Nitrogen concentration within Saxifraga oppositifolia in different successional stages on a glacier foreland in the high Arctic     

Atsushi Kume  Yukiko S. Bekku  Yuko T. Hanba  Takashi Nakano  Hiroshi Kanda 《Polar Science》2008,2(2):143-147

We measured and compared the δ¹³C values and nitrogen concentrations within the photosynthetic parts (Np) of phototrophs growing in different successional stages and different soil conditions at Ny-Ålesund, Svalbard, Norway. At all study sites, the Np value of vascular plants ranged from 1.0 to 2.2%. The Np value for most moss species was less than 1.0%; values for lichens were about 0.5%. No significant correlation was detected between Np and δ¹³C; however, different plant species occupied distinct fields on a δ¹³C–Np plot, with minimal overlap between species. The Np value of Saxifraga oppositifolia, which grew at all of the study sites, ranged from 1.1 to 1.5%. Differences in growth form had no effect on Np. The Np and δ¹³C values obtained for S. oppositifolia were confined to within a narrow range regardless of site conditions.  相似文献   

Influence of light intensity on diatom physiology and nutrient dynamics in the Oyashio region     

Hiroaki Saito  Atsushi Tsuda 《Progress in Oceanography》2003,57(3-4):251

The spring diatom bloom characterizes the plankton and nutrient dynamics in the Oyashio region, the westernmost part of the subarctic Pacific. Previous studies have shown that NO₃ was not depleted during the spring bloom, and an increase in the consumption ratio of Si(OH)₄ to NO₃ (ΔSi(OH)₄:ΔNO₃) was observed as the spring bloom progressed. The increase in ΔSi(OH)₄:ΔNO₃ has been suggested to be caused by growth stresses of diatoms, e.g. light limitation by self-shading. In the present study, incubation experiments of sea-surface water from the Oyashio region under saturated irradiance showed that NO₃ was depleted first and ΔSi(OH)₄:ΔNO₃ was more or less constant until the NO₃ depletion occurred. The increase in ΔSi(OH)₄:ΔNO₃ was observed after the NO₃ depletion had occurred in contrast with the field observation. This result of the increase in ΔSi(OH)₄:ΔNO₃ under saturated irradiance after NO₃ depletion suggests that the in situ increase in ΔSi(OH)₄:ΔNO₃ before the NO₃ depletion might be caused by light limitation for diatoms. Responses to a reduction in irradiance were examined using diatom species isolated from the Oyashio region. Variable responses to a reduced irradiance were observed for cell specific C, N, Si and chlorophyll a (Chl) contents. However, the examined diatom species showed similar tendencies for increases in Si:C and Si:N and decreases in C:Chl ratios with the reduction in irradiance. We conclude that light limitation changes the uptake ratio of nutrients and the elemental composition of diatoms and that light limitation is one of the factors influencing the physiology of diatoms and nutrient dynamics in the Oyashio region during the spring bloom.  相似文献   

Frequency–Magnitude Distribution of −3.7 ≤ M W  ≤ 1 Mining-Induced Earthquakes Around a Mining Front and b Value Invariance with Post-Blast Time     

Makoto Naoi  Masao Nakatani  Shigeki Horiuchi  Yasuo Yabe  Joachim Philipp  Thabang Kgarume  Gilbert Morema  Sifiso Khambule  Thabang Masakale  Luiz Ribeiro  Koji Miyakawa  Atsushi Watanabe  Kenshiro Otsuki  Hirokazu Moriya  Osamu Murakami  Hironori Kawakata  Nana Yoshimitsu  Anthony Ward  Ray Durrheim  Hiroshi Ogasawara 《Pure and Applied Geophysics》2014,171(10):2665-2684

We investigated frequency-magnitude distribution (FMD) of acoustic emissions (AE) occurring near an active mining front in a South African gold mine, using a catalog developed from an AE network, which is capable of detecting AEs down to M _W  ?5. When records of blasts were removed, FMDs of AEs obeyed a Gutenberg?Richter law with similar b values, not depending on post-blasting time from the initial 1-min interval through more than 30 h. This result denies a suggestion in a previous study (Richardson and Jordan Bull Seismol Soc Am, 92:1766–1782, 2002) that new fractures generated by blasting disturb the size distribution of background events, which they interpreted as slip events on existing weak planes. Our AE catalog showed that the GR law with b ～ 1.2 was valid between M _W  ?3.7 and 0 for AEs around the mining front. Further, using the mine’s seismic catalog, which covers a longer time period of the same area, we could extend the validity range of the GR law with the same b value up to M _W 1.  相似文献   

Differential Fractionation of Rare Earth Elements in Oxidized and Reduced Granitic Rocks: Implication for Heavy Rare Earth Enriched Ion Adsorption Mineralization          下载免费PDF全文

Yasushi Watanabe  Yoshiaki Kon  Takuya Echigo  Atsushi Kamei 《Resource Geology》2017,67(1):35-52

Ion adsorption rare earth element (REE) deposits in southern China are the exclusive source of heavy REEs (HREEs) in the world, and this HREE‐enriched character of the deposits is inherited from the REE compositions of the underlying granitic rocks. Such HREE‐enriched rocks form from heavy fractionation of reduced granitic magmas. We explore why reduced granitic magmas are enriched in HREEs during the fractionation, based on the REE geochemistry of granitic rocks and abundance of REEs in their constituent minerals in the southwestern Japan arc of Cretaceous to Paleogene age. The compilation of the whole rock geochemistry and REE compositions of the granitic rocks of the Sanin (oxidized), Sanyo (reduced) and Ryoke (reduced) belts in the southwestern Japan arc indicates that: (i) light REEs (LREEs) decease with fractionation of the granitoids in the Sanin belt but this trend is not clear in the granitoids in the Sanyo belt and LREEs rather increase in the Ryoke granitoids; (ii) Eu decreases with fractionation in all the belts; and (iii) HREEs slightly, but steadily decrease in the Sanin belt but enrich significantly in the Sanyo and Ryoke belts with fractionation. Analytical results of REE concentrations by scanning electron microscope with energy dispersive X‐ray spectroscope and laser ablation‐inductively coupled plasma mass spectrometer in the constituent minerals in a granodiorite sample from the Sanin belt show a moderate concentration of REEs in hornblende (577 ppm) in addition to high concentrations in allanite (~20 %), britholite (~30 %), primary titanite (8922 ppm), apatite (4062 ppm), and zircon (1693 ppm). Because primary titanite and allanite are commonly present in the oxidized granitoids but not in the reduced ones, the REE depletion in the fractionated, oxidized granites is attributed to the crystallization of these minerals. In contrast, scarcity of these minerals in the reduced granitoids enriches REEs, in particular HREEs in the fractionated magmas, which finally precipitate REEs in the granites and pegmatites. Both positive, but different correlation ratios between the Nb and Dy concentrations in the granitoids of the Sanin and Sanyo‐Ryoke belts suggest that columbite–pyrochlore‐group and fergusonite‐group minerals are the major HREE host in the oxidized and reduced granites, respectively.  相似文献   

Assessing the role of forests in mitigating eutrophication downstream of pasture during spring snowmelt          下载免费PDF全文

Masaaki Chiwa  Sachiko Inoue  Naoaki Tashiro  Daisuke Ohgi  Yoshitoshi Uehara  Hideaki Shibata  Atsushi Kume 《水文研究》2015,29(4):615-623

Little research has examined whether forests reduce stream water eutrophication in agricultural areas during spring snowmelt periods. This study evaluated the role of forests in ameliorating deteriorated stream water quality in agricultural areas, including pasture, during snowmelt periods. Temporal variation in stream water quality at a mixed land‐use basin (565 ha: pasture 13%, forestry 87%), northern Japan, was monitored for 7 years. Synoptic stream water sampling was also conducted at 16 sites across a wide range of forest and agricultural areas in a basin (18.3 km²) in spring, summer and fall. Atmospheric nitrogen (N) and phosphorus (P) deposition were measured for 4 years. The results showed that concentration pulses of nitrate, organic N and total P in stream water were observed when discharge increased during spring snowmelt. Their concentrations were high when silicate concentrations were low, suggesting surface water exported from pasture largely contributed to stream water pollution during snowmelt. Atmospheric N and P deposition (4.1 kg N ha^?1 y^?1; 0.09 kg P ha^?1 y^?1, respectively) was too low to affect the background concentrations of N and P in streams from forested areas. Reduction of eutrophication caused by nutrients from pasture was mainly due to dilution by water containing low concentrations of N and P exported from forested areas, whereas in‐stream reduction was not a dominant process. Results indicate that forests have a limited capacity to reduce the concentration pulses of N and P in stream water during snowmelt in this study basin. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

Identification of 1771 Meiwa Tsunami deposits using a combination of radiocarbon dating and oxygen isotope microprofiling of emerged massive Porites boulders     

Atsushi Suzuki  Yusuke Yokoyama  Hironobu Kan  Kayo Minoshima  Hiroyuki Matsuzaki  Nozomu Hamanaka  Hodaka Kawahata   《Quaternary Geochronology》2008,3(3):226-234

The Meiwa Tsunami, one of the largest tsunamis recorded in historical documents in Japan struck Ishigaki Island and neighboring islands of the Ryukyu Arc in April 1771 AD, killing more than 12 000 people. An enormous number of massive Porites coral boulders are scattered on the shore and in the reef moat of eastern Ishigaki Island. Although these boulders likely were cast ashore by the Meiwa Tsunami, a detailed examination has not yet been conducted. When the marine reservoir effect is taken into account, one of mode values of calibrated radiocarbon dates possibly corresponds to the time of the 1771 event. However, the range of calibrated radiocarbon ages indicates that the transport of the boulders cannot be ascribed solely to the tsunami. Oxygen isotope microprofiling, which indicates sea-surface temperature variation, was therefore conducted to further investigate the mechanism of transport. The results suggest that the skeletal growth of most coral colonies was interrupted in summer or autumn; hence, tropical storms and typhoons are also very likely to be agents of transport. Thus, by combining radiocarbon dating with oxygen isotope microprofiling to investigate Porites coral boulders, it is possible to separate paleotsunami boulders from those transported by storm events as far as tsunamis occurred during the non-storm season.  相似文献   

Late Jurassic (Tithonian) radiolarians from a clastic unit of the Khabarovsk complex (Russian Far East): Significance for subduction accretion timing and terrane correlation   总被引：7，自引：0，他引：7  

Sergei Zyabrev  & Atsushi Matsuoka 《Island Arc》1999,8(1):30-37

A well-preserved radiolarian fauna from a clastic unit of the Khabarovsk accretionary complex (southern part of the Badzhal accretionary wedge terrane in the Russian Far East) is assigned to the basal part of the Pseudodictyomitra carpatica zone. The age of the fauna is most likely late Tithonian. This is the first reliable dating of the clastic unit and makes it possible to constrain the timing of subduction accretion in the Badzhal terrane. The Khabarovsk complex is correlated chronologically with the Bikin and Samarka terranes (Russian Far East), Mino, Southern Chichibu and North Kitakami terranes (Japan), and Nadanhada terrane (northeast China).  相似文献   

Eocene extensional tectonics in the Amakusa region,northern Ryukyu arc     

Kentaro Ushimaru  Atsushi Yamaji 《Island Arc》2024,33(1):e12511

Paleogene surface tectonics in Japan is not well understood because of the paucity of onshore Paleogene stratigraphic records except for those from accretionary complexes. Paralic Paleogene formations remaining in SW Japan are usually so thin that it is difficult to decipher the tectonics from them. However, the Eocene paralic sedimentary package with a thickness of kilometers indicates syn-depositional tectonic subsidence by a few kilometers in the Amakusa archipelago, west of Kyushu Island. Thus, we made a detailed geological map of the Eocene formations in an area of ~50 square kilometers in the northwestern part of the archipelago. We identified NE-SW and NW-SE trending normal faults, most of which were recognized by previous researchers, and also discovered low-angle faults. NW-SE trending ones are known to be of the Miocene. NE-SW trending and low-angle normal faults are the oldest map-scale structures in the Eocene ones. It is not obvious within the above-mentioned area whether those normal faults are accompanied by growth strata. However, the significant southeastward thickening of the Eocene formations across the Amakusa archipelago suggests that they filled a large half graben with the basin margin fault along the eastern side of the archipelago. This basin model is consistent with the N-S to NW-SE transport directions of the low-angle and NE-SW trending normal faults. Since many NE-SW to EW trending Eocene grabens were formed in the offshore regions west of Kyushu Island and in the East China Sea, the Amakusa region was probably a northeastern branch of the rift system. The geologic structures and depositional ages of the Eocene formations indicate that the Eocene extensional tectonics removed the overlying strata to some extent for the high-P/T Takahama Metamorphic Rocks which crops out to the south of our study area.  相似文献   

Trends in pCO2 and sea–air CO2 flux over the global open oceans for the last two decades     

Yosuke Iida  Atsushi Kojima  Yusuke Takatani  Toshiya Nakano  Hiroyuki Sugimoto  Takashi Midorikawa  Masao Ishii 《Journal of Oceanography》2015,71(6):637-661

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Formation of propagation pattern in two-phase flow systems with application to volcanic eruptions   总被引：1，自引：0，他引：1  

Atsushi Toramaru 《Geophysical Journal International》1988,95(3):613-623

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