Biogeochemistry of nitrous oxide in groundwater in a forested ecosystem elucidated by nitrous oxide isotopomer measurements   总被引：3，自引：0，他引：3  

K. Koba  K. Osaka  Y. Tobari  S. Toyoda  N. Ohte  M. Katsuyama  N. Suzuki  M. Itoh  H. Yamagishi  M. Kawasaki  S.J. Kim  N. Yoshida  T. Nakajima 《Geochimica et cosmochimica acta》2009,73(11):3115-1037

The biological and physical controls on microbial processes that produce and consume N₂O in soils are highly complex. Isotopomer ratios of N₂O, with abundance of ¹⁴N¹⁵N¹⁶O, ¹⁵N¹⁴N¹⁶O, and ¹⁴N¹⁴N¹⁸O relative to ¹⁴N¹⁴N¹⁶O, are promising for elucidation of N₂O biogeochemistry in an intact ecosystem. Site preference, the nitrogen isotope ratio of the central nitrogen atom minus that of the terminal nitrogen atom, is useful to distinguish between N₂O via hydroxylamine oxidation and N₂O via nitrite reduction.We applied this isotopomer analysis to a groundwater system in a temperate coniferous-forested ecosystem. Results of a previous study at this location showed that the N₂O concentration in groundwater varied greatly according to groundwater chemistry, i.e. NO₃⁻, DOC, and DO, although apportionment of N₂O production to nitrification or denitrification was ambiguous. Our isotopic analysis (δ¹⁵N and δ¹⁸O) of NO₃⁻ and N₂O implies that denitrification is the dominant production process of N₂O, but definitive information is not derived from δ¹⁵N and δ¹⁸O analysis because of large variations in isotopic fractionations during production and consumption of N₂O. However, the N₂O site preference and the difference in δ¹⁵N between NO₃⁻ and N₂O indicate that nitrification contributes to total N₂O production and that most measured N₂O has been subjected to further N₂O reduction to N₂. The implications of N₂O biogeochemistry derived from isotope and isotopomer data differ entirely from those derived from conventional concentration data of DO, NO₃⁻, and N₂O. That difference underscores the need to reconsider our understanding of the N cycle in the oxic-anoxic interface.  相似文献   

Multiple sulfur isotope chemostratigraphy across the Permian–Triassic boundary at Chaotian,China: Implications for a shoaling model of toxic deep-waters     

Masafumi Saitoh  Yuichiro Ueno  Yukio Isozaki  Naohiro Yoshida 《Island Arc》2021,30(1):e12398

Previous studies on multiple sulfur isotopes (³²S, ³³S, and ³⁴S) in sedimentary pyrite at the end-Permian suggested a shoaling of anoxic/sulfidic deep-water contributing to the extinction. This scenario is based on an assumption that the sedimentary sulfur cycle was largely controlled by benthos activity, though a stratigraphic correlation between the sulfur records and ichnofabrics of the sediments at the end-Permian has not yet been examined. We report the multiple sulfur isotopic composition of pyrite in the Permian–Triassic boundary interval at Chaotian, South China. Our data can be generally explained by a mixing of sulfur in sulfide from two different sources: one produced via sulfate reduction in an open system with respect to sulfate and the other produced in a closed system. In particular, the former with the substantially low δ³⁴S (<−40 ‰) and high ∆³³S (up to +0.100 ‰) values was likely produced via water-mass sulfate reduction or via sulfate reduction in oxic sediments with common burrows. The frequent occurrence of small pyrite framboids (mostly <5 μm in diameter) in the Lopingian (Late Permian) Dalong Formation of deep-water facies supports the enhanced water-mass sulfate reduction in an anoxic deep-water mass. The negative ∆³³S values are observed only in the oxic limestones, and no substantial ∆³³S change is observed across the extinction horizon despite of the disappearance of bioturbation. Our results are apparently inconsistent with the previous shoaling model. We expand the model and infer that, when the deep-water was sulfidic and its shoaling rate was high, a substantial amount of hydrogen sulfide (H₂S) was supplied onto the shelf via the shoaling; that resulted in the positive ∆³³S value of the bulk sediments. The observed ∆³³S variation on a global scale suggests a substantial variation in H₂S concentration and/or in upwelling rate of shoaling deep-waters during the Permian–Triassic transition.  相似文献   

The anisotropy of cosmic ray arrival directions around 10 eV     

N. Hayashida  M. Nagano  D. Nishikawa  H. Ohoka  N. Sakaki  M. Sasaki  M. Takeda  M. Teshima  R. Torii  T. Yamamoto  S. Yoshida  K. Honda  N. Kawasumi  I. Tsushima  N. Inoue  E. Kusano  K. Shinozaki  N. Souma  K. Kadota  F. Kakimoto  K. Kamata  S. Kawaguchi  Y. Kawasaki  H. Kitamura  Y. Matsubara  K. Murakami  Y. Uchihori  H. Yoshii 《Astroparticle Physics》1999,10(4):125-311

Anisotropy in the arrival directions of cosmic rays with energies above 10¹⁷ eV is studied using data from the Akeno 20 km² array and the Akeno Giant Air Shower Array (AGASA), using a total of about 114 000 showers observed over 11 years. In the first harmonic analysis, we have found a strong anisotropy of 4% around 10¹⁸ eV, corresponding to a chance probability of 0.2% after taking the number of independent trials into account. with two-dimensional analysis in right ascension and declination, this anisotropy is interpreted as an excess of showers near the directions of the Galactic Center and the Cygnus region.  相似文献   

A new, automatic hydrothermal fluid sampler using a shape-memory alloy   总被引：2，自引：0，他引：2  

Takeshi Naganuma  Masanori Kyo  Tatsuhiko Ueki  Kazuhiko Takeda  Jun-ichiro Ishibashi 《Journal of Oceanography》1998,54(3):241-246

A new hydrothermal fluid sampler has been developed to provide more maneuverability in underwater operation. The sampler characteristically employs a shape-memory alloy, which senses high temperature and actuates the suction mechanism. A shape-memory alloy is also used to switch the intake valve of the sampler, the intention being to avoid missampling when the inlet is in low temperature water. Prototype samplers were designed to collect the fluids hotter than 80°C. Test sampling was performed at hydrothermal vents (1372–1374 m deep) in the submarine volcano, Suiyo Seamount, Izu-Bonin Arc, northwestern Pacific. Observed fluid temperature was between 138 and 298°C, while the ambient seawater temperature was 3.1°C. Each prototype collected about 100 ml fluid as designed. The magnesium concentration in the samples indicated a seawater content of 47.5–90.8%, which indicates the entrainment of ambient seawater. Microscopic observatinn revealed the occurrence of microorganisms in the sample fluids at a population density of 10⁵ to 10⁶ cells ml⁻¹, which is 2–3 orders of magnitude higher than those in seawater at that depth. The use of the newly developed fluid sampler will greatly facilitate the collection of vent-associated microorganisms, which are of potential biological and biotechnological interest.  相似文献   

Spatial distribution of sister species of vesicomyid bivalves Calyptogena okutanii and Calyptogena soyoae along an environmental gradient in chemosynthetic biological communities in Japan     

Hiromi Watanabe  Eriko Seo  Yoshimi Takahashi  Takao Yoshida  Shigeaki Kojima  Katsunori Fujikura  Hiroshi Miyake 《Journal of Oceanography》2013,69(1):129-134

Vesicomyid bivalves have a substantial biomass in deep-sea chemosynthetic biological communities in the Pacific. Using a novel multiplex-PCR (mPCR) method to identify the co-occurring vesicomyids in Sagami Bay, we analyzed the distribution of Calyptogena okutanii and Calyptogena soyoae along environmental gradients. All the known distributions of C. okutanii indicated the different preferences in salinity and temperature to those of C. soyoae, and in Sagami Bay, depth seemed to be an important environmental factor, too. Although the concentration of hydrogen sulfide in sediment was not examined, our results showed that the distributions of these two Calyptogena clams were affected by salinity and temperature.  相似文献   

Volume transports proceeding to the Kuroshio Extension region and recirculating in the Shikoku Basin   总被引：4，自引：1，他引：3  

Akira Nagano  Kaoru Ichikawa  Hiroshi Ichikawa  Masanori Konda  Kiyoshi Murakami 《Journal of Oceanography》2013,69(3):285-293

The volume transport of the Kuroshio, the western boundary current of the North Pacific subtropical gyre, varies vigorously due to merging of disturbances propagating from the entire North Pacific. Taking into account the recirculation in the Shikoku Basin by the zonal observation line at 30°N to the west of the Izu–Ogasawara Ridge, we estimated the volume transport in the top 1,000 m layer toward the Kuroshio Extension region. The volume transport of the local recirculation gyre in the Shikoku Basin increases associated with the westward extension of the gyre, particularly in the period of the large meandering path of the Kuroshio south of Japan. Meanwhile, most of the transport variations toward the Kuroshio Extension region correspond to those of the Kuroshio transport on the continental slope south of Japan, which vary independently of those of the recirculation gyre.  相似文献   

Seismic vertical array analysis for phase decomposition     

Kunikazu Yoshida  Tsutomu Sasatani 《Geophysical Journal International》2008,174(2):707-718

We propose a vertical array analysis method that decomposes complex seismograms into body and surface wave time histories by using a velocity structure at the vertical array site. We assume that the vertical array records are the sum of vertically incident plane P and S waves, and laterally incident Love and Rayleigh waves. Each phase at the surface is related to that at a certain depth by the transfer function in the frequency domain; the transfer function is obtained by Haskell's matrix method, assuming a 1-D velocity structure. Decomposed P , S and surface waves at the surface are estimated from the vertical array records and the transfer functions by using a least-squares method in the frequency domain; their time histories are obtained by the inverse Fourier transform. We carried out numerical tests of this method based on synthetic vertical array records consisting of vertically incident plane P and S waves and laterally incident plane Love and Rayleigh waves. Perfect results of the decomposed P , S , Love and Rayleigh waves were obtained for synthetic records without noise. A test of the synthetic records in which a small amount of white noise was added yielded a reasonable result for the decomposed P , S and surface waves. We applied this method to real vertical array records from the Ashigara valley, a moderate-sized sedimentary valley. The array records from two earthquakes occurring at depths of 123 and 148 km near the array (epicentral distance of about 31 km) exhibited long-duration later phases. The analysis showed that duration of the decomposed S waves was a few seconds and that the decomposed surface waves appeared a few seconds after the direct S -wave arrival and had very long duration. This result indicated that the long-duration later phases were generated not by multireflected S waves, but by basin-induced surface waves.  相似文献   

Internal differentiation of Kutsugata lava flow from Rishiri Volcano,Japan: Processes and timescales of segregation structures' formation     

Takeshi Kuritani  Takeyoshi Yoshida  Yoshitaka Nagahashi 《Journal of Volcanology and Geothermal Research》2010

Internal differentiation processes in a solidifying lava flow were investigated for the Kutsugata lava flow from Rishiri Volcano in northern Japan. In a representative 6-m thick lava flow that was investigated in detail in this study, segregation products darker than the host lavas manifested mainly in the form of pipes (vesicle cylinders) and layers (vesicle sheets), occurring around 0.5–2.3 m and 2.0–4.0 m above the base, respectively. Both the cylinders and sheets are significantly richer in incompatible elements such as TiO₂ and K₂O than the host lavas, which suggest that these products essentially represent residual melt produced during solidification of the lava flow. Field observation and the geochemical features of the lavas suggest that the vesicle cylinders grew upward from near the base of the flow by continuous feeding of residual melt from the neighboring host lavas to the heads of the cylinders. On the other hand, the vesicle sheets were produced in situ in the solidifying lava flow as fracture veins caused by horizontal compression. The vesicle cylinders have a remarkably higher MgO content (up to 8 wt.%) than the host lava (< 6 wt.%), whereas the vesicle sheets display MgO depletion (as low as 3.5 wt.%). The relatively high MgO content of the vesicle cylinders cannot be explained solely by the mechanical mixing of olivine phenocrysts with the residual melt. It is suggested that the vesicle cylinders were produced by the extraction of olivine-bearing interstitial melt from an augite-plagioclase network in the host lava, whereas the vesicle sheets were formed by the migration of the residual melt from a crystal network consisting of plagioclase, augite, and olivine in the host lava into platy fractures. We infer that this selective crystal fractionation for forming the vesicle cylinders resulted from processes in which abundant vesicles rejected from the upward-migrating floor solidification front prevented olivine crystals from being incorporated into the crystal network in the host lava. The vesicle cylinders are considered to have formed in ∼ 1 day after the lava flow came to rest, while relatively large vesicle sheets (> 1 cm thick) appeared much later (after ∼ 9 days). The formation of these segregation products was essentially complete within 20 days after the lava emplacement.  相似文献   

Chemical and Isotopic Characteristics of the Kuroko‐Forming Volcanism     

Ryoichi Yamada  Takeyoshi Yoshida  Jun‐Ichi Kimura 《Resource Geology》2012,62(4):369-383

The Miocene northeast Honshu magmatic arc, Japan, formed at a terrestrial continental margin via a stage of spreading in a back‐arc basin (23–17 Ma) followed by multiple stages of submarine rifting (19–13 Ma). The Kuroko deposits formed during this period, with most forming during the youngest rifting stage. The mode of magma eruption changed from submarine basalt lava flows during back‐arc basin spreading to submarine bimodal basalt lava flows and abundant rhyolitic effusive rocks during the rifting stage. The basalts produced during the stage of back‐arc basin spreading are geochemically similar to mid‐ocean ridge basalt, with a depleted Sr–Nd mantle source, whereas those produced during the rifting stage possess arc signatures with an enriched mantle source. The Nb/Zr ratios of the volcanic rocks show an increase over time, indicating a temporal increase in the fertility of the source. The Nb/Zr ratios are similar in basalts and rhyolites from a given rift zone, whereas the Nd isotopic compositions of the rhyolites are less radiogenic than those of the basalts. These data suggest that the rhyolites were derived from a basaltic magma via crystal fractionation and crustal assimilation. The rhyolites associated with the Kuroko deposits are aphyric and have higher concentrations of incompatible elements than do post‐Kuroko quartz‐phyric rhyolites. These observations suggest that the aphyric rhyolite magma was derived from a relatively deep magma chamber with strong fractional crystallization. Almost all of the Kuroko deposits formed in close temporal relation to the aphyric rhyolite indicating a genetic link between the Kuroko deposits and highly differentiated rhyolitic magma.  相似文献   

Geological Traverse from Yangtze Craton to the North China Craton Through Qinling-Dabie Mobile Belt, Central China: a Post-Symposium Field Trip of IGCP-368/411/440 in 1999     

S. Sengupta  M. Yoshida  X. Wang 《Gondwana Research》2000,3(4):566-569

  相似文献