Northeast Taiwan Research Articles

Onshore and Offshore Seawater Exchange off Northeast Taiwan Driven by the Combined Effects of Kuroshio Intrusion and Tidal Currents

Abstract The exchange of materials and energy between boundary currents and the surrounding marginal seas largely influences the environment of those seas. In addition to the reported currents over the continental shelf northeast of Taiwan, a process of onshore and offshore water exchange (OOWE) across the northeast-southwest-oriented shelf break is newly introduced in this study. This exchange is constituted by the synergy of Kuroshio intrusion (northwestward) and ebb tide (southeastward). The total velocity obtained by combining Copernicus Marine Service (CMS) satellite geostrophic currents and modeled Ekman currents through the GLOBCURRENT project, along with numerical modeling based on the Regional Ocean Modeling System (ROMS), are used to describe the spatiotemporal characteristics of OOWE and explain its generation dynamics. OOWE occurs in a highly dynamic active area, sandwiched between two current jets: the Kuroshio Current (KC) and the Taiwan Strait Current (TSC). The seaward increase of northward currents off northeast Taiwan (due to a stronger KC and a weaker TSC) provides a favorable environment of positive vorticity that steers the Kuroshio onto the shelf, constituting the north branch of OOWE. Additionally, the ebb tide drives water away from the shore, producing a southeastward current along the north coast of Taiwan, forming the southern branch of OOWE. Uneven wind forcing in the spatial domain slightly modulates the OOWE pattern, though it plays only a secondary role in its generation. Given the potential to induce vigorous exchange and mixing between continental shelf waters and the Kuroshio, the OOWE identified in this study warrants further attention.

Non-linear analysis of soil 222Rn time series recorded at Jiaosi in north-east Taiwan for possible earthquake precursor study

Non-linear analysis of soil 222Rn time series recorded at Jiaosi in north-east Taiwan for possible earthquake precursor study

Opportunities and constraints for accessible nature-based destinations from the management perspective

ABSTRACT Offering an accessible environment to visitors in nature-based destinations often involves various challenges due to the need to balance accessibility with conservation. This study investigates the influences of practical methods, design elements, and other factors that affect visitors’ experience with reduced accessibility at eight nature-based destinations in the Taipei and northeast Taiwan area. Interviews with the destination managers of these eight sites have been conducted to understand their views on what constitutes ‘accessible tourism’, their experiences and views on the aspects of accessible tourism policy planning and management, including destination planning and design, accessibility facilities, and other management factors affecting strategies to attract visitors of various accessibility conditions. A qualitative analysis of the interviews affirms the importance placed by destination managers in providing accessible facilities. The management of the study sites combines physical facilities, visitor services, and accessible design into an all-around strategy to improve destination accessibility while maintaining the conservation of nature-based resources, which is an issue. A notable advantage is a people-oriented strategy to learn from the visitors, meet visitor demand, and improve visitor satisfaction with the sites.

Impact of shallow hydrothermal vent waters on monsoonal copepod distribution and abundance around active volcanic island off northeast Taiwan, West Pacific

Extreme oceanic environments such as shallow hydrothermal vents (HVs) have rarely been investigated with respect to their impact on the water column and its organisms, such as zooplankton. We collected mesozooplankton from the near shore shallow HV areas off northeast Taiwan during three distinct monsoonal periods in 2022. The results showed the occurrence of 99 copepod species belonging to 24 families and 49 genera from a one-year study. The results from similarity percentage (SIMPER) and indicator species analysis (IndVal) identified that top 5 species namely Temora turbinata, Oncaea venusta, Clausocalanus furcatus, Macrosetella gracilis, and Canthocalanus pauper showed variations in their abundance between HV and non-HV sites which contributed to 72.12 % dissimilarity with only four of the species with significantly higher contributions during the SW monsoon season. This distinction is explained by the fact that copepods were negatively affected by HV water. Furthermore, Temora turbinata (3530.7 ± 4967.83 ind. m−3), Calanus sinicus (70.86 ± 163.78 ind. m−3), and Paracalanus parvus (40.47 ± 85.67 ind. m−3) emerging as the dominant species with a clear seasonal succession pattern during the southwest monsoon, northeast-southwest monsoon transition, and northeast monsoon prevailing phase, respectively. The total abundance of copepod was significantly higher during the southwest monsoon than during the other two monsoonal periods (p < 0.01, one-way ANOVA). In contrast, the number of species and the richness index were significantly higher during the northeast-southwest and northeast monsoon than during the southwest monsoon period (p < 0.05, one-way ANOVA) indicating temporal succession in the copepod community.

Characteristics Analysis of Acoustic Doppler Current Profile Measurements in Northeast Taiwan Offshore

A comprehensive study was conducted at a wave energy device test site located off the northeastern coast of Taiwan to assess the influence of oceanic currents on experimental equipment. A bottom-mounted 600 kHz acoustic Doppler current profiler, equipped with integrated temperature and pressure sensors, was deployed at a depth of approximately 31 m. This study, spanning from 6 June 2023 to 11 May 2024, recorded ocean current profiles by assembling data from 50 pings every 10 min, with a resolution of one meter per depth layer. The findings reveal that variations in water levels were predominantly influenced by the M2 tidal constituent, followed by the O1, K1, and S2 tides. Notably, seawater temperature fluctuations at the seabed were modulated by tides, especially the M2 tide. A significant drop in seawater temperature was also observed as the typhoon passed through the south of Taiwan. In terms of sea surface currents, the measured maximum current speed was 71.89 cm s−1, but the average current speed was only 15.47 cm s−1. Tidal currents indicated that the M4 and M2 tides were the most significant, with semimajor axes and inclination angles of 8.48 cm s−1 and 102.60°, and 7.00 cm s−1 and 97.76°, respectively. Seasonally, barotropic tidal currents were the strongest in winter. Additionally, internal tides were identified, with the first baroclinic mode being dominant. The zero-crossing depths varied between 14 and 18 m. During the summer, the M2 baroclinic tidal current displayed characteristics of the second baroclinic mode, with zero-crossing depths at approximately 7 m and 22 m. This node aligns with results from the empirical orthogonal function analysis and correlates with the depths’ significant shifts in seawater temperature as measured by a conductivity, temperature, and depth instrument. Despite the velocities of internal tides not being strong, the directional variance between surface and bottom flows presents critical considerations for the deployment and operation of moored wave energy devices.

Changes in the particulate organic carbon pump efficiency since the Last Glacial Maximum in the northwestern Philippine Sea

Changes in bottom and pore water oxygenation over glacial – interglacial cycles have influenced the ocean's capacity to store particulate organic carbon regardless of its source, either the marine primary productivity or the continent-to-ocean transfer of terrestrial organic matter. In the Philippine Sea, east off Taiwan, despite being currently oligotrophic, the enhanced East Asian Winter Monsoon during the Last Glacial Maximum and the Heinrich Stadial 1 might have altered the nutrient budget in surface waters by providing nutrients from the Eurasian loess dust and deepening the vertical mixing, bringing nutrients from the nutrient-enriched Kuroshio Current subsurface waters to the surface. During the deglaciation, previous studies also suggest an overall weakening of the marine biological pump during the Heinrich Stadial 1, and the rise in sea level is expected to have led to a global significant decline in the ability of continents to bury their particulate organic carbon in marine sediments. However, changes in the continent-ocean transfer of terrestrial organic matter and on the marine biological pump around Taiwan remain poorly constrained.In the present study, we have thus aimed to reconstruct bottom – pore water oxygenation, past marine primary productivity and continental-ocean transfer of terrestrial particulate organic carbon to the ocean since the end of the Last Glacial Maximum, in order to better constrain the ability of marine sediments to capture atmospheric carbon over the past 20,000 years. To this end, sediment core MD18-3523 has been recovered from a levee of Hoping Canyon, north-east of Taiwan, in the Ryukyu forearc basin. The reconstructions were made possible by the application of multivariate statistics and transfer functions on benthic foraminiferal assemblages, by the measurement of total organic carbon concentration and by the investigation of chemical element ratios obtained from X-ray fluorescence (XRF).We observed a transition across the Bølling–Allerød and the Younger Dryas from suboxic-dysoxic bottom – pore waters during Heinrich Stadial 1 to oxic-suboxic during the Holocene, and revealed an increase in marine primary productivity during Heinrich Stadial 1 in all probability due to intensified East Asian Winter Monsoon winds. We have also identified periods of enhanced terrestrial particulate organic carbon transfer to the ocean driven by short-lived extreme events, most likely typhoons, during the Bølling–Allerød, at the beginning of the Early Holocene and the end of the Late Holocene, when the typhoon dynamics affecting Taiwan were intensified. Overall, these findings suggest an enhanced marine biological pump during the Heinrich Stadial 1 and an efficient carbon turbidity pump during the Bølling–Allerød, the Early and Late Holocene, contrasting with the western coast of Taiwan.

Track Deflection of Typhoon Chanthu (2021) near Taiwan as Investigated Using a High-Resolution Global Model

Abstract The Model for Prediction Across Scales (MPAS) with variable resolution (60-15-1 km) is used to investigate the track deflection of Typhoon Chanthu (2021) near Taiwan. Chanthu exhibited a rightward track deflection as it approached southeast Taiwan and underwent a leftward deflection when moving northward offshore of northeast Taiwan. Numerical experiments are conducted to identify the physical processes for the track deflection. The rightward deflection of the northbound typhoon is induced by the recirculating flow resulting from the effect of Taiwan’s topography. A wavenumber-one potential vorticity (PV) budget analysis indicates that horizontal PV advection dominates the earlier rightward deflection, while the later leftward deflection is mainly in response to stronger asymmetric cloud heating at low levels at the offshore quadrant of the typhoon. A pair of cyclonic and anticyclonic gyres in the wavenumber-one flow difference is induced by Taiwan’s topography. These rotate counterclockwise to drive the track deflection, most often in westbound typhoons. Idealized WRF simulations are also conducted to explore the track deflection under different northbound conditions. The simulations confirm the track deflection mechanism with similar PV dynamics to the MPAS simulations for Chanthu and illustrate the variabilities of the track deflection for different steering conditions and vortex origins. The rightward deflection of northbound typhoons is essentially determined by a reduced ratio of R/LE where R is the vortex size and LE is the effective length of the mountain range.

Connecting link between a sediment source and its deep-sea sink: Ilan Shelf offshore northeastern Taiwan

The northeast Taiwan margin provides an excellent example of the route of sediment flux from a small mountainous river, the Lanyang River, to a deep-sea basin, the Southern Okinawa Trough (SOT), via a very narrow（8–14 km in width）Ilan Shelf at different time scales. Based on seismic and sub-bottom chirp profiles and onshore borehole and offshore core data, we identify three echo types on the Ilan Shelf that delineate sheets of sediment, mass movement deposits, and echoes indicative of igneous activity. By recognizing lithofacies and seismic facies changes, the Last Glacial Maximum Unconformity and maximum flooding surface are correlated in onshore cores and offshore reflection seismic profiles. With the aids of sequence stratigraphic analysis, the postglacial sedimentation rates on the Ilan Shelf are estimated to range from 0.04 to 1.53 cm/yr. Considering its sediment budget in a source-to-sink system, the Ilan Shelf can be regarded primarily as a temporary trap for fluvial sediment discharged from the Lanyang River. Overall, it has trapped at least 50% of the discharged sediment during the Holocene, and the bulk of sediment was transported, primarily via mass movement to SOT. We deduce that earthquake-induced faulting, axial incision in the channel, and retrogressive failures appear to be triggers for mass wasting, which then combined with channel transport, can play leading roles in rapid downslope transportation to the trough. This inference is indicated by high deposition rates in the western end of SOT and widely distributed mass transport deposits observed in the shallow strata of SOT. We found that the deep strata of SOT are deformed by normal faults, indicating that the sediment accommodation space is structurally controlled by the active back-arc extension. This study documents that frequent typhoons and flooding events, together with strong tidal currents, are significant agents of sediment input over the short term. In contrast, earthquakes and volcanic events occasionally affect sediment dispersal from the Ilan Shelf to SOT.

Surface deformation of northeastern Taiwan revealed by geomorphic indices

In northeast Taiwan, many areas are affected by various tectonic forcings. Some areas appear to have a subsidence tendency, whereas others reflect uplift activities on the surface, due to tectonic northward compressive forcing growth and decline. Owing to the presence of widespread mountain areas, limited geodetic surveys in the field have made data scarce in the study area in the past decades. The distribution of the geomorphic indices, which were calculated along the river channels, were used to analyze the activities on a regional scale in this study. The long-term landscape evolution of drainage basins can record topographic changes through the river channels. By calculating the location and drop height of knickpoint in the river longitudinal profile, as well as the spatial distribution of the normalized steepness index ({K}_{sn}) value, it is possible to comprehensively discuss the perturbations that were caused by possible factors in river channels. Our results from the geomorphic indices synthetically suggest that the river channel of drainage basins is mainly influenced by the perturbations such as geological structures, tectonic activity, various lithologies, potential ruptures. In the study area, tectonic forcing act on a large area from north to south, which is reflected in the long-term incision of the river into the bedrock. Moreover, the potential ruptures on the surface may also induce displacement in the local area.

Seasonal Variability of Eddy Kinetic Energy along the Kuroshio Current

Abstract The seasonal variability of the eddy kinetic energy (EKE) along the Kuroshio Current (KC) is examined using outputs from an eddy-resolving (1/10°) ocean model. Using a theoretical framework for climatological monthly mean EKE, the mechanisms governing the seasonal cycle of upper-ocean EKE are investigated. East of Taiwan, the EKE shows two comparable peaks in spring and summer in the surface layer; only the spring one is evident in the subsurface layer. The seasonality is determined by mixed barotropic (BTI) and baroclinic (BCI) instabilities. Northeast of Taiwan, the EKE is also elevated during spring–summer but with a sole peak in summer, which is dominated by the meridional EKE advection by the KC. In the middle part of the KC in the East China Sea, the mesoscale (&gt;150 km) EKE (EKEMS) is relatively strong during spring–summer, whereas the submesoscale (50–150 km) EKE (EKESM) is significantly enhanced during winter–spring. The seasonal cycles of EKEMS and EKESM are primarily controlled by the external forcing and BCI, respectively. In particular, the higher EKEMS level in summer is mainly due to the increased wind work. West of the Tokara Strait, the EKE exhibits a prominent peak in winter and has its minimum in summer, which is regulated by the BCI. As the submesoscale signals are partially resolved by the model, further studies with higher-resolution simulations and observations are needed for a better understanding of the EKESM seasonality and its contribution to the seasonally modulating EKEMS along the KC.

Assessing the ecological loss of mining areas in Taiwan.

Mines are mostly located in the mountains and national forestlands in Taiwan. The development and use of mines have severely damaged the environment. Despite the long history of mining, the value of forest ecological services lost during mining operations have not yet been incorporated into the expenses borne by miners, and miners are not liable for compensation for ecological damage. This study evaluated the forest ecosystem service benefits lost since mining began, with the aim of providing future reference for calculating ecological damage related to mining. We investigated Mount Taibai mines in Yilan (northeast Taiwan) and Mount Yongshi mines in Hualian (east Taiwan), which are richly forested areas. According to Article 13 of the Mining Act in Taiwan, mining rights have a limitation of 20years, and the two mines in this study have been in operation for 20years. By using four ecological services-forest production, carbon sequestration, water resource replenishment, and forest recreation-we estimated the loss of ecological values in both mining regions. The result indicated that the loss of total forest production benefits over 20years was 7,498.6k New Taiwanese dollars (NTD) in Mount Taibai mines and 6,543.1k NTD for Mount Yongshi mines, while the loss for the total carbon sequestration benefits over 20years was 19,950k NTD in Mount Taibai mines and 17,400k NTD in Mount Yongshi mines. The loss of value for the total water conservation benefits over 20years was 11,160k NTD in Mount Taibai mines and 5,070k NTD in Mount Yongshi mines. The loss value of forest recreation over 20years was 1,443,855k NTD for the two mines.

Characteristics of wave energy resources on coastal waters of northeast Taiwan

Hourly measurements of wave data for 10–14 years from four field stations were analyzed to evaluate wave energy resource characteristics in medium wave power potential coastal waters of northeast Taiwan. Spectral parameters, resource index, and constitutive energy periods were discussed. Time series of water surface displacement in each hour for three consecutive years at two stations were first adopted to obtain period transferring coefficient Cep of 0.86–0.87 for JONSWAP's peak enhancement factor γ of 1.5–1.6. The derived average wave energy scatter maps characterized indices of monthly and seasonal variations and highlighted the effects of typhoon and higher potentials by monsoons with increasing waves from NE. Comparisons with previous numerical simulations on sites offshore northeastern coasts pointed out slightly higher energy potentials at present field stations suggesting field measurements being vital for resource assessment. From energy scatter maps of two representative geographical zones, 15 and 16 top-ranked bin conditions were selected to display concentrations on constitutive energy periods from 6 s to 10 s. Similar selections were applied to foreign energy resources in Pacific and Atlantic coastal waters to show major energy potentials at higher latitudes concentrated on constitutive period ranges by 2 s longer.

Comparison of polycyclic aromatic hydrocarbon accumulation in crab tissues with the ambient marine particles from shallow hydrothermal vents, northeast Taiwan

This study investigated and compared polycyclic aromatic hydrocarbons (PAHs) in crab (Xenograpsus testudinatus), suspended particulate matter, and surface sediment sampled from Kuei-shan-tao (KST) shallow water vents just offshore northeast Taiwan. The total concentrations of PAHs (t-PAHs) in suspended particles near the vents (533–685 ng g−1 dw) were two orders of magnitude higher than the overlying sediment (3.42–6.06 ng g−1 dw). The t-PAHs in sediment were significantly lower than those found in suspended particulate matter and all crab tissues tested, including hepatopancreas (192–1154 ng g−1 dw), gill (221–748 ng g−1 dw), muscle (30–174 ng g−1 dw), and exoskeleton (22–96 ng g−1 dw). Principal component analysis (PCA) indicated tissue-specific bioaccumulation of PAHs in crabs. The compositions of PAHs in gill, muscle, and exoskeleton were mainly low molecular weight, while the composition in the hepatopancreas included both high and low molecular weight PAHs. Highly variable but characteristic PAH congeners and concentrations in crab tissues and ambient aquatic particles reflect bioaccumulation.

Seismicity and Stress State in the Ryukyu Islands Subduction Zone

Based on the newly compiled and mostly complete unified earthquake catalogue for China’s seas and adjacent areas, further information was obtained about the structural shape and dip angle of the Benioff zone in the Ryukyu Islands subduction zone during the different subduction stages. In addition, using the damped regional stress tensor inversion method, we were able to investigate the complex stress field characteristics and the dynamic significance of the shallow and intermediate earthquakes in the Ryukyu Islands subduction zone. The results show that the tectonic stress field of the Ryukyu Islands subduction zone was extensional along the subduction direction in the northern area of the Tokara Strait and was compressional along the subduction direction in the southern area of the Tokara Strait. The R value of the shallow stress field of the Okinawa Trough was low, and the σ3 was stable in the NNW direction with a small dip angle (&gt;30°). The type of stress field in the shallow part of the Okinawa Trough transitioned from strike-slip type to normal fault type from north to south, reflecting the difference in the degree of development of the trough, and the southern segment of the trough began to transform into the expansion stage. The northeastern portion of the study area and southeast Taiwan constituted the high R value (0.68–0.87) region where the σ2 had tensile components. The stress state was biaxial tension–uniaxial compression, and the principal compressive stress was determined to be in the SEE direction with a large dip angle (&gt;30°). The σ1 in northeast Taiwan exhibited a nearly vertical (&gt;60°) plunge, while the σ2 and σ3 were nearly horizontal. The σ2 was thrust in the ENE–WSW direction, and the σ3 was extended in the NNW direction. Through this research, a greater understanding has been gained of the seismicity characteristics and shape of the Ryukyu Islands subduction zone. Supplementary research has also been completed on the focal mechanism solution and stress field of the Ryukyu Islands subduction zone. Finally, this research is important for earthquake hazard analysis and earthquake engineering safety evaluation in this area.

Influences of Tidal Effect on Upper Ocean Responses to Typhoon Passages Surrounding Shore Region off Northeast Taiwan

In this study, the Regional Ocean Modelling System (ROMS) with a spatial resolution of 2 km is used to understand the cooling responses in the sea northeast of Taiwan associated with multiple typhoons. Sea level measurements derived from in situ tidal gauges and continuous temperature measured by a moored buoy deployed at Longdong were used to validate the model’s performance. Six far-field typhoons with similar tracks, namely, Utor (2001), Dujuan (2003), Sanvu (2005), Nanmadol (2011), Usagi (2013), and Meranti (2016), were systematically investigated to demonstrate the influences of tidal effect on upper ocean responses to typhoon passages surrounding shore regions. After integrating tidal forcing, model-simulated cold wakes behind typhoon passages were essentially enhanced. Compared with observations, the cold wakes were reproduced more realistically. Tides could promote a cooling response through the following potential mechanisms: (1) tidal mixing destratifies the water column, (2) a stronger northward current leads to a sharper bottom thermocline, (3) tidal residual currents (southward) drive the offshore-ward (downslope) bottom Ekman flow and lead to the overturning of cold bottom water and warm subsurface water, (4) the increase in bottom stress due to the interaction of tidal currents and bottom topography results in the destratification of the bottom water column, and (5) the wind–tide coupled effect. Nevertheless, the exact mechanism dominating the process of a typhoon–tide-induced stronger upper ocean response depends on different typhoon activities, tidal regimes, stratification, and bathymetry and needs further investigations. In this study, we suggest that including tidal effects is essential for the modeling of upper ocean responses to typhoon passages near the shore regions.

Radiocarbon and Stable Carbon Isotope Constraints on the Propagation of Vent CO 2 to Fluid in the Acidic Kueishantao Shallow Water Hydrothermal System

We report radiocarbon and stable carbon isotope measurements from vent gas (CO2(g)), dissolved inorganic carbon (DIC), and particulate organic carbon (POC), from two vents of the Kueishantao (KST) shallow-water hydrothermal system, offshore northeast Taiwan. The purpose of this research is to investigate how magmatic-sourced carbon enters various carbon pools in the hydrothermal system. We utilize a precipitation method to eliminate sulfur compounds from CO2 samples to facilitate Accelerator Mass Spectrometry (AMS) analysis, and evaluate radiocarbon background levels during processing to characterize hydrothermal-sourced CO2 that contains negligible radiocarbon. The result shows that both CO2(g) and DIC in the fluids below two vent orifices fall within a narrow range of fraction of modern carbon (F14C) from 0.013 to 0.136 and δ13C from −8.3‰ to −5.1‰. The F14C values correspond to approximately 90% magmatic-sourced carbon in CO2(g) and DIC. A combination of equilibrium and kinetic isotopic fractionation can adequately explain relatively high CO2(g) δ13C to DIC, beneath vent orifices. Above the vent orifices, DIC becomes enriched in both 14C and 13C as a result of physical mixing with ambient seawater. POC F14C values confirm a significant magmatic carbon contribution into the POC pool within the KST system, with rapid hydrothermal circulation. Our results identify the physiochemical processes responsible for magmatic carbon migration from CO2(g) into the DIC pool, and demonstrate how a dual carbon isotope approach can serve as an effective tool in understanding carbon flow in high temperature-low pH hydrothermal systems.

Copepods as Indicators of Different Water Masses during the Northeast Monsoon Prevailing Period in the Northeast Taiwan.

Simple SummaryHow the origin and pathways of water masses can be traced by particular bioindicators remains an intriguing issue in biological oceanography. In the present zooplankton study focusing on copepods, calanoid copepodites were most abundant, with an average abundance of 774.24 ± 289.42 (inds. m−3) in the northeastern waters of Taiwan during the prevailing northeast monsoon, followed by the dominant copepod species Paracalanus aculeatus and Clausocalanus furcatus. According to hydrological parameters, the water masses were mainly derived from northeast monsoon surface waters, Kuroshio intrusion water, and mixed water masses. Indicator species were Temora turbinata, Calanopia elliptica, and Canthocalanus pauper in the northeast monsoon-derived water mass. Farranula concinna and Copilia mirabilis represented suitable indicators for the Kuroshio intrusion water mass in the research area. In the mixed water mass, the indicator species were Paracandacia truncata, Oncaea clevei, and P. aculeatus in the research area during the sampling campaign in late autumn.During this research, the average surface temperature, salinity, dissolved oxygen, and pH were 24.65 ± 1.53 (°C), 34.21 ± 0.07 (PSU), 6.85 ± 0.18 (mg/L), and 8.36 ± 0.03, respectively. Based on these environmental parameters, stations were arranged into three groups. Group A represents stations located around Keelung Island with the relative highest average dissolved oxygen, lowest average temperature, and pH values. Instead, the lowest average dissolved oxygen and highest average temperature, salinity, and pH values were recorded at the offshore stations. Keelung Island area was charged by cold water masses, which were driven by the Northeast monsoon, and stations in group C were affected by the Kuroshio Current. Kueishan Island area was mainly affected by mixed water masses resulting from the Kuroshio intrusion and monsoon-derived cold water. In this study, a total of 108 copepod species were identified, with an average abundance of 774.24 ± 289.42 (inds. m−3). Most species belong to the orders Calanoida and Poecilostomatoida, with an average relative abundance (RA) of 62.96% and 30.56%, respectively. Calanoid copepodites were the most dominant group, with a RA of 28.06%. This was followed by Paracalanus aculeatus, with a RA of 18.44%. The RA of Clausocalanus furcatus and Canthocalanus pauper was 4.80% and 3.59%, respectively. The dominant species P. aculeatus, C. pauper, Paracalanus parvus, and Temora turbinata were positively correlated with dissolved oxygen and negatively correlated with temperature in the surface waters. pH showed a negative correlation with P. parvus and T. turbinata, while the temperature was negatively correlated with these two dominant species. Indicator species were selected by an indicator value higher than 50%. Temora turbinata, Calanopia elliptica, C. pauper, Euchaeta concinna, Temora discaudata, Acartia pacifica, Macrosetella gracilis, Corycaeus speciosus, and P. parvus were considered as monsoonal cold water indicator species in Group A. Indicator copepod species for the Kuroshio Current were Farranula concinna, Copilia mirabilis, Candacia aethiopica, Corycaeus agilis, Farranula gibbula and Acrocalanus monachus in the study area. Paracandacia truncata, Oncaea clevei, P. aculeatus, and Centropages furcatus were considered suitable indicators for mixed water masses.

Long-Term Trend and Inter-Annual Variation of Ocean Heat Content in the Bohai, Yellow, and East China Seas

The long-term trend and interannual variation of ocean heat content (OHC) in the Bohai Sea, Yellow Sea, and East China Sea (BYECS) were examined using 27 years (1993–2019) of daily reanalysis data from the Japan Coastal Ocean Predictability Experiment 2 (JCOPE2M). The annual mean OHC was 4.25 × 1021 J, with a linear warming rate of 0.13 W m−2 with a confidence level of 95%. The spatial distributions for the annual and linear trends of OHC in the BYECS were inhomogeneous, and a considerable quantity of heat was stored on the outer shelf. The warming rate was considerably elevated in the areas northeast of Taiwan and southwest of Kyushu, showing a rate greater than that of the Pacific and global oceans by a factor of 4–5. Heat budget analysis indicated that the Taiwan Strait (TAS) is the dominant source of heat for the BYECS. The mechanisms of the OHC interannual variation in the outer and inner shelves varied. On the outer shelf, the OHC interannual variation was dependent on the Kuroshio onshore intrusion, while on the inner shelf, the OHC interannual variation was related to the variation in air-sea heat flux. The rapid warming in the outer shelf corresponded to the increasing trends of heat transport across northeast Taiwan and southwest Kyushu, which were dominated by the temporal variation of current velocity.

First record of butterflyfish, Roa haraguchiae (Actinopterygii: Perciformes: Chaetodontidae), from northeast Taiwan

A recently-described butterflyfish, Roa haraguchiae Uejo, Senou et Motomura, 2020, is herewith for the first time reported from northeast Taiwan. In Taiwan, the genus Roa has been known represented by a single species, Roa modesta (Temminck et Schlegel, 1844). This study presents a comparison of R. haraguchiae with its congeners and includes diagnostic characters on the basis of morphology and genetic differences by life-barcoding. Our specimens have some differences that may be attributed to the individual variations, which are compared and discussed.

Strontium, Hydrogen and Oxygen Behavior in Vent Fluids and Plumes from the Kueishantao Hydrothermal Field Offshore Northeast Taiwan: Constrained by Fluid Processes

Strontium (Sr), hydrogen (H) and oxygen (O) in vent fluids are important for understanding the water–rock interaction and hydrothermal flux in hydrothermal systems. We have analyzed the Sr, H and O isotopic compositions of seawater, vent fluid and hydrothermal plume samples in the Kueishantao hydrothermal field, as well as their calcium (Ca), total sulfur (S), Sr, arsenic (As), stibium (Sb), chlorine (Cl) and manganese (Mn) concentrations for understanding the origin and processes of fluids. The results suggest that most As, Sb and Mn are leached from andesitic rocks into the fluids, and most Ca and Cl remained in the deep reaction zone during the fluid–andesitic rock interaction. The ranges of 87Sr/86Sr, δDV-SMOW and δ18OV-SMOW values in the yellow spring, white spring and plumes are small. The 87Sr/86Sr, δDV-SMOW and δ18OV-SMOW values of fluids and plumes are like those of ambient seawater, indicating that the Sr, H and O of vent fluids and hydrothermal plumes are derived primarily from seawater. This suggests that the interaction of andesite and subseafloor fluid is of short duration and results in the majority of As, Sb and Mn being released into fluids, while most Ca and Cl remained in the deep reaction zone. In addition, there was no significant variation of Sr, H and O isotopic compositions in the upwelling fluid, keeping the similar isotopic compositions of seawater. There are obvious correlations among the pH values, As and Sb concentrations, and H isotopic compositions of the vent fluids and hydrothermal plumes, implying that the As and Sb concentrations and H isotopic compositions can trace the dispersion of plumes in the ambient seawater. According to the Sr concentrations and 87Sr/86Sr values, the water/rock ratios are 3076~8124, which is consistent with the idea that the interaction between fluid and andesite at the subseafloor is of short duration. The hydrothermal flux of Sr discharged from the yellow spring into the seawater is between 2.06 × 104 and 2.26 × 104 mol/yr, and the white spring discharges 1.18 × 104~1.26 × 104 mol/yr Sr if just andesites appear in the reaction zone.