An analysis of a 68-year monthly hindcast output from an eddy-resolving ocean general circulation model reveals the relationship between the interannual variability of the Kerama Gap transport(KGT)and the Kuroshio/Ryu...An analysis of a 68-year monthly hindcast output from an eddy-resolving ocean general circulation model reveals the relationship between the interannual variability of the Kerama Gap transport(KGT)and the Kuroshio/Ryukyu Current system.The study found a significant difference in the interannual variability of the upstream and downstream transports of the East China Sea-(ECS-)Kuroshio and the Ryukyu Current.The interannual variability of the KGT was found to be of paramount importance in causing the differences between the upstream and downstream ECS-Kuroshio.Additionally,it contributed approximately 37%to the variability of the Ryukyu Current.The interannual variability of the KGT was well described by a two-layer rotating hydraulic theory.It was dominated by its subsurface-intensified flow core,and the upper layer transport made a weaker negative contribution to the total KGT.The subsurface flow core was found to be mainly driven by the subsurface pressure head across the Kerama Gap,and the pressure head was further dominated by the subsurface density anomalies on the Pacific side.These density anomalies could be traced back to the eastern open ocean,and their propagation speed was estimated to be about 7.4 km/d,which is consistent with the speed of the local first-order baroclinic Rossby wave.When the negative(positive)density anomaly signal reached the southern region of the Kerama Gap,it triggered the increase(decrease)of the KGT towards the Pacific side and the formation of an anticyclonic(cyclonic)vortex by baroclinic adjustment.Meanwhile,there is an increase(decrease)in the upstream transport of the entire Kuroshio/Ryukyu Current system and an offshore flow that decreases(increases)the downstream Ryukyu Current.展开更多
According to the seismic data (mb≥5. 0) from 1977 to 1991 and the focal mechanisms of 68 earthquakes from 1961 to 1991, the characters of seismicity and stress field in Okinawa Trough and Ryukyu regions are discussed...According to the seismic data (mb≥5. 0) from 1977 to 1991 and the focal mechanisms of 68 earthquakes from 1961 to 1991, the characters of seismicity and stress field in Okinawa Trough and Ryukyu regions are discussed in this paper, and the paper suggests that: ① The Tokara Channel fault belt is a fault belt with seismicity, cutting through lithosphere. ② The different stress state in the both subducting slabs on the both sides of Tokara Channel fault belt are caused by the difference of subducting depth of the both slabs. ③ The seismicity and stress field in the Okinawa Trough and Ryukyu regions are related not only to the subduction of the Philippine Sea Plate but also to the self-expanding action of Okinawa Trough.展开更多
A modified inverse method is used to compute the circulations east of Taiwan and in the East China Sec and east of the Ryukyu Islands with hydrographic data obtained during early summer of 1985. The computational regi...A modified inverse method is used to compute the circulations east of Taiwan and in the East China Sec and east of the Ryukyu Islands with hydrographic data obtained during early summer of 1985. The computational region covers an area west of 129°E and from 21°45'N to 35°N. The computed results show that: (1 ) The net volume transport (VT ) of the Kuroshio through 21°45'N Section east of Ta Taiwan and west of 123°E is about 45 × 10 ̄6 m ̄3/sduring early summer of 1985. The Kuroshio has. two current cores. One is located near Taiwan, and its velocity isvery large and its maximum velocity is 226 cm/s at the 100 m level, which is close to the maximum velocity of the beginning of the Kuroshio east of the Philippines. The other is located further to the east, and its maximum velocity is159 cm/s at the 100m level; (2) through a transect northwest Of Miyakojima Island and a transect southwest of Okinawa laaed the volume transports of the Kuroshio in the East China Sea both are about 25 × 10 ̄6 m ̄3/s. The maximumvelocity of the Kuroshio at these two sections is 194 and 128 cm/s, respectively, and both are located on the shelfbreak; (3) beneath and east of the Kurohio there are the countercurrent (4) southeast of Okinawa Island there is anortheastward current, and its VT at Section HI is about 12. 6 × 10 ̄6 m ̄3/s, and it comes from a westward flow at 129° This project was supported by the National Natural Science Foundation of China under contract No. 49476278.(Second Institute of Oceanography, State Oceanic Administration, Hongzhou310012, China) (Institute of Oceanography, Taiwan University, Taipei, China)E Section and the recirculating gyre, and does not originate from the Kuroshio east of Taiwan during early summer of 1985. There is a southwestward abyssal current east of Okinawa Islands (5) there are several different scale eddies in this computational region. For example, there is a meso-scale strong cyclonic eddy east of Miyakojima Island.展开更多
In this study, the inverse method is used to compute the Kuroshio in the East China Sea and southeast of Kyushu and the currents east of the Ryukyu Islands, on the basis of hydrographic data obtained during September-...In this study, the inverse method is used to compute the Kuroshio in the East China Sea and southeast of Kyushu and the currents east of the Ryukyu Islands, on the basis of hydrographic data obtained during September-October, 1987 by R/V Chofu Maru. The results show that: (1)A part of the Taiwan Warm Current has a tendency to converge to the shelf break; (2) the Kuroshio flows across the section C3 (PN) with a reduced current width, and the velocity of the Kuroshio at the section C3 increases and its maximum current speed is about 158 cm/s, and its volume transport here is about 26×106m3/s; (3) the Kuroshio has two current cores at the sections C3 (PN) and B2 (at the Tokara Strait); (4) the currents east of the Ryukyu Islands are found to flow northward over the Ryukyu Trench during September-October, 1987. The velocities of the currents are not strong throughout the depths. At the section C2 east of the Ryukyu Islands, the maximum current speed is at the 699 m levei and its magnitude is 25 cm/s, and its volume transport is about 21×06 m3/s; (5) the volume transports of the Kuroshio through the sections B2 (at the Tokara Strait) and C6 (southeast of Kyushu) are 23. 33, 67. 31×106 m3/s, respectively; (6) there are two meso-scale anticyclonic warm eddies between 135° E and the area east of the Ryukyu Islands, and their characters and hydrographic structure are discussed.展开更多
The origin of the Ryukyu Current(RC)and the formation of its subsurface velocity core were investigated using a 23-year(1993–2015)global Hybrid Coordinate Ocean Model(HYCOM)dataset.The volume transport of the RC come...The origin of the Ryukyu Current(RC)and the formation of its subsurface velocity core were investigated using a 23-year(1993–2015)global Hybrid Coordinate Ocean Model(HYCOM)dataset.The volume transport of the RC comes from the Kuroshio eastward branch(KEB)east of Taiwan and part of the North Pacific Subtropical Gyre(p-NPSG).From the surface to 2000m depth,the KEB(p-NPSG)transport contributes 41.5%(58.5%)to the mean total RC transport.The KEB originally forms the subsurface velocity core of the RC east of Taiwan due to blockage of the subsurface Kuroshio by the Ilan Ridge(sill depth:700 m).Above 700m,the Kuroshio can enter the East China Sea(ECS)over the Ilan Ridge,meanwhile,the blocked Kuroshio below 700m turns to the right and flows along the Ryukyu Islands.With the RC flowing northeastward,the p-NPSG contribution strengthens the subsurface maximum structure of the RC owing to the blockage of the Ryukyu Ridge.In the surface layer,the p-NPSG cannot form a stable northeastward current due to frequent disturbance by mesoscale eddies and water exchange through the gaps(with net volume transport into ECS)between the Ryukyu Islands.展开更多
The X-discontinuity,which appears at the depth of approximately 300 km,is an important seismic interface with positive velocity contrasts in the upper mantle.Detecting its presence and topography can be useful to unde...The X-discontinuity,which appears at the depth of approximately 300 km,is an important seismic interface with positive velocity contrasts in the upper mantle.Detecting its presence and topography can be useful to understand phase transformations of relevant mantle minerals under the high-temperature and high-pressure circumstance of the Earth's interior.In this study,we detect the X-discontinuity beneath the Ryukyu subduction zone using five intermediate-depth events recorded by the dense Alaska Regional Network(AK).The X-discontinuity is successfully revealed from the robust slant stacking of the secondary down-going and converting Sd P phases.From the depth distribution of conversion points,we find that the X-discontinuity's depth ranges between 269 km and 313 km,with an average depth of 295 km.All the conversion points are located beneath the down-dipping side of the Philippine Sea slab.From energy comparisons in vespagrams for observed and synthetic seismograms,the strong converted energy is more likely from a thin high-velocity layer,and the S-wave velocity jumps across the X-discontinuity are up to 5% to 8% with an average of 6.0%.According to previous petrological and seismological studies,the X-discontinuity we detected can be interpreted as the phase transformation of coesite to stishovite in eclogitic materials within the oceanic crust.展开更多
Skeletochronology is a method commonly used for estimating the age of amphibians and reptiles in the wild. However, the number of lines of arrested growth (LAGs) does not necessarily reflect age in some species. We ...Skeletochronology is a method commonly used for estimating the age of amphibians and reptiles in the wild. However, the number of lines of arrested growth (LAGs) does not necessarily reflect age in some species. We validated the applicability of this method to an endangered eublepharid gecko, Goniurosaurus kuroiwae, then inferred its longevity and age structures in wild populations. We classified young geckos into three groups using previously published data for early growth: Group 1 contained hatchlings before the first winter, Group 2 contained hatchlings after the first win- ter, and Group 3 included yearlings after the second winter. LAG numbers in these groups were then compared. All individuals in Group 1 possessed a single LAG, which was considered as a hatching line. Most individuals in Groups 2 and 3 possessed one and two additional LAGs, respectively (LAG1 and LAG2), corroborating the notion that LAGs are formed annually. A few geckos exhibited fewer LAGs than expected. Analysis of variations in LAG and marrow cavity diameter demonstrated that in animals with fewer LAGs, endosteal resorption or fusion of hatching line and LAG1 had occurred. LAG2 was never lost by endosteal resorption and was identifiable by its diameter. Thus, the age of adult geckos could be determined by counting LAGs outward from LAG2. Application of this method to wild populations re- vealed that the longevity of this species is not less than 83 months, but that almost all individuals in fragmented habitats die before 50 months, suggesting lower population sustainability in such habitats.展开更多
The influence of the Kuroshio on neighboring Chinese seas and the Ryukyu Current is a very important subject of interest in physical oceanography. To deeply explain the research progress made by Chinese scientists fro...The influence of the Kuroshio on neighboring Chinese seas and the Ryukyu Current is a very important subject of interest in physical oceanography. To deeply explain the research progress made by Chinese scientists from July2010 to May 2015, the following three aspects are reviewed in this paper. The first concerns the Kuroshio intrusion into the South China Sea(SCS) and its circulation around the Luzon Strait. There are two very important points to be explained: the seasonal and inter-annual variation of the Kuroshio intrusion and the mechanisms of the Kuroshio intrusion and the influence of the Kuroshio on currents in the Luzon Strait and circulation in the northern SCS. The second concerns the variability of the Kuroshio and its interaction with the East China Sea(ECS). There are following four interesting topics to be explained: an overview of studies on the Kuroshio in the ECS; the Kuroshio intrusion into the ECS, water exchange, and dynamic impacts; the downstream increase of nutrient transport by the Kuroshio; and the application of satellite remote sensing on terrestrial material transport by the Kuroshio intrusion into the ECS. Third, the interaction between the Ryukyu Current and Kuroshio in the ECS are also discussed. Finally, the main results are summarized and areas of further study are simply discussed.展开更多
Forty two CTD profiles gathered in summertime of 1997 were used for finestructure studies around the Ryukyu Islands indicating that finestructure properties varied with depth; and that the wavenumber spectra density i...Forty two CTD profiles gathered in summertime of 1997 were used for finestructure studies around the Ryukyu Islands indicating that finestructure properties varied with depth; and that the wavenumber spectra density is a negative (-3~-4) power function of the wavenumber in the high wavenumber range. The identical finestructure spectral features in different stations indicate considerable water exchange through the Kerama Trench. The wavelet spectrum’s spatial structure and intermittency is related to the vertical mixing of water.展开更多
Samlpes of O isotopic tracer ware collected at Sections P_3, P_(25), P_(CM-1/2-E) and P_(CM-1/2-W) in both the EastChina Sea and the area to the east Of the Ryukyu-gunto during October-November, 1991.Analytical result...Samlpes of O isotopic tracer ware collected at Sections P_3, P_(25), P_(CM-1/2-E) and P_(CM-1/2-W) in both the EastChina Sea and the area to the east Of the Ryukyu-gunto during October-November, 1991.Analytical results of the δ ̄(18) O are as follows: (1) In the Kuroshio area, the δ ̄(18) o isolines are almost parallel to the200 m isobath. The value of δ ̄(18)O is nagative and reaches minimum on the main axis of the Kuroshio,and increases on both sides. (2) In the Taiwan Warm Current (TWC) area there is a high δ ̄(18) O tongue extending to the northeast. (3)In the area near the coast, the distribution of δ ̄(18)O isoline shows that the Changjiang River runoff diffuses seaward andthe land-ocean isotopic effect from the nearshore to the offshore. (4) The values of δ ̄(18) O are from-1. 0 x 10 ̄(-3) to -0.5 x 10 ̄(-3) in the shelf. (5) There is a low core of δ ̄(18) O value (< -1 .6 X 10 ̄(-3)) at the 600 m layer in the Kuroshioarea, which is quite in accord with the ekistence of a low salinity core (S 34. 30) between the 600 and 800 m layersin the same area. Finally, the correlations of the δ ̄(18)O with the salinity and temperature, the upwelling and so on arediscussed.(This study was supported by the National Natural Science Foundation of China under contract No. 4907257.)Yuan Yaochu et al. The Northwest Pacific circulation and its impacts on the current near the Chinese coast, 1991-1993.展开更多
Results of the Ocean General Circulation Model for the Earth Simulator(OFES) from January 1977 to December2006 are used to investigate mesoscale eddies near the Ryukyu Islands. The results show that:(1) Larger ed...Results of the Ocean General Circulation Model for the Earth Simulator(OFES) from January 1977 to December2006 are used to investigate mesoscale eddies near the Ryukyu Islands. The results show that:(1) Larger eddies are mainly east of Taiwan, above the Ryukyu Trench and south of the Shikoku Island. These three sea areas are all in the vicinity of the Ryukyu Current.(2) Eddies in the area of the Ryukyu Current are mainly anticyclonic, and conducive to that current. The transport of water east of the Ryukyu Islands is mainly toward the northeast.(3)The Ryukyu Current is significantly affected by the eddies. The lower the latitude, the greater these effects.However, the Kuroshio is relatively stable, and the effect of mesoscale eddies is not significant.(4) A warm eddy south of the Shikoku Island break away from the Kuroshio and move southwest, and is clearly affected by the Ryukyu Current and Kuroshio. Relationships between the mesoscale eddies, Kuroshio meanders, and Ryukyu Current are discussed.展开更多
Careful investigations of live coloration and other characters in the eublepharid gecko Goniurosaurus kuroiwae orientalis from Tonakijima Island, the type locality of the subspecies in the Central Ryukyus, Japan, reve...Careful investigations of live coloration and other characters in the eublepharid gecko Goniurosaurus kuroiwae orientalis from Tonakijima Island, the type locality of the subspecies in the Central Ryukyus, Japan, revealed its slight but consistent external differences from the consubspecific Tokashikijima population, whose phylogenetically divergent status against the former had been strongly suggested in a previous molecular study. A new subspecies, Goniurosaurus kuroiwae sengokui subsp. nov., is thus described for the Tokashikijima population. In life, Goniurosaurus k. sengokui subsp. nov. can be discriminated from G. k. orientalis in showing tint of reddish or pinkish, instead of yellowish, coloration in dorsal body pattern, and also usually darker and more or less reddish, instead of yellowish or grayish, iris in both adults and juveniles. Recalculation of sequence data at hand with relevant Gen Bank data confirmed substantial sequence divergences of G. k. sengokui from all other congeneric taxa of the Ryukyus described so far.展开更多
Study of CTD data collected by the R/V DONG FANG HONG 2 in a 1997 summercruise in the ocean region around the Ryukyu Islands showed: 1) the existence, in the upper layer, of ahigh salinity water (HSW) core at about 20...Study of CTD data collected by the R/V DONG FANG HONG 2 in a 1997 summercruise in the ocean region around the Ryukyu Islands showed: 1) the existence, in the upper layer, of ahigh salinity water (HSW) core at about 200 dbar, and a low salinity water (LSW) core, centered atabout 700 dbar on the Pacific Ocean side of the Ryukyu Ridge, and located shallower on the East Chinafor (ECS) side; 2) the existence, in the upper layer, of warm water regions (WWR) west of Amami Is-land and Ishigaki Island, and a cold water region (CWR) east of Okinawa Ieland; in the lower layer, ofa CWR (WWR) southwest (southeast) of Okinawa Island; 3) the intrusion of North Pacific IntermediateWater into the ECS through the Kerama Trench located south of Okinawa Island and the strait east of Tai-wan Island.展开更多
Inverse calculations using data from 16 repeat hydrographic transects collected from April 2003 to June 2007 have yielded velocity structures and volume transports(VTs) of the Ryukyu Current in the region east of the ...Inverse calculations using data from 16 repeat hydrographic transects collected from April 2003 to June 2007 have yielded velocity structures and volume transports(VTs) of the Ryukyu Current in the region east of the northern Ryukyu Islands.The inverse calculation results show that the Ryukyu Current is dominated by a subsurface velocity core with maximum velocities from 15.1 to 80.0 cm/s,whose positions vary between 110 and 600 dbar and 27.2°-28.2°N along the transect.The mean velocity exhibits a subsurface velocity core with a maximum value of 24.6 cm/s at 326 dbar depth,a VT of 14.0 Sv(1 Sv≡106 m3/s),a vertical dimension of 800 m,and a horizontal dimension of 60 km.The seasonal mean velocities show that the Ryukyu Current is stronger in autumn than in other seasons.It is suggested that this seasonal variation is coincident with the intensification of the anticyclonic eddy south of Shikoku,Japan.展开更多
The late 16th and early 17th centuries witnessed a significant change in the geopolitical structure of East Asia. The power of the Ming dynasty was declining due to internal and external troubles and depleted finances...The late 16th and early 17th centuries witnessed a significant change in the geopolitical structure of East Asia. The power of the Ming dynasty was declining due to internal and external troubles and depleted finances, whereas Japan had been rising steadily since Toyotomi Hideyoshi unified the country. The traditional East Asian international order, centered on the Ming dynasty and based on the tributary system, faced a challenge from Japan. Against this background, the invasion of the Ryukyu Kingdom by the Japanese feudal domain of Satsuma had a great effect on the existing regional geopolitical structure. With the establishment of the "dual subordination" of the Ryukyu Kingdom, a new geopolitical structure gradually took shape in which the two great powers, China and Japan, competed for dominance. The Ming dynasty's limited awareness of maritime issues and of the geostrategic importance of the Ryukyu Islands, its passive attitude towards Satsuma's invasion, and especially, its tolerance of the Ryukyu Kingdom's "dual subordination" fed Japan's ambitions for further expahsion and encouraged its ultimate annexation of the kingdom by force. It can be said that the military conquest of the Ryukyu Kingdom by Satsuma foreshadowed the decline of the Ming and the rise of Japan.展开更多
Based on the observation of the Ryukyu ethnic group during the World WarⅡand the need for post-war military occupation,the United States formulated the rule of“pro-U.S.and separating from the Japan,strengthening the...Based on the observation of the Ryukyu ethnic group during the World WarⅡand the need for post-war military occupation,the United States formulated the rule of“pro-U.S.and separating from the Japan,strengthening the initiative of natives.”1 in the early days of the occupation of Ryukyu.In the field of culture,the United States has carried out activities such as the compilation of post-war textbooks,attempts to restore native language,protection of traditional art and historical sites,and they also revived the traditional culture of Ryukyu.Since then,due to the transformation of the U.S.Asia-Pacific strategy,the U.S.’s traditional culture policy for Ryukyu has gradually changed to allow Japanese culture to re-enter Ryukyu.The Ryukyu traditional cultural rejuvenation policy in the early postwar period led to the development and strengthening of the community awareness of the Ryukyu community,which had disappeared and been suppressed for a long time.展开更多
基金The Fundamental Research Funds for the Central Universities under contract No.B220201024.
文摘An analysis of a 68-year monthly hindcast output from an eddy-resolving ocean general circulation model reveals the relationship between the interannual variability of the Kerama Gap transport(KGT)and the Kuroshio/Ryukyu Current system.The study found a significant difference in the interannual variability of the upstream and downstream transports of the East China Sea-(ECS-)Kuroshio and the Ryukyu Current.The interannual variability of the KGT was found to be of paramount importance in causing the differences between the upstream and downstream ECS-Kuroshio.Additionally,it contributed approximately 37%to the variability of the Ryukyu Current.The interannual variability of the KGT was well described by a two-layer rotating hydraulic theory.It was dominated by its subsurface-intensified flow core,and the upper layer transport made a weaker negative contribution to the total KGT.The subsurface flow core was found to be mainly driven by the subsurface pressure head across the Kerama Gap,and the pressure head was further dominated by the subsurface density anomalies on the Pacific side.These density anomalies could be traced back to the eastern open ocean,and their propagation speed was estimated to be about 7.4 km/d,which is consistent with the speed of the local first-order baroclinic Rossby wave.When the negative(positive)density anomaly signal reached the southern region of the Kerama Gap,it triggered the increase(decrease)of the KGT towards the Pacific side and the formation of an anticyclonic(cyclonic)vortex by baroclinic adjustment.Meanwhile,there is an increase(decrease)in the upstream transport of the entire Kuroshio/Ryukyu Current system and an offshore flow that decreases(increases)the downstream Ryukyu Current.
文摘According to the seismic data (mb≥5. 0) from 1977 to 1991 and the focal mechanisms of 68 earthquakes from 1961 to 1991, the characters of seismicity and stress field in Okinawa Trough and Ryukyu regions are discussed in this paper, and the paper suggests that: ① The Tokara Channel fault belt is a fault belt with seismicity, cutting through lithosphere. ② The different stress state in the both subducting slabs on the both sides of Tokara Channel fault belt are caused by the difference of subducting depth of the both slabs. ③ The seismicity and stress field in the Okinawa Trough and Ryukyu regions are related not only to the subduction of the Philippine Sea Plate but also to the self-expanding action of Okinawa Trough.
文摘A modified inverse method is used to compute the circulations east of Taiwan and in the East China Sec and east of the Ryukyu Islands with hydrographic data obtained during early summer of 1985. The computational region covers an area west of 129°E and from 21°45'N to 35°N. The computed results show that: (1 ) The net volume transport (VT ) of the Kuroshio through 21°45'N Section east of Ta Taiwan and west of 123°E is about 45 × 10 ̄6 m ̄3/sduring early summer of 1985. The Kuroshio has. two current cores. One is located near Taiwan, and its velocity isvery large and its maximum velocity is 226 cm/s at the 100 m level, which is close to the maximum velocity of the beginning of the Kuroshio east of the Philippines. The other is located further to the east, and its maximum velocity is159 cm/s at the 100m level; (2) through a transect northwest Of Miyakojima Island and a transect southwest of Okinawa laaed the volume transports of the Kuroshio in the East China Sea both are about 25 × 10 ̄6 m ̄3/s. The maximumvelocity of the Kuroshio at these two sections is 194 and 128 cm/s, respectively, and both are located on the shelfbreak; (3) beneath and east of the Kurohio there are the countercurrent (4) southeast of Okinawa Island there is anortheastward current, and its VT at Section HI is about 12. 6 × 10 ̄6 m ̄3/s, and it comes from a westward flow at 129° This project was supported by the National Natural Science Foundation of China under contract No. 49476278.(Second Institute of Oceanography, State Oceanic Administration, Hongzhou310012, China) (Institute of Oceanography, Taiwan University, Taipei, China)E Section and the recirculating gyre, and does not originate from the Kuroshio east of Taiwan during early summer of 1985. There is a southwestward abyssal current east of Okinawa Islands (5) there are several different scale eddies in this computational region. For example, there is a meso-scale strong cyclonic eddy east of Miyakojima Island.
文摘In this study, the inverse method is used to compute the Kuroshio in the East China Sea and southeast of Kyushu and the currents east of the Ryukyu Islands, on the basis of hydrographic data obtained during September-October, 1987 by R/V Chofu Maru. The results show that: (1)A part of the Taiwan Warm Current has a tendency to converge to the shelf break; (2) the Kuroshio flows across the section C3 (PN) with a reduced current width, and the velocity of the Kuroshio at the section C3 increases and its maximum current speed is about 158 cm/s, and its volume transport here is about 26×106m3/s; (3) the Kuroshio has two current cores at the sections C3 (PN) and B2 (at the Tokara Strait); (4) the currents east of the Ryukyu Islands are found to flow northward over the Ryukyu Trench during September-October, 1987. The velocities of the currents are not strong throughout the depths. At the section C2 east of the Ryukyu Islands, the maximum current speed is at the 699 m levei and its magnitude is 25 cm/s, and its volume transport is about 21×06 m3/s; (5) the volume transports of the Kuroshio through the sections B2 (at the Tokara Strait) and C6 (southeast of Kyushu) are 23. 33, 67. 31×106 m3/s, respectively; (6) there are two meso-scale anticyclonic warm eddies between 135° E and the area east of the Ryukyu Islands, and their characters and hydrographic structure are discussed.
基金The National Natural Science Foundation of China under contract Nos 41576001,41920104006,41776107,41906023,41621064,41476020 and 41606113the Scientific Research Fund of SIO under contract Nos JG1626,JG1621 and JT1604+2 种基金the Project of State Key Laboratory of Satellite Ocean Environment Dynamics,SIO under contract Nos SOEDZZ1901,SOEDZZ1804 and SOEDZZ1806the National Programme on Global Change and Air-sea Interaction under contract No.GASI-IPOVAI-01-02the Zhejiang Provincial Natural Science Foundation of China under contract No.LQ17D060003
文摘The origin of the Ryukyu Current(RC)and the formation of its subsurface velocity core were investigated using a 23-year(1993–2015)global Hybrid Coordinate Ocean Model(HYCOM)dataset.The volume transport of the RC comes from the Kuroshio eastward branch(KEB)east of Taiwan and part of the North Pacific Subtropical Gyre(p-NPSG).From the surface to 2000m depth,the KEB(p-NPSG)transport contributes 41.5%(58.5%)to the mean total RC transport.The KEB originally forms the subsurface velocity core of the RC east of Taiwan due to blockage of the subsurface Kuroshio by the Ilan Ridge(sill depth:700 m).Above 700m,the Kuroshio can enter the East China Sea(ECS)over the Ilan Ridge,meanwhile,the blocked Kuroshio below 700m turns to the right and flows along the Ryukyu Islands.With the RC flowing northeastward,the p-NPSG contribution strengthens the subsurface maximum structure of the RC owing to the blockage of the Ryukyu Ridge.In the surface layer,the p-NPSG cannot form a stable northeastward current due to frequent disturbance by mesoscale eddies and water exchange through the gaps(with net volume transport into ECS)between the Ryukyu Islands.
基金supported by the China Postdoctoral Science Foundation(119103S282)National Natural Science Foundation of China(41704090,41474040 and 41504050)
文摘The X-discontinuity,which appears at the depth of approximately 300 km,is an important seismic interface with positive velocity contrasts in the upper mantle.Detecting its presence and topography can be useful to understand phase transformations of relevant mantle minerals under the high-temperature and high-pressure circumstance of the Earth's interior.In this study,we detect the X-discontinuity beneath the Ryukyu subduction zone using five intermediate-depth events recorded by the dense Alaska Regional Network(AK).The X-discontinuity is successfully revealed from the robust slant stacking of the secondary down-going and converting Sd P phases.From the depth distribution of conversion points,we find that the X-discontinuity's depth ranges between 269 km and 313 km,with an average depth of 295 km.All the conversion points are located beneath the down-dipping side of the Philippine Sea slab.From energy comparisons in vespagrams for observed and synthetic seismograms,the strong converted energy is more likely from a thin high-velocity layer,and the S-wave velocity jumps across the X-discontinuity are up to 5% to 8% with an average of 6.0%.According to previous petrological and seismological studies,the X-discontinuity we detected can be interpreted as the phase transformation of coesite to stishovite in eclogitic materials within the oceanic crust.
基金supported by the Zoshinkai Fund for Protection of Endangered Animals and the Grant from the Japan Society for the Promotion of Science (JSPS KAKENHI Grant number 22510244)
文摘Skeletochronology is a method commonly used for estimating the age of amphibians and reptiles in the wild. However, the number of lines of arrested growth (LAGs) does not necessarily reflect age in some species. We validated the applicability of this method to an endangered eublepharid gecko, Goniurosaurus kuroiwae, then inferred its longevity and age structures in wild populations. We classified young geckos into three groups using previously published data for early growth: Group 1 contained hatchlings before the first winter, Group 2 contained hatchlings after the first win- ter, and Group 3 included yearlings after the second winter. LAG numbers in these groups were then compared. All individuals in Group 1 possessed a single LAG, which was considered as a hatching line. Most individuals in Groups 2 and 3 possessed one and two additional LAGs, respectively (LAG1 and LAG2), corroborating the notion that LAGs are formed annually. A few geckos exhibited fewer LAGs than expected. Analysis of variations in LAG and marrow cavity diameter demonstrated that in animals with fewer LAGs, endosteal resorption or fusion of hatching line and LAG1 had occurred. LAG2 was never lost by endosteal resorption and was identifiable by its diameter. Thus, the age of adult geckos could be determined by counting LAGs outward from LAG2. Application of this method to wild populations re- vealed that the longevity of this species is not less than 83 months, but that almost all individuals in fragmented habitats die before 50 months, suggesting lower population sustainability in such habitats.
基金The National Basic Research Program of China under contract No.2014CB441501the National Natural Science Foundation of China under contract Nos 41576001,41176021,41176020,91128204,41276031,41406021,41276095 and 41321004+1 种基金the fund from the State Key Laboratory of Satellite Ocean Environment Dynamics,Second Institute of Oceanography under contract No.SOEDZZ1501the National Program on Global Change and Air-Sea Interaction under contract No.GASI-03-01-01-02
文摘The influence of the Kuroshio on neighboring Chinese seas and the Ryukyu Current is a very important subject of interest in physical oceanography. To deeply explain the research progress made by Chinese scientists from July2010 to May 2015, the following three aspects are reviewed in this paper. The first concerns the Kuroshio intrusion into the South China Sea(SCS) and its circulation around the Luzon Strait. There are two very important points to be explained: the seasonal and inter-annual variation of the Kuroshio intrusion and the mechanisms of the Kuroshio intrusion and the influence of the Kuroshio on currents in the Luzon Strait and circulation in the northern SCS. The second concerns the variability of the Kuroshio and its interaction with the East China Sea(ECS). There are following four interesting topics to be explained: an overview of studies on the Kuroshio in the ECS; the Kuroshio intrusion into the ECS, water exchange, and dynamic impacts; the downstream increase of nutrient transport by the Kuroshio; and the application of satellite remote sensing on terrestrial material transport by the Kuroshio intrusion into the ECS. Third, the interaction between the Ryukyu Current and Kuroshio in the ECS are also discussed. Finally, the main results are summarized and areas of further study are simply discussed.
文摘Forty two CTD profiles gathered in summertime of 1997 were used for finestructure studies around the Ryukyu Islands indicating that finestructure properties varied with depth; and that the wavenumber spectra density is a negative (-3~-4) power function of the wavenumber in the high wavenumber range. The identical finestructure spectral features in different stations indicate considerable water exchange through the Kerama Trench. The wavelet spectrum’s spatial structure and intermittency is related to the vertical mixing of water.
文摘Samlpes of O isotopic tracer ware collected at Sections P_3, P_(25), P_(CM-1/2-E) and P_(CM-1/2-W) in both the EastChina Sea and the area to the east Of the Ryukyu-gunto during October-November, 1991.Analytical results of the δ ̄(18) O are as follows: (1) In the Kuroshio area, the δ ̄(18) o isolines are almost parallel to the200 m isobath. The value of δ ̄(18)O is nagative and reaches minimum on the main axis of the Kuroshio,and increases on both sides. (2) In the Taiwan Warm Current (TWC) area there is a high δ ̄(18) O tongue extending to the northeast. (3)In the area near the coast, the distribution of δ ̄(18)O isoline shows that the Changjiang River runoff diffuses seaward andthe land-ocean isotopic effect from the nearshore to the offshore. (4) The values of δ ̄(18) O are from-1. 0 x 10 ̄(-3) to -0.5 x 10 ̄(-3) in the shelf. (5) There is a low core of δ ̄(18) O value (< -1 .6 X 10 ̄(-3)) at the 600 m layer in the Kuroshioarea, which is quite in accord with the ekistence of a low salinity core (S 34. 30) between the 600 and 800 m layersin the same area. Finally, the correlations of the δ ̄(18)O with the salinity and temperature, the upwelling and so on arediscussed.(This study was supported by the National Natural Science Foundation of China under contract No. 4907257.)Yuan Yaochu et al. The Northwest Pacific circulation and its impacts on the current near the Chinese coast, 1991-1993.
基金The National Natural Science Foundation of China under contract No.41076003the Youth Science and Technology Foundation of East China Sea Branch,SOA under contract Nos 201314 and 201203the open fund of State Key Laboratory of Satellite Ocean Environment Dynamics under Contract No.SOED1402
文摘Results of the Ocean General Circulation Model for the Earth Simulator(OFES) from January 1977 to December2006 are used to investigate mesoscale eddies near the Ryukyu Islands. The results show that:(1) Larger eddies are mainly east of Taiwan, above the Ryukyu Trench and south of the Shikoku Island. These three sea areas are all in the vicinity of the Ryukyu Current.(2) Eddies in the area of the Ryukyu Current are mainly anticyclonic, and conducive to that current. The transport of water east of the Ryukyu Islands is mainly toward the northeast.(3)The Ryukyu Current is significantly affected by the eddies. The lower the latitude, the greater these effects.However, the Kuroshio is relatively stable, and the effect of mesoscale eddies is not significant.(4) A warm eddy south of the Shikoku Island break away from the Kuroshio and move southwest, and is clearly affected by the Ryukyu Current and Kuroshio. Relationships between the mesoscale eddies, Kuroshio meanders, and Ryukyu Current are discussed.
基金partially supported by a Grant-in-Aid from the Japan Ministry of Education, Culture, Sports, Science and Technology (Scientific Research C No.22510244 to M. Honda)a grant from the Zoshinkai Fund for Protection of Endangered Animals (to H.Ota)
文摘Careful investigations of live coloration and other characters in the eublepharid gecko Goniurosaurus kuroiwae orientalis from Tonakijima Island, the type locality of the subspecies in the Central Ryukyus, Japan, revealed its slight but consistent external differences from the consubspecific Tokashikijima population, whose phylogenetically divergent status against the former had been strongly suggested in a previous molecular study. A new subspecies, Goniurosaurus kuroiwae sengokui subsp. nov., is thus described for the Tokashikijima population. In life, Goniurosaurus k. sengokui subsp. nov. can be discriminated from G. k. orientalis in showing tint of reddish or pinkish, instead of yellowish, coloration in dorsal body pattern, and also usually darker and more or less reddish, instead of yellowish or grayish, iris in both adults and juveniles. Recalculation of sequence data at hand with relevant Gen Bank data confirmed substantial sequence divergences of G. k. sengokui from all other congeneric taxa of the Ryukyus described so far.
文摘Study of CTD data collected by the R/V DONG FANG HONG 2 in a 1997 summercruise in the ocean region around the Ryukyu Islands showed: 1) the existence, in the upper layer, of ahigh salinity water (HSW) core at about 200 dbar, and a low salinity water (LSW) core, centered atabout 700 dbar on the Pacific Ocean side of the Ryukyu Ridge, and located shallower on the East Chinafor (ECS) side; 2) the existence, in the upper layer, of warm water regions (WWR) west of Amami Is-land and Ishigaki Island, and a cold water region (CWR) east of Okinawa Ieland; in the lower layer, ofa CWR (WWR) southwest (southeast) of Okinawa Island; 3) the intrusion of North Pacific IntermediateWater into the ECS through the Kerama Trench located south of Okinawa Island and the strait east of Tai-wan Island.
基金supported by National Natural Science Foundation of China (Grant Nos.40776021,40706018)National Basic Research Program of China (Grant No.2006CB400603)+1 种基金National High Technology Research and Development Program of China (Grant No.2006AA09Z102)JSPS KAKENHI (Grant No.21310012)
文摘Inverse calculations using data from 16 repeat hydrographic transects collected from April 2003 to June 2007 have yielded velocity structures and volume transports(VTs) of the Ryukyu Current in the region east of the northern Ryukyu Islands.The inverse calculation results show that the Ryukyu Current is dominated by a subsurface velocity core with maximum velocities from 15.1 to 80.0 cm/s,whose positions vary between 110 and 600 dbar and 27.2°-28.2°N along the transect.The mean velocity exhibits a subsurface velocity core with a maximum value of 24.6 cm/s at 326 dbar depth,a VT of 14.0 Sv(1 Sv≡106 m3/s),a vertical dimension of 800 m,and a horizontal dimension of 60 km.The seasonal mean velocities show that the Ryukyu Current is stronger in autumn than in other seasons.It is suggested that this seasonal variation is coincident with the intensification of the anticyclonic eddy south of Shikoku,Japan.
基金supported by the National Natural Science Foundation of China(Grant No.41171135)
文摘The late 16th and early 17th centuries witnessed a significant change in the geopolitical structure of East Asia. The power of the Ming dynasty was declining due to internal and external troubles and depleted finances, whereas Japan had been rising steadily since Toyotomi Hideyoshi unified the country. The traditional East Asian international order, centered on the Ming dynasty and based on the tributary system, faced a challenge from Japan. Against this background, the invasion of the Ryukyu Kingdom by the Japanese feudal domain of Satsuma had a great effect on the existing regional geopolitical structure. With the establishment of the "dual subordination" of the Ryukyu Kingdom, a new geopolitical structure gradually took shape in which the two great powers, China and Japan, competed for dominance. The Ming dynasty's limited awareness of maritime issues and of the geostrategic importance of the Ryukyu Islands, its passive attitude towards Satsuma's invasion, and especially, its tolerance of the Ryukyu Kingdom's "dual subordination" fed Japan's ambitions for further expahsion and encouraged its ultimate annexation of the kingdom by force. It can be said that the military conquest of the Ryukyu Kingdom by Satsuma foreshadowed the decline of the Ming and the rise of Japan.
文摘Based on the observation of the Ryukyu ethnic group during the World WarⅡand the need for post-war military occupation,the United States formulated the rule of“pro-U.S.and separating from the Japan,strengthening the initiative of natives.”1 in the early days of the occupation of Ryukyu.In the field of culture,the United States has carried out activities such as the compilation of post-war textbooks,attempts to restore native language,protection of traditional art and historical sites,and they also revived the traditional culture of Ryukyu.Since then,due to the transformation of the U.S.Asia-Pacific strategy,the U.S.’s traditional culture policy for Ryukyu has gradually changed to allow Japanese culture to re-enter Ryukyu.The Ryukyu traditional cultural rejuvenation policy in the early postwar period led to the development and strengthening of the community awareness of the Ryukyu community,which had disappeared and been suppressed for a long time.