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  • 1
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    Cs-137 in waters surrounding Taiwan from 2018 to 2021 (2022)
    PANGAEA
    Details
    Publication Date: 2023-01-30
    Description: The Fukushima accident released short-lived Cs-134 and longer-lived Cs-137 to the ocean. The amount, although substantial, is much less than that produced during the atomic bomb tests 60 yrs ago. Cs-134 and Cs-137 are anthropogenic radionuclides and soluble in seawater, hence, the radioactivity can be used as a tracer for special event or currents. Here we collected Cs-134 and Cs-137 samples in seawaters surrounding Taiwan including the Kuroshio, the northern South China Sea, the Taiwan Strait, and the southern East China Sea from 2018 to 2021. Most surface seawater samples were collected from boats using 20-L tanks, and a few samples were gathered from the shore. Non-surface seawater samples were taken from R/Vs Ocean Researcher I, II, and III with Niskin bottles mounted on a CTD rosette. All samples were determined in the Radian Monitor Center, Atomic Energy Council of Taiwan. Ammonium molybdophosphate (AMP) was used to pre-concentrated Radiocesium. Each 40-L (60-L) sample was counted for 200,000 s (120,000 s) using a high-purity germanium (HPGe) detector with lead shielding. The detection limits of 137Cs was 0.5 Bq m−3. The averaged surface Cs-137 activities was 1.18±0.25 Bq m-3, however, the activities of Cs-134 samples were all under detection limit. Complete data are archived, including sampling date, location, water depth, temperature, salinity, and Cs-137 activity; total sample amount is 577.
    Keywords: Caesium-137; Cs-137; DATE/TIME; DEPTH, water; East China Sea; Fukushima accident; High-purity Germanium (HPGe) detector; Kuroshio; LATITUDE; LONGITUDE; MULT; Multiple investigations; Salinity; South China Sea; Taiwan_Seawater; Taiwan Strait; Temperature, water
    Type: Dataset
    Format: text/tab-separated-values, 1731 data points
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  • 2
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    Internal solitons in the northeastern south China Sea. Part I: sources and deep water propagation (2006)
    IEEE
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © IEEE, 2004. This article is posted here by permission of IEEE for personal use, not for redistribution. The definitive version was published in IEEE Journal of Oceanic Engineering 29 (2004): 1157-1181, doi:10.1109/JOE.2004.840839.
    Description: A moored array of current, temperature, conductivity, and pressure sensors was deployed across the Chinese continental shelf and slope in support of the Asian Seas International Acoustics Experiment. The goal of the observations was to quantify the water column variability in order to understand the along- and across-shore low-frequency acoustic propagation in shallow water. The moorings were deployed from April 21–May 19, 2001 and sampled at 1–5 min intervals to capture the full range of temporal variability without aliasing the internal wave field. The dominant oceanographic signal by far was in fact the highly nonlinear internal waves (or solitons) which were generated near the Batan Islands in the Luzon Strait and propagated 485 km across deep water to the observation region. Dubbed trans-basin waves, to distinguish them from other, smaller nonlinear waves generated locally near the shelf break, these waves had amplitudes ranging from 29 to greater than 140 m and were among the largest such waves ever observed in the world’s oceans. The waves arrived at the most offshore mooring in two clusters lasting 7–8 days each separated by five days when no waves were observed.Within each cluster, two types of waves arrived which have been named type-a and type-b. The type-a waves had greater amplitude than the type-b waves and arrived with remarkable regularity at the same time each day, 24 h apart. The type-b waves were weaker than the type-a waves, arrived an hour later each day, and generally consisted of a single soliton growing out of the center of the wave packet. Comparison with modeled barotropic tides from the generation region revealed that: 1) The two clusters were generated around the time of the spring tides in the Luzon strait; and 2) The type-a waves were generated on the strong side of the diurnal inequality while the type-b waves were generated on the weaker beat. The position of the Kuroshio intrusion into the Luzon Strait may modulate the strength of the waves being produced. As the waves shoaled, the huge lead solitons first split into two solitons then merged together into a broad region of thermocline depression at depths less than 120 m. Elevation waves sprang up behind them as they continued to propagate onshore. The elevation waves also grew out of regions where the locally-generated internal tide forced the main thermocline down near the bottom. The “critical point” where the upper and lower layers were equal was a good indicator of when the depression or elevation waves would form, however this was not a static point, but rather varied in both space and time according to the presence or absence of the internal tides and the incoming trans-basin waves themselves.
    Description: The planning, execution, and analysis of this work was supported by the U.S. Office of Naval Research Ocean Acoustics and Physical Oceanography Programs. Significant funding contributions were also made by the National Science Council of Taiwan.
    Keywords: Baroclinic tides ; Nonlinear internal waves ; Ocean currents
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 3
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    The Kuroshio and Luzon Undercurrent east of Luzon Island (2016)
    The Oceanography Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © The Oceanography Society, 2015. This article is posted here by permission of The Oceanography Society for personal use, not for redistribution. The definitive version was published in Oceanography 28, no. 4 (2015): 54–63, doi:10.5670/oceanog.2015.81.
    Description: Current structure, transport, and water mass properties of the northward-flowing Kuroshio and the southward-flowing Luzon Undercurrent (LU) were observed for nearly one year, June 8, 2012–June 4, 2013, across the Kuroshio path at 18.75°N. Observations were made from four platforms: an array of six subsurface ADCP moorings, two Seagliders, fivepressure inverted echo sounders (PIES), and five horizontal electric field (HEF) sensors, providing the most detailed time series of the Kuroshio and Luzon Undercurrent water properties to date. Ocean state estimates of the western boundary current system were performed using the MIT general circulation model—four-dimensional variational assimilation (MITgcm-4D-Var) system. Prominent Kuroshio features from observations are simulated well by the numerical model. Annual mean Kuroshio transport, averaged over all platforms, is ~16 Sv with a standard deviation ~4 Sv. Kuroshio and LU transports and water mass pathways east of Luzon are revealed by Seaglider measurements. In a layer above the salinity maximum associated with North Pacific Tropical Water (NPTW), Kuroshio transport is ~7 Sv and contains North Equatorial Current (NEC) and Western Philippine Sea (WPS) waters, with an insignificant amount of South China Sea water on the shallow western flank. In an intermediate layer containing the core of the NPTW, Kuroshio transport is ~10 Sv, consisting mostly of NEC water. In the lower layer of the Kuroshio, transport is ~1.5 Sv of mostly North Pacific Intermediate Water (NPIW) as a part of WPS waters. Annual mean Luzon Undercurrent southward transport integrated to 1,000 m depth is ~2.7 Sv with a standard deviation ~2 Sv, carrying solely WPS waters below the salinity minimum of the NPIW. The transport of the western boundary current integrated over the full ocean depth east of Luzon Island is ~14 ± 4.5 Sv. Sources of the water masses in the Kuroshio and Luzon Undercurrent are confirmed qualitatively by the numerical model.
    Description: This work was supported by the US Office of Naval Research (N00014-10-1-0273 and N00014-15-1-2285 to BDC, N00014-10-1-0273 to GG, N00014-14-1-0065 to ALG, N00014-10-1-0468 to TBS, N0001-10-1-0273 to LRC, N00014-10-1-0308 to CML, N00014-10-1-0397 and N00014-10-1-0273 to BM, N00014-10-1-0397 to RCL, and N00014-10-1-0268 to SRJ) and the Taiwan Ministry of Science and Technology. Yang, Chang, and Mensah are supported by the Taiwan Ministry of Science and Technology.
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 4
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    Internal tide and nonlinear internal wave behavior at the continental slope in the northern south China Sea (2006)
    IEEE
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © IEEE, 2004. This article is posted here by permission of IEEE for personal use, not for redistribution. The definitive version was published in IEEE Journal of Oceanic Engineering 29 (2004): 1105-1130, doi:10.1109/JOE.2004.836998.
    Description: A field program to measure acoustic propagation characteristics and physical oceanography was undertaken in April and May 2001 in the northern South China Sea. Fluctuating ocean properties were measured with 21 moorings in water of 350- to 71-m depth near the continental slope. The sea floor at the site is gradually sloped at depths less than 90 m, but the deeper area is steppy, having gradual slopes over large areas that are near critical for diurnal internal waves and steep steps between those areas that account for much of the depth change. Large-amplitude nonlinear internal gravity waves incident on the site from the east were observed to change amplitude, horizontal length scale, and energy when shoaling. Beginning as relatively narrow solitary waves of depression, these waves continued onto the shelf much broadened in horizontal scale, where they were trailed by numerous waves of elevation (alternatively described as oscillations) that first appeared in the continental slope region. Internal gravity waves of both diurnal and semidiurnal tidal frequencies (internal tides) were also observed to propagate into shallow water from deeper water, with the diurnal waves dominating. The internal tides were at times sufficiently nonlinear to break down into bores and groups of high-frequency nonlinear internal waves.
    Description: This work was supported in part by grants from the U.S. Office of Naval Research, Physical Oceanography and Ocean Acoustics Programs, and by the National Science Council of Taiwan.
    Keywords: Baroclinic tides ; Internal waves ; Nonlinear waves
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 5
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    Mean structure and variability of the cold dome northeast of Taiwan (2012)
    The Oceanography Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © The Oceanography Society, 2011. This article is posted here by permission of The Oceanography Society for personal use, not for redistribution. The definitive version was published in Oceanography 24 no. 4 (2011): 100–109, doi:10.5670/oceanog.2011.98.
    Description: The "cold dome" off northeastern Taiwan is one of the distinctive oceanic features in the seas surrounding Taiwan. The cold dome is important because persistent upwelling makes the region highly biologically productive. This article uses historical data, recent observations, and satellite-observed sea surface temperatures (SST) to describe the mean structure and variability of the cold dome. The long-term mean position of the cold dome, using the temperature at 50 m depth as a reference, is centered at 25.625°N, 122.125°E. The cold dome has a diameter of approximately 100 km, and is maintained by cold (〈 21°C) and salty (〉 34.5) waters upwelled along the continental slope. The ocean currents around the cold dome, although weak, flow counterclockwise. The monsoon-driven winter intrusion of the Kuroshio current onto the East China Sea shelf intensifies the upwelling and carries more subsurface water up to the cold dome than during the summer monsoon season. On a shorter timescale, the cold dome's properties can be significantly modified by the passage of typhoons, which creates favorable physical conditions for short-term Kuroshio intrusions in summer. The surface expression of the cold dome viewed from satellite SST images is often not domelike but instead is an irregular shape with numerous filaments, and thus may contribute substantially to shelf/slope exchange. As a result of persistent upwelling, typhoon passage, and monsoon forcing, higher chlorophyll a concentrations, and thus higher primary productivity, are frequently observed in the vicinity of the cold dome.
    Description: The National Science Council (NSC) of Taiwan sponsored this study under grant NSC98-2611-M-002-019-MY3. NSC supported C.-C. Chen under grant NSC98-2611-M-003-001-MY3.
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 6
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    Mean structure and fluctuations of the Kuroshio east of Taiwan from in situ and remote observations (2016)
    The Oceanography Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © The Oceanography Society, 2015. This article is posted here by permission of The Oceanography Society for personal use, not for redistribution. The definitive version was published in Oceanography 28, no. 4 (2015): 74–83, doi:10.5670/oceanog.2015.83.
    Description: The Kuroshio is important to climate, weather prediction, and fishery management along the northeast coast of Asia because it transports tremendous heat, salt, and energy from east of the Philippines to waters southeast of Japan. In the middle of its journey northward, the Kuroshio’s velocity mean and its variability east of Taiwan crucially affect its downstream variability. To improve understanding of the Kuroshio there, multiple platforms were used to collect intensive observations off Taiwan during the three-year Observations of the Kuroshio Transports and their Variability (OKTV) program (2012–2015). Mean Kuroshio velocity transects show two velocity maxima southeast of Taiwan, with the primary velocity core on the onshore side of the Kuroshio exhibiting a mean maximum velocity of ~1.2 m s–1. The two cores then merge and move at a single velocity maximum of ~1 m s–1 east of Taiwan. Standard deviations of both the directly measured poleward (v) and zonal (u) velocities are ~0.4 m s–1 in the Kuroshio main stream. Water mass exchange in the Kuroshio east of Taiwan was found to be complicated, as it includes water of Kuroshio origin, South China Sea Water, and West Philippine Sea Water, and it vitally affects heat, salt, and nutrient inputs to the East China Sea. Impinging eddies and typhoons are two of the principal causes of variability in the Kuroshio. This study’s models are more consistent with the observed Kuroshio than with high-frequency radar measurements.
    Description: This study was sponsored by the Ministry of Science and Technology (MOST) of the ROC (Taiwan) under grants NSC 101-2611-M-002-018-MY3, NSC 101-2611- M-019-002, NSC 102-2611-M-002-017, NSC 102-2611- M-019-012, MOST 103-2611-M-002-014, and MOST 103-2611-M-002-018. MA was sponsored by the US Office of Naval Research under grant N00014- 12-1-0445. YHT was supported by NSF Earth System Model (EaSM) Grant 1419292.
    Repository Name: Woods Hole Open Access Server
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  • 7
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    Circulation and intrusions northeast of Taiwan : chasing and predicting uncertainty in the cold dome (2012)
    The Oceanography Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © The Oceanography Society, 2011. This article is posted here by permission of The Oceanography Society for personal use, not for redistribution. The definitive version was published in Oceanography 24 no. 4 (2011): 110–121, doi:10.5670/oceanog.2011.99.
    Description: An important element of present oceanographic research is the assessment and quantification of uncertainty. These studies are challenging in the coastal ocean due to the wide variety of physical processes occurring on a broad range of spatial and temporal scales. In order to assess new methods for quantifying and predicting uncertainty, a joint Taiwan-US field program was undertaken in August/September 2009 to compare model forecasts of uncertainties in ocean circulation and acoustic propagation, with high-resolution in situ observations. The geographical setting was the continental shelf and slope northeast of Taiwan, where a feature called the "cold dome" frequently forms. Even though it is hypothesized that Kuroshio subsurface intrusions are the water sources for the cold dome, the dome's dynamics are highly uncertain, involving multiple scales and many interacting ocean features. During the experiment, a combination of near-surface and profiling drifters, broad-scale and high-resolution hydrography, mooring arrays, remote sensing, and regional ocean model forecasts of fields and uncertainties were used to assess mean fields and uncertainties in the region. River runoff from Typhoon Morakot, which hit Taiwan August 7–8, 2009, strongly affected shelf stratification. In addition to the river runoff, a cold cyclonic eddy advected into the region north of the Kuroshio, resulting in a cold dome formation event. Uncertainty forecasts were successfully employed to guide the hydrographic sampling plans. Measurements and forecasts also shed light on the evolution of cold dome waters, including the frequency of eddy shedding to the north-northeast, and interactions with the Kuroshio and tides. For the first time in such a complex region, comparisons between uncertainty forecasts and the model skill at measurement locations validated uncertainty forecasts. To complement the real-time model simulations, historical simulations with another model show that large Kuroshio intrusions were associated with low sea surface height anomalies east of Taiwan, suggesting that there may be some degree of predictability for Kuroshio intrusions.
    Description: We thank the National Science Council of Taiwan as well as the Office of Naval Research for generous support of this effort.
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 8
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    Experimental and numerical studies of sound propagation over a submarine canyon northeast of Taiwan (2015)
    IEEE
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © IEEE, 2015. This article is posted here by permission of IEEE for personal use, not for redistribution. The definitive version was published in IEEE Journal of Ocean Engineering 40 (2015): 237-249, doi:10.1109/JOE.2013.2294291.
    Description: A study of sound propagation over a submarine canyon northeast of Taiwan was made using mobile acoustic sources during a joint ocean acoustic and physical oceanographic experiment in 2009. The acoustic signal levels (equivalently, transmission losses) are reported here, and numerical models of 3-D sound propagation are employed to explain the underlying physics. The data show a significant decrease in sound intensity as the source crossed over the canyon, and the numerical model provides a physical insight into this effect. In addition, the model also suggests that reflection from the canyon seabed causes 3-D sound focusing when the direction of propagation is along the canyon axis, which remains to be validated in a future experiment. Environmental uncertainties of water sound speed, bottom geoacoustic properties, and bathymetry are addressed, and the implications for sound propagation prediction in a complex submarine canyon environment are also discussed.
    Description: The Quantifying, Predicting and Exploiting (QPE) Uncertainty Initiative Experiment was supported jointly by the National Science Council, Taiwan, under Project NSC98-2623-E002-018-D and the U.S. Office of Naval Research (ONR) under Grant N00014-08-1-0763. The work of Y.-T. Lin was supported by the U.S. ONR under Grants N00014-10-1-0040 and N00014-13-1-0026. The work of T. F. Duda was supported by the U.S. ONR under Grant N00014-11-1-0194.
    Keywords: Acoustics ; Noise ; Numerical models ; Solid modeling ; Sonar equipment ; Underwater vehicles ; Vehicles
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 9
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    The formation and fate of internal waves in the South China Sea (2015)
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © The Author(s), 2015. This is the author's version of the work. It is posted here by permission of Nature Publishing Group for personal use, not for redistribution. The definitive version was published in Nature 521 (2015): 65-69, doi:10.1038/nature14399.
    Description: Internal gravity waves, the subsurface analogue of the familiar surface gravity waves that break on beaches, are ubiquitous in the ocean. Because of their strong vertical and horizontal currents, and the turbulent mixing caused by their breaking, they impact a panoply of ocean processes, such as the supply of nutrients for photosynthesis1, sediment and pollutant transport2 and acoustic transmission3; they also pose hazards for manmade structures in the ocean4. Generated primarily by the wind and the tides, internal waves can travel thousands of kilometres from their sources before breaking5, posing severe challenges for their observation and their inclusion in numerical climate models, which are sensitive to their effects6-7. Over a decade of studies8-11 have targeted the South China Sea, where the oceans’ most powerful internal waves are generated in the Luzon Strait and steepen dramatically as they propagate west. Confusion has persisted regarding their generation mechanism, variability and energy budget, however, due to the lack of in-situ data from the Luzon Strait, where extreme flow conditions make measurements challenging. Here we employ new observations and numerical models to (i) show that the waves begin as sinusoidal disturbances rather than from sharp hydraulic phenomena, (ii) reveal the existence of 〉200-m-high breaking internal waves in the generation region that give rise to turbulence levels 〉10,000 times that in the open ocean, (iii) determine that the Kuroshio western boundary current significantly refracts the internal wave field emanating from the Luzon Strait, and (iv) demonstrate a factor-of-two agreement between modelled and observed energy fluxes that enables the first observationally-supported energy budget of the region. Together, these findings give a cradle-to-grave picture of internal waves on a basin scale, which will support further improvements of their representation in numerical climate predictions.
    Description: Our work was supported by the U.S. Office of Naval Research and the Taiwan National Science Council.
    Description: 2015-10-29
    Repository Name: Woods Hole Open Access Server
    Type: Preprint
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  • 10
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    Research highlights from the Asian Seas International Acoustics Experiment in the South China Sea (2006)
    IEEE
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © IEEE, 2004. This article is posted here by permission of IEEE for personal use, not for redistribution. The definitive version was published in IEEE Journal of Oceanic Engineering 29 (2004): 1067-1074, doi:10.1109/JOE.2005.843162.
    Description: The Asian Seas International Acoustics Experiment (ASIAEX) included two major field programs, one in the South China Sea (SCS) and the other in the East China Sea (ECS). This paper summarizes results from the work conducted during April and May 2000 and 2001 over the continental shelf and slope in the northeastern South China Sea, just east of Dongsha Island (Pratis Reef). The primary emphasis of the field program was on water-column variability and its impact on acoustic propagation loss. The reader is steered to the appropriate paper within this Special Issue when more information on a specific topic is desired.
    Description: The planning, execution, and analysis of this work was funded by the U.S. Office of Naval Research Ocean Acoustics and Physical Oceanography Programs. Significant support was also made by the National Science Council of Taiwan.
    Keywords: Acoustic propagation ; Asian Seas International Acoustics Experiment (ASIAEX) ; Internal waves ; Ocean currents ; South China Sea
    Repository Name: Woods Hole Open Access Server
    Type: Article
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