caused gradual decrease of the ⁸⁷Sr/⁸⁶Sr ratios of the seawater and deposition of carbonate with normal δ⁸⁸Sr ratios. The combination of ⁸⁷Sr/⁸⁶Sr and δ⁸⁸Sr isotope systematics gives us new insights on the surface evolution after the Snowball Earth.  相似文献   

Quadruple sulfur isotope analysis of ca. 3.5 Ga Dresser Formation: New evidence for microbial sulfate reduction in the early Archean     

Yuichiro Ueno  Shuhei Ono  Douglas Rumble 《Geochimica et cosmochimica acta》2008,72(23):5675-5691

Multiple sulfur isotope system is a powerful new tracer for atmospheric, volcanic, and biological influences on sulfur cycles in the anoxic early Earth. Here, we report high-precision quadruple sulfur isotope analyses (³²S/³³S/³⁴S/³⁶S) of barite, pyrite in barite, and sulfides in related hydrothermal and igneous rocks occurring in the ca. 3.5 Ga Dresser Formation, Western Australia. Our results indicate that observed isotopic variations are mainly controlled by mixing of mass-dependently (MD) and non-mass-dependently fractionated (non-MD) sulfur reservoirs. Based on the quadruple sulfur isotope systematics (δ³⁴S-Δ³³S-Δ³⁶S) for these minerals, four end-member sulfur reservoirs have been recognized: (1) non-MD sulfate (δ³⁴S = −5 ± 2‰; Δ³³S = −3 ± 1‰); (2) MD sulfate (δ³⁴S = +10 ± 3‰); (3) non-MD sulfur (δ³⁴S > +6‰; Δ³³S > +4‰); and (4) igneous MD sulfur (δ³⁴S = Δ³³S = 0‰). The first and third components show a clear non-MD signatures, thus probably represent sulfate and sulfur aerosol inputs. The MD sulfate component (2) is enriched in ³⁴S (+10 ± 3‰) and may have originated from microbial and/or abiotic disproportionation of volcanic S or SO₂. Our results reconfirm that the Dresser barites contain small amounts of pyrite depleted in ³⁴S by 15-22‰ relative to the host barite. These barite-pyrite pairs exhibit a mass-dependent relationship of δ³³S/δ³⁴S with slope less than 0.512, which is consistent with that expected for microbial sulfate reduction and is significantly different from that of equilibrium fractionation (0.515). The barite-pyrite pairs also show up to 1‰ difference in Δ³⁶S values and steep Δ³⁶S/Δ³³S slopes, which deviate from the main Archean array (Δ³⁶S/Δ³³S = −0.9) and are comparable to isotope effects exhibited by sulfate reducing microbes (Δ³⁶S/Δ³³S = −5 to −11). These new lines of evidence support the existence of sulfate reducers at ca. 3.5 Ga, whereas microbial sulfur disproportionation may have been more limited than recently suggested.  相似文献   

Relation between mean and variance in catch numbers of fish egg and larva     

Masahiro Ueno 《Journal of Oceanography》1990,46(3):125-134

In each of six areas with various horizontal scale from 0.4 to 15.6 nautical miles, many surveys with vertical net hauls are made for sampling fish eggs and larvae. Though values ofC _A are widely spread in each area, the variances ² and the meanm of catch numbers calculated from each survey follow approximately the relation from a Poisson mixture model (PMM).

相似文献    9. Sobolev's Φ-function of radiative transfer in planar and spherical scattering media      P. T. Y. Poon  S. Ueno 《Astrophysics and Space Science》1974,28(1):233-244 In recent years Sobolev's -function of radiative transfer has been discussed in connection with the resolvent of Milne's integral equation such that it plays an important role in the determination of the radiation field in semi-infinite (or finite) atmospheres with internal sources (cf. Sobolev, 1963). In the present paper, the part of Sobolev's -function in plane-parallel and spherical, isotropically scattering, atmospheres with internal source distribution is investigated from analytical and numerical aspects. With the aid of invariant imbedding (cf. Bellmanet al., 1968), we computed Sobolev's -function of Milne's integral equation for the planar case by solving the Cauchy system for the auxiliary function and Chandrasekhar'sX- andY-functions. The corresponding -function for the spherical case is readily obtained from the for the planar case.Investigation supported by the National Science Foundation under Grant No. GP 29049, the Atomic Energy Commission, Division of Research under Contract No. AT(04-3)-113, Project 19, and the National Institutes of Health under Grant No. 16197-05.  相似文献    10. Carbon and oxygen isotope chemostratigraphies of the Yangtze platform,South China: Decoding temperature and environmental changes through the Ediacaran      Miyuki Tahata  Yuichiro Ueno  Tomoko Ishikawa  Yusuke Sawaki  Kazuki Murakami  Jian Han  Degan Shu  Yong Li  Junfeng Guo  Naohiro Yoshida  Tsuyoshi Komiya 《Gondwana Research》2013,23(1):333-353 Multicellular animals first appeared on the earth during the Ediacaran period. However, the relationship between the abrupt biological evolution and environmental changes is still ambiguous. In order to examine seawater temperature and the carbon cycle through the Ediacaran, we analyzed the carbon and oxygen isotope compositions of carbonate rocks from drill cores from the Three Gorges area, South China. Importantly, the core samples include the Nantuo tillite, corresponding to the Marinoan glaciation, through the Doushantuo to the lower Dengying Fms. in ascending order.The δ13C profile displays five positive and five negative anomalies (PI-1 to 5 and NI-1 to 5), and the oxygen isotopes display very high absolute values around 0‰ with the highest at + 1.83‰. The combined δ18O and δ13C chemostratigraphies display both positive and negative correlations between the δ18O and δ13C values. The occurrence of the negative correlations supports the preservation of primary δ18O and δ13C values.The sample NI-4 has a negative correlation of the δ18O and δ13C excursions. The correlation supports a primary signature for both δ18O and δ13C variations. The positive δ18O excursion, accompanied by evidence of a eustatic sea-level fall, provides direct evidence for global cooling in the mid-Ediacaran; the 580 Ma Gaskiers Glaciation is a potential candidate for this global cooling event. The negative δ13C excursion was possibly caused by an increase in remineralization of dissolved organic carbon (DOC) due to enhanced continental weathering during the glaciation.Sample NI-5 is characterized by very low δ13C values, down to ? 10‰, corresponding to the Shuram-Wonoka-Pertatataka Excursion. The cause of the δ13C negative excursion is still not clear. However, a ubiquitous occurrence in excursions worldwide, and the lower δ13C values in deeper sections favor the enhancement of remineralization and respiration rather than secondary alteration, a restricted sea environment and lithification in coastal areas.  相似文献    1 [2] [3] [4] [5] [6] [7] [8] [9] 下一页 » 末  页»