Effect of seawater intrusion on microorganisms in the River Teshio,Hokkaidô, Japan     

Humitake Seki  Arinobu Ebara 《Journal of Oceanography》1980,36(1):30-34

Microorganisms and their activity were studied in the lower reaches of the River Teshio with special reference to the mixing of freshwater and seawater. The nature and processes observed therein were similar to those studied in the Nanaimo River, and they could be generalized as common in the subtemperate zone. The profile of microbial activity reflected the transition from freshwater to seawater in the River Teshio.  相似文献   

SON microbiological sampler for hydrobiological investigation     

Humitake Seki  Hirotaka Otobe  Toshisuke Nakai 《Journal of Oceanography》1974,30(4):203-204

A cylinder-type sampler, which is attached to the rod of Van Dorn sampler, was newly deviced for microbiological collection of 3-liter water samples from shallow layers.  相似文献   

Grain formation in the expanding gas flow around cool luminous stars     

Takashi Kozasa  Hiroichi Hasegawa  Junji Seki 《Astrophysics and Space Science》1984,98(1):61-79

We studied grain formation process and flow structure around cool luminous mass-loss stars. The nucleation and growth theory of Yamamoto and Hasegawa was extended to the case of expanding gas flow.The envelope was assumed to be steady, spherically symmetric, in thermal and radiative equilibrium, optically thin, and driven by radiation pressure on grains. For oxygen rich stars, Mg-silicate was found to be the first condensate which can drive the gas effectively. The following stellar parameters were chosen; stellar massM _*=1M , effective temperatureT _*=3000K, stellar luminosityL _* from 7.5×10³ to 2.0×10⁴ L , and mass-loss rate |M| from 1.0×10^–6 to 1.0×10^–4 M yr^–1.Main results of calculations are as follows; (1) grain condensation temperatureT _c9801080 K; (2) total gas pressure at the condensation pointP _t6×10^–116×10^–9 atm; (3) scale parameterA _c10³6×10⁴; and (4) final grain sizer _f=400Å1m. For the smaller |M| or the largerL _*, these values are the smaller. We recognized two types of flow solutions (1) Dust driven flow for large |M|, which reaches the sonic point near the condensation point; and (2) Modified Parker flow for small |M| for which grain sizer _f is almost independent of |M|.A comparison with observational results ofL _* and gas terminal velocityV suggests that Mg-silicate grains are of submicron size, which are effective for interstellar extinction in visible and infrared. Fe-grains condense in the rarefied outflow with a size probably smaller than 100Å, which may contribute for interstellar ultraviolet extinction. The envelope has three-layer structure inner dense region with small outflow velocity, grain formation layer and outer rarefied region with fast outflow velocity.No flow solutions exist forM _* greater than a critical stellar massM _*cr for a given stellar luminosityL _* and mass-loss rate |M|.For example, critical stellar massM _*cr=1.8M forL _*=10⁴ L ,T _*=3000 K, and |M|=10^-5 M yr^-1.  相似文献   

Time-series sediment trap record of alkenones from the western Sea of Okhotsk     

Osamu Seki  Takeshi Nakatsuka  Kimitaka Kawamura  Sei-Ichi Saitoh  Masaaki Wakatsuchi 《Marine Chemistry》2007,104(3-4):253-265

C₃₇–C₃₉ alkenones were measured in time-series sediment trap samples collected from August 1998 to June 2000 at two depths in the seasonal sea ice region of the western Sea of Okhotsk, off Sakhalin, in order to investigate alkenone production and water-column processes in the region. Measurable export fluxes of alkenones are ranged from < 0.1 to 5.8 μg/m²/day and clearly showed that the alkenone production was restricted to autumn. In 1998, maximum export flux of alkenones occurred in September when surface water column was well stratified with low nutrients in the surface mixing layer. In the next year, the maximum flux is observed in October. Comparison between alkenone temperature and satellite based sea surface temperature (SST) shows that the estimated alkenone temperatures in August 1998 were found to be  10 °C lower than the temporal satellite SST, suggesting that alkenones are produced in surface to subsurface thermocline layers during the period. Annual mean flux of alkenones is lower in the lower traps than that of the upper traps, suggesting rapid degradation of alkenones in water column, but the U^K₃₇′ value is not significantly altered. This study indicates that U^K₃₇′ values preserved in the surface sediments off Sakhalin reflect the seasonal temperature signal of near surface water, rather than annual mean surface temperature.  相似文献   

Mid- to- late Holocene hydroclimatic changes on the Chinese Loess Plateau: evidence from <Emphasis Type="Italic">n</Emphasis>-alkanes from the sediments of Tianchi Lake     

Huiling Sun  James Bendle  Osamu Seki  Aifeng Zhou 《Journal of Paleolimnology》2018,60(4):511-523

We have reconstructed the history of mid-late Holocene paleohydrological changes in the Chinese Loess Plateau using n-alkane data from a sediment core in Tianchi Lake. We used P_aq (the proportion of aquatic macrophytes to the total plant community) to reflect changes in lake water level, with a higher abundance of submerged macrophytes indicating a lower water level and vice versa. The P_aq-based hydrological reconstruction agrees with various other lines of evidence, including ACL (average chain length), CPI (carbon preference index), C/N ratio and the n-alkane molecular distribution of the sediments in Tianchi Lake. The results reveal that the lake water level was relatively high during 5.7–3.2 ka BP, and decreased gradually thereafter. Our paleohydrological reconstruction is consistent with existing paleoclimate reconstructions from the Loess Plateau, which suggest a humid mid-Holocene, but is asynchronous with paleoclimatic records from central China which indicate an arid mid-Holocene. Overall, our results confirm that the intensity of the rainfall delivered by the EASM (East Asian summer monsoon) is an important factor in affecting paleohydrological changes in the region and can be considered as further evidence for the development of a spatially asynchronous “northern China drought and southern China flood” precipitation pattern during the Holocene.  相似文献   

The transition zone chlorophyll front, a dynamic global feature defining migration and forage habitat for marine resources   总被引：2，自引：0，他引：2  

Jeffrey J. Polovina  Evan Howell  Donald R. Kobayashi  Michael P. Seki 《Progress in Oceanography》2001,49(1-4)

Pelagic ecosystem dynamics on all temporal scales may be driven by the dynamics of very specialized oceanic habitats. One such habitat is the basin-wide chlorophyll front located at the boundary between the low chlorophyll subtropical gyres and the high chlorophyll subarctic gyres. Global satellite maps of surface chlorophyll clearly show this feature in all oceans. In the North Pacific, the front is over 8000 km long and seasonally migrates north and south about 1000 km. In the winter this front is located at about 30–35°N latitude and in the summer at about 40–45°N. It is a zone of surface convergence where cool, vertically mixed, high chlorophyll, surface water on the north side sinks beneath warm, stratified, low chlorophyll water on the south side. Satellite telemetry data on movements of loggerhead turtles and detailed fisheries data for albacore tuna show that both apex predators travel along this front as they migrate across the North Pacific. The front is easily monitored with ocean color satellite remote sensing. A change in the position of the TZCF between 1997 and 1998 appears to have altered the spatial distribution of loggerhead turtles. The position and dynamics of the front varied substantially between the 1998 El Niño and the 1999 La Niña. For example, from May to July 1999 the transition zone chlorophyll front (TZCF) remained between about 35°N and 40°N latitude showing very little meandering, whereas in 1998, during the same period, the TZCF exhibited considerable meandering and greater monthly latitudinal movement. Catch rates for albacore were considerably higher in 1998 than in 1999, and we hypothesize that a meandering TZCF creates regions of convergence, which enhances the foraging habitat for apex predators along the front.  相似文献   

An integrated analysis platform merging SuperDARN data within the THEMIS tool developed by ERG-Science Center (ERG-SC)     

Tomoaki Hori  Nozomu Nishitani  Yoshizumi Miyoshi  Yukinaga Miyashita  Kanako Seki  Tomonori Segawa  Keisuke Hosokawa 《极地研究(英文版)》2013,24(1)

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Hydrogen isotopic ratios of plant wax n-alkanes in a peat bog deposited in northeast China during the last 16 kyr     

Osamu Seki  Philip A. Meyers  Kimitaka Kawamura  Yanhong Zheng  Weijian Zhou 《Organic Geochemistry》2009,40(6):671-677

Based on paleoclimatic reconstructions using various proxies, the Holocene Climate Optimum (10.5–6 ka) has been characterized as a warmer and wetter period in most of East Asia. The summer monsoons associated with the East Asian Monsoon evidently intensified and extended further inland from the Pacific Ocean, a source region of moisture. A notable exception to this general pattern exists in northeast China, where less wet conditions are recorded. We determined molecular compositions of individual plant wax hydrocarbons and their hydrogen isotope compositions (δD values) in a radiocarbon-dated peat core recovered from the Hani marsh in Jilin Province (China) and confirmed that the temperature-dependent effective precipitation in northeast China decreased during the Holocene Climate Optimum. A combination of P_aq, an indicator of the relative contribution of aquatic to terrestrial plants, and the difference in δD between low (C₂₃, C₂₅ and C₂₇) and high molecular weight (C₃₁) n-alkanes in the Hani peat bog indicates a dramatic change in vegetation from the deglaciation to the Holocene. No significant differences were observed between the δD values of low and high molecular weight n-alkanes with relatively high δD values and low P_aq during the early Holocene, indicating that all n-alkanes were produced by evapotranspiration-sensitive terrestrial plants during that time. However, lower δD values of mid-chain n-alkanes (C₂₃, C₂₅ and C₂₇) relative to the long chain n-alkane (C₃₁), together with higher P_aq values during the deglaciation (14–11 ka), suggest an increase in the contribution of aquatic plants and a higher water level during the period. The study demonstrates that northeast China was under a markedly wetter climate condition during the late deglaciation. For the 16 kyr record in the Hani peat sequence, we infer that moisture delivery by the East Asian Monsoon was relatively invariable in northeast China, but increased evaporation during the warmer Holocene Climate Optimum reduced the effective precipitation, defined by the balance between precipitation and evaporation.  相似文献   

Microbial biomass in the Eutrophic Bay of Shimoda as compared by estimations of several biomass parameters     

Yukuya Yamaguchi  Humitake Seki 《Journal of Oceanography》1977,33(1):38-44

Microbial biomass in seawater of Shimoda Bay was assessed using some biomass parameters, such as ATP, DNA, RNA, protein, chlorophylla, and bacterial number and every estimate is in the same order. The estimates based on the amounts of ATP, DNA and RNA showed good correlation.  相似文献   

Random network model of electrical conduction in two-phase rock     

Fuji-ta  Kiyoshi  Seki  Masayuki  Ichiki  Masahiro 《Mineralogy and Petrology》2018,112(6):857-864

Mineralogy and Petrology - We developed a cell-type lattice model to clarify the interconnected conductivity mechanism of two-phase rock. We quantified electrical conduction networks in rock and...  相似文献