Air-Sea Gas Transfer Velocity in Stormy Winter Estimated from Radon Deficiency     

Hitoshi Kawabata  Hisashi Narita  Koh Harada  Shizuo Tsunogai  Masashi Kusakabe 《Journal of Oceanography》2003,59(5):651-661

Thirteen vertical profiles of ²²⁶Ra and ²²²Rn in the near-surface water were obtained in the western North Pacific in winter, and the gas transfer velocities across the air-sea interface were estimated. The transfer velocities found by applying a steady state model varied widely from 2.1 to 30.2 m day⁻¹ with a mean of 9.4 m day⁻¹. The mean value is almost 5 times higher than that in summer in other oceans, and the maximum value is a record high for world oceans. This is partly due to the inadequacy of the steady state model, which overestimates when stronger winds blow in more recent days than the ²²²Rn half-life of about 4 days. In fact, a strong low pressure zone passed through the station about 2 days earlier, which was one of the low pressure zones that with a period of develop once a week or so in the northwestern North Pacific in winter. Instead of steady-state removal, if half of the radon removal occurred sporadically every 7 days, and the last removal took place two days before the observation, the transfer velocity would be 26 m day⁻¹. Our mean transfer velocity, which is less than 20% different from the steady state value including both overestimated and underestimated values, 9.4 ± 4.8 m day⁻¹, seems to represent the mean state of this region in winter. This suggests that the gas exchange fluxes under extremely rough conditions in the open ocean are larger than those estimated by using a transfer velocity equation with a linear or quadratic relationship with wind speed. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

The phytoplankton of some saline lakes in Central Asia     

Yoshiko Kawabata  Hiroyuki Nakahara  Yukio Katayama  Norio Ishida 《International Journal of Salt Lake Research》1997,6(1):5-16

The Aral Sea, Lake Balkhash, and Lake Kamyslybas are closed lakes in Central Asia. They range from oligosaline to metasaline. The salinity of the Aral Sea has increased by more than 30 g L⁻¹ since widespread irrigation began in its catchment area. Few studies of the phytoplankton have been conducted on these lakes since extensive irrigation started. The investigation reported here compares the flora of phytoplankton in these saline lakes. In the Small Aral Sea, phytoplankton density gradually decreased with increasing electrical conductivity (EC) (∼ salinity), but there was no such relation in Lake Balkhash and Lake Kamyslybas. In the Aral Sea, Dinophyceae and Bacillariophyceae were frequently observed in most areas of high EC value, and Cyanophyceae were most conspicuous in the area of medium and lower EC values. In Lake Balkhash, Cyanophyceae were most conspicuous, but Chlorophyceae were also noticeable. Most Cyanophyceae in Aral Sea formed filaments with heterocysts. The distinct characteristic of the phytoplankton of the Lake Balkhash was that all dominant species form colonies covered with a gelatinous film. Siliceousplankton diversity gradually decreased with increasing EC values in the Aral Sea and Lake Balkhash.  相似文献   

A study of microearthquake seismicity and focal mechanisms within the Sea of Marmara (NW Turkey) using ocean bottom seismometers (OBSs)   总被引：1，自引：0，他引：1  

Toshinori Sato  Junzo Kasahara  Tuncay Taymaz  Masakazu Ito  Aya Kamimura  Tadaaki Hayakawa  Onur Tan 《Tectonophysics》2004,391(1-4):303

We have carried out seismological observations within the Sea of Marmara (NW Turkey) in order to investigate the seismicity induced after Gölcük–İzmit (Kocaeli) earthquake (M_w 7.4) of August 17, 1999, using ocean bottom seismometers (OBSs). High-resolution hypocenters and focal mechanisms of microearthquakes have been investigated during this Marmara Sea OBS project involving deployment of 10 OBSs within the Çınarcık (eastern Marmara Sea) and Central-Tekirdağ (western Marmara Sea) basins during April–July 2000. Little was known about microearthquake activity and their source mechanisms in the Marmara Sea. We have detected numerous microearthquakes within the main basins of the Sea of Marmara along the imaged strands of the North Anatolian Fault (NAF). We obtained more than 350 well-constrained hypocenters and nine composite focal mechanisms during 70 days of observation. Microseismicity mainly occurred along the Main Marmara Fault (MMF) in the Marmara Sea. There are a few events along the Southern Shelf. Seismic activity along the Main Marmara Fault is quite high, and focal depth distribution was shallower than 20 km along the western part of this fault, and shallower than 15 km along its eastern part. From high-resolution relative relocation studies of some of the microearthquake clusters, we suggest that the western Main Marmara Fault is subvertical and the eastern Main Marmara Fault dips to south at 45°. Composite focal mechanisms show a strike-slip regime on the western Main Marmara Fault and complex faulting (strike-slip and normal faulting) on the eastern Main Marmara Fault.  相似文献   

High-reliability zircon separation for hunting the oldest material on Earth: An automatic zircon separator with image-processing/microtweezers-manipulating system and double-step dating     

Yukio Isozaki  Shinji Yamamoto  Shuhei Sakata  Hideyuki Obayashi  Takafumi Hirata  Ken-ichi Obori  Toshinori Maebayashi  Satoshi Takeshima  Toshikazu Ebisuzaki  Shigenori Maruyama 《地学前缘(英文版)》2018,9(4):1073-1083

Despite the recent development in radiometric dating of numerous zircons by LA-ICPMS, mineral separation still remains a major obstacle, particularly in the search for the oldest material on Earth. To improve the efficiency in zircon separation by an order of magnitude, we have designed/developed a new machine-an automatic zircon separator(AZS). This is designed particularly for automatic pick-up of100 μm-sized zircon grains out of a heavy mineral fraction after conventional separation procedures. The AZS operates in three modes:(1) image processing to choose targeted individual zircon grains out of all heavy minerals spread on a tray,(2) automatic capturing of the individual zircon grains with microtweezers, and(3) placing them one-by-one in a coordinated alignment on a receiving tray. The automatic capturing was designed/created for continuous mineral selecting without human presence for many hours. This software also enables the registration of each separated zircon grain for dating, by recording digital photo-image, optical(color) indices, and coordinates on a receiving tray. We developed two new approaches for the dating; i.e.(1) direct dating of zircons selected by LA-ICPMS without conventional resin-mounting/polishing,(2) high speed U-Pb dating, combined with conventional sample preparation procedures using the new equipment with multiple-ion counting detectors(LA-MIC-ICPMS).With the first approach, Pb-Pb ages obtained from the surface of a mineral were crosschecked with the interior of the same grain after resin-mounting/polishing. With the second approach, the amount of time required for dating one zircon grain is ca. 20 s, and a sample throughput of 150 grains per hour can be achieved with sufficient precision(ca. 0.5%).We tested the practical efficiency of the AZS, by analyzing an Archean Jack Hills conglomerate in Western Australia with the known oldest(4.3 Ga) zircon on Earth. Preliminary results are positive; we were able to obtain more than 194 zircons that are over 4.0 Ga out of ca. 3800 checked grains, and 9 grains were over 4300 Ma with the oldest at 4371 ± 7 Ma. This separation system by AZS, combined with the new approaches, guarantees much higher yield in the hunt for old zircons.  相似文献   

Preliminary results of a study on the responses of sedimentary rocks to shaft excavation     

Kozo Sugihara  Hisaya Yoshioka  Hiroya Matsui  Toshinori Sato 《Engineering Geology》1993,35(3-4):223-228

A shaft with a diameter of 6 m and a depth of 150 m was excavated in sedimentary rocks. Anin situ study was carried out to identify the size and rock properties of the zone disturbed by the excavation and to estimate the applicability of existing methods for measuring and modelling such a zone. The study detected displacements and changes in the properties of the rock within about 1 m of the shaft wall. Numerical analysis using a model of continuous rock mass can simulate some features of disturbance due to excavation, although slight discrepancies exist between the measured and analysed results. The excavation disturbance detected in this study is probably due to fracturing, the redistribution of stress and undersaturation. However, the relationships between the disturbance due to excavation and these processes have not been quantified. The existing methods for measurements and numerical analysis can provide important information on the disturbance due to excavation but need to be improved to understand disturbance due to excavation further.  相似文献   

A kinematic model for evolution of island arc-trench systems   总被引：1，自引：0，他引：1  

Toshinori Sato  Mitsuhiro Matsu'ura 《Geophysical Journal International》1993,114(3):512-530

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Calibration of the parameters for a hardening–softening constitutive model using genetic algorithms     

Md. Rokonuzzaman  Toshinori Sakai 《Computers and Geotechnics》2010

The present paper introduces a genetic algorithm-based optimization technique to calibrate a nonlinear strain hardening–softening constitutive model for soils using five material parameters. The efficiency of the proposed technique is analyzed through the use of different GA techniques. The effects of elitism, crossover, and mutation, as well as population size, on the performance of the conventional GAs for this problem are investigated. Micro-genetic algorithms (mGAs) are chosen and tested for different population sizes. The mGAs with a population size of five yields the optimal parameter values after fewer function evaluations and capture the overall simulated or experimental behavior at every point in stress–strain and strain paths in triaxial compression. The proposed calibration technique is validated through comparison with the traditional calibration technique.  相似文献   

Wet and Dry Basalt Magma Evolution at Torishima Volcano, Izu Bonin Arc, Japan: the Possible Role of Phengite in the Downgoing Slab   总被引：1，自引：0，他引：1  

Tamura  Y.; Tani  K.; Chang  Q.; Shukuno  H.; Kawabata  H.; Ishizuka  O.; Fiske  R. S. 《Journal of Petrology》2007,48(10):1999-2031

The arc-front volcanoes of Sumisu (31·5°N, 140°E)and Torishima (30·5°N, 140·3°E) in thecentral Izu–Bonin arc are similar in size and rise asrelatively isolated edifices from the seafloor. Together theyprovide valuable along-arc information about magma generationprocesses. The volcanoes have erupted low-K basalts originatingfrom both wet and dry parental basaltic magmas (low-Zr basaltsand high-Zr basalts, respectively). Based on models involvingfluid-immobile incompatible element ratios (La/Sm), the parentalbasalts appear to result from different degrees of partial meltingof the same source mantle (20% and 10% for wet and dry basaltmagmas, respectively). Assuming that the wet basalts containgreater abundances of slab-derived components than their drycounterparts, geochemical comparison of these two basalt typespermits the identification of the specific elements involvedin fluid transport from the subducting slab. Using an extensiveset of new geochemical data from Torishima, where the top ofthe downgoing slab is about 100 km deep, we find that Cs, Pb,and Sr are variably enriched in the low-Zr basalts, which cannotbe accounted for by fractional crystallization or by differencesin the degree of mantle melting. These elements are interpretedto be selectively concentrated in slab-derived metasomatic fluids.Variations in K, high field strength element and rare earthelement concentrations are readily explained by variations inthe degree of melting between the low- and high-Zr basalts;these elements are not contained in the slab-derived fluids.Rb and Ba exhibit variable behaviour in the low-Zr basalts,ranging from immobile, similar to K, to mildly enriched in somelow-Zr basalts. We suggest that the K-rich mica, phengite, playsan important role in determining the composition of fluids releasedfrom the downgoing slab. In arc-front settings, where slab depthis 100 km, phengite is stable, and the fluids released fromthe slab contain little K. In back-arc settings, however, wherethe slab is at 100–140 km depth, phengite is unstable,and K-rich fluids are released. We conclude that cross-arc variationsin the K content of arc basalts are probably related to differingcompositions of released fluids or melts rather than the widelyheld view that such variations are controlled by the degreeof partial melting. KEY WORDS: arc volcano; degrees of melting; mantle wedge; water; wet and dry basalts  相似文献   

A dislocation model for the earthquake cycle at convergent plate boundaries   总被引：1，自引：0，他引：1  

Mitsuhiro Matsu'ura  Toshinori Sato 《Geophysical Journal International》1989,96(1):23-32

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Ground subsidence in Semarang-Indonesia investigated by ALOS–PALSAR satellite SAR interferometry     

Ashar Muda Lubis  Toshinori Sato  Nobuhiro Tomiyama  Nobuhiro Isezaki  Tsutomu Yamanokuchi 《Journal of Asian Earth Sciences》2011,40(5):1079-1088

The focus of this study is investigation of land subsidence in Semarang city Indonesia with the use of Interferometry Synthetic Aperture Radar (InSAR) of ALOS–PALSAR satellite. We processed 22 ascending SAR images during January 2007 to January 2009 plus two descending SAR images acquired on 6 June 2006 and 17 June 2007. The time series analysis of interferometry was performed by using 12 pairs of interferogram relative to 21 January 2007 and 8 pairs of interferogram relative 24 January 2008. The topographic phase contribution was removed using the 3-arcsec (90 m) Shuttle Radar Topography Mission (SRTM), Digital Elevation Model (DEM). We performed precision baseline estimation to vanish the fringes from baseline effect between master and slave data. In order to investigate the contribution of horizontal movement in our analysis, we constructed two interferograms of ascending orbit and descending orbit. The time series results exhibited that the area is subsiding continuously without a significant seasonal effect during January 2007 to January 2009. The land subsidence observed from InSAR data is approximately up to 8 cm/year. Three cross sections on image displacement show the extreme land subsidence occurred especially along the coastal area and lowland area where this area is considered as industrial with high-density settlements, consuming a lot of groundwater, and land is changed from agriculture and cultivation purposes to industrial estates and house. Our result also shows a consistency with historical pattern of subsidence measured by leveling data. The results highlight the potential use of InSAR measurements to provide better constraints for land subsidence in Semarang city Indonesia.  相似文献