Biweekly periodic variation of the Kuroshio axis northeast of Taiwan as revealed by ocean high-frequency radar     

Daisuke Takahashi  Xinyu Guo  Akihiko Morimoto  Shoichiro Kojima 《Continental Shelf Research》2009,29(15):1896-1907

An analysis of surface current data obtained from 2002 to 2005 using long-range high-frequency radar provides the first evidence for the presence of biweekly (11–14 day) periodic variations of the Kuroshio axis northeast of Taiwan. This analysis clarifies the spatiotemporal characteristics of these variations and reveals that cyclonic/anticyclonic eddies propagating along the shelf slope from the vicinity of the deep channel east of Taiwan induce these variations northeast of Taiwan. The behavior of the cyclonic/anticyclonic eddies on the shelf slope is well explained by 2nd-mode interior shelf waves advected by the Kuroshio's mean flow. Remote effects from the vicinity of the deep channel east of Taiwan, or from outside the East China Sea, are believed to play an important role in the generation of these biweekly periodic variations of the Kuroshio axis northeast of Taiwan. Moreover, on the shelf slope, these variations cause an onshore current across the shelf slope, suggesting topographically controlled upwelling. Therefore, the biweekly periodic variations of the Kuroshio axis northeast of Taiwan might contribute not only to the onshore transport of Kuroshio surface water but also to transport nutrient-rich Kuroshio subsurface water onto the shelf in the East China Sea.  相似文献   

Organohalogen contaminants in striped dolphins (Stenella coeruleoalba) from Japan: Present contamination status, body distribution and temporal trends (1978-2003)     

Tomohiko Isobe  Karri Ramu  Yuko Tajima  Masao Amano  Shin Takahashi 《Marine pollution bulletin》2009,58(3):396-401

Organohalogen contaminants including PCBs, DDTs, CHLs, HCHs, HCB, PBDEs and HBCDs were determined in striped dolphins (Stenella coeruleoalba) found stranded at Gogo-shima (n = 6, 2003) and collected from Taiji (n = 15, 1978-1992) in Japan. All target compounds were significantly detected in all the specimens, indicating ubiquitous contamination of oceanic cetaceans in northwest Pacific Ocean. Examination of body distribution of organohalogens in the six specimens from Gogo-shima showed no significant difference in concentrations among the analyzed tissues, except for brain, which had lower levels possibly due to the existence of blood-brain barrier. For evaluating temporal trends, archived blubber samples of adult male stripped dolphins collected in 1978, 1979, 1986 and 1992 were analyzed. Concentrations of PCBs, DDTs and HCHs did not change significantly during 1978-2003. In contrast, remarkable increasing trends of PBDEs and HBCDs were observed, suggesting growing consumption in Japan and surrounding countries in recent years.  相似文献   

Nitrogen isotope ratios of nitrate as a clue to the origin of nitrogen on the Pacific coast of Japan     

Ryo Sugimoto  Akihide Kasai  Toshihiro Miyajima  Kouichi Fujita 《Continental Shelf Research》2009

To clarify the sources and transformation of NO₃⁻ on the Pacific coast of Japan, observations over the continental shelf were conducted during the summer in 2005 and 2006 when the Kuroshio flowed close to and away from the coastal area, respectively. Below the halocline, there are two prominent salinity peaks that originated in two different waters. In the subsurface layer, the salinity maximum (S_max) was indicative of the Kuroshio Water (KW), while the salinity minimum (S_min) in the middle layer at ∼400 m depth was indicative of the North Pacific Intermediate Water (NPIW). δ¹⁵N_NO3 ranged from 4.1‰ to 5.1‰ with a mean of 4.8±0.4‰ in the deeper water around S_min. Below 50 m depth over the shelf break, δ¹⁵N_NO3 values (3.1±0.8‰ in 2005 and 4.6±0.3‰ in 2006) clearly increased as contribution of NPIW increased in 2006. On the contrary, subsurface δ¹⁵N of NO₃⁻ values (−1.1±0.1‰) remained unchanged in both years, although the contribution of the KW to the subsurface water changed significantly. This suggests that the source of NO₃⁻ has little effect on the δ¹⁵N of NO₃⁻ in this layer. The negative δ¹⁵N values also coincided with the base of the chlorophyll maximum layer suggesting that these isotopic signals must be evidence of active nitrification in the upper layer.  相似文献   

Forces acting on bridge abutments over liquefied ground     

Akihiro Takahashi  Hideki Sugita  Shunsuke Tanimoto 《Soil Dynamics and Earthquake Engineering》2010

Large earthquake-induced displacements of a bridge abutment can occur, when the bridge is built on a floodplain or reclaimed area, i.e., liquefiable ground, and crosses a water channel. Seismic responses of a bridge abutment on liquefiable ground are the consequence of complex interactions between the abutment and surrounding soils. Therefore identification of the factors dominating the abutment response is important for the development of simplified seismic design methods. This paper presents the results of dynamic three-dimensional finite element analyses of bridge abutments adjacent to a river dike, including the effect of liquefaction of the underlying ground using earthquake motions widely used in Japan. The analysis shows that conventional design methods may underestimate the permanent abutment displacements unless the following two items are considered: (1) softening of the soil beneath the liquefiable layer, due to cyclic shearing of the soil surrounding the piles, and (2) the forces acting on the side faces of the abutment.  相似文献   

Response of a summertime anticyclonic eddy to wind forcing in Funka Bay,Hokkaido, Japan     

Daisuke Takahashi  Hideo Miyake  Takeyasu Nakayama  Naoto Kobayashi  Kazuo Kido  Yoshinori Nishida 《Continental Shelf Research》2010

Flow fluctuations inside an anticyclonic eddy in summertime Funka Bay were examined using three moorings and hydrographic data. The flow pattern above a sharp pycnocline with a concave isopycnal structure during the mooring period was characterized by high mean kinetic energy and relatively low eddy kinetic energy. The ratios of eddy to mean kinetic energy were equal to or less than one, and the mean flow field and isopycnal structure indicated the existence of a stable anticyclonic eddy above the sharp pycnocline under approximate geostrophic balance. Larger flow fluctuations with periods longer than 7 days were dominant inside the eddy. The low-frequency flow fluctuations are accompanied by north to northeastward movement of the eddy with deepening of the pycnocline and spin-up of the anticyclonic circulation. The wind field over Funka Bay is characterized by bay-scale wind fluctuations. The bay-scale winds are greatly influenced by the land topography around Funka Bay, resulting in non-uniform structure with significant wind stress curl. The bay-scale wind fluctuations are termed “locally modified wind” in the present study. The locally modified wind has a negative (positive) wind stress curl in the central–northeastern (southwestern) region of Funka Bay. The north to northeastward movement of the eddy is caused by horizontal non-uniform supply of vorticity from the locally modified wind forcing by the Ekman pumping process. Through this process, the anticyclonic circulation is enhanced (weakened) in the central–northeastern (southwestern) part of the eddy, resulting in the eddy moving north to northeastward with the pycnocline deepening and spin-up of the anticyclonic circulation. The locally modified wind forcing induces low-frequency flow fluctuations through the movement of the eddy in summertime Funka Bay.  相似文献   

Comparison of carbon cycle between the western Pacific subarctic and subtropical time-series stations: highlights of the K2S1 project     

Makio C. Honda  Masahide Wakita  Kazuhiko Matsumoto  Tetsuichi Fujiki  Eko Siswanto  Kosei Sasaoka  Hajime Kawakami  Yoshihisa Mino  Chiho Sukigara  Minoru Kitamura  Yoshikazu Sasai  Sherwood L. Smith  Taketo Hashioka  Chisato Yoshikawa  Katsunori Kimoto  Shuichi Watanabe  Toru Kobari  Toshi Nagata  Koji Hamasaki  Ryo Kaneko  Mario Uchimiya  Hideki Fukuda  Osamu Abe  Toshiro Saino 《Journal of Oceanography》2017,73(5):647-667

A comparative study of ecosystems and biogeochemistry at time-series stations in the subarctic gyre (K2) and subtropical region (S1) of the western North Pacific Ocean (K2S1 project) was conducted between 2010 and 2013 to collect essential data about the ecosystem and biological pump in each area and to provide a baseline of information for predicting changes in biologically mediated material cycles in the future. From seasonal chemical and biological observations, general oceanographic settings were verified and annual carbon budgets at both stations were determined. Annual mean of phytoplankton biomass and primary productivity at the oligotrophic station S1 were comparable to that at the eutrophic station K2. Based on chemical/physical observations and numerical simulations, the likely “missing nutrient source” was suggested to include regeneration, meso-scale eddy driven upwelling, meteorological events, and eolian inputs in addition to winter vertical mixing. Time-series observation of carbonate chemistry revealed that ocean acidification (OA) was ongoing at both stations, and that the rate of OA was faster at S1 than at K2 although OA at K2 is more critical for calcifying organisms.  相似文献   

Asia-Pacific mussel watch: monitoring contamination of persistent organochlorine compounds in coastal waters of Asian countries   总被引：27，自引：0，他引：27  

Monirith I  Ueno D  Takahashi S  Nakata H  Sudaryanto A  Subramanian A  Karuppiah S  Ismail A  Muchtar M  Zheng J  Richardson BJ  Prudente M  Hue ND  Tana TS  Tkalin AV  Tanabe S 《Marine pollution bulletin》2003,46(3):281-300

Contamination of persistent organochlorines (OCs) such as PCBs (polychlorinated biphenyls), DDT and its metabolites (DDTs), HCH (hexachlorocyclohexane) isomers (HCHs), chlordane compounds (CHLs), and HCB (hexachlorobenzene) were examined in mussels collected from coastal waters of Asian countries such as Cambodia, China, Hong Kong, India, Indonesia, Japan, Korea, Malaysia, Philippines, Far East Russia, Singapore, and Vietnam in 1994, 1997, 1998, 1999, and 2001 to elucidate the contamination status, distribution and possible pollution sources and to assess the risks on aquatic organisms and human. OCs were detected in all mussels collected from all the sampling sites investigated. Considerable residue levels of p,p(')-DDT and alpha-HCH were found in mussels and the concentrations of DDTs and HCHs found in mussels from Asian developing countries were higher than those in developed nations suggesting present usage of DDTs and HCHs along the coastal waters of Asian developing countries. On the other hand, lower concentrations of PCBs detected in mussels from Asian developing countries than those in developed countries indicate that PCBs contamination in mussels is strongly related to industrial and activities. To our knowledge, this is a first comprehensive report on monitoring OCs pollution in the Asia-Pacific region.  相似文献   

Estimation of water requirement per unit carbon fixed by<Emphasis Type="Italic">Eucalyptus camaldulensis</Emphasis> in semi-arid land of Western Australia     

T. Kojima  Y. Tanaka  S. Katoh  K. Tahara  N. Takahashi  K. Yamada 《中国科学D辑(英文版)》2002,45(1):142-147

Afforestation in arid land is a promising method for carbon fixation, but the effective utilization of water is highly important and required. Thus, the evaluation of the amount of water per unit carbon fixed with the tree growth is required to minimize the amount of water supplied to the plants. In this research, a tree is regarded as a carbon fixation reactor with inflows of water and nutrients from roots, and CO₂ as the carbon source from leaves with outflow of water vapor from leaves and accumulation in the tree itself. In the process of photosynthesis and respiration nutritional elements are dissolved in water flow in trees. They do not flow out by these reactions, but are accumulated in trees. Thus, we have treated the behaviour of nutrients as a marker to evaluate the water/carbon ratio.Assuming that nutrient concentration is constant in sap, and the differences in the ratios of nutrient to carbon in living trees and dead (i.e. litter fall, etc.) are neglected, the ratio of the used water to fixed carbon is given as the ratio of nutrient to carbon in the tree body divided by the ratio of nutrient to water in sap. However, some nutrients are translocated and concentrated within the tree and some may be discarded through litter fall. Thus it is important to examine which nutrient element is the most suitable as the tracer.In this paper, the results of the above method applied toEucalyptus camaldulensis in semiarid land of Western Australia are shown. The value of water requirement per unit carbon fixation determined from potassium balance is between 421 kg-H₂O/kg-C for mature trees and 285 kg-H₂O/kg-C for young trees, while the values from calcium balance are much larger than these. The cause of the discrepancy between these values is discussed based on the measured element concentrations in sap and trees and the plant physiology. Finally, the actual average value through the life of a tree is suggested to fall between the two values.  相似文献   

Tail emission of prompt gamma-ray burst jets     

Ryo Yamazaki  Kenji Toma  Kunihito Ioka  Takashi Nakamura 《Monthly notices of the Royal Astronomical Society》2006,369(1):311-316

Tail emission of the prompt gamma-ray burst (GRB) is discussed using a multiple emitting sub-shell (inhomogeneous jet, sub-jets or mini-jets) model, where the whole GRB jet consists of many emitting sub-shells. One may expect that such a jet with angular inhomogeneity should produce spiky tail emission. However, we found that the tail is not spiky but is decaying roughly monotonically. The global decay slope of the tail is not so much affected by the local angular inhomogeneity but affected by the global sub-shell energy distribution. The fact that steepening GRB tail breaks appeared in some events prefers the structured jets. If the angular size of the emitting sub-shell is around 0.01–0.02 rad, some bumps or fluctuations appear in the tail emission observed frequently in long GRBs. If the parameter differences of sub-shell properties are large, the tail has frequent changes of the temporal slope observed in a few bursts. Therefore, the multiple emitting sub-shell model has the advantage of explaining the small-scale structure in the observed rapid decay phase.  相似文献   

The trade in wild pig meat: Australia and Japan     

Shunjo Takahashi  Clem Tisdell 《The Australian geographer》1989,20(1):88-94

Socioeconomic developments in Japan since World War Two have influenced the supply of wild pig meat (inoshishi niku) from Japanese domestic sources. Trends in the supply of meat from wild boar as well as the development of the farming of wild boar in Japan are discussed. The special nature of trading in wild pig meat in Japan is outlined. Australian exports of wild pig meat to Japan depend upon developments within Japan and the relevant links are identified. Some historical background is also provided on the Australian game industry supplying wild pig meat, the location and the structure of the industry are specified and the economic value of the industry is discussed, including its exports and prices paid for wild pig meat. Comparative aspects of the industry and of trade in wild pig meat in Japan and in Australia are highlighted. In conclusion, difficulties involved in identifying the Australian product in the Japanese market are noted.  相似文献