scholarly journals Radiocesium in the Taiwan Strait and the Kuroshio east of Taiwan from 2018 to 2019

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Wei-Jen Huang ◽  
Ming-Ta Lee ◽  
Kuei-Chen Huang ◽  
Kai-Jung Kao ◽  
Ming-An Lee ◽  
...  
Keyword(s):  
Water Column ◽  
Surface Waters ◽  
Half Life ◽  
North Pacific Ocean ◽  
Taiwan Strait ◽  
Depth Range ◽  
Near Surface ◽  
Activity Concentrations ◽  
The Taiwan Strait ◽  
The Kuroshio

AbstractThe release of anthropogenic radiocesium to the North Pacific Ocean (NPO) has occurred in the past 60 years. Factors controlling 137Cs (half-life, 30.2 year) and 134Cs (half-life, 2.06 year) activity concentrations in the Kuroshio east of Taiwan and the Taiwan Strait (latitude 20° N–27° N, longitude 116° E–123° E) remain unclear. This study collected seawater samples throughout this region and analyzed 134Cs and 137Cs activity concentrations between 2018 and 2019. A principal component analysis (PCA) was performed to analyze the controlling factors of radiocesium. Results of all 134Cs activity concentrations were below the detection limit (0.5 Bq m−3). Analyses of water column 137Cs profiles revealed a primary concentration peak (2.1–2.2 Bq m−3) at a depth range of 200–400 m (potential density σθ: 25.3 to 26.1 kg m−3). The PCA result suggests that this primary peak was related to density layers in the water column. A secondary 137Cs peak (1.90 Bq m−3) was observed in the near-surface waters (σθ = 18.8 to 21.4 kg m−3) and was possibly related to upwelling and river-to-sea mixing on the shelf. In the Taiwan Strait, 137Cs activity concentrations in the near-surface waters were higher in the summer than in the winter. We suggest that upwelling facilitates the vertical transport of 137Cs at the shelf break of the western NPO.

scholarly journals On the Kuroshio branch in the Taiwan strait during wintertime

1988 ◽  
Vol 21 (3-4) ◽  
pp. 469-491 ◽  
Author(s):  
Wang Joe ◽  
Ching-Sheng Chern
Keyword(s):  
Taiwan Strait ◽  
The Taiwan Strait ◽  
The Kuroshio

scholarly journals An Oceanic Current against the Wind: How Does Taiwan Island Steer Warm Water into the East China Sea?

2007 ◽  
Vol 37 (10) ◽  
pp. 2563-2569 ◽  
Author(s):  
Jiayan Yang
Keyword(s):  
Pressure Gradient ◽  
Wind Stress ◽  
Pressure Difference ◽  
East Coast ◽  
Taiwan Strait ◽  
Momentum Balance ◽  
Western Boundary ◽  
Current Layer ◽  
The Taiwan Strait ◽  
The Kuroshio

Abstract Along the Taiwan Strait (<100 m in depth) a northeastward flow persists in all seasons despite the annually averaged wind stress that is strongly southwestward. The forcing mechanism of this countercurrent is examined by using a simple ocean model. The results from a suite of experiments demonstrate that it is the Kuroshio that plays the deciding role for setting the flow direction along the Taiwan Strait. The momentum balance along the strait is mainly between the wind stress, friction, and pressure gradient. Since both wind stress and friction act against the northward flow, it is most likely the pressure gradient that forces the northward flow, as noted in some previous studies. What remains unknown is why there is a considerable pressure difference between the southern and northern strait. The Kuroshio flows along the east coast of Taiwan, and thus the western boundary current layer dynamics applies there. Integrating the momentum equation along Taiwan’s east coast shows that there must be a pressure difference between the southern and the northern tip of Taiwan to counter a considerable friction exerted by the mighty Kuroshio. This same pressure difference is also felt on the other side of the island where it forces the northward flow through Taiwan Strait. The model shows that the local wind stress acts to dampen this northward flow. This mechanism can be illustrated by an integral constraint for flow around an island.

scholarly journals Water Exchange across Isobaths over the Continental Shelf of the East China Sea

2017 ◽  
Vol 47 (5) ◽  
pp. 1043-1060 ◽  
Author(s):  
Jing Zhang ◽  
Xinyu Guo ◽  
Liang Zhao ◽  
Yasumasa Miyazawa ◽  
Qun Sun
Keyword(s):  
Continental Shelf ◽  
East China Sea ◽  
Water Exchange ◽  
Bottom Layer ◽  
Taiwan Strait ◽  
East China ◽  
The East China Sea ◽  
China Sea ◽  
The Taiwan Strait ◽  
The Kuroshio

AbstractOnshore and offshore currents and the associated volume transport across three isobaths (50, 100, and 200 m) over the continental shelf of the East China Sea were examined using daily reanalysis data in 1993–2012. After being averaged along the isobaths, the velocities across 100 and 50 m are onshore in the bottom layer but offshore in the surface layer. In contrast, those across the 200-m isobath are onshore in the surface and bottom layers but without a clear direction in the midlayer, suggesting a three-layer structure. The surface offshore current across the 100-m isobath mainly arises from the Taiwan Strait Current, while the surface onshore current across the 200-m isobath mainly arises from the Kuroshio, both of which converge in the area between the 100- and 200-m isobaths and flow toward the Tsushima Strait. The control of bottom Ekman dynamics on the onshore bottom currents is important at the 100-m isobath, partly important at the 200-m isobath, and slightly important at the 50-m isobath. The seasonal variations of onshore and offshore currents in the surface layers across the three isobaths are likely caused by local winds, the Taiwan Strait Current, and the Changjiang discharge, while those in midlayer across the 200-m isobath demonstrate a strong geostrophic control and can be interpreted from a traditional viewpoint on the Kuroshio intrusion over the entire water column across the shelf slope. The close connection of bottom onshore currents across the three isobaths suggests that the bottom layer is an important pathway for water exchange of shelf water and the open sea.

Influence of monsoon-driven hydrographic features on siphonophore assemblages in the Taiwan Strait, western North Pacific Ocean

2013 ◽  
Vol 64 (4) ◽  
pp. 348 ◽  
Author(s):  
Hung-Yen Hsieh ◽  
Shwu-Feng Yu ◽  
Wen-Tseng Lo
Keyword(s):  
Western North Pacific ◽  
North Pacific Ocean ◽  
Distribution Patterns ◽  
Common Species ◽  
Taiwan Strait ◽  
Zooplankton Biomass ◽  
Dynamic Nature ◽  
The North ◽  
Hydrographic Features ◽  
The Taiwan Strait

The spatial patterns of siphonophores were analysed in relation to local hydrographic features during two different monsoon seasons (the north-easterly monsoon in winter v. the south-westerly monsoon in summer) in the Taiwan Strait. Forty-eight species were identified, with five types of calycophoran siphonophores (Lensia subtiloides, Chelophyes appendiculata, Chelophyes contorta, Bassia bassensis, and Diphyes chamissonis) being most common in both seasons. Significantly higher abundances of four of the five common species were recorded in summer than in winter. Differences in the siphonophore species compositions were also observed between the northern and southern part of Taiwan Strait, with significantly higher diversity occurring in the southern waters. The distribution patterns of siphonophore assemblages were closely linked to the hydrographic features, influenced by the dynamic nature of the currents in the study area, with temperature, salinity and zooplankton biomass being the three most important factors.

scholarly journals The Kuroshio Onshore Intrusion along the Shelf Break of the East China Sea: The Origin of the Tsushima Warm Current

2006 ◽  
Vol 36 (12) ◽  
pp. 2205-2231 ◽  
Author(s):  
Xinyu Guo ◽  
Yasumasa Miyazawa ◽  
Toshio Yamagata
Keyword(s):  
Taiwan Strait ◽  
Density Field ◽  
Shelf Break ◽  
Ekman Transport ◽  
Kuroshio Intrusion ◽  
The East China Sea ◽  
Kuroshio Water ◽  
Warm Current ◽  
The Taiwan Strait ◽  
The Kuroshio

Abstract A 1/18° nested ocean model is used to determine locations, volume transports, and temporal variations of Kuroshio onshore fluxes across the shelf break of the East China Sea (ECS). The Kuroshio onshore flux shows strong seasonality: maximum (∼3 Sv; 1 Sv ≡ 106 m3 s−1) in autumn and minimum (<0.5 Sv) in summer. Another short-term (∼17 days) variation due to Kuroshio meanders introduces large fluctuations in the onshore fluxes but its seasonal average almost vanishes. The Kuroshio onshore fluxes have two major sources, Kuroshio intrusion northeast of Taiwan and Kuroshio separation southwest of Kyushu; the former provides larger onshore flux than the latter. Therefore, in addition to the waters from the Taiwan Strait and the Kuroshio separation region southwest of Kyushu, the water due to the Kuroshio intrusion northeast of Taiwan is also a major source of the Tsushima Warm Current. A vorticity equation is used to separate the contribution of surface Ekman transport to the Kuroshio onshore fluxes in the ECS from that relating to density fields. For the total Kuroshio onshore flux across the entire shelf break, its seasonal variation is primarily controlled by the Ekman transport while the change in density field is secondary. For the Kuroshio onshore flux at a fixed location along the shelf break, its seasonal variation is primarily related to the change in density field and the Ekman transport is secondary. Furthermore, the role of the Taiwan Strait water and the Kuroshio water across the shelf break on material transport in the ECS is examined with passive tracer experiments. In summer, about half of the tracer in the Tsushima Strait originates in the Taiwan Strait, while the other half comes from the Kuroshio. From summer to winter, the ratio changes dramatically; the contribution from the Taiwan Strait decreases to 20% and that from the Kuroshio increases up to 80%. The tracer originating in the Kuroshio water dominates the bottom layer of the continental shelf in the ECS throughout the year.

scholarly journals Characteristic Analysis of Sea Surface Currents around Taiwan Island from CODAR Observations

2021 ◽  
Vol 13 (15) ◽  
pp. 3025
Author(s):  
Yu-Hao Tseng ◽  
Ching-Yuan Lu ◽  
Quanan Zheng ◽  
Chung-Ru Ho
Keyword(s):  
Taiwan Strait ◽  
Ocean Dynamics ◽  
Sea Surface ◽  
Surface Currents ◽  
Spatiotemporal Resolution ◽  
The North ◽  
Taiwan Island ◽  
The Taiwan Strait ◽  
The Kuroshio ◽  
Kuroshio Region

Sea surface currents observed by high-frequency (HF) radars have been widely used in ocean circulation research. In this study, hourly sea surface currents observed by the Taiwan Coastal Ocean Dynamics Applications Radar (CODAR) system from 2015 to 2019 were analyzed by the empirical orthogonal function (EOF) analysis to reveal the characteristics of the sea surface currents around Taiwan Island. The study area is divided into two regions, the Kuroshio region east of Taiwan Island and the Taiwan Strait west of Taiwan Island. In the Kuroshio region, the first EOF mode shows that the Kuroshio is characterized by higher current speeds with greater variability in summer. The second and third EOF modes present a dipole eddy pair and single eddy impingement on the Kuroshio during different periods. The seasonal variation of the dipole eddy pair indicates that the cyclonic/anticyclonic eddy on the north/south side appears more frequently in summer. Single eddy impingement occurs at multiple periods, including daily, intraseasonal, interseasonal, and annual periods. For the Taiwan Strait, the first EOF mode displays the tide signals. The tides enter the Taiwan Strait from the north and south, forming strong sea surface currents around the northern tip of Taiwan Island and the Penghu Archipelago. The second EOF mode exhibits the seasonal changes of the sea surface currents driven by the monsoon winds. The sea surface currents in the northern Taiwan Strait are relatively strong, possibly due to the narrow and shallow terrain there. The high spatiotemporal resolution of sea surface currents derived from CODAR observations provide more detailed characteristics of sea surface circulation around Taiwan Island.

Temporal water column dynamics control microbial methane oxidation above an active cold seep (Doggerbank, North Sea)

2020 ◽  
Author(s):  
Tim de Groot ◽  
Malika Menoud ◽  
Thomas Röckmann ◽  
Hossein Maazallahi ◽  
Darci Rush ◽  
...  
Keyword(s):  
Time Series ◽  
Water Column ◽  
Methane Oxidation ◽  
North Sea ◽  
Surface Waters ◽  
Temporal Dynamics ◽  
Tidal Dynamics ◽  
Near Surface ◽  
Methane Efflux ◽  
Mixed Water

<p>Methane is a potent greenhouse gas with strongly increasing atmospheric concentrations since industrialisation. In the ocean, methane is most dominantly produced in sediments and is of microbial and/or thermogenic origin. Uprising methane may escape from the ocean floor to the overlying water column where it can be oxidized by methane oxidizing bacteria. The aerobic methane oxidation (MOx) is thus an important final barrier, which can mitigate methane release from the ocean to the atmosphere where it contributes to global warming. Nevertheless, there is rather little knowledge on the temporal dynamics of the microbial methane filter capacity in the water column. To gain a better understanding of the dynamics, we conducted two 48 hours’ time-series experiments during highly stratified conditions in summer and and mixed water column conditions in autumn above an active methane seep in the North Sea (Doggerbank, 41m water depth). At Doggerbank, dissolved CH<sub>4 </sub> δ<sup>13</sup>C-values (<-65 ‰) indicate a microbial CH<sub>4</sub> origin, and seismic data suggest a gas pocket at >50 m sediment depth. Our time series measurement showed that CH<sub>4</sub> concentrations were highly elevated with up to 2100 nM in bottom and 350 nM in surface waters under stratified conditions. The maxima showed a ~12h periodicity, indicating that the flux of CH<sub>4</sub> from the seep was linked to tidal dynamics with the lowest CH<sub>4</sub> concentrations at rising tide and enhanced flux at falling tide. In contrast, during mixed water column conditions we found lower maxima of only up to 450 nM. Yet, during mixed conditions we found that surface water methane concentrations were on average XX-fold higher compared to stratified conditions, suggesting a higher methane efflux to the atmosphere during this time period.  MOx activity showed a similar temporal behaviour suggesting that tidal dynamics are an important control on the efficiency of the microbial CH<sub>4</sub> filter in the water column. Under stratified conditions MOx rates were highest in bottom waters (<5.7 nM/day), however we also found high MOx rates in near-surface waters at times of elevated seep activity during stratified (<3.2 nM/day) and mixed water column conditions (<16.2 nM/day). Our results indicate that the efficiency of the microbial filter is affected by temporal dynamics and seasonality.</p>

scholarly journals Dynamics of the Toxic Dinoflagellate Alexandrium pacificum in the Taiwan Strait and Its Linkages to Surrounding Populations

Water ◽  
2021 ◽  
Vol 13 (19) ◽  
pp. 2681
Author(s):  
Minlu Liu ◽  
Jing Zheng ◽  
Bernd Krock ◽  
Guangmao Ding ◽  
Lincoln MacKenzie ◽  
...  
Keyword(s):  
South China Sea ◽  
Water Column ◽  
South China ◽  
Yellow Sea ◽  
River Estuary ◽  
Taiwan Strait ◽  
The Yellow Sea ◽  
China Sea ◽  
Minjiang River ◽  
The Taiwan Strait

The dinoflagellate Alexandrium pacificum can produce paralytic shellfish toxins and is mainly distributed in the Pacific. Blooms of A. pacificum have been frequently reported in offshore areas of the East China Sea, but not along the coast. To investigate the bloom dynamics of A. pacificum and their potential origins in the Taiwan Strait, we performed intensive sampling of both water and sediments from 2017 to 2020. Ellipsoidal cysts were identified as A. pacificum and enumerated based on microscopic observation. Their abundances were quite low but there was a maximum of 9.6 cysts cm−3 in the sediment near the Minjiang River estuary in May 2020, consistent with the high cell abundance in the water column in this area. Cells of A. pacificum were examined using a quantitative polymerase chain reaction, and they appeared to be persistent in the water column across the seasons. High densities of A. pacificum (103 cells L−1) were observed near the Jiulongjiang and Minjiang River estuary in early May 2020, where high nutrients (dissolved inorganic nitrogen and phosphate), and relatively low temperatures (20–21 °C) were also recorded. Strains isolated from the East and South China Sea exhibited the highest division rate (0.63 and 0.93 divisions d−1) at 20 and 23 °C, respectively, but the strain from the Yellow Sea showed the highest division (0.40 divisions d−1) at 17–23 °C. Strains from the East and South China Sea shared similar toxin profiles dominated by the N-sulfocarbamoyl toxins C1/2, but the strain from the Yellow Sea predominantly produced the carbamoyl toxins GTX1/4 and no C1/2. Our results suggest that both cyst germination and persistent cells in the water column might contribute to the bloom formation in the Taiwan Strait. Our results also indicate that the East and South China Sea populations are connected genetically through similar toxin formation but separated from the Yellow Sea population geographically.

Sign in / Sign up

Export Citation Format

Share Document