Hydrographic Features off the Southeast Coast of Kyushu during the Kuroshio Small Meanders: A Case Study for Small Meanders that Occurred in 1994 and 1995 Spring

Three Kuroshio small meanders off the southeast coast of Kyushu that occurred during 1994 to 1995 were investigated by using satellite-derived sea surface temperature (SST) and sea surface height (SSH) maps, World Ocean Circulation Experiment (WOCE) Hydrographic Program (WHP) repeat section and Japan Meteorological Agency (JMA) hydrographic observations. Based on the satellite data, we observed that the three small meanders are formed by different processes: the triggering and growth of these meanders are caused by a cyclonic eddy propagating from the Kuroshio recirculation region or Kuroshio front meanders traveling from the East China Sea. Investigation of the two small meanders in 1994 and 1995 spring that are captured by the WHP observation showed quite consistent hydrographic features. On the nearshore side of the meandering Kuroshio, a countercurrent appears, associated with vertically uniform upward lifts of the isopycnals from sea surface to bottom at the boundary between the countercurrent and the Kuroshio. In the countercurrent region, the waters in the density ranges of the North Pacific subtropical mode water (NPSTMW) and the North Pacific Intermediate Water (NPIW) are more saline and less saline than typical waters that the Kuroshio carries in a non-small meander state, respectively. There are indications that high-salinity NPSTMW and low-salinity NPIW distributed off the Kuroshio was supplied to the countercurrent region. In the meandering Kuroshio flow, while there is no notable change in properties around the NPSTMW density range, salinity of the NPIW is significantly higher than that carried by the Kuroshio in a non-small meander state, but not higher than that in the Kuroshio at the Tokara Strait, which suggests that saline NPIW from the Tokara Strait, less mixed with low-salinity NPIW off the Kuroshio, may be carried by the meandering Kuroshio. This revised version was published online in July 2006 with corrections to the Cover Date.     

Uncertainty Reduction of Estimated Geostrophic Volume Transports with Altimeter Observations East of Taiwan

The common geostrophic estimation of ocean current velocity uses only water temperature and conductivity profiles. The geostrophic volume transport of a western boundary current, like the Taiwan Current (Kuroshio east of Taiwan), between the coast and its eastern boundary can be easily estimated based on hydrographic survey data. But the eastern boundary of the Taiwan Current is very uncertain due to extremely variable hydrographic conditions. This uncertainty is strongly correlated with the propagating mesoscale eddies originating from the interior of the western North Pacific Ocean. The uncertainty of estimated transport can be greatly reduced if eddy distribution is considered when determining the integration boundaries with the assistance of satellite altimeter measurements. Eight hydrographic surveys east of Taiwan between November 1992 and June 1996 are demonstrated in this study. The average geostrophic transport of the Taiwan Current with a reference set to 1000 dbar at 22°N between the east coast of Taiwan and 124°E is 22.9 ±14.2 Sv and changes to 22.1 ± 8.3 Sv, the uncertainty of which is nearly halved after taking account of the eddy distribution. The estimation uncertainty is insensitive to vertical displacements of the reference level within the depth range between 800 and 2000 dbar. This revised version was published online in July 2006 with corrections to the Cover Date.     

PN断面东海黑潮的地转经验模态分析

基于东海PN断面近50年的历史水文数据,本文中作者应用一种斜压流函数空间投影的方法分析冲绳海槽北部黑潮水团的季节性和年代际变异.诊断生成的地转经验模态(GEM)显示黑潮中层水的盐度在夏季相对较低,春季达到最高.通过比较1987年之后CTD数据生成的GEM场与1987年之前BOttle数据生成的GEM场,得以证实黑潮的年代际变化特征,即黑潮表层水近20年来温度升高而盐度减小,同时发现黑潮热带水具有盐度增加而中层水具有盐度减小的趋势.     

南海环流动力机制研究综述

南海的环流复杂,但通过近20 a来的研究工作,国内外学者对此已取得了不少的成果.本文就南海环流框架性的问题,综述了有关的文献,认为对南海上层海洋三方面的环流分量的驱动机制已有了初步的认识.这三方面分别是:(1)准季节性风场;(2)黑潮向南海的净输运;(3)黑潮向南海的涡度平流输送.但是对这些驱动的时空变化仍相当不清楚.三者皆增强了南海北部的海盆尺度气旋式环流,其强化的西南向西边界流靠近东沙群岛,建议称为“东沙海流”.没有水文证据显示黑潮水是以分支形式进入南海,其向南海的输运也不可能主要通过中尺度涡过程,具体机制有待研究.每年在南海生成的中尺度涡平均约有10个,风场与沿岸地形所生成的强风应力旋度可能是其主要的驱动机制.作为框架性的认识,也有三方面的工作进行得较少,即:(1)吕宋海峡的上层水交换;(2)南海的中尺度涡生成机制,虽然强风应力旋度及前述的第三种环流驱动机制也有中尺度涡伴生;(3)自吕宋海峡进入的深层水对南海上层海洋环流的影响.     

A study on the source of the Tsushima Warm Current water

On the basis of the hydrographic data in the area west of Kyushu from four cruises of R/V Xiangyanghong No. 9 from 1987 to 1988 , the circulation features in the investigation area are described and the source of the Tsushima Warm Current water (TWCW) is explored by using the observed and geostrophic current results and tracking the Kuroshio Subsurface High Salinity Core (KSHSC).     

Southward intrusion of the intermediate Oyashio water along the east coast of the Boso Peninsula I. Coastal salinity-minimum-layer water off the Boso Peninsula

Index species of zooplankton of the Oyashio water are found in and beneath the salinity minimum layer in Sagami Bay. In order to clarify the intrusion path of the intermediate Oyashio Water (or the water of the Mixed Water Region), the oceanographic conditions off the Boso Peninsula are studied by using available hydrographic data obtained mainly by Japan Meteorological Agency. The cross-sectional salinity distribution along KJ line which extends southeastward from off the tip of the peninsula always indicates the existence of a low salinity patch just off the coast in the salinity minimum layer. This water is well separated from the offshore low salinity water which is considered as the water in the western margin of the so-called North Pacific Intermediate Water. We refer to the former water as the coastal salinity-minimum-layer (SML) water and to the latter as the offshore SML water. The coastal SML water is usually bounded by the current zone of the Kuroshio. The existence of the coastal SML water seems to indicate the possible pathway of the intermediate Oyashio water along the Boso Peninsula into Sagami Bay. The detailed water type analysis is made in T-S plane, S-_st plane, and O₂-_st plane. There is no significant difference in distribution ranges of the water types between the coastal SML water and the offshore SML water. However, the water types of the coastal SML water is not uniformly distributed, and the water can be classified into two groups: group A with relatively high oxygen content and relatively low salinity value and group B with relatively low oxygen content and relatively high salinity value. Group A is thought to be associated with strong event-like intrusions, the details of which will be discussed in Part II.     

Phytoplankton distribution in a frontal region of Tokyo Bay,Japan in November 1985

Phytoplankton distribution in a frontal region of Tokyo Bay was investigated in relation to hydrography in November 1985. The frontal region was observed from the central to the mouth area of the bay and consisted of a series of fine scale discontinuities of salinity and temperature. Among them the Kenzaki offshore front (KOF) and the Yokosuka inshore front (YIF) were most prominent in terms of the duration and the magnitudes of the hydrographic gaps. Three major phytoplankton assemblages were observed: (A) neritic and offshore diatoms in the mouth area of Tokyo Bay, (B) a diatomLeptocylindrus danicus and dinoflagellates in the central area, and (C) bloom forming cryptophyceans, dinoflagellates andL. danicus from the inner Tokyo Bay. The KOF was an approximate boundary of the outside assemblage (A) and the intermediate population (B), and the YIF was that of (B) and the inner bay population (C). Species changes across the fronts were rather gradual in the KOF making a strong contrast to distinct jumps in temperature, salinity,in vivo chlorophyll fluorescence and nitrate plus nitrite. An outward surface flow of the inside population along the western coast off Yokosuka was detected.     

Temporal variations of the net Kuroshio transport and its relation to atmospheric variations

Temporal variations of the net Kuroshio transport are investigated using long-term hydrographic data from repeat section of the 137°E meridian from the south of Japan (34°N) to New Guinea (1°S) conducted by the Japan Meteorological Agency. In this study, boundaries of the Kuroshio and the Kuroshio Counter Current (KCC) are defined based on the sea surface dynamic height distribution. Westward flows associated with the KCC and cold-core eddy north of the Kuroshio are removed from the eastward flow associated with the Kuroshio in order to estimate the net Kuroshio transport strictly. The net Kuroshio transport reveals low-frequency variations: significant signals on a decadal (about 10-year) timescale. The variations of net Kuroshio transport are predominantly caused by changes in the magnitude of oceanic current speed fields associated with a vertical movement of the main pycnocline depth around the southern boundary of the Kuroshio: deepening of the main pycnocline around the southern boundary of the Kuroshio forms a sharp northern upward-tilting slope of the isopycnal surfaces at the Kuroshio region, and eventually the net Kuroshio transport increases together with the Kuroshio eastward transport. By using a wind-driven hindcast model, it is found that the main pycnocline depth variation results from the first-mode baroclinic Rossby waves attributable to two types of Aleutian Low (AL) changes: a change in the magnitude of AL and meridional movement of AL.     

Three-dimensional numerical calculations of currents east of Taiwan Island in December 1997

numerical calculationsI~IOXAInong the numerical studies Of the circulation east of Taiwan Island, there were some studies, such as Yuan et al. (1998a, b), Wang et al. (1998). In their work, the Kuroshio east ofTaiwan Island and the currents southeast of Rgukyu-guntO were computed by using three-dimensional diagnOStic, semidiagnostic and prognostic model, respectively, based on the wind and hydrographic data obtained from two cruises, i. e., one cruise during October 1995, and the otherin…     

Warm water intrusion from the Kuroshio into the coastal areas south of Japan

Sea surface temperature (SST) has been measured in the south of Japan using a thermometer set up in the ferry boat to investigate the characteristics of the warm water intrudes into the coastal areas from the Kuroshio. Time series analysis was applied to the SST data with satellite images and hydrographic observation data from April 1987 to September 1989. The results indicate that the warm Kuroshio water intruded into the coastal areas on the Enshu-nada and the Kumano-nada Seas intermittently with periods of about 50 and 20 days associated with the fluctuation of the Kuroshio path and the Kuroshio frontal disturbance respectively. The intrusion with a 50-day period was dominant when the Kuroshio took a stationary small meander path (B- and C-types). The warm water spread to the west at 20 cm s^–1, and was estimated to have a depth of 150 m at least and supply enough heat to make up the loss due to the evaporation in the coastal area. During the straight path of the Kuroshio, it was detected that the warm water intruded into coastal areas only with a 20-day period. The warm water that intrudes with a period of 20 days spreads to the west at 25 cm s^–1 in a small scale.     

Intraannual variability of sea level around Tosa Bay

Through analysis of monthly in situ hydrographic, tide gauge, altimetry and Kuroshio axis data for the years 1993–2001, the intraannual variability of sea level around Tosa Bay, Japan, with periods of 2–12 months is examined together with the intraannual variability of the Kuroshio south of the bay. It is shown that the intraannual variation of steric height on the slope in Tosa Bay can account for that of sea level at the coast around the bay as well as on this slope. It is found that the steric height (or sea level) variation on the slope in this bay is mainly controlled by the subsurface thermal variation correlated with the Kuroshio variation off Cape Ashizuri, the western edge of Tosa Bay. That is, when the nearshore Kuroshio velocity south of the cape is intensified [weakened] concurrently with the northward [southward] displacement of the current axis, temperature in an entire water column decreases [increases] simultaneously, mainly due to the upward [downward] displacement of isotherms, coincident with that of the main thermocline. It follows that the steric height (or sea level) decreases [increases].     

Spreading and salinity change of North Pacific Tropical Water in the Philippine Sea

Newly formed North Pacific Tropical Water (NPTW) is carried to the Philippine Sea (PS) by the North Equatorial Current (NEC) as a subsurface salinity maximum. In this study its spreading and salinity change processes are explored using existing hydrographic data of the World Ocean Database 2009 and Argo floats. Spreading of NPTW is closely associated with the transports of the NEC, Mindanao Current (MC), and Kuroshio. Estimated for subsurface water with salinity S greater than 34.8?psu, the southward (northward) geostrophic transport of NPTW by the MC (Kuroshio) at 8°N (18°N) is about 4.4 (5.7)?Sv (1?Sv?=?10⁶?m³?s^?1), which is not sensitive to reference level choice. Fields of salinity maximum, geostrophic current, sea level variation, and potential vorticity suggest that the equatorward spreading of NPTW to the tropics is primarily afforded by the MC, whereas its poleward spreading is achieved by both the Kuroshio transport along the coast and open-ocean mesoscale eddy fluxes in the northern PS. The NPTW also undergoes a prominent freshening in the PS. Lying beneath fresh surface water, salinity decreases quicker in the upper part of the NPTW, which gradually lowers the salinity maximum of NPTW to denser isopycnals. Salinity decrease is especially fast in the MC, with along-path decreasing rate reaching O (10^?7?psu?s^?1). Both diapycnal and isopycnal mixing effects are shown to be elevated in the MC owing to enhanced salinity gradient near the Mindanao Eddy. These results suggest intensive dispersion of thermal anomalies along the subtropical-to-tropical thermocline water pathway near the western boundary.     

水团对吕宋海峡浮游植物群落结构的影响

根据2008年8月18日至9月19日在吕宋海峡3个断面获得的0~200 m层浮游植物数据,探讨了群落结构及其与不同理化性质水团的关系。本研究共鉴定浮游植物4门61属169种（包括变种、变型和未定种）,其中甲藻和硅藻物种数基本相当,各占所有物种数的50%左右;另记录了金藻门3属3种;蓝藻门1种。海区优势种为卡氏前沟藻Amphisdinium carterae、锥状施克里普藻Scrippsiella trochiodea、角毛藻Chaetoceros sp.和原甲藻Prorocentrum sp.。丰度范围是（0.08~9.48）×106个/m3,平均为1.448×106个/m3。甲藻占总细胞丰度的74.68%;硅藻占24.96%。在水平方向,B断面和C5站浮游植物丰度较高,甲藻主要分布于远离陆地的海峡中部,而硅藻主要分布于台湾岛和吕宋岛附近;浮游植物垂直分布主要在水体的0~50 m层。聚类分析并结合水文数据表明浮游植物基本可划分为3个类群,分别受南海水、黑潮水和混合水的影响。南海水与黑潮水交汇的锋面区域,具有较周围区域更高的物种数、水柱平均丰度及硅甲藻丰度比,体现出强烈的锋面效应。     

环台湾岛海域冬季水文要素的数值模拟

本文利用POM模式对环台湾岛海域冬季的水文要素进行了数值模拟,对有代表性的水平环流、温度场和上升流三个要素所进行的分析表明:模式再现了台湾岛东岸的高温高盐强流速区即黑潮,黑潮在冬季并无直接进入台湾海峡的分支存在;西岸的东北向流在冬季各个层次上都存在,台湾东北部的冷涡模拟与实况较为一致。温度场和上升流的分布与水平环流有很好的对应关系。本文还进一步验证了前人的一些研究成果,并对一些特殊物理现象的成因进行了定性解释。     

东海东北部春季若干重要水文结构的分析

本文主要基于韩国海洋研究所在东海沿岸海洋过程试验中收集的ＣＴＤ资料，分析了１９９５年春季出现在东海东北部的一些重要水文结构。结果表明，一种锋涡状结构出现在黑潮向东转折点附近。它不仅使邻近海域的水文结构变得更复杂，而且诱发黑潮水与陆架水间活跃的交换。在陆架坡折处观测到若干孤立的陆架水块，可能是锋涡的卷挟作用所致；该海域存在４个水团，即黑潮水、对马暖流水、陆架水和混合水。对马暖流水分为上下两层：上层水为变性黑潮水，盐度比黑潮水约低０．１，底层对马暖流水仅位于冲绳海槽区，并有着与黑潮中层水相同的温、盐特性；一种双锋结构出现在邻近黑潮的陆架边缘附近。在内陆架形成的陆架锋，由北向南伸展时，愈来愈偏向陆架边缘。而黑潮锋沿九州以西深槽的陆架边缘向北伸展。在黑潮转折点附近，两锋几乎合并为一条锋。狭窄的锋带由黑潮水及其变性水和陆架水的混合水所占据。     

1996年春季副热带环流区浮游植物生态的初步研究

鉴定浮游植物种类54属184种(含变种和变型),其中暖水种为140种(占76.5%).硅藻类和甲藻类等浮游植物的平均总细胞密度为198.71×102个/m3;蓝藻类藻丝体平均密度为44.55×102条/m3.浮游植物各类别的分布与水域的磷酸盐含量、黑潮以及其他水系(涌升水和沿岸水等)等相关;蓝藻类的束毛藻(Trichodesmium)的分布还与50m以浅水体的平均水温关系密切.     

Hydrographic structure of the Kuroshio large meander-cold water mass region down to the deeper layers of the ocean

The hydrographic structure of the region of large meander of the Kuroshio and the large cold water mass, which were formed in 1975, was observed down to the ocean bottom, during three cruises of the R/VHakuho Maru in September 1975, September 1976, and December 1977. The analysis of observed data indicates the following common features: the horizontal gradient of the specific volume anomaly exists down to a 3,500 db surface, corresponding to the existence of baroclinic geostrophic current down to this depth. These facts demonstrate that the current of the Kuroshio is not confined to the upper layer during periods of existence of the large meander. On a T-S diagram, the Kuroshio water and the water in the large cold water mass can be discriminated down to a 5°C surface, but there is evidence of mixing due to conspicuous interleaving between the two water masses, near the thermocline. Below the thermocline, water types defined by points on the T-S diagram can be traced from a deeper level in the Kuroshio water to a shallower level in the cold water mass, indicating that in the deeper layers the Kuroshio water continues to be uplifted toward the center of the cold water mass. The same inference is also obtained from the distribution of dissolved oxygen.     

Formation, Distribution and Volume Transport of the North Pacific Intermediate Water Studied by Repeat Hydrographic Observations

In order to examine the formation, distribution and transport of North Pacific Intermediate Water (NPIW), repeated hydrographic observations along several lines in the western North Pacific were carried out in the period from 1996 to 2001. NPIW formation can be described as follows: (1) Oyashio water extends south of the Subarctic Boundary and meets Kuroshio water in intermediate layers; (2) active mixing between Oyashio and Kuroshio waters occurs in intermediate layers; (3) the mixing of Oyashio and Kuroshio waters and salinity minimum formation around the potential density of 26.8σ_θ proceed to the east. It is found that Kuroshio water flows eastward even in the region north of 40°N across the 165°E line, showing that Kuroshio water extends north of the Subarctic Boundary. Volume transports of Oyashio and Kuroshio components (relative to 2000 dbar) integrated in the potential density range of 26.6–27.4σθ along the Kuroshio Extension across 152°E–165°E are estimated to be 7–8 Sv (10⁶ m³s⁻¹) and 9–10 Sv, respectively, which is consistent with recent work. This revised version was published online in July 2006 with corrections to the Cover Date.     

黑潮水入侵南海的水文分析──Ⅱ.1994年8—9月期间的观测结果

利用1994年8－9月期间，由台湾海峡两岸的4艘海洋调查船在南海东北部海域所获之CTD和ADCP资料，并结合1992年3月间在同一海域获取的CTD资料及部分历史水文资料，对该区域的海水特性以及黑潮水入侵南海等问题进行了分析探讨。结果表明：调查期间，本海区水团分布与冬末、春初（1992年3月）航次基本相似，即南海和西北太平洋海域的海水结构有着各自相对独立的温、盐度特性。虽发现有黑潮水穿越巴上海峡进入南海，但其势力甚弱。因此，在夏末秋初，黑潮亦无直接的分支深入南海，即使在巴士海峡北端进入台湾海峡的黑潮水，其影响也是十分微弱的。由等密度面、地转流分析和实测ADCP资料显示，在调查海区的东南海域存在一支较强的N向流动。它沿菲律宾西海岸北上，绕过吕宋岛西北角流向东北，在巴上海峡呈现与黑潮水混合的迹象，其水体在冬季明显呈高温、低盐的特性；夏季则为相对低温、低盐。故在冬季的几幅卫星图像上也有较好的体现，很有可能长年存在。     

The Adriatic sea hydrography and circulation in spring and autumn (1985–1987)

The Adriatic basin-wide circulation and its temporal variability are reviewed on the basis of results from the analysis of hydrographic data collected during four POEM cruises. Major well known features in the circulation are revealed in the data set which covers the period from October 1985 to April 1987. A prominent signal associated with the seasonal variability is identified in the water outflowing along the Italian coast. Differences between autumn and spring in the vein of cold and fresh water flowing along the Italian shelf manifest mainly in the temperature field. During the stratified season the fresh water spreads over the entire surface layer of the southern Adriatic. On the other hand, during spring, when the sea is vertically homogeneous, the fresh water remains confined to the surface longshore boundary layer over the entire length of the Italian coast. Layers below the seasonal thermocline at the eastern portion of the sea display very weak seasonal signals. A strong signal associated with the inter-annual variations also has been documented from the analysed data set; it mainly appears in the salinity field. It is shown that in spring 1986, the salinity averaged over the entire water column north of the Palagruza Sill is lower by 0.3 psu than in spring 1987. A similar, but less prominent difference is noted in the southern Adriatic. An attempt is made to associate these differences with variations in climatic conditions over the area, the river runoff and the Mediterranean water inflow.