Hasil untuk "Oceanography"

Jia-Wei Bian, Ruo-Shan Tseng, Chih-Min Hsieh et al.

Coastal sediment transport is a dynamic process influenced by the continuous interplay of waves and currents. However, traditional models based on linear wave theory often fail to capture the full complexity of nearshore turbulence. In this study, we present the first field-based application of nonlinear wave theories—including third-order Stokes and cnoidal wave formulations—to quantify wave-induced shear stress and evaluate its impact on turbidity. Utilizing in situ measurements from four extreme hydrodynamic events—Typhoon Dujuan (2015), Extreme Cold Surge (2016), Prolonged Heavy Rainfall (2018), and Typhoon Wipha (2019)—off the coast of Houwan, Taiwan, we reveal a compelling pattern: third-order Stokes theory not only predicts higher magnitudes of shear stress but also exhibits remarkable temporal alignment with observed turbidity surges. In contrast, current-induced shear stress remains relatively low. These findings challenge the prevalent reliance on linear wave assumptions and establish a validated nonlinear modeling framework for coastal morphodynamics. By capturing the episodic chaos associated with storm-driven seas, this study provides critical insights for predicting sediment transport in light of intensifying climatic extremes.

Simone Bozzo, Diego Villa, Simone Mancini

The assessment for the resistance of a new ship under design can be performed through the Experimental Fluid Dynamics (EFD) or the Computational Fluid Dynamics (CFD) approach; both have their own Uncertainty Assessment (UA). In CFD field, the Verification and Validation (V&V) procedures take into account the approximations for numerical issues and the assumptions adopted to describe the physical phenomena to assess UA. Different theoretical approaches have become available over time; nevertheless, a single comprehensive solution to achieve the UA remains still unknown because as the theoretical methodology varies, the outcome changes. In current work, four different literature approaches will be augmented to perform a V&V analysis for two kinds of model hulls, tested at different speeds and compared with the experimental data. The investigations performed among results lead to the division of all the approaches into the three and four solutions families and to define a robust procedure to identify a reasonable value for the numerical uncertainty assessment. Regarding the robustness and the UA of the approaches, the first family proved successful in only 55% of cases with a UA mean value below 2.01%, while the second one always provides a quantification but with a mean value of 6.65%.

Zoe Moorton, Kamlesh Mistry, Rebecca Strachan et al.

Being able to accurately identify litter in a marine environment is crucial to cleaning up our seas and oceans. Research into object detection techniques to support this identification has been underway for over two decades. However, there have been substantial advancements in the past five years due to the implementation of deep learning techniques. Following the PRISMA-ScR guidelines, we provide an in-depth summary and analysis of recent and significant research contributions to the object detection of macro marine debris. From cross-referencing the results of the literature review, we deduce that there is currently no benchmarked framework for evaluating and comparing computer vision techniques for marine environments. Subsequently, we use the results from our analysis to provide a suggested checklist for future researchers in this field. Furthermore, many of the respected researchers in this field have advocated for a comprehensive database of underwater debris to support research developments in intelligent object detection and identification.

Paul van Wiechen, Jantien Rutten, Sierd de Vries et al.

Abstract Nearshore hydro- and morphodynamic data were collected during a field experiment under calm conditions, moderate conditions, and storm conditions with dune erosion in the collision regime. The experiment was conducted on the Sand Engine near Kijkduin, the Netherlands, from October 18, 2021, to January 7, 2022. Two artificial unvegetated dunes were constructed just above the high water line to measure storm erosion and dune impacts from higher water levels and waves. During the experiment, three storms occurred that resulted in significant erosion of both dunes. The collected hydrodynamic data include pressure sensor and velocimeter data along two cross-shore transects. The collected morphodynamic data include bathymetry and topography surveys, optical backscatter sensor data in the inner surf zone, and a continuous cross-shore line-scanning lidar data set of the dune face. This comprehensive data set can be used to (1) study relevant nearshore hydrodynamic and morphodynamic processes that occur during calm conditions, moderate conditions, and storm conditions with dune erosion in the collision regime, and (2) validate existing dune erosion models.

Melissa H. Pecundo, Tao Chen, Thomas Edison E. dela Cruz et al.

Heterocyte-forming cyanobacteria form symbiotic relationships with several lineages of plants. Here, twenty (20) strains of endosymbiotic cyanobacteria (cyanobionts) with <i>Nostoc</i>-like morphologies were isolated from the highly specialized coralloid roots of five host species in Cycadales—<i>Cycas debaoensis</i>, <i>C. fairylakea</i>, <i>C. elongata</i>, <i>Ceratozamia robusta</i>, and <i>Macrozamia moorei</i>. Molecular phylogeny based on the 16S rRNA gene placed these strains into seven different taxa within the Nostocaceae, specifically under the genera <i>Desmonostoc</i> and <i>Dendronalium</i>. The percent dissimilarity and unique patterns in the secondary structures of the D1-D1′, Box-B, V2, and V3 helices, which were based on the 16S–23S rRNA internal transcribed spacer (ITS) regions, supported three distinct species in <i>Desmonostoc</i>. These three morphologically distinct novel species are described in this report: <i>Desmonostoc debaoense</i> sp. nov., <i>Desmonostoc meilinense</i> sp. nov., and <i>Desmonostoc xianhuense</i> sp. nov. Other investigated strains were phylogenetically identified as members of the recently discovered genus <i>Dendronalium</i> and represent the first report of association of that genus with cycads. Our findings suggest that the order Cycadales hosts diverse species of cyanobionts in their coralloid roots and that many potential unreported or novel taxa are present in cycads occurring in their natural habitat and await discovery.

Myeong-Taek Kwak, Yang-Ki Cho

A high-resolution, three-dimensional numerical ocean model was employed to understand the exchange flow through Noryang Channel, which connects Gwangyang Bay and Jinju Bay. These two bays exhibit contrasting topographies, with Gwangyang Bay connected to the open ocean through a broad and deep channel, whereas Jinju Bay is relatively isolated from the open ocean by a narrow and shallow channel. Numerical experiments were conducted to determine the contribution of river discharge, wind stress, surface heat flux, and tides to the exchange flow between the two bays during summer. The results suggested that river discharge was the dominant factor affecting the exchange flow along Noryang Channel. Particularly, a high river discharge during summer increased the sea level in Jinju Bay, creating a barotropic flow toward Gwangyang Bay. However, the dense water entering Gwangyang Bay through the wide and deep channel generated a baroclinic flow toward Jinju Bay along the lower layer of Noryang Channel. An analytical model supported the conclusion that river discharge is the main driver of the exchange flow in Noryang Channel.

Wenlong Yang, Hui Zhou, Yonggang Wang et al.

Measurements of the turbulent kinetic energy dissipation rate (<i>ε</i>) were conducted by a free-fall microstructure profiler in the western Pacific North Equatorial Current (WPNEC) during a continuous period of 25 h, from the sea surface to about 160 m depth. In the mixed layer (ML), <i>ε</i> values were typically on the order of 10⁻⁸∼10⁻⁷ W kg⁻¹, and an obvious diurnal cycle existed in the upper 40 m of the surface mixing layer. Below the ML, <i>ε</i> was reduced to 10⁻⁹∼10⁻⁸ W kg⁻¹ with some patches of high <i>ε</i> reaching 10^−7.5 W kg⁻¹. The barrier layer was identified in the nighttime with a maximum thickness of 20 m, and it was eroded by the advection of freshwater within the lower part of the isothermal layers associated with an anticyclonic eddy in the afternoon. A simple scaling relevant to shear (<i>S</i>²) instability and stratification (<i>N</i>²) that can predict turbulent dissipation rates in the transition layer, between the well-mixed layer and the thermocline below, was obtained through the scaling <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>ε</mi><mo>∼</mo><msup><mrow><mfenced close="|" open="|"><mi>S</mi></mfenced></mrow><mrow><mo>−</mo><mn>0.40</mn></mrow></msup><msup><mrow><mfenced close="|" open="|"><mi>N</mi></mfenced></mrow><mrow><mn>0.20</mn></mrow></msup></mrow></semantics></math></inline-formula>. Besides turbulence, double-diffusive processes also contributed to the vertical mixing levels in the upper WPNEC.

ChenYan Wu, XiaoGu Wang, JunSheng Zhong et al.

The objective of this study was to investigate influence of meso-scale eddies in the western South China Sea on species composition and spatial patterns of fish larvae and juveniles based on the data collected during summer and autumn in 2012. Nintyeight species belonging to 38 families were collected, including 78 species in summer and 41 species in autumn. The dominant species in summer were Vinciguerria sp. (39.70%), Stephanolepis cirrhifer (11.21%), Caranx sp. (5.45%) and Benthosema pterotum (1.97%). The dominant species in autumn were Gobiidae sp. (15.32%), Ceratoscopelus townsendi (7.26%), Diaphus sp. (6.45%), Astronesthes sp. (5.65%) and Callionymidae sp. (4.03%). Abundance of fish larvae and juveniles in summer was higher than that found in autumn. Similarity cluster analysis results indicated that larval fish assemblages in summer can be divided into two communities: (1) larval fish in the cyclonic eddy; (2) larval fish in the anticyclonic eddies. While in autumn, the larval fish assemblages can be divided into three communities: (1) larval fish without influence of the cyclonic eddy; (2) larval fish influenced slightly by the cyclonic eddy; (3) larval fish gathered near the center of the cyclonic eddy. The variations of abundance and assemblage of larval fish might be attributed to sea surface temperature (SST), sea surface salinity (SSS) and sea level anomaly (SLA).

Fabián Pina Amargós, Tamara Figueredo - Martín, Noel López Fernández

En los meses de marzo y mayo de 2018 se realizaron inventarios de la ictiofauna en el Parque Nacional Ciénaga de Zapata, al sur de la provincia de Matanzas. Este trabajo pre- senta el primer inventario publicado en revista arbitrada de la ictiofauna para esta área protegida. La identificación de los peces se realizó principalmente in situ, mediante buceo libre al azar, así como a través de la revisión de 3968 minutos de videos submarinos remotos con carnada (BRUVs en inglés) y de fotografías de alta resolución. La ictiofauna está compuesta por 169 especies agrupadas en 53 familias. Se adicionan 67 especies a la lista de peces (no publicada) del Área Protegida de Recursos Manejados Península de Zapata. Se destaca la alta frecuencia de la especie invasora Pez león (Pterois volitans). En el Parque Nacional Ciénaga de Zapata está representado el 16 % de la ictiofauna cubana, el 17 % de los peces estrictamente marinos, el 11 % de los Chondrichthyes y el 18 % de los Actinopterygii. La diversidad de taxa en el Parque Nacional Ciénaga de Zapata es alta, siendo las familias más diversas similares a otras regiones, aunque el orden varía entre unas y otras. Se consignan Hypoplectrus randallorum y H. maculiferus para el área. Se detectaron dos potenciales nuevos sitios de agregación reproductiva de peces, uno de bonací gato (Mycteroperca tigris) y otro de aguají (M. bonaci).   Recibido: 15-10-2021 Aceptado: 12-01-2022 Editor temático: Tsai García Galano  

Ursula Siebert, Miguel L. Grilo, Tina Kesselring et al.

Evaluating populational trends of health condition has become an important topic for marine mammal populations under the Marine Strategy Framework Directive (MSFD). In the Baltic Sea, under the recommendation of Helsinki Commission (HELCOM), efforts have been undertaken to use blubber thickness as an indicator of energy reserves in marine mammals. Current values lack geographical representation from the entire Baltic Sea area and a large dataset is only available for grey seals (Halichoerus grypus) from Sweden and Finland. Knowledge on variation of blubber thickness related to geography throughout the Baltic Sea is important for its usage as an indicator. Such evaluation can provide important information about the energy reserves, and hence, food availability. It is expected that methodological standardization under HELCOM should include relevant datasets with good geographical coverage that can also account for natural variability in the resident marine mammal populations. In this study, seasonal and temporal trends of blubber thickness were evaluated for three marine mammal species—harbor seal (Phoca vitulina), grey seal (Halichoerus grypus) and harbor porpoise (Phocoena phocoena)—resident in the southern Baltic Sea collected and investigated under stranding networks. Additionally, the effects of age, season and sex were analyzed. Seasonal variation of blubber thickness was evident for all species, with harbor seals presenting more pronounced effects in adults and grey seals and harbor porpoises presenting more pronounced effects in juveniles. For harbor seals and porpoises, fluctuations were present over the years included in the analysis. In the seal species, blubber thickness values were generally higher in males. In harbor seals and porpoises, blubber thickness values differed between the age classes: while adult harbor seals displayed thicker blubber layers than juveniles, the opposite was observed for harbor porpoises. Furthermore, while an important initial screening tool, blubber thickness assessment cannot be considered a valid methodology for overall health assessment in marine mammals and should be complemented with data on specific health parameters developed for each species.

Fiona Bairstow, Sven Gastauer, Sven Gastauer et al.

Antarctic krill are subject to precautionary catch limits, based on biomass estimates, to ensure human activities do not adversely impact their important ecological role. Accurate target strength models of individual krill underpin biomass estimates. These models are scaled using measured and estimated distributions of length and orientation. However, while the length distribution of a krill swarm is accessible from net samples, there is currently limited consensus on the method for estimating krill orientation distribution. This leads to a limiting factor in biomass calculations. In this work, we consider geometric shape as a variable in target strength calculations and describe a practical method for generating a catalog of krill shapes. A catalog of shapes produces a more variable target strength response than an equivalent population of a scaled generic shape. Furthermore, using a shape catalog has the greatest impact on backscattering cross-section (linearized target strength) where the dominant scattering mechanism is mie scattering, irrespective of orientation distribution weighting. We suggest that shape distributions should be used in addition to length and orientation distributions to improve the accuracy of krill biomass estimates.

Yingcheng Zhao, Xichuan Liu, Minghao Xian et al.

The large-scale monitoring of rainfall is of great significance in the research of meteorology, hydrology, and atmospheric measurement science. In recent years, with the quick development of communication satellite constellation, the use of earth-space link (ESL) to measure rainfall in the atmosphere is expected to be a potential approach for the large-scale monitoring of global rainfall. In this article, to verify the long-term performance of rainfall measurement using ESL, the data of an ESL at the Ku band and a Thies Laser Precipitation Monitor (LPM) in Nanjing were collected. The rainfall inversion model using ESL was optimized according to the height of 0&#x00A0;&#x00B0;C-layer from the radiosonde data of ten years, and the inversion results in the different types of rainfall were discussed. The results show that the rainfall inversed by the optimized ESL model are in good agreement with the rainfall measured by LPM (correlative coefficient is 0.985), the relative errors of rain intensity inversed by ESL in light rain, moderate rain, heavy rain, and extreme rain are 20&#x0025;, 15.17&#x0025;, 8.93&#x0025;, and 8.99&#x0025;, respectively. The average relative errors of rain intensity measured by the ESL in convective rainfall and stratiform rainfall are 16.01&#x0025; and 26.59&#x0025;, respectively.

T. J. Hart

Hon-Kit Lui, Chen-Tung Arthur Chen, Chen-Tung Arthur Chen et al.

Since half a century ago, the number and area of dead zones (dissolved oxygen (DO) &lt; 2 mg L–1 or 30% saturation) in the coastal oceans has increased dramatically. As widely recognized, the increased terrestrial nutrient and organic matter inputs are the two main factors causing the eutrophication of many coastal oceans. Here we show with decadal observed time series data from stations off the Pearl River Estuary and in the northern South China Sea (nSCS) that a strong intrusion into the nSCS of the West Philippine Sea (WPS) seawater in the form of Kuroshio branch occurred during the warm phase of the Pacific Decadal Oscillation (PDO) around 2003–2004 and 2015–2016 (also a strong El Niño event). Consequently, the DO concentration increased but NO3– and PO43– concentrations decreased in the subsurface layers of the nSCS. The WPS seawater was observed to reach the hypoxic area off the Pearl River Estuary in 2003–2004. Likely, due to the oxygen supply carried by the Kuroshio, little hypoxia developed. Yet, anoxic condition developed in the cold phase of PDO or strong La Niña years with weak Kuroshio intrusions.

Bian HE, Yongqiang YU, Qing BAO et al.

The datasets of the Chinese Academy of Sciences (CAS) Flexible Global Ocean–Atmosphere–Land System (FGOALS-f3-L) model for the baseline experiment of the fully coupled runs in the Diagnostic, Evaluation and Characterization of Klima (DECK) common experiments of phase 6 of the Coupled Model Intercomparison Project (CMIP6) are described in this study. The CAS FGOALS-f3-L model team submitted the piControl run with a near equilibrium ocean state for 561 model years, and 160-year integrations for three ensemble members of abrupt-4× CO2 and 1pctCO2, respectively. The ensemble members restart from the 600, 650 and 700 model years in the piControl run, respectively. The baseline performances of the model are validated in this article. The preliminary evaluation suggests that the CAS FGOALS-f3-L model can preserve the long-term stability well for a mean net radiation flux of 0.31 W m−2 at the top of the atmosphere, and a limited decreasing trend of −0.03 W m−2/100 yr. The global annual mean SST is 16.45°C for the 561-year mean, with an increase of 0.03°C/100 yr. The model captures the basic spatial patterns of climate-mean SST and precipitation, but still underestimates the SST over the warm pool. The coupled model mitigates the precipitation bias in the ITCZ compared with the results from CMIP5. Moreover, the model’s climate sensitivity represented by the equilibrium climate sensitivity has been reduced from 4.5°C in CMIP5 to 3.0°C in CMIP6. All these datasets contribute to the benchmark of model behaviors for the desired continuity of CMIP.

Shanjun Luo, Yingbin He, Zhuozhuo Wang et al.

Leaf area index (LAI) is one of the important variables for crop growth monitoring and yield estimating. In this article, the potato LAI was retrieved by several vegetation indices (VIs) and spectral parameters of the continuum removal method (SPCRM) to provide accurate estimates. A comparison of the two methods of retrieving precision was completed. The data source for computing VIs and SPCRM was hyperspectral reflectance data for the life cycle, derived from two potato cultivars, Favorite (early maturing variety) and Yanshu 4 (late maturing variety), through field experiments. Sensitive bands were identified to indicate seven VIs by correlation analysis. Additionally, seven SPCRM were computed. Based on these methods, the potato LAI was retrieved and tested. Meanwhile, a comparison of the retrieving precision was implemented. The results showed that compared with the filtered spectral reflectance and VIs, the correlation between the potato LAI and the continuum removal spectral reflectance and its retrieved SPCRM were higher. The determination coefficients (R2) of the retrieving models of four parameters, the total area (S), the left area (Sl), the right area (Sr) and the depth area ratio (W), derived from the continuum removal method were all above 0.801, and their fitting coefficients (r) were all above 0.868, with the mean relative errors (MRE) all <0.14. It was identified that W was the most suitable parameter for retrieving the potato LAI. Although the effectiveness of SPCRM requires further research, this study manifests that SPCRM have the potential to accurately retrieve the potato LAI.

F. Kestner, C. Officer

Y. Luo, D. Wang, T. P. Gamage et al.

We present a continuous in situ hydro-meteorology observational dataset from a set of instruments first deployed in December 2012 in the south of Sri Lanka, facing toward the north Indian Ocean. In these waters, simultaneous records of wind and wave data are sparse due to difficulties in deploying measurement instruments, although the area hosts one of the busiest shipping lanes in the world. This study describes the survey, deployment, and measurements of wind and waves, with the aim of offering future users of the dataset the most comprehensive and as much information as possible. This dataset advances our understanding of the nearshore hydrodynamic processes and wave climate, including sea waves and swells, in the north Indian Ocean. Moreover, it is a valuable resource for ocean model parameterization and validation. The archived dataset (Table 1) is examined in detail, including wave data at two locations with water depths of 20 and 10 m comprising synchronous time series of wind, ocean astronomical tide, air pressure, etc. In addition, we use these wave observations to evaluate the ERA-Interim reanalysis product. Based on Buoy 2 data, the swells are the main component of waves year-round, although monsoons can markedly alter the proportion between swell and wind sea. The dataset (Luo et al., 2017) is publicly available from Science Data Bank (<a href="https://doi.org/10.11922/sciencedb.447" target="_blank">https://doi.org/10.11922/sciencedb.447</a>).

Steven A. Hughes, Christopher I. Thornton

Engineers require estimates of tolerable overtopping limits for grass-covered levees, dikes, and embankments that might experience steady overflow. Realistic tolerance estimates can be used for both resilient design and risk assessment. A simple framework is developed for estimating tolerable overtopping on grass-covered slopes caused by slowly-varying (in time) overtopping discharge (e.g., events like storm surges or river flood waves). The framework adapts the well-known Hewlett curves of tolerable limiting velocity as a function of overflow duration. It has been hypothesized that the form of the Hewlett curves suggests that the grass erosion process is governed by the flow work on the slope above a critical threshold velocity (referred to as excess work), and the tolerable erosional limit is reached when the cumulative excess work exceeds a given value determined from the time-dependent Hewlett curves. The cumulative excess work is expressed in terms of overflow discharge above a critical discharge that slowly varies in time, similar to a discharge hydrograph. The methodology is easily applied using forecast storm surge hydrographs at specific locations where wave action is minimal. For preliminary planning purposes, when storm surge hydrographs are unavailable, hypothetical equations for the water level and overflow discharge hydrographs are proposed in terms of the values at maximum overflow and the total duration of overflow. An example application is given to illustrate use of the methodology.