Improvements in navigation using SeaBeam crossing errors     

Clyde E. Nishimura  Donald W. Forsyth 《Marine Geophysical Researches》1988,9(4):333-352

Adjustments to satellite constrained navigation are required to match SeaBeam bathymetric data at track crossings due to errors in dead reckoning and inaccuracies in satellite fixes. By shifting one of the SeaBeam swaths involved in a track crossing relative to the other and calculating the sum of the squares of the differences in bathymetry within the area of overlapping coverage, we map a two-dimensional error surface whose minimum corresponds to the best estimate of the correction to navigation required at the crossing point. Estimates of the covariance of this correction are derived from the error surface. We employ the curve fitting technique of Tarantola and Valette (1982) to invert for a smooth correction function to a starting model of the position of the ship as a function of time. This technique incorporates formal errors assigned to dead reckoning, satellite fixes, and the shifts required to match bathymetric swaths at crossing points in a simultaneous inversion for the correction function for all tracks within the study area.In a test of the method in a study area on the southern Mid-Atlantic Ridge, a data set involving two cruises, 30 days of SeaBeam data, and 753 track crossings, we found that crossing SeaBeam swaths can potentially resolve the relative position of the ship on the two tracks to within 30 to 70 m. The inversion procedure yielded a much better constrained navigation function and much improved match of bathymetry. The final model of the navigation fit crossing shifts about as well as satellite data (with respect to their assigned data errors) with the RMS value of the crossing shifts decreasing from 1200 m in the original satellite-constrained navigation to 200 m in the final solution. However, the potential resolution of position using SeaBeam swaths was not fully achieved in the solution because there are systematic bathymetric artifacts in SeaBeam data, multiple local minima in the error surfaces in highly lineated topography, inadequate dead reckoning data, occasional bad satellite fixes, and limitations on the short period corrections allowed in the model.  相似文献   

Interannual fluctuations in recruitment of walleye pollock in the Oyashio region related to environmental changes     

Osamu Shida  Tomonori Hamatsu  Akira Nishimura  Akifumi Suzaki  Jun Yamamoto  Kazushi Miyashita  Yasunori Sakurai 《Deep Sea Research Part II: Topical Studies in Oceanography》2007,54(23-26):2822

The Japanese Pacific walleye pollock (Theragra chalcogramma) stock is the largest stock of this species in Japanese waters. It is a key component of the Oyashio ecosystem. In southern Hokkaido waters, these fish spawn mainly during January and February near the mouth of Funka Bay (FB), and most eggs and larvae are transported into FB. During midsummer juvenile pollock migrate along the southern coast of Hokkaido to a nursery ground on the continental shelf off eastern Hokkaido (Doto area). However, some eggs and larvae are transported southward to the Tohoku region (TR). Transport depends largely on the Oyashio, which generally flows southward along the eastern coasts of Hokkaido and Tohoku. Thus, this stock has two different recruitment routes: FB–Doto and FB–TR. In the 1980s, when the southward flow of the Oyashio was strong, the number of age-2 pollock estimated from a virtual population analysis (VPA) indicated that recruitment to the entire stock remained at a medium level. In the 1990s, when the Oyashio weakened, strong year-classes occurred in 1991, 1994, and 1995, but not in the latter half of the 1990s. Juvenile catches in the TR by commercial fisheries, which can be taken as indices of recruitment level via FB–TR, were high during the 1980s and decreased in the 1990s. Although there was no significant difference in the average number of recruits between the 1980s and the 1990s as estimated from a VPA, the recruitment patterns differed between the two decades. Here, we propose that recruitment routes of this stock shifted in response to environmental changes.  相似文献   

Spatial and temporal distributions of water temperature in aSargassum forest     

Teruhisa Komatsu  Hiroyuki Ariyama  Hiroyuki Nakahara  Wataru Sakamoto 《Journal of Oceanography》1982,38(2):63-72

The present study examined the influence of aSargassum forest on the spatial and temporal distributions of water temperature in a small cove on a time scale of the order of hours. Water temperature and algal density were measured along a fixed transect at the cove for almost 2 days. The measurements were carried out in May 1977 during the season of luxuriant seaweed growth, and in August during the season of little growth. The average standing crop per unit volume, named the spatial algal density, was employed as a means of expressing the growth condition of the seaweed forest along the transect. Using the spatial algal density and by analyzing water temperature distribution the following facts were revealed. The diurnal fluctuation of water temperature was influenced by theSargassum forest during the season of luxuriant growth, and the seaweed forest delayed the ascent and descent of water temperature, especially under its canopy, on a time scale of the order of hours, i.e., the temperature distribution patterns were influenced by the heights and densities of theSargassum forest during its season of luxuriant growth. It is thought that these phenomena are brought about by two effects: one is the absorption by the seaweed forest of short-wave radiation passing through the sea surface, and the other is the suppression of convection by the seaweed.  相似文献   

Physical control of sediment carbon content in an estuarine tidal flat system (Nanakita River, Japan): A mechanistic case study     

Takashi Sakamaki  Osamu Nishimura 《Estuarine, Coastal and Shelf Science》2007,73(3-4):781-791

Temporal variations in sediment carbon content were tracked by sampling every 2 weeks for 6 to 33 months at 6 tidal flat stations with different carbon content levels (0.05–1.64%) in a single estuary. Three temporal series of current velocity at 5 cm above the sediment were also obtained. Non-cohesive and cohesive sediment stations differed in patterns of temporal variation in sediment carbon content, suggesting the difference in processes controlling sediment carbon content. In the stations of non-cohesive sandy sediment with relatively low carbon content (0.05–0.15%), sediment carbon content fluctuated within ranges specific to each station. In these stations, current velocity data suggested that frequency of sand resuspension washing out sediment carbon controls sediment carbon content level. In the stations of cohesive sediment with relatively high carbon content (0.77–1.64%), sediment carbon contents showed some unusual upward and downward peaks, recovered to usual levels specific to the stations, and was always kept higher than that in the non-cohesive sediment stations. We speculate that in the cohesive sediment stations, sand inputs may significantly control processes establishing the consolidated sediments with various carbon content levels. Spatial transitions from non-cohesive to cohesive sediments and from low to high sediment carbon contents likely occur as sand resuspension at spring tides become more irregular and less frequent. Based on these results, conceptual models describing physical processes controlling sediment carbon content at the studied stations were proposed.  相似文献   

Tidal time-scale variation in nutrient flux across the sediment–water interface of an estuarine tidal flat     

Takashi Sakamaki  Osamu Nishimura  Ruichi Sudo 《Estuarine, Coastal and Shelf Science》2006,67(4):653-663

We determined the range of the tidal variations in nutrient flux across the sediment–water interface and elucidated mechanisms of the flux variation in two estuarine intertidal flats (one sand, one mud) in northeastern Japan. Nutrient flux was measured using in situ light and dark chambers, which were incubated for 2 h, 2–6 times per day. Results showed that nutrient concentration in overlying water varied by tide and was also affected by sewage-treated water inflow. The nutrient fluxes responded quickly to the tidal variation in overlying water chemistry and the range of the variation in flux was as large as the seasonal-scale variation reported in previous studies. In the sand flat, salinity increase likely enhanced benthos respiration and led to increases in both O₂ consumption and PO₄³⁻ regeneration under low illumination, while benthic microalgae were likely to actively generate O₂, uptake PO₄³⁻ and suppress PO₄³⁻ release under high illumination (>900 μmol photons m⁻² s⁻¹). Also in the mud flat, PO₄³⁻ flux was related with O₂ flux, although the range of temporal variation in PO₄³⁻ flux was small. In both the flats, NH₄⁺ flux was always governed by NH₄⁺ concentration in the overlying water; either an increase in NH₄⁺ uptake or a decrease in NH₄⁺ release was observed as the NH₄⁺ concentration rose due to inflow of river water or input of sewage-treated water. Although NO₃⁻ tended to be released in both tidal flats when low NO₃⁻ concentration seawater dominated, their relationship was likely to be weakened under conditions of low oxygen consumption and suppressed denitrification. It is likely that tidal variation in nutrient flux is governed more by the nutrient concentration than other factors, such as benthic biological processes, particularly in the case where nutrient concentration in the overlying water is relatively high and with wide amplitude.  相似文献   

Development of an ROV operated both as towed and self-propulsive vehicle   总被引：1，自引：0，他引：1  

Masahiko Nakamura  Hiroyuki Kajiwara  Wataru Koterayama 《Ocean Engineering》2001,28(1):406

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Effects of fixation and storage on flow cytometric analysis of marine bacteria     

Eriko Kamiya  Shinji Izumiyama  Masahiko Nishimura  James G. Mitchell  Kazuhiro Kogure 《Journal of Oceanography》2007,63(1):101-112

Flow cytometry (FCM) is now becoming a routine tool for the enumeration and optical characterization of bacteria in marine environments. We investigated the effects of sample fixation and storage upon flow cytometric determination of marine bacteria. Fixed and unfixed seawater samples were analyzed by FCM immediately aboard ship and/or later in the laboratory, and the appearances of the fluorescence signals and bacterial counts of these samples were compared. Fixation and storage led to the formation of multiple peaks in fluorescence histograms; this was also seen in 22 out of 36 samples frozen in liquid nitrogen. Fixation did not, but storage did induce a decrease of bacterial counts: a rapid decrease during the first 3 days followed by a slower decline. The decline of cell numbers in stored samples was expressed by a regression model. Our studies indicate that precaution is necessary when interpreting the data from fixed and/or stored marine bacterial samples analyzed by FCM. The possibility that the procedure of fixation and storage leads to the appearance of high DNA and low DNA bacterial groups should be considered.  相似文献   

Unquenchable high-pressure perovskite polymorphs of MnSnO3 and FeTiO3     

Kurt Leinenweber  Wataru Utsumi  Yoshihiko Tsuchida  Takehiko Yagi  Kei Kurita 《Physics and Chemistry of Minerals》1991,18(4):244-250

New high-pressure orthorhombic (GdFeO₃-type) perovskite polymorphs of MnSnO₃ and FeTiO₃ have been observed using in situ powder X-ray diffraction in a diamond-anvil cell with synchrotron radiation. The materials are produced by the compression of the lithium niobate polymorphs of MnSnO₃ and FeTiO₃ at room temperature. The lithium niobate to perovskite transition occurs reversibly at 7 GPa in MnSnO₃, with a volume change of -1.5%, and at 16 GPa in FeTiO₃, with a volume change of -2.8%. Both transitions show hysteresis at room temperature. For MnSnO₃ perovskite at 7.35 (8) GPa, the orthorhombic cell parameters are a=5.301 (2) A, b=5.445 (2) Å, c=7.690 (8) Å and V= 221.99 (15) ų. Volume compression data were collected between 7 and 20 GPa. The bulk modulus calculated from the compression data is 257 (18) GPa in this pressure region. For FeTiO₃ perovskite at 18.0 (5) GPa, cell parameters are a=5.022 (6) Å, b=5.169 (5) Å, c=7.239 (9) Å and V= 187.94 (36) ų. Based on published data on the quench phases, the FeTiO₃ perovskite breaks down to a rocksalt + baddelyite mixture of FeO and TiO₂ at 23 GPa. This is the first experimental verification of the pressure-induced breakdown of a perovskite to simple oxides.  相似文献   

Controlling CO2 emissions for each area in a region: the case of Japan     

Tamaki  Tetsuya  Nozawa  Wataru  Managi  Shunsuke 《Carbon balance and management》2019,14(1):1-10

Background

Unlike in the developed countries, Ethiopia does not have carbon inventories and databank to monitor and enhance carbon sequestration potential of different forests. Only small efforts have been made so far to assess the biomass and soil carbon sequestration at micro-level. This study was carried out to obtain sufficient information about the carbon stock potential of Gerba-Dima forest in south-western Ethiopia. A total of 90 sample plots were laid by employing stratified random sampling. Nested plots were used to collect data of the four carbon pools. For trees with a diameter range of 5 cm < diameter < 20 cm, the carbon stock was assessed from a plot size of 49 m² (7 m * 7 m). For trees with a diameter range of 20 cm < diameter < 50 cm, the carbon stock was assessed from a plot size of 625 m² (25 m * 25 m). For trees > 50 cm diameter, an additional larger sample of 35 * 35 m² was used. Litter, herb and soil data were collected from 1 m² subplot established at the center of each nested plot. To compute the above ground biomass carbon stock of trees and shrubs with DBH > 5 cm, their DBH and height were measured. The biomass carbon assessment of woody species having DBH < 5 cm, litter and herb were conducted by measuring their fresh weight in the field and dry weight in the laboratory.

Results

The mean total carbon stock density of Gerba-Dima forest was found to be 508.9 tons carbon ha⁻¹, out of which 243.8, 45.97, 0.03 and 219.1 tons carbon ha⁻¹ were stored in the above ground biomass, below ground biomass, litter biomass and soil organic carbon, respectively.

Conclusions

The existence of high carbon stock in the study forest shows the potential of the area for climate change mitigation. Thus, all stakeholders at the local and national level should work together to implement effective conservation measures and get benefit from the biocarbon fund.

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Sea-floor methane blow-out and global firestorm at the K–T boundary     

M. D. Max  W. P. Dillon  C. Nishimura  B. G. Hurdle 《Geo-Marine Letters》1998,18(4):285-291

A previously unsuspected source of fuel for the global firestorm recorded by soot in the Cretaceous–Tertiary impact layer may have resided in methane gas associated with gas hydrate in the end-Cretaceous seafloor. End-Cretaceous impact-generated shock and megawaves would have had the potential to initiate worldwide oceanic methane gas blow-outs from these deposits. The methane would likely have ignited and incompletely combusted. This large burst of methane would have been followed by longer-term methane release as a part of a positive thermal feedback in the disturbed ocean-atmosphere system.  相似文献