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16 pages, 4814 KiB  
Article
Geomorphological Characteristics and Evolutionary Process of a Typical Isolated Carbonate Platform Slope in the Xisha Sea: A Case Study of the Northwestern Dongdao Platform
by Xudong Guo, Dongyu Lu, Xuelin Li, Xiaochen Fang, Fei Tian, Changfa Xia, Lei Huang, Mei Chen, Luyi Wang and Zhongyu Sun
Water 2025, 17(9), 1259; https://doi.org/10.3390/w17091259 - 23 Apr 2025
Viewed by 426
Abstract
The northwestern slope of the Dongdao Platform in the Xisha Sea exhibits a complex geomorphological structure. Utilizing high-resolution multibeam bathymetric data and 2D seismic profiles, this study systematically reconstructs the slope morphology and its evolutionary processes. The study area displays a distinct threefold [...] Read more.
The northwestern slope of the Dongdao Platform in the Xisha Sea exhibits a complex geomorphological structure. Utilizing high-resolution multibeam bathymetric data and 2D seismic profiles, this study systematically reconstructs the slope morphology and its evolutionary processes. The study area displays a distinct threefold zonation: the upper slope (160–700 m water depth) has a steep gradient of 15°–25°, characterized by deeply incised V-shaped channels and slump deposits, primarily shaped by gravity-driven erosion; the middle slope (700–1200 m water depth) features a gentler gradient of 10°–15°, where channels stabilize, adopting U-shaped cross-sections with the development of lateral accretion deposits; the lower slope (1200–1500 m water depth) exhibits a milder gradient of 5°–10°, dominated by a mixture of fine-grained carbonate sediments and hemipelagic mud–marine sediments originating partly from the open ocean and partly from the nearby continental margin. The slope extends from 160 m to 1500 m water depth, hosting the C1–C4 channel system. Seismic facies analysis reveals mass-transport deposits, channel-fill facies, and facies modified by bottom currents—currents near the seafloor that redistribute sediments laterally—highlighting the interplay between fluid activity and gravity-driven processes. The slope evolution follows a four-stage model: (1) the pockmark formation stage, where overpressured gas migrates vertically through chimneys, inducing localized sediment instability and forming discrete pockmarks; (2) the initial channel development stage, during which gravity flows exploit the pockmark chains as preferential erosional pathways, establishing nascent incised channels; (3) the channel expansion and maturation stage, marked by intensified erosion from high-density debris flows, resulting in a stepped longitudinal profile, while bottom-current reworking enhances lateral sediment differentiation; (4) the stable transport stage, wherein the channels fully integrate with the Sansha Canyon, forming a well-connected “platform-to-canyon” sediment transport system. Full article
(This article belongs to the Special Issue Regional Geomorphological Characteristics and Sedimentary Processes)
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24 pages, 8500 KiB  
Article
A Study on the Spatial Morphological Evolution and Driving Factors of Coral Islands and Reefs in the South China Sea Based on Multi-Source Satellite Imagery
by Fengyu Li, Wenzhou Wu, Peng Zhang, Bingyue Zhang and Fenzhen Su
J. Mar. Sci. Eng. 2025, 13(4), 820; https://doi.org/10.3390/jmse13040820 - 20 Apr 2025
Viewed by 582
Abstract
The spatial morphology of coral islands and reefs is a fundamental physical and ecological attribute that reflects the developmental and evolutionary processes of coral islands and reefs. The spatial morphology of coral islands and reefs in the South China Sea is highly dynamic. [...] Read more.
The spatial morphology of coral islands and reefs is a fundamental physical and ecological attribute that reflects the developmental and evolutionary processes of coral islands and reefs. The spatial morphology of coral islands and reefs in the South China Sea is highly dynamic. Understanding the evolutionary trends of the spatial morphology of these coral islands and reefs is crucial for their sustainable development and utilization. This study proposes a set of stability evaluation indicators for reef spatial morphology and conducts a systematic analysis of the spatial morphological changes in coral islands and reefs in the South China Sea over the past 15 years, based on 96 satellite images. Additionally, the driving factors behind these changes are explored and discussed. The results indicate the following: (1) The spatial morphology of the Xisha islands and reefs exhibits more significant changes compared to the Nansha islands and reefs. Although both the Xisha and Nansha islands and reefs areas are increasing, the area change in Xisha is 1.3 times greater than that in Nansha. (2) The spatial morphology of the Xisha islands and reefs is shifting in all directions, while the Nansha islands and reefs show a more pronounced northwestward movement. (3) Both the Xisha and Nansha islands and reefs show an overall growth trend, with the growth rate of the Xisha islands and reefs being faster than that of the Nansha islands and reefs. The average growth rate of the Xisha islands and reefs is 1.77 times that of the Nansha islands and reefs. This research provides significant scientific evidence for the protection and resource management of coral islands and reefs in the South China Sea. Full article
(This article belongs to the Section Coastal Engineering)
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18 pages, 28824 KiB  
Article
Multifactorial Controls on the Dongdaobei Submarine Canyon System, Xisha Sea, South China Sea
by Meijing Sun, Hongjun Chen, Chupeng Yang, Xiaosan Hu and Jie Liu
J. Mar. Sci. Eng. 2025, 13(3), 564; https://doi.org/10.3390/jmse13030564 - 14 Mar 2025
Viewed by 545
Abstract
The submarine canyons system is the most widely distributed geomorphic unit on the global continental margin. It is an important concept in the field of deep-water sedimentation and geohazards. Based on high-resolution multibeam bathymetry and two-dimensional seismic data, the dendritic canyon system north [...] Read more.
The submarine canyons system is the most widely distributed geomorphic unit on the global continental margin. It is an important concept in the field of deep-water sedimentation and geohazards. Based on high-resolution multibeam bathymetry and two-dimensional seismic data, the dendritic canyon system north of Dongdao island is studied at the eastern Xisha area of the South China Sea. The Dongdaobei submarine canyon is distributed in water depths between 1000 and 3150 m. The main source area in the upper course of the canyon originates from the northwest of Dongdao platform and the Yongxing platform. The sediments from the source area are transported to the main canyon in the form of various gravity flows. Landslides on the slope significantly impact canyon evolution by delivering sediment to the canyon head and causing channel deflection through substrate failure and flow-path reorganization. A large number of pockmarks are distributed around the north slope of the main canyon. The small-scale channels, which are formed as a result of the continuous erosion of the pockmark chains, are connected to the canyon sidewalls. The seamounts are distributed along the south bank of the canyon, exerting a controlling influence on the directional changes in the main canyon’s downstream segment. The formation and evolution of the Dongdaobei submarine canyon are primarily influenced by several factors, including tectonic activity and inherited negative topography, erosion by sedimentary gravity flows, sediment instability, and the shielding effect of seamounts. Full article
(This article belongs to the Special Issue Marine Geohazards: Characterization to Prediction)
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17 pages, 4173 KiB  
Article
Microplastic Pollution and Its Ecological Risks in the Xisha Islands, South China Sea
by Wenchao Wei, Yun Zhang, Licheng Wang, Qiao Xing, Jun Xiang, Yuquan Zhang, Qifei Peng, Yongfu Chen, Yufeng Hu, Yini Ma and Ling Mo
Toxics 2025, 13(3), 205; https://doi.org/10.3390/toxics13030205 - 12 Mar 2025
Viewed by 1010
Abstract
China is facing increasing marine microplastic pollution. Despite the fact that the South China Sea is the largest marine area in China, the ecological danger and present state of microplastic contamination in this region have not been systematically and comprehensively investigated. This study [...] Read more.
China is facing increasing marine microplastic pollution. Despite the fact that the South China Sea is the largest marine area in China, the ecological danger and present state of microplastic contamination in this region have not been systematically and comprehensively investigated. This study analyzed the abundance, distribution, and characteristics of microplastics in different environmental media and biological samples from the Xisha Islands in the South China Sea, and then the ecological risk assessment of microplastic pollution in this area was conducted. The findings indicated that the quantities of sediments, soil, water, fish, and birds were 41.56 ± 19.12 items/kg, 92.94 ± 111.05 items/kg, 2.89 ± 1.92 items/L, 2.57 ± 2.12 items/ind, and 1.702 ± 1.50 items/ind, respectively. By evaluating the pollution load index (PLI), polymer hazard index (PHI), and potential ecological risk index (PERI), the PLI of the Xisha Islands in the South China Sea as a whole indicated that the hazard level was slightly polluted, the PHI was at a high-risk level, and the PERI samples were at no risk, except for the soil and seawater, which were at a medium-risk level. Full article
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24 pages, 6485 KiB  
Article
Study on the Reconstruction of the Spectral Pattern of Near-Island Reef Bimodal Waves
by Weihang Sun, Yuguo Pei, Leilei Qu and Xiaobo Wang
J. Mar. Sci. Eng. 2025, 13(3), 499; https://doi.org/10.3390/jmse13030499 - 3 Mar 2025
Viewed by 768
Abstract
Accurately fitting bimodal wave spectra is crucial for understanding complex ocean conditions and promoting ocean-related research. In this context, this paper aims to solve the problem of reconstructing bimodal wave spectra in domestic island and reef areas. Taking measured data from the Jiangsu [...] Read more.
Accurately fitting bimodal wave spectra is crucial for understanding complex ocean conditions and promoting ocean-related research. In this context, this paper aims to solve the problem of reconstructing bimodal wave spectra in domestic island and reef areas. Taking measured data from the Jiangsu Xiangshui station in August 2017 and the Xisha Sea area on 1–3 August 2014 as case studies, the researchers selected three types of original bimodal wave spectra. After obtaining the sample spectra through fast Fourier transform and wave spectrum non-dimensionalization, this paper selected a novel wave spectrum—the rational fractional unimodal spectrum—and two classical wave spectra—the Jonswap spectrum and the Neumann spectrum. Three bimodal wave spectra were constructed by superimposing the low-frequency sub-spectrum and the high-frequency sub-spectrum. After using the improved PSO algorithm to optimize the parameters of these three bimodal wave spectra, the specific parameters were obtained. Comparisons were made between the above three bimodal wave spectra and three high-precision double-peak fitting spectra, the Huang Peiji six-parameter spectrum, the Ochi-Hubble spectrum, and the Shen Zhichun fitting spectrum, and the fitting effects were analyzed. The results demonstrated that when fitting the bimodal spectrum dominated by wind waves and the bimodal spectrum with comparable wind and swell energy, the combination of the rational fractional unimodal spectrum and the Neumann spectrum can achieve a fitting accuracy of up to 99%. When fitting the bimodal spectrum dominated by swell waves, the combination of the rational fractional unimodal spectrum and the Jonswap spectrum can also achieve a fitting accuracy of 99%. The findings of this paper provide valuable references for the study of other types of double-peak wave spectra in China. Full article
(This article belongs to the Section Ocean Engineering)
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32 pages, 23698 KiB  
Article
Water Depth Correction-Based Classification Combination Method for Extracting Shallow Sea Reef Geomorphological Information: A Case Study of Xisha Chau and Zhaoshu Island
by Zhigang Lu, Weidong Zhu, Daxing Lei, Yi Zhu, Yifan Chen, Zilin Yue and Zhongqiang Wu
J. Mar. Sci. Eng. 2025, 13(2), 300; https://doi.org/10.3390/jmse13020300 - 6 Feb 2025
Viewed by 791
Abstract
Remote sensing monitoring and geomorphologic change analysis of coral reefs are of great practical significance for the ecological protection and sustainable development of coral reef area resources. A WBMD scheme is proposed to better extract coral reef information from island environments of Xisha, [...] Read more.
Remote sensing monitoring and geomorphologic change analysis of coral reefs are of great practical significance for the ecological protection and sustainable development of coral reef area resources. A WBMD scheme is proposed to better extract coral reef information from island environments of Xisha, China. Satellite imagery, after preprocessing, is subjected to water depth correction to mitigate the influence of water depth on reflectance. A maximum likelihood classification model is then used for geomorphological classification, followed by refinement through a decision tree classification model, forming the WBMD scheme. The overall accuracy of geomorphological classification for Xisha Chau and Zhaoshu Island based on the WBMD scheme was 97.07% and 95.07%. Using this scheme to analyze the geomorphology of Xisha Chau and Zhaoshu Island from 2014 to 2018 reveals that the degradation of coral reef on Xisha Chau is mainly distributed in the lagoon slope and around the lagoon, and the lagoon area on Zhaoshu Island has been shrinking year by year, while the area of the gray sand island has increased, and the areas of other geomorphological types exhibit fluctuating changes. Previous studies on coral reefs have indicated that coral reefs are mainly distributed in the lagoon slope area, where significant coral reef degradation has also been observed, raising an alarm for coral reef conservation efforts in China. Full article
(This article belongs to the Special Issue New Advances in Marine Remote Sensing Applications)
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23 pages, 25801 KiB  
Article
A Large-Scale Focused Fluid Flow Zone Between Atolls in the Xisha Islands (South China Sea): Types, Characteristics, and Evolution
by Jixiang Zhao, Benjun Ma, Zhiliang Qin, Wenjian Lan, Benyu Zhu, Shuyi Pang, Mingzhe Li and Ruining Wang
J. Mar. Sci. Eng. 2025, 13(2), 216; https://doi.org/10.3390/jmse13020216 - 23 Jan 2025
Viewed by 785
Abstract
A large number of seabed depressions, covering an area of 2500 km2 in the Xisha Massif of the South China Sea, are investigated using newly collected high-resolution acoustic data. By analyzing the morphological features and seismic attributes of the focused fluid flow [...] Read more.
A large number of seabed depressions, covering an area of 2500 km2 in the Xisha Massif of the South China Sea, are investigated using newly collected high-resolution acoustic data. By analyzing the morphological features and seismic attributes of the focused fluid flow system, five geological structures are recognized and described in detail, including pockmarks, volcanic mounds, pipes, faults, and forced folds. Pockmarks and volcanic mounds occur as clustered groups and their distributions are related to two large-scale volcanic zones with chaotic seismic reflections. Pipes, characterized by disordered seismic reflections, mainly occur within the focused fluid flow zone (FFFZ) and directly link with the large-scale deep volcano and its surrounding areas. Faults and fractures mainly occur along pipes and extend to the seafloor, commonly presenting lateral walls of mega-pockmarks. Forced folds are primarily clustered above volcanic zones and commonly restricted between faults or pipes, characterized by sediment deformations as indicated in seismic profiles. By comprehensive analysis of the above observations and a simplified simulation model, the volcanism-induced hydrothermal fluid activities are argued herein to contribute to these focused fluid flow structures. In addition, traces of suspected submarine instability disasters such as landslides have been found in this sea area, and more observational data will be needed to determine whether seafloor fluid flow zones can be used as a predictor of seafloor instability in the future. Full article
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16 pages, 16100 KiB  
Article
Sedimentary Model and Geological Control of the Ganquan Platform in the Xisha Sea Area, South China Sea
by Xuelin Li, Lei Huang, Kang Lin, Mingyuan Sun, Jiangyong Zhang, Xining Liu, Lieyu Tian and Wei Chen
Water 2024, 16(23), 3516; https://doi.org/10.3390/w16233516 - 6 Dec 2024
Viewed by 900
Abstract
The Ganquan Platform, located in the South China Sea, exhibits distinctive topographic and geomorphological features shaped by complex geological processes. Utilizing high-resolution multibeam bathymetry and multi-channel seismic data, this study provides a comprehensive investigation into the sedimentary evolution and stratigraphic framework of the [...] Read more.
The Ganquan Platform, located in the South China Sea, exhibits distinctive topographic and geomorphological features shaped by complex geological processes. Utilizing high-resolution multibeam bathymetry and multi-channel seismic data, this study provides a comprehensive investigation into the sedimentary evolution and stratigraphic framework of the platform. Morphologically, the platform is identified as an elongated seamount, with water depths ranging from 530 m to 800 m and a maximum elevation of 538.115 m. Seismic facies analysis reveals seven distinct facies, reflecting a dynamic and intricate history of carbonate deposition. The stratigraphic framework delineates three primary evolutionary stages: the growth phase (Early Miocene), characterized by the initial accumulation of carbonate sediments; the flourishing phase (Middle Miocene), marked by extensive deposition and platform expansion; and the submergence phase (Late Miocene), defined by progressive submersion and erosion of carbonate features. This evolutionary trajectory was driven by key factors such as terrigenous clastic input, tectonic activity, sea-level fluctuations, and paleoenvironmental dynamics. The findings contribute to a deeper understanding of the Ganquan Platform’s geological history and its role in the broader context of submarine geology in the Xisha region. Full article
(This article belongs to the Special Issue Analysis of Coastal Sediment)
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19 pages, 9113 KiB  
Article
Application of a GIS-Based Multi-Criteria Decision-Making Approach to the Siting of Ocean Thermal Energy Conversion Power Plants: A Case Study of the Xisha Sea Area, China
by Fei Tian, Xuelin Li, Mengdi Liu, Changfa Xia, Xudong Guo, Xiaocheng Fang and Lei Huang
Energies 2024, 17(20), 5097; https://doi.org/10.3390/en17205097 - 14 Oct 2024
Viewed by 1510
Abstract
In order to achieve the goals of carbon neutrality and reduced carbon emissions, China is increasingly focusing on the development and utilization of renewable energy sources. Among these, ocean thermal energy conversion (OTEC) has the advantages of small periodic fluctuations and large potential [...] Read more.
In order to achieve the goals of carbon neutrality and reduced carbon emissions, China is increasingly focusing on the development and utilization of renewable energy sources. Among these, ocean thermal energy conversion (OTEC) has the advantages of small periodic fluctuations and large potential reserves, making it an important research field. With the development of the “Maritime Silk Road”, the Xisha Islands in the South China Sea will see a growing demand for electricity, providing the potential for OTEC development in this region. Optimal site selection of OTEC power plants is a prerequisite for developing thermal energy provision, affecting both the construction costs and future benefits of the power plants. This study establishes a scientific evaluation model based on the decision-making frameworks of geographic information systems (GISs) and multi-criteria decision-making (MCDM) methods, specifically the analytic hierarchy process (AHP) for assigning weights, the Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS) to reclassify the factors, and weighted linear combination (WLC) to compute the suitability index. In addition to commonly considered factors such as temperature difference and marine usage status, this study innovatively incorporates geological conditions and maximum offshore distances of cold seawater based on cost control. The final evaluation identifies three suitable areas for OTEC development near the Xuande Atoll and the Yongle Atoll in the Xisha Sea Area, providing valuable insights for energy developers and policymakers. Full article
(This article belongs to the Section B2: Clean Energy)
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16 pages, 24109 KiB  
Article
The Effects of Controlling Gas Escape and Bottom Current Activity on the Evolution of Pockmarks in the Northwest of the Xisha Uplift, South China Sea
by Xuelin Li, Xudong Guo, Fei Tian and Xiaochen Fang
J. Mar. Sci. Eng. 2024, 12(9), 1505; https://doi.org/10.3390/jmse12091505 - 1 Sep 2024
Cited by 4 | Viewed by 1097
Abstract
Submarine pockmarks are typical indicators of submarine gas escape activity. The deep strata of the Xisha Uplift are rich in biogenic and thermogenic gas, accompanied by strong bottom current activity. Investigating the effects of controlling submarine gas escape and bottom current activity on [...] Read more.
Submarine pockmarks are typical indicators of submarine gas escape activity. The deep strata of the Xisha Uplift are rich in biogenic and thermogenic gas, accompanied by strong bottom current activity. Investigating the effects of controlling submarine gas escape and bottom current activity on the formation and development of pockmarks in the Xisha Uplift is significant for understanding the evolution of submarine topography and geomorphology. This study utilized high-resolution multibeam data to identify 261 submarine pockmarks in the northwest of the Xisha Uplift. These pockmarks were categorized based on their morphology into circular, elliptical, elongated, crescent-shaped, and irregular types. The diameters of pockmarks in the study area range from 0.21 to 4.96 km, with maximum depths reaching 30.88 m. Using high-resolution multi-channel seismic data, we conducted a detailed analysis of the subsurface strata characteristics of the pockmarks, identifying chaotic weak reflections, bright spots, and high-angle reflectors. We believe that deep gas in the northwest of the Xisha Uplift escapes to the seafloor through migration pathways, such as faults, fractures, and gas chimneys, resulting in the formation of submarine pockmarks. Bottom current activity has a significant impact on already-formed pockmarks. Crescent-shaped and elongated pockmarks in the Xisha Uplift are largely the result of bottom current modifications of pre-existing pockmarks. Full article
(This article belongs to the Special Issue Advances in Marine Gas Hydrate Exploration and Discovery)
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16 pages, 6965 KiB  
Article
Spatiotemporal Variation and Predictors of the Purpleback Flying Squid (Sthenoteuthis oualaniensis) Distribution Surrounding the Xisha and Zhongsha Islands during a Fishing Moratorium
by Liangming Wang, Changping Yang, Binbin Shan, Yan Liu, Jianwei Zou, Dianrong Sun and Tao Guo
Fishes 2024, 9(7), 253; https://doi.org/10.3390/fishes9070253 - 1 Jul 2024
Cited by 2 | Viewed by 1052
Abstract
As an economic species widely distributed in the South China Sea (SCS), the purpleback flying squid (Sthenoteuthis oualaniensis) still has a large potential for exploitation, and the variations in its use as a resource are highly correlated with environmental and other [...] Read more.
As an economic species widely distributed in the South China Sea (SCS), the purpleback flying squid (Sthenoteuthis oualaniensis) still has a large potential for exploitation, and the variations in its use as a resource are highly correlated with environmental and other factors. In this study, using a generalized additive model (GAM) and gradient forest analysis (GFA), in conjunction with environmental factors, the distribution of purpleback flying squid surrounding the Xisha and Zhongsha islands during the fishing moratorium period was investigated. The results indicated that catch per unit effort (CPUE) had a gradual increase from May to July 2023 in the primary fishing area surrounded the Xisha Islands during May to June, then moved southward towards 13–15° N after July. CPUE is used as an important indicator to reflect the abundance of the fishery, while the GFA results show that CPUE has a better fit than catch in this study. Therefore, the subsequent analysis focused on CPUE. Longitude and sea surface temperature (SST) were of relative higher importance, followed by sea surface salinity (SSS), latitude, chlorophyll a concentration (Chla), sea surface height (SSH), and mixed layer depth (MLD). Longitude and CPUE had a significant, positive correlation. The CPUE gradually increased with latitude within 14–16° N. The CPUE increased slowly as SST increased from 29.5 to 30.5 °C in the primary fishing area. The Chla in this fishing zone was 0–0.2 mg/m3 and displayed a significant positive association with CPUE. Conversely, SSS, SSH, and MLD had negative correlations with CPUE. These findings will promote the sustainable utilization of purpleback flying squid in the SCS. Full article
(This article belongs to the Special Issue Assessment and Management of Fishery Resources)
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26 pages, 9704 KiB  
Article
Atmospheric Ducts and Their Electromagnetic Propagation Characteristics in the Northwestern South China Sea
by Ning Yang, Debin Su and Tao Wang
Remote Sens. 2023, 15(13), 3317; https://doi.org/10.3390/rs15133317 - 28 Jun 2023
Cited by 13 | Viewed by 3938
Abstract
The propagation of electromagnetic waves beyond the line of sight can be caused by atmospheric ducts, which are significant concerns in the fields of radar and communication. This paper utilizes data from seven automatic weather stations and five radio-sounding stations to statistically analyze [...] Read more.
The propagation of electromagnetic waves beyond the line of sight can be caused by atmospheric ducts, which are significant concerns in the fields of radar and communication. This paper utilizes data from seven automatic weather stations and five radio-sounding stations to statistically analyze the characteristics of the atmospheric ducts in the northwest region of the South China Sea (SCS). After verifying the practicality of numerical analysis data from NCEP CFSv2 and ECMWF in studying atmospheric ducts using measured data, we analyzed the spatial–temporal distribution characteristics of the height of the regional evaporation duct and the bottom height of the elevated duct. The study found that the NCEP CFSv2 data accurately capture the evaporation duct height and duct occurrence rate in the study area, and the elevated duct bottom height calculated from ERA5 and the measured data have good consistency. The occurrence rate and height of the evaporation duct in coastal stations in the northwest of the SCS vary significantly by month, demonstrating clear monthly distribution patterns; conversely, changes in the Xisha station are minimal, indicating good temporal uniformity. For lower atmospheric ducts, the difference in occurrence rates between 00:00 and 12:00 (UTC) is negligible. The occurrence probability of elevated ducts in the Beibu Gulf area is relatively high, mainly concentrated from January to April, and the Xisha area is dominated by surface ducts without foundation layers, mainly concentrated from June to August. Monsoons play a critical role in the generation and evolution of atmospheric ducts in the northwest of the SCS, with the height of the evaporation duct increasing and the bottom height of the elevated duct decreasing after the onset of the summer monsoon. In the end, we simulated electromagnetic propagation loss under different frequencies and radiation elevation angles in various duct environments within a typical atmospheric duct structure. Full article
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16 pages, 9835 KiB  
Article
Tectonic Subsidence and Its Response to Geological Evolution in the Xisha Area, South China Sea
by Zhen Yang, Guangxue Zhang, Guozhang Fan, Yintao Lu, Dali Shao, Songfeng Liu and Weiwei Wang
Appl. Sci. 2023, 13(12), 7268; https://doi.org/10.3390/app13127268 - 18 Jun 2023
Cited by 1 | Viewed by 2139
Abstract
The evolution and mechanisms of tectonic subsidence in the Xisha area are poorly investigated, especially the spatiotemporal distribution features and reasons for the variations in tectonic subsidence. In this study, multi-channel seismic data and stratigraphic and lithologic features of wells are used to [...] Read more.
The evolution and mechanisms of tectonic subsidence in the Xisha area are poorly investigated, especially the spatiotemporal distribution features and reasons for the variations in tectonic subsidence. In this study, multi-channel seismic data and stratigraphic and lithologic features of wells are used to examine tectonic subsidence in the Xisha area from the Paleogene to Quaternary. The largest tectonic subsidence in the Xisha area is located in the Changchang Depression, with a maximum subsidence of 5.4 km, while the smallest tectonic subsidence is located on the Guangle Uplift and Xisha Uplift, which are close to 1.0 km and 1.5 km, respectively. Two rapid tectonic subsidence phases were mainly in the Oligocene, and from Middle to Late Miocene, with maximum subsidence rates of 0.45 m/ky and 0.32 m/ky, respectively. Five phases for the tectonic subsidence are proposed since the Paleogene based on our data. (1) The slow subsidence phase during the Eocene (53.5–32 Ma) was due to the transchronicity of the basement in the pro-rifted stage. (2) The rapid subsidence phase was common in the south and north margins of Qiongdongnan Basin, because of the faults triggered by the inherited stretched and thinned of crust in the Oligocene from 32 to 23.3 Ma. (3) The interim phase followed the rapid subsidence phase was in the Early Miocene (23.3–15.5 Ma) and marked the end of the rifted stage. (4) The accelerated rise phase started from the Middle Miocene (15.5 Ma) to the Late Miocene (5.5 Ma), and the reversal of the Red River Fault Zone may be tied to the acceleration of the tectonic subsidence. (5) The transitional phase started in the Pliocene (5.5 Ma) and lasts to the present. As the Red River Fault Zone changed from sinistral to dextral movement, the stress field of the study area has changed. Our results are helpful to better understand the spatiotemporal coupling relationship between tectonic subsidence and regional geological evolution in the Xisha area, South China Sea. Full article
(This article belongs to the Section Earth Sciences)
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18 pages, 7356 KiB  
Article
Geological Distribution of the Miocene Carbonate Platform in the Xisha Sea Area of the South China Sea, and Its Implications for Hydrocarbon Exploration
by Zhen Yang, Guangxue Zhang, Shiguo Wu, Youhua Zhu, Cong Wu, Li Zhang, Songfeng Liu, Wei Yan, Ming Sun, Yaoming Zhang, Xuebin Du and Chenlu Xu
Appl. Sci. 2022, 12(22), 11831; https://doi.org/10.3390/app122211831 - 21 Nov 2022
Cited by 2 | Viewed by 2407
Abstract
The newly collected seismic data and the existing drilling data provide a good opportunity to better understand the carbonate platform distribution characteristics and the hydrocarbon resource potential in the Xisha sea area of the South China Sea. Based on the seismic data and [...] Read more.
The newly collected seismic data and the existing drilling data provide a good opportunity to better understand the carbonate platform distribution characteristics and the hydrocarbon resource potential in the Xisha sea area of the South China Sea. Based on the seismic data and the reflection characteristics of the carbonate platform’s edge, three boundary indicators were established: abrupt lithological interfaces, fault interfaces, and tidal channels. Combined with the regional geological settings, its spatial and temporal distribution was clearly identified for the first time. The development of the Miocene carbonate platform in the Xisha sea area is divided into six phases, which are further assigned to three evolutionary stages: the bloom stage, the recession stage, and the submerged stage. The sedimentary facies belt of the carbonate platform in each stage is well developed, and the reefs are mainly distributed on the west and southwest edges of the platform. The analysis of the data indicates that the area of the reef and carbonate platform reached 80,000 km2 during the mature period, followed by a retreat period where the scale decreased with the platform’s decline. The Miocene carbonate rocks in the Xisha sea area are widely distributed. They have experienced multiple periods of exposure and infiltration, which further improved the quality of their physical properties for hydrocarbon reservoirs. According to the regional hydrocarbon geological conditions in this area—including the source rock, migration system and the capping layer—the hydrocarbon accumulation potential is preliminarily discussed in this paper. A reservoir model of the reef and carbonate platform is established, which is proposed as typical characteristics of “lower generation, upper accumulation”. It is pointed out that the carbonate platform in the Xisha sea area adjacent to the Huaguang Sag in the Qiongdongnan Basin and the northern Zhongjiannan Basin is a potential area for oil and gas exploration. Full article
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18 pages, 8178 KiB  
Article
Numerical Simulation Study on Interactions between the Wave and Newborn Sandbank in the Xisha Islands of the South China Sea
by Huiming Huang, Zhenwen Liu, Chun Chen, Xiang Lin, Siqi Li, Xiantao Huang, Mee Mee Soe and Mohammad Saydul Islam Sarkar
Water 2022, 14(21), 3566; https://doi.org/10.3390/w14213566 - 6 Nov 2022
Viewed by 2044
Abstract
As a unique landform in the island and reef area, the newborn sandbank is not only the initial stage of island development, but also has a rapid evolution and a complex dynamic mechanism. However, the dynamic geomorphology mechanism of the newborn sandbank is [...] Read more.
As a unique landform in the island and reef area, the newborn sandbank is not only the initial stage of island development, but also has a rapid evolution and a complex dynamic mechanism. However, the dynamic geomorphology mechanism of the newborn sandbank is still lacking extensive study and direct evidence of the interaction process between the marine dynamics and the newborn sandbank geomorphology. Therefore, in order to reveal the interaction mechanisms between marine dynamics and newborn sandbanks, a newborn sandbank in the sea area of the Xisha Islands, in the South China Sea, has been selected as the focus of this research. The method of numerical simulation was used to discuss and analyze the wave field characteristics around the newborn sandbank and their impacts on the sandbank’s migration and development. The results show that: (1) The islands and reefs have significant refraction, diffraction, and energy dissipation effects on waves, and the newborn sandbank has the same effect, but with a weaker function. The wave height around the reef islands reduced by approximately 60–67% in dominated and strong wave directions. At the same time, the wave height attenuation in the wave shadow zone, behind the newborn sandbank, can reach approximately 27–33%. (2) Wind is important for the evolution of wave fields; in particular, when the wind speed exceeds grades four and five, the effect of the wind on the waves is particularly significant, causing the winds to control the wave characteristics around the islands and newborn sandbanks. This results in significant seasonal differences in wave fields within the sea area. (3) The wave direction primarily controls the migration direction of the newborn sandbank, and the wave height primarily controls the migration speed and distance. After one month of wave action in the strong wave direction, the maximum eastward deposition length was approximately 50 m. After one month of wave action in the dominated wave direction, the maximum eastward deposition length was approximately 60 m. Therefore, the topography of the newborn sandbank affects the wave propagation, meanwhile, the wave conversely determines migration and development of the newborn sandbank in a short term. The dynamic geomorphology action between the wave and newborn sandbank is a fast two-way process, and occurs not only during storms or the winter monsoon, but also during other, more common, weather events. Full article
(This article belongs to the Special Issue Numerical Modelling of Ocean Waves and Analysis of Wave Energy)
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