The Kuroshio current (KC) is the major current of the western Pacific Ocean, and its main stream flows northward off the east coast of Taiwan. Since there have been few researches on sinking particle flux in the regime of Kuroshio have been reported, a time-series sediment trap mooring was deployed to investigate the particulate organic carbon (POC) and total nitrogen (TN) and their fluxes at KC station (21o28' N, 122o11' E) at depths of 2000 m and 3500 m from April 2008 to December 2009. Results show that, the mass fluxes at 2000 m and 3500 m of mean are 162.3 mg m-2 d-1 and 201.6 mg m-2 d-1, POC fluxes are 3.8 mgC m-2 d-1 and 3.7 mgC m-2 d-1, and TN fluxes are 0.5 mgN m-2 d-1 and 0.5 mgN m-2 d-1, respectively. The averages of POC, TN content and C/N ratio at 2000 m and 3500 m are 2.5 and 1.8 wt%, 0.3 and 0.2 wt%, and 9.27 and 9.21, separately. The depths and temporal variability of POC and TN contents respond closely to bio-degradation and dilution by bottom movement at KC station. Comparison with SEATS station (18o15¡¦N, 115o50¡¦E), the variability of POC and TN compositions and their fluxes at KC are lower than SEATS station. The fluxes of KC exhibit intermittent high-value in the summer, and the fluxes of SEATS in the winter are higher than other seasons. For site comparison and global synthesis, an average e-ratio of 0.08 and the b-value of 0.53 are derived. These results should help a better understanding of POC in the world.

In the last decade the lowered Acoustic Doppler Current Profiler (LADCP) has become an important instrument in measuring full-water-depth profile of velocity in the open ocean. The basic principle of the LADCP is to lower one or two self-contained ADCP, one looking downward and the other looking upward, together with the CTD rosette during the hydrographic cast. After careful analysis of the ADCP data it is possible to retrieve surface ¡Vto-bottom profile of horizontal current velocity. In the present study we have conducted three cruises (21-25 April, 7-10 July and 11-13 October of 2007) in the Lanyu area to survey the Kuroshio flow structure by using the first set of LADCP in Taiwan. A total of 34 LADCP/CTD casts were completed. The results indicate that a major branch of the Kuroshio is located at the region between Taiwan and Lanyu, with a seasonal variation of flow intensity and vertical extent. Surface currents can reach a maximum speed of 70-140 cm/s northward. Kuroshio has a strongest speed (~140 cm/s) in October followed by July (~100 cm/s) and April (~90 cm/s). The vertical extent of the Kuroshio can extend to 400-m depth in October, 600-m depth in July and 400-m depth in April. A southward reverse current can be observed off the southeast Taiwan coast in depths between 200 and 800 m and the speed ranges between 30 and 60 cm/s. This southward flow is strongest in April (~60 cm/s), followed by July (~40 cm/s) and October (~30 cm/s). A cyclonic, cold eddy was observed in the eastern side of Lanyu from the shipboard ADCP data during the April cruise. The Kuroshio flows to the northwest during ebbs and to the northeast during floods from the LADCP observations at different tidal phases in July. Finally, analysis of the temperature-salinity characteristics of the CTD data reveals that the South China Sea waters can penetrate into and mix with the Kuroshio waters more significantly in summertime than in other season.

This study used Vanadium (III) reduction- chemiluminescence method to measure the very low concentration of nitrite plus nitrate (N+N) in oligotrophic seawaters with a detection limit of 0.7nM. In addition, the high temperature catalytic oxidation (HTCO) ¡V chemiluminescence method was applied to determine the concentration of total dissolved nitrogen (TDN) with a detection limit of 0.5£gM based on a volume of 150£gL seawater. Both methods have high degree of precision and accuracy. Furthermore, the Magic method and persulfate oxidation method were conducted to measure the concentrations of soluble reactive phosphorus (SRP) and total dissolved phosphorus (TDP) with detection limits about 10 nM (original seawater) and 100 nM, respectively. All these analytical methods meet the ranges of parameters in most oligotrophic oceans. According to the hydrology data, the Kuroshio of east Taiwan may be classified into four types: 1. Kuroshio Waters affected by the East China Seawater (ECS-KW)¡F2. typical Kuroshio Waters (KW)¡F3. Kuroshio Waters affected by the South China Seawater (SCS- KW) and 4.Kuroshio waters affected by riverplume (plume- KW). In the euphotic zone, the concentrations of N+N, SRP, DON and DOP in the plume-KW are about 0.6 ~ 4 £gM, 0.03 ~ 0.4 £gM, 2 ~ 6 £gM, and 0.05 ~ 0.2 £gM, respectively, higher than those in other type waters. The plume-KW is apparently influenced by the input of freshwater. Besides, the nitrogen and phosphorus species in the SCS-KW and ECS-KW are higher than those in the KW. Positive correlations are significant between Ch1 a and DON and DOP, indicating that biological activity controls primarily on the distributions of DON and DOP in the euphotic zone. KW has oligotrophic characteristics, and in the euphotic zone, the concentrations of N+N and SRP are generally lower than those in other water types. The Chl a has positive correlations with DON and N+N, resulted likely from their same features of subsurface maxima. The ratio between N+N and SRP in the euphotic zone is about 0.02~0.15, and the value increases gradually in deep water, and eventually close the Redfield ratio. Judging from the distribution of the nitrate anomaly (2.5~ 1.5£gM), nitrogen fixation may prevail in the KW. The N+N and SRP values in the euphotic zone in the SCS-KW near the southeastern coast of Taiwan are about 0.02£gM higher in spring than in summer. DON and DOP are also about 1~2.5£gM and 0.02~0.2£gM higher, respectively, in spring than in summer. This feature may be caused from getting stratification torward the summer season in the SCS-KW.

In order to understand the influence of topography and geometry to the flow and hydrological environments at Southeast coast of Taiwan, this study analyze data collected by tow-ADCPs in multiple cruises. The results are verified by Argos drifters. Field operations of tow-ADCP were carried out on April and September 2009 in the vicinity of Fugang harbor, Taitung. Drifters data were download from the web for the domain 15¢XN-25¢XN, 110¢XE-125¢XE during January 1st 1986 to July 31st 2010, with a total of 706 drift trajectories. The results show that: (1) There is a strong northward current near the coast of Taitung with maximum speed of 180 cm/s. The averaged flow velocity is 56 cm/s. The core of the current is centered at 10 km offshore in 200 m water depth. (2) The flow velocity decreases with depth. The average velocity is 97 cm/s in the upper 200 m, 42 cm/s in the middle layer 200m~400 m, and drop to 30 cm/s below 400 m. (3) The flow near the coast is deflected by the bottom topography, with upper layer flow to the northeast along the coastal line. The lower layer flows turn to west and southwest directions. (4) The transport estimated 3.3~7.2 Sv between Taiwan and LuDao (green island). (5) The flows are deflected by the ridge between LuDao and Cheng-Gong. The turns of flow can be explain by the conservation of vorticities, estimated 0.8*10-4s-1~1.2*10-4s-1. (6) The tidal current of is about a half of a knot, shoreward during flood with push Kuroshio northward. The tidal current is offshore during ebb. (7) The drifters data suggest there are eddies in this region. The surface current has seasonality, 80 cm/s in Spring , 100 cm/s in summer, 90 cm/s in fall, and 70 cm/s in winter.

This research studied the seasonal and spatial dynamics for abundance of picophytoplanktons (including Prochlorococcus spp., Synechococcus spp. and picoeukaryotes) in the South China Sea (SCS) and the Kuroshio. Waters were collected during five cruises between August 2009 and December 2010. Growth rates were determined in two size fractioned waters, <2 um and <10 um, after incubation. The differences of growth rates between the two size fractions were defined as the grazing rates. Before the incubation, waters were enriched with FeCl3, EDTA, or NH4Cl to examine the possible shortage of Fe or nitrogen. Abundances of picophytoplanktons and nanoflagellates were examined using a flow-cytometry and a microscope, respectively. Prochlorococcus was more abundant in the warm than the cold seasons and in the Kuroshio and the basin of the SCS than in the shelf and slope of the SCS. In the high abundance seasons/regions, low irradiance enhanced the growth rates of Prochlorococcus. Although both of the growth rates and grazing rates were high during then, the growth rates were found higher than the grazing rates. Addition of EDTA enhanced the growth rates that was likely attributed to its chelating with toxic trace metals (such as Cd2+, Cd2+) and/or with growth necessity trace metals (such as Co2+). The seasonal/spatial distributions for Synechococcus were in contrast to that of Prochlorococcus. High growth rates of Synechococcus were related to high nitrate concentrations and the low irradiance. The growth rates were higher than the grazing rates in the high nitrogen seasons/regions when/where irradiance was also relatively low. EDTA also enhanced the growth of Synechococcus, and was likely due to its chelating to remove Cd2+ and/or to retain Co2+. Distributions of picoeukaryotes were similar to that of Synechococcus. Factors affected its dynamics were not clear because of its complicated compositions.

Abstract This study investigates the distributions and controls of transparent exopolymer particles (TEP) in marginal seas around Taiwan. In the euphotic zone of Kuroshio Water off southeast Taiwan, the concentration of TEP generally reached a maximum in the subsurface and then decreased with depth. The maximum concentration of TEP in every station in the Kuroshio Water coincides with the subsurface maximum of chlorophyll a (Chl. a). This implied that TEP in the euphotic zone was controlled by biological rather than physical processes. Furthermore, the ratios of TEP /POC and TEP/DOC increased with Chl. a indicating that the increase of primary production may enhance DOC transformation to POC through the formation of TEP. Concentrations of TEP in the Taiwan Strait and Gaoping coastal sea decreased generally with the increase of seaward distance, showing the same pattern of nutrient distribution. Apparently, the terrestrial input of nutrient may increase phytoplankton abundance and enhance the formation of TEP. Positive correlations were significant between TEP and Chl. a, suggesting that the distribution of TEP in the euphotic zone of Taiwan Strait and Gaoping coastal sea are also controlled by biological processes. During the study period, the concentrations of nutrient and Chl. a were elevated in the surface water around the Dongsha Island in the South China Sea (SCS), due to the influence of internal wave. According to the close relation between TEP and Chl. a, concentrations of TEP around Dongsha Island were also likely controlled by phytoplankton activity, but the different strength of internal wave may lead to the different conditions of TEP, Chl. a and POC distributions. The results of factor analysis support the fact that distributions of TEP are mainly controlled by biological processes, but various physical conditions could also influence distributions of TEP in the water column. Overall, concentrations of TEP are generally higher in the Taiwan Strait and Gaoping coastal sea than in the Donshia shelf sea and Kuroshio Water off southeast Taiwan. Nevertheless, distributions of TEP are all comparable with previous findings in other coastal and marginal seas.

This research studied the iron deficient condition of the nitrogen-fixing filamentous cyanobacteria Trichodesmium in neighboring oligotrophic northern South China Sea and upstream Kuroshio. The iron deficiency was detected by the immunocytochemical analysis of the expression of iron deficiency induced protein A (IdiA), a protein translated by Trichodesmium cells under iron deficiency. IdiA expression rate (percentage of cells stained by IdiA antiserum in total cells) was used to represent the iron deficiency status. Trichodesmium samples were collected in four cruises by net-towing or bottle-sampling in the Kuroshio and the shelf, slope and basin of the South China Sea between December 2008 and May 2010, representing three seasons: Spring (CR899 and CR1455), Summer (CR910) and Winter (CR886). The results showed that the IdiA expression rates vaied greatly among the stations in the South China Sea. Iron supplies from various sources decreased the IdiA expressions rates (i.e., less iron deficient). These sources include: (1) Mixing from deep layer, such as in the continental shelf of the South China Sea in which internal wave occured, and upwelling occurred in the continental slope; (2) Mixing at some stations in the South China Sea basin from the input of river dischange, especially in the events after typhoon. During these events, stations with lower surface water salinities usually implied lower IdiA expression rates. In contrast, the basin station that were high in salinities showed high IdiA expression rates, higher than the rates in the Kuroshio. These stations generally had strongly stratified water coulumn, and therefore might limit the ward mixing of deep water. The incubation experiment conducted showed that 24 hours after adding iron, Trichodesmium IdiA expression rates were significantly decreased. The Kuroshio, with its water column stratification weaker than South China Sea, the IdiA expression rates were lower than the basin stations in South China Sea, and positively relatied with the stratification index, indicating that deep advection may be the main source of iron. In the incubation experiments in Kuroshio, the expression rates did not significantly differ with iron or without iron addition. The IdiA expression rates in both regions were not related to flux of atmospheric dust, indicating the input from the dust was not key point to decrease iron deficiency of Tricodesmium in this two region. This study shows that iron deficient condition of diazotrophic Trichodesmium in South China Sea and upstream Kuroshio were related to vertical mixing and horizontal discharge, but not dust flux. This study is first time to apply immunocytochemical analysis on field experiments to explain iron deficiency in the ocean.

In order to understand tidal circulation and oceanic current for the seas around Taiwan, this study use a baroclinic unstructured grid model to build a high resolution model. This model use semi-implicit method to solve the dynamic of ocean movement and larger time step can be used to calculate. Unstructured grid can be used to resolve complex coastline and variation of depth. TaiDBMv6 depth data were chosen to describe the depth distribution and grid mesh size were determined by local depth, minimum mesh size is about 0.75 minutes, and maximum 13 minutes. Tidal boundaries use 8 constituents derived from FES2004 and calibrated with 34 tide station records. Data of 2009 were used to evaluate the model results. The average of all station root mean square error was 10.1 cm. Station at east side of Taiwan have smaller errors, which almost lower than 5 cm. The maximum error can be found inside Taiwan Strait, about 25cm, mainly caused by lack of depth data near the coastal area. For oceanic current model, GFS and NFS-MC CWB wind forecast were used as meteorology input. Initial fields and boundary condition are derived from HYCOM results. Nudging of salinity and temperature also were used to stabilize the model. Transport of Kuroshio of 2009 is about 17.0¡Ó3.2Sv. Maximum value is about 28.6Sv, occurred in summer. Minimum value is about 8.3Sv, occurred in winter.

In order to understand the input of South China Sea Water (SCSW) onto the Kuroshio and the distributions of carbonate parameters in Kuroshio Water (KW), the temperature, salinity, pH and TCO2 were measured for the seawater samples collected from the Kuroshio regime off eastern Taiwan during the cruise ORI 650 in July 2002. The distributions of temperature and salinity show that a front existed approximately along 123.5&#x00BA;E, which separated the influenced KW by SCSW from typical KW. East of this front the water is characterized by temperature and salinity of KW, while west of it the water was mainly a mixture of the SCSW and the KW. After flowing out from the Luson Straint, the SCSW deflected northward along the east cost of Taiwan, and continuously mixed with the KW. The mixing of SCSW with KW could be traced northward as far as 22&#x00BA;N and reach as deep as 1250m. Based on the measured carbonate data, the calculated IC/OC ratio ranges from 22% to 23% in the deep water of the Kuroshio region. Additionally, the penetration depth of anthropogenic CO2 was estimated to be about 1200m by using Chen¡¦s equation (Chen et al., 1986). Furthermore, the difference of pCO2 between atmosphere and surface seawater was evaluated to be about -5matm, indicating that the surface water in the study area was nearly saturated with pCO2 during the sampling period.

Temporal and spatial distribution in species composition and abundance of chaetognaths in relation to hydrographic variables in the waters off southern Taiwan were investigated from January 2005 to October 2006. There were 23 species of chaetognaths belonging 4 families and 12 genera recognized in this region. The 4 most dominate species were Flaccisagitta enflata (32.2%), Serratosagitta pacifica (20.6%), Zonosagitta bedfordii (12%) and Pterosagitta draco (8.8%), together comprised about 74% of total chaetognaths. The distribution in abundance of chaetognaths generally decreased from west to east along the transect, and showed clear seasonal change, with the higher abundance occurred from July to October and the lower abundance from January to May. Abundance of chaetognaths increased significantly in July 2006 and positively correlated with the abundance of copepods. Our hydrographic results indicated that South China Sea Current with higher nutrients might dominante over Kuroshio Current in this region from January 2006 to July 2006, and might lead to the increases of phytoplankton (Chl a) and copepods consequently. Furthermore, temperature and salinity also interactively influenced the distribution in abundance and species richness of chaetognaths. Stage I individuals made up the majority of chaetognaths abundance (80%). The breeding period of predominant chaetognaths (F. enflata, S. pacifica, Z. bedfordii and P. draco) are year around. Results from gut content analysis implied that copepods is the main food for chaetognaths in the study area, but the predation impact of chaetognaths on copepods was only about 0.25%¡ã2.47 %.