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231.
Masahide Wakita Makio C. Honda Kazuhiko Matsumoto Tetsuichi Fujiki Hajime Kawakami Sayaka Yasunaka Yoshikazu Sasai Chiho Sukigara Mario Uchimiya Minoru Kitamura Toru Kobari Yoshihisa Mino Akira Nagano Shuichi Watanabe Toshiro Saino 《Journal of Oceanography》2016,72(5):665-685
The annual flux of biologically produced organic carbon from surface waters is equivalent to annual net community production (NCP) at a steady state and equals the export of particulate and dissolved organic carbon (POC and DOC, respectively) to the ocean interior. NCP was estimated from carbon budgets of salinity-normalized dissolved inorganic carbon (nDIC) inventories at two time-series stations in the western subarctic (K2) and subtropical (S1) North Pacific Ocean. By using quasi-monthly biogeochemical observations from 2004 to 2013, monthly mean nDIC inventories were integrated from the surface to the annual maximum mixed layer depth and corrected for changes due to net air–sea CO2 exchange, net CaCO3 production, vertical diffusion from the upper thermocline, and horizontal advection. The annual organic carbon flux at K2 (1.49 ± 0.42 mol m?2 year?1) was lower than S1 (2.81 ± 0.53 mol m?2 year?1) (p < 0.001 based on t test). These fluxes consist of three components: vertically exported POC fluxes (K2: 1.43 mol m?2 year?1; S1: 2.49 mol m?2 year?1), vertical diffusive DOC fluxes (K2: 0.03 mol m?2 year?1; S1: 0.25 mol m?2 year?1), and suspended POC fluxes (K2: 0.03 mol m?2 year?1; S1: 0.07 mol m?2 year?1). The estimated POC export flux at K2 was comparable to the sum of the POC flux observed with drifting sediment traps and active carbon flux exported by migrating zooplankton. The export fluxes at both stations were higher than those reported at other time-series sites (ALOHA, the Bermuda Atlantic Time-series Study, and Ocean Station Papa). 相似文献
232.
233.
Benzo(a)pyrene (BP) in the sediment of Osaka Bay were determined. High concentration was found at two stations near the mouth of Shin-Yodo and off Kobe respectively (0.98g g–1 dry mud basis, 1.1g g–1). The concentration decreases regularly from the mouth of the river further into the bay. The other supplemental determination was carried on the sediment and the seawater of Keihin Canal. Notable BP concentration of 89g g–1 was observed in the sediment beneath the effluent outlet of a gasworks. The BP in the sediment near the ironworks was also considerable, while the BP was relatively less in the sediment beneath the effluent outlet of refineries. These data suggest that coke plants working in gasworks or ironworks may be the larger sources of BP than refineries. The results of Osaka Bay coincide with this hypothesis.Cadmium, lead, copper, zinc, nickel, ignition loss and fine sand content were measured from the same sediment samples of Osaka Bay. Cd, Pb, Cu and ignition loss showed the regular distributions which resemble to BP and accordingly, good correlations with BP. No significant correlations were found between BP and Ni, Zn and fine sand content which showed no regular distributions. 相似文献
234.
Atsushi Noda Hajime Katayama Tsumoru Sagayama Kazuya Suga Yasuhito Uchida Kenji Satake Kohei Abe Yukinobu Okamura 《Sedimentary Geology》2007,200(3-4):314-327
A combined approach of field geology and numerical simulation was conducted for evaluating the tsunami impacts on the shelf sediments. The 2003 Tokachi-oki earthquake, M 8.0, that occurred on 25 September 2003 off southeastern Hokkaido, northern Japan, generated a locally destructive tsunami. Maximum run-up height of the tsunami waves reached 4 m above sea level. In order to estimate the tsunami impacts on shallow marine sediments, we compared pre- and post-tsunami marine sediments in water depths of 38–112 m in terms of grain size, sedimentary structure, and microfossil content. Decreases of fine fractions, especially finer than very fine sand, which led to coarsen the mean grain size, were detected in the inner shelf of the northern part of the study area. Foraminiferal assemblages also changed in the coarsened sediments. On the other hand, the other shelf sediments largely unchanged or slightly fined. We also simulated the tsunami wave velocity and direction, and grain size entrained by the modeled tsunami. The numerical simulation resulted in that the 2003 tsunami could transport very fine sand in water depths shallower than 45–95 m at the northern part of the study area. This is comparable with the actual grain-size changes after the tsunami had passed. However, some storms and tidal currents might also be possible to stir the surface sediments after the pre-tsunami survey, so we could not conclude that the grain-size changes had been caused only by the tsunami. Nevertheless, a combined approach of sampling and modeling was powerful for estimating the tsunami impacts under the sea. 相似文献
235.
Flood susceptibility mapping using geomorphologic approaches is effective for delineating flood extent and various degrees of potential flood-affected areas. This approach is useful where the channel system and floodplain morphology change dynamically and in regions where detailed digital elevation models are not available. The first important step in flood zonation using this approach is detailed geomorphologic mapping, also called landform classification. This study aims to describe landform classification using the rule-based method of Ho et al. (Int J Geoinform 8(4):27–38, 2012) adapted to local characteristics in the western plain of the Red River delta, northern Vietnam. The original classification scheme is generally based on the moist condition classification, local land-surface parameters, and relative position indices derived from multi-temporal Landsat data and a shuttle radar topographic mission digital elevation model (SRTM DEM). This study uses average elevations and the standard deviation of elevations as local land-surface parameters rather than local relief, which was used in the study by Ho et al. (Int J Geoinform 8(4):27–38, 2012). Multi-temporal land cover classification was performed using an integrated method to effectively correct the SRTM DEM. The overall classification is consistent with manual mapping by visual comparison. The quantitative comparison between landform units and past flood-affected areas demonstrates a precise boundary delineation of landform objects using this method. The high agreement between the boundaries of landform units and flood-inundated areas suggests the applicability of this method taking advantage of readily available remotely sensed datasets in alluvial floodplains. 相似文献
236.
Joji Ishizaka Eko Siswanto Tetsuya Itoh Hiroshi Murakami Yukuya Yamaguchi Naho Horimoto Takashi Ishimaru Shinji Hashimoto Toshiro Saino 《Journal of Oceanography》2007,63(3):517-524
The Vertically Generalized Production Model (VGPM) was verified by the primary production data of the Sagami Bay, Japan. The
VGPM with open ocean parameters including P
B
opt
, maximum primary production per unit of chlorophyll a in the water column, explained only 40% of the variability of integrated primary production. Formulations of the open ocean
P
B
opt
showed no correlation with in situ
P
B
opt
. Adjustment of the parameters of chlorophyll a and temperature dependent P
B
opt
improved the estimation of integrated primary production to 47% of the variation. Vertical integration parameters of VGPM
also have to be adjusted to improve the estimation. Integrated primary production calculated with a stronger light dependency
and with the adjusted P
B
opt
model can explain 74% of the variation. This model was used to estimate primary production of the Sagami Bay during 2003
with satellite data. In situ measurements on cloudy days indicate that the use of satellite data from sunny days only overestimates primary production. 相似文献
237.
Jidapa Koomklang Hitomi Yamaguchi Kazuhiko Ichimi Kuninao Tada 《Journal of Oceanography》2018,74(1):13-21
A superficial sediment layer (SL) is the top 2–3 mm layer of surface sediment that may contribute to high upward nutrient flux. To study the characteristics and the biogeochemical processes in the superficial layer, the seasonal variation in the total phytopigments (chlorophyll a and pheo-pigments), total organic carbon (TOC), and total nitrogen (TN) of the surface sediments in a shallow coastal area, Shido Bay, were measured, and the influence of the superficial sediment layer on nutrient flux at the sediment–water interface was investigated. TOC and TN content were relatively constant for the SL and subsurface layers (0–1 and 1–2 cm) during the study period. In contrast, total phytopigments content was higher in the SL layer than in the subsurface layers. The results of upward nutrient flux experiments showed higher nutrient release within the whole sediment core (SL remaining) than the SL-less (SL removed) core. Moreover, high nutrient fluxes were observed during the high temperature season, indicating that seasonal variation in nutrient flux was regulated by temperature. Moreover, in the low temperature season, the SL seemed to absorb nutrients, probably because of microphytobenthos photosynthesis that took up the nutrients under the sufficient light penetration to the sea floor. 相似文献
238.
Dynamics of land use/cover changes and the analysis of landscape fragmentation in Dhaka Metropolitan, Bangladesh 总被引:3,自引:0,他引:3
Rapid urban expansion due to large scale land use/cover change, particularly in developing countries becomes a matter of concern since urbanization drives environmental change at multiple scales. Dhaka, the capital of Bangladesh, has been experienced break-neck urban growth in the last few decades that resulted many adverse impacts on the environment. This paper was an attempt to document spatio-temporal pattern of land use/cover changes, and to quantify the landscape structures in Dhaka Metropolitan of Bangladesh. Using multi-temporal remotely sensed data with GIS, dynamics of land use/cover changes was evaluated and a transition matrix was computed to understand the rate and pattern of land use/cover change. Derived land use statistics subsequently integrated with landscape metrics to determine the impact of land use change on landscape fragmentation. Significant changes in land use/cover were noticed in Dhaka over the study period, 1975–2005. Rapid urbanization was manifested by a large reduction of agricultural land since urban built-up area increased from 5,500?ha in 1975 to 20,549?ha in 2005. At the same time, cultivated land decreased from 12,040 to 6,236?ha in the same period. Likewise, wetland and vegetation cover reduced to about 6,027 and 2,812?ha, respectively. Consequently, sharp changes in landscape pattern and composition were observed. The landscape became highly fragmented as a result of rapid increase in the built-up areas. The analysis revealed that mean patch size decreased while the number of patches increased. Landscape diversity declined, urban dominance amplified, and the overall landscape mosaics became more continuous, homogenous and clumped. In order to devise sustainable land use planning and to determine future landscape changes for sound resource management strategies, the present study is expected to have significant implications in rapidly urbanizing cities of the world in delivering baseline information about long term land use change and its impact on landscape structure. 相似文献
239.
Naoya Miyoshi Hisao Satoh Yoshiaki Yamaguchi Harue Masuda 《Geostandards and Geoanalytical Research》2003,27(1):91-98
Five synthetic silica glasses have been prepared for microprobe determination of trace aluminium in quartz. The glasses were synthesized from tetraethoxysilane (TEOS) into which between 0 and 1431 μg g-1 aluminium had been doped. The aluminium concentrations of the glasses were independently determined by ICP-AES analysis. X-ray wavelength shift in the Al Kα peak was minimised relative to unknown quartz samples when these glasses were used for calibration. A set of these five glasses yielded a linear calibration line, and are available for trace aluminium analysis of quartz in routine microprobe systems. 相似文献
240.
Y. Uchida S. Hirose S. Morita M. Torii T. Tanaka T. Yabiku T. Miyagoshi S. Uemura T. Yamaguchi 《Astrophysics and Space Science》1998,264(1-4):145-169
We discuss here some of the new aspects about solar flares and active regions found by the Solar X-ray Satellite Yohkoh, by
taking advantage of the wider dynamic range and higher cadence observations with higher spatial resolution compared with the
previous satellites. Those new aspects have lead us to new ways of understandings, with contradictions to the previous views
about flares and active regions that are widely conceived for a long time. We give some models that explain those newly revealed
observational results.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献