Nutrient and Phytoplankton Dynamics in Harima-Nada, Eastern Seto Inland Sea, Japan During a 35-Year Period from 1973 to 2007     

Tetsuya Nishikawa  Yutaka Hori  Satoshi Nagai  Kazutaka Miyahara  Yukinobu Nakamura  Kazuhiro Harada  Minoru Tanda  Takehiko Manabe  Kuninao Tada 《Estuaries and Coasts》2010,33(2):417-427

Long-term monitoring of water quality and phytoplankton was conducted at 19 sampling stations in Harima-Nada, eastern Seto Inland Sea, Japan for 35 years from 1973 to 2007. There were two significant long-term changes, an increase in winter water temperatures of 0.042°C year^?1, and a decrease in dissolved inorganic nitrogen (DIN) from about 10 μM in the 1970s to ~5 μM in the late 1990s due to the reduction in nutrient inputs. DIN concentrations and total phytoplankton cell density were both higher during the 1970s to the early 1980s and then exhibited a significant decrease in the mid 1980s and remained relatively constant thereafter. Diatoms were the dominant phytoplankton group (>90%) over the 35-year period, and there was a dramatic shift from Skeletonema dominance (~70%) to Chaetoceros in the mid 1980s. This shift in diatom species may be attributed to differences in the life cycle of Skeletonema and Chaetoceros and the response to the decrease in DIN concentration.  相似文献   

Cell contact-dependent lethal effect of the dinoflagellate Heterocapsa circularisquama on phytoplankton–phytoplankton interactions     

Yasuhiro Yamasaki  Yanan Zou  Jyoji Go  Tomoyuki Shikata  Yukihiko Matsuyama  Kiyohito Nagai  Yohei Shimasaki  Kenichi Yamaguchi  Yuji Oshima  Tatsuya Oda  Tsuneo Honjo 《Journal of Sea Research》2011,65(1):76-83

We used bi-algal culture experiments to investigate and verify the roles of growth interaction between Heterocapsa circularisquama and Prorocentrum dentatum in monospecific bloom formation. Growth of H. circularisquama was slightly inhibited when inoculated at 10² cells mL^–1 along with P. dentatum at 10⁴ cells mL^–1. In other combinations of inoculation densities, P. dentatum density rapidly decreased to extremely low levels in the presence of H. circularisquama. We used a mathematical model to simulate growth and interactions of H. circularisquama and P. dentatum in bi-algal cultures. The model indicates that one species will always inhibit the growth of the other and that the relative initial cell densities of the species are critical in determining the outcome. When cultured together under conditions without cell contact, growth of H. circularisquama and P. dentatum was not inhibited. As with P. dentatum, the growth of Heterosigma akashiwo and Skeletonema costatum was inhibited in intact cell suspensions with H. circularisquama, but a nontoxic species, Heterocapsa triquetra, did not affect the growth of P. dentatum or the other species. Similarly, cell suspensions of H. circularisquama showed hemolytic activity toward rabbit erythrocytes, but those of H. triquetra did not. In addition, the cell-free supernatant of H. circularisquama cultures showed no significant hemolytic activity. These results suggest that H. circularisquama causes lethality in P. dentatum by direct cell contact in which live-cell-mediated hemolytic activity might be a contributing factor.  相似文献   

Aeolian dust experiment on climate impact: An overview of Japan–China joint project ADEC   总被引：1，自引：1，他引：0  

M. Mikami  G.Y. Shi  I. Uno  S. Yabuki  Y. Iwasaka  M. Yasui  T. Aoki  T.Y. Tanaka  Y. Kurosaki  K. Masuda  A. Uchiyama  A. Matsuki  T. Sakai  T. Takemi  M. Nakawo  N. Seino  M. Ishizuka  S. Satake  K. Fujita  Y. Hara  K. Kai  S. Kanayama  M. Hayashi  M. Du  Y. Kanai  Y. Yamada  X.Y. Zhang  Z. Shen  H. Zhou  O. Abe  T. Nagai  Y. Tsutsumi  M. Chiba  J. Suzuki 《Global and Planetary Change》2006,52(1-4):142

The Aeolian Dust Experiment on Climate Impact (ADEC) was initiated in April 2000 as a joint five-year Japan–China project. The goal was to understand the impact of aeolian dust on climate via radiative forcing (RF). Field experiments and numerical simulations were conducted from the source regions in northwestern China to the downwind region in Japan in order to understand wind erosion processes temporal and spatial distribution of dust during their long-range transportation chemical, physical, and optical properties of dust and the direct effect of radiative forcing due to dust. For this, three intensive observation periods (IOP) were conducted from April 2002 to April 2004.The in situ and network observation results are summarized as follows: (1) In situ observations of the wind erosion process revealed that the vertical profile of moving sand has a clear size dependency with height and saltation flux and that threshold wind velocity is dependent on soil moisture. Results also demonstrated that saltation flux is strongly dependent on the parent soil size distribution of the desert surface. (2) Both lidar observations and model simulations revealed a multiple dust layer in East Asia. A numerical simulation of a chemical transport model, CFORS, illustrated the elevated dust layer from the Taklimakan Desert and the lower dust layer from the Gobi Desert. The global-scale dust model, MASINGAR, also simulated the dust layer in the middle to upper free troposphere in East Asia, which originated from North Africa and the Middle East during a dust storm in March 2003. Raman lidar observations at Tsukuba, Japan, found the ice cloud associated with the dust layer at an altitude of 6 to 9 km. Analysis from lidar and the radio-sonde observation suggested that the Asian dust acted as ice nuclei at the ice-saturated region. These results suggest the importance of dust's climate impact via the indirect effect of radiative forcing due to the activation of dust into ice nuclei. (3) Studies on the aerosol concentration indicated that size distributions of aerosols in downwind regions have bimodal peaks. One peak was in the submicron range and the other in the supermicron range. The main soluble components of the supermicron peak were Na⁺, Ca²⁺, NO₃⁻, and Cl⁻. In the downwind region in Japan, the dust, sea salt, and a mixture of the two were found to be dominant in coarse particles in the mixed boundary layer. (4) Observation of the optical properties of dust by sky-radiometer, particle shoot absorption photometer (PSAP), and Nephelometer indicated that unpolluted dust at source region has a weaker absorption than originally believed.A sensitivity experiment of direct RF by dust indicated that single scattering albedo is the most important of the optical properties of dust and that the sensitivity of instantaneous RF in the shortwave region at the top of the atmosphere to the refractive index strongly depends on surface albedo. A global scale dust model, MASINGAR, was used for evaluation of direct RF due to dust. The results indicated the global mean RF at the top and the bottom of the atmosphere were − 0.46 and − 2.13 W m^− 2 with cloud and were almost half of the RF with cloud-free condition.  相似文献   

Recent developments in the radiation belt environment model     

M.-C. Fok  A. Glocer  Q. Zheng  R.B. Horne  N.P. Meredith  J.M. Albert  T. Nagai 《Journal of Atmospheric and Solar》2011,73(11-12):1435-1443

The fluxes of energetic particles in the radiation belts are found to be strongly controlled by the solar wind conditions. In order to understand and predict the radiation particle intensities, we have developed a physics-based Radiation Belt Environment (RBE) model that considers the influences from the solar wind, ring current and plasmasphere. Recently, an improved calculation of wave-particle interactions has been incorporated. In particular, the model now includes cross diffusion in energy and pitch-angle. We find that the exclusion of cross diffusion could cause significant overestimation of electron flux enhancement during storm recovery. The RBE model is also connected to MHD fields so that the response of the radiation belts to fast variations in the global magnetosphere can be studied. We are able to reproduce the rapid flux increase during a substorm dipolarization on 4 September 2008. The timing is much shorter than the time scale of wave associated acceleration.  相似文献   

Pressure responses of portlandite and H–D isotope effects on pressure-induced phase transitions     

Riko Iizuka  Hiroyuki Kagi  Kazuki Komatsu  Daichi Ushijima  Satoshi Nakano  Asami Sano-Furukawa  Takaya Nagai  Takehiko Yagi 《Physics and Chemistry of Minerals》2011,38(10):777-785

The pressure responses of portlandite and the isotope effect on the phase transition were investigated at room temperature from single-crystal Raman and IR spectra and from powder X-ray diffraction using diamond anvil cells under quasi-hydrostatic conditions in a helium pressure-transmitting medium. Phase transformation and subsequent peak broadening (partial amorphization) observed from the Raman and IR spectra of Ca(OH)₂ occurred at lower pressures than those of Ca(OD)₂. In contrast, no isotope effect was found on the volume and axial compressions observed from powder X-ray diffraction patterns. X-ray diffraction lines attributable to the high-pressure phase remained up to 28.5 GPa, suggesting no total amorphization in a helium pressure medium within the examined pressure region. These results suggest that the H–D isotope effect is engendered in the local environment surrounding H(D) atoms. Moreover, the ratio of sample-to-methanol–ethanol pressure medium (i.e., packing density) in the sample chamber had a significant effect on the increase in the half widths of the diffraction lines, even at pressures below the hydrostatic limit of the pressure medium.  相似文献   

Global tectonic significance of the Solomon Islands and Ontong Java Plateau convergent zone   总被引：3，自引：0，他引：3  

Paul Mann  Asahiko Taira   《Tectonophysics》2004,389(3-4):137

Oceanic plateaus, areas of anomalously thick oceanic crust, cover about 3% of the Earth's seafloor and are thought to mark the surface location of mantle plume “heads”. Hotspot tracks represent continuing magmatism associated with the remaining plume conduit or “tail”. It is presently controversial whether voluminous and mafic oceanic plateau lithosphere is eventually accreted at subduction zones, and, therefore: (1) influences the eventual composition of continental crust and; (2) is responsible for significantly higher rates of continental growth than growth only by accretion of island arcs. The Ontong Java Plateau (OJP) of the southwestern Pacific Ocean is the largest and thickest oceanic plateau on Earth and the largest plateau currently converging on an island arc (Solomon Islands). For this reason, this convergent zone is a key area for understanding the fate of large and thick plateaus on reaching subduction zones.This volume consists of a series of four papers that summarize the results of joint US–Japan marine geophysical studies in 1995 and 1998 of the Solomon Islands–Ontong Java Plateau convergent zone. Marine geophysical data include single and multi-channel seismic reflection, ocean-bottom seismometer (OBS) refraction, gravity, magnetic, sidescan sonar, and earthquake studies. Objectives of this introductory paper include: (1) review of the significance of oceanic plateaus as potential contributors to continental crust; (2) review of the current theories on the fate of oceanic plateaus at subduction zones; (3) establish the present-day and Neogene tectonic setting of the Solomon Islands–Ontong Java Plateau convergent zone; (4) discuss the controversial sequence and timing of tectonic events surrounding Ontong Java Plateau–Solomon arc convergence; (5) present a series of tectonic reconstructions for the period 20 Ma (early Miocene) to the present-day in support of our proposed timing of major tectonic events affecting the Ontong Java Plateau–Solomon Islands convergent zone; and (6) compare the structural and deformational pattern observed in the Solomon Islands to ancient oceanic plateaus preserved in Precambrian and Phanerozoic orogenic belts. Our main conclusion of this study is that 80% of the crustal thickness of the Ontong Java Plateau is subducted beneath the Solomon island arc; only the uppermost basaltic and sedimentary part of the crust (7 km) is preserved on the overriding plate by subduction–accretion processes. This observation is consistent with the observed imbricate structural style of plateaus and seamount chains preserved in both Precambrian and Phanerozoic orogenic belts.  相似文献   

Incipient subduction of the Ontong Java Plateau along the North Solomon trench     

A. Taira  P. Mann  R. Rahardiawan   《Tectonophysics》2004,389(3-4):247

The Ontong Java Plateau (OJP) in the western central Pacific is the largest and thickest oceanic plateau and one of a few oceanic plateaus converging on an island arc (Solomon island arc—SIA). To better understand the evolution of the North Solomon trench (NST), active oblique convergence between the OJP and SIA, and late Neogene development of Malaita accretionary prism (MAP), we present 850 km of multichannel seismic reflection data integrated with 7832 km² of IZANAGI side-scan sonar coverage. We have focussed the study at the transition area between the well-defined northwestern end of the North Solomon trench and a diffusely deformed area where the trench is actively propagating in a northwestward direction. The deeper structure beneath the survey area is discussed by Phinney et al. [Oceanic plateau accretion in the Malaita accretionary prism inferred from multi-channel seismic reflection data, this issue] using deeper penetration, multichannel seismic reflection lines. The serial cross sections provided by multichannel seismic profiling combined with the IZANAGI backscattering imagery provides a time series evolution for the development of the North Solomon trench. The main evolutionary stages include (1) the incipient trench in the northern area marked by a diffuse zone of deformation above a broad arch in the crust. Deeper penetration profiles by Phinney et al. show the bulge is related to a deeper decollement fault that is propagating upward and seaward through the crust. (2) The formation of a continuous thrust front in the central area. Deeper penetration profiles by Phinney et al. show this thrust front is surface expression of the same decollement present at depth to the north. The boundary between the surface trace of the thrust and the diffuse area of deformation in the northern area is inferred as a vertical, high-angle tear fault with left-lateral offset. (3) The formation of a deep, elongate trench which controls gravitationally related slumping and sedimentation around the steep edges of the trench fill basin. The areas to the southeast are those that have undergone convergence for the longest period of time and therefore show better developed trench structures and a reduced width of the MAP. Areas to the northwest have undergone convergence for a shorter period of time and show less developed trench structures and a wide area of the MAP.  相似文献   

Imaging of three-dimensional small-scale heterogeneities in the Hidaka, Japan region: coda spectral analysis     

Taka'aki Taira  Kiyoshi Yomogida 《Geophysical Journal International》2004,158(3):998-1008

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Southward intrusion of the intermediate Oyashio water along the east coast of the Boso Peninsula,Japan II. Intrusion events into Sagami Bay     

Sung-Kee Yang  Yutaka Nagata  Keisuke Taira  Masaki Kawabe 《Journal of Oceanography》1993,49(2):173-191

In the previous paper (Yanget al., 1993), it was shown that there always exists the coastal salinity-minimum-layer (SML) water just off the Boso Peninsula. The coastal SML water is bounded by the current zone of the Kuroshio, and a relatively high salinity domain separates it from the offshore SML water which would be a continum of the North Pacific Intermediate Water. We suggested that the coastal SML water region indicates the pathway along which the Intermediate Oyashio Water intrudes into Sagami Bay. In this paper, by selecting seven cases where we found the coastal SML water having abnormally high oxygen content and low salinity, we try to follow the intrusion manner of the Intermediate Oyashio Water into Sagami Bay by using available hydrographic data taken routinely by various organizations in the period from 1973 to 1986. Some of these water can be traced from the observation line near the cape of Inubo to the central part of Sagami Bay, and its propagation speed along the coast is shown to be of order of 1 cm/s. The intruding intermediate Oyashio water usually has a complicated layered structure in it, and its time scale of persistence is shown to be only a few months.  相似文献   

Occurrence characteristics of chaetognath species along the PM transect in the Japan sea during 1972–2002     

Naoki Nagai  Kazuaki Tadokoro  Kazunori Kuroda  Takashige Sugimoto 《Journal of Oceanography》2006,62(5):597-606

A long-term variation in dominant species of chaetognaths in the Tsushima Warm Current was analyzed using samples collected four times a year from 1972 to 2002 by the Maizuru Marine Observatory along the PM transect in the Japan Sea. Of 19 occurring species, 13 subtropical species formed a major portion of the standing stock. Species richness in the study area was similar to that in the East China Sea and the South China Sea. Four species, Sagitta minima, S. nagae, S. enflata, S. elegans dominated in the upper 150 m water column. The most dominant species per season were S. minima in both winter and autumn, S. elegans in spring and S. nagae in summer. Water temperature and salinity ranges of the most frequent occurrence for three dominant species revealed a common tendency in the order of S. nagae > S. minima > S. enflata towards colder temperature and higher salinity. Inter-annual abundance of chaetognath species fluctuated proportionally in response to the warm or cool phases in water temperature. Water temperature was a fundamental factor in regulating distributional occurrence, being more decisive than salinity. Changes of both dominant species and species numbers in relation to the reduced abundance during winter to spring and the subsequent increase during summer to autumn might be caused by specific differences in optimum temperature. Chaetognath species are important as an indicator of water masses and significant for our understanding of changes and evaluations of the Japan Sea ecosystem.  相似文献