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, Available online , doi: 10.12284/hyxb2024041
Abstract:
Taiwan Strait is the largest strait in China and the main channel for material and energy exchange between the East China Sea and the South China Sea. The topography changes dramatically and the tidal environment is complex in the Strait. In addition, many mountainous streams on both sides carry a large amount of sediment into the Strait. It is an ideal place to study dynamic sedimentation processes. Currently, due to a lack of high-resolution bathymetry and relevant data for the entire Taiwan Strait, there are few studies on modeling the tide and sediment behaviors of the Taiwan Strait as a whole. In this study, based on high-resolution bathymetric and relevant hydrological data, a two-dimensional tidal current numerical model of the Taiwan Strait has been established, and a sediment transport module has been coupled to simulate the sediment transport in the Taiwan Strait. The dynamic simulation results indicate that the tidal current field in the Taiwan Strait is governed by two tidal waves from the south and north, exhibiting distinct temporal and spatial characteristics. The tidal flow velocity is higher in summer than in winter, and it is lower in the central part of the strait compared to the southern and northern sides, with the northern side being less than the southern side. Based on the deposition and erosion simulation results, the Taiwan Strait is categorized into three main types and a total of seven sedimentary subdivisions: deposition zones, erosion zones, and deposition-erosion equilibrium zones. The maximum sedimentation rate in the accumulation zones can reach 5 cm/a, primarily concentrated in the northern part of the Taiwan Bank, with erosion rates ranging from 2 cm/a to 5 cm/a in the erosion zones. Leveraging these simulation outcomes, this study constructs a sediment transport model and a 'source-to-sink' pattern model for the Taiwan Strait, elucidating the dynamic mechanisms behind the strait's deposition and erosion changes and the 'source-to-sink' process.
Taiwan Strait is the largest strait in China and the main channel for material and energy exchange between the East China Sea and the South China Sea. The topography changes dramatically and the tidal environment is complex in the Strait. In addition, many mountainous streams on both sides carry a large amount of sediment into the Strait. It is an ideal place to study dynamic sedimentation processes. Currently, due to a lack of high-resolution bathymetry and relevant data for the entire Taiwan Strait, there are few studies on modeling the tide and sediment behaviors of the Taiwan Strait as a whole. In this study, based on high-resolution bathymetric and relevant hydrological data, a two-dimensional tidal current numerical model of the Taiwan Strait has been established, and a sediment transport module has been coupled to simulate the sediment transport in the Taiwan Strait. The dynamic simulation results indicate that the tidal current field in the Taiwan Strait is governed by two tidal waves from the south and north, exhibiting distinct temporal and spatial characteristics. The tidal flow velocity is higher in summer than in winter, and it is lower in the central part of the strait compared to the southern and northern sides, with the northern side being less than the southern side. Based on the deposition and erosion simulation results, the Taiwan Strait is categorized into three main types and a total of seven sedimentary subdivisions: deposition zones, erosion zones, and deposition-erosion equilibrium zones. The maximum sedimentation rate in the accumulation zones can reach 5 cm/a, primarily concentrated in the northern part of the Taiwan Bank, with erosion rates ranging from 2 cm/a to 5 cm/a in the erosion zones. Leveraging these simulation outcomes, this study constructs a sediment transport model and a 'source-to-sink' pattern model for the Taiwan Strait, elucidating the dynamic mechanisms behind the strait's deposition and erosion changes and the 'source-to-sink' process.
, Available online , doi: 10.12284/hyxb2024023
Abstract:
The annual, seasonal, monthly and diurnal variations of sea surface wind over the Taiwan Strait were analyzed based on the new version of Cross-Calibrated Multi-PlatformVersion 3.1(CCMP V3.1)wind data from 1993 to 2022. The results showed that the wind field in the Taiwan Strait and the water around Taiwan Island had obvious spatial distribution characteristics, the topographic effect leads to the maximum and minimum wind speed regions in different sea areas. Because the central Taiwan Strait was affected by the “narrow tube effect”, the wind speed was the highest and the wind direction was basically parallel to the strait in winter; the wind speed in summer was lower than the speed outside the channel, and there was no “narrow tube effect”. In addition, the sea surface wind field also had obvious seasonal and monthly variation characteristics. The northeast wind prevailed in winter,and in this season the wind speed was the highest in the whole year; the southwest wind prevailed in summer with the lowest wind speed;the characteristics of spring and autumn monsoon fields were similar, both prevailing northeast wind; winter monsoon last longer than summer monsoon, accounting for about three quarters of the year. The analysis of the inter-annual variation of wind field showed that the wind direction tended to deflect at a large angle in summer. The annual mean wind speed maintained a basically flat linear trend, and the abnormal high or low in some years was related to the occurrence of El Niño-Southern Oscillation(ENSO). When the diurnal variation characteristics were studied, it was found that the wind speed and direction fluctuated most at 20 PM. The wind speed varied periodically within a day. The diurnal variation of wind direction deflection was most obvious in summer.
The annual, seasonal, monthly and diurnal variations of sea surface wind over the Taiwan Strait were analyzed based on the new version of Cross-Calibrated Multi-PlatformVersion 3.1(CCMP V3.1)wind data from 1993 to 2022. The results showed that the wind field in the Taiwan Strait and the water around Taiwan Island had obvious spatial distribution characteristics, the topographic effect leads to the maximum and minimum wind speed regions in different sea areas. Because the central Taiwan Strait was affected by the “narrow tube effect”, the wind speed was the highest and the wind direction was basically parallel to the strait in winter; the wind speed in summer was lower than the speed outside the channel, and there was no “narrow tube effect”. In addition, the sea surface wind field also had obvious seasonal and monthly variation characteristics. The northeast wind prevailed in winter,and in this season the wind speed was the highest in the whole year; the southwest wind prevailed in summer with the lowest wind speed;the characteristics of spring and autumn monsoon fields were similar, both prevailing northeast wind; winter monsoon last longer than summer monsoon, accounting for about three quarters of the year. The analysis of the inter-annual variation of wind field showed that the wind direction tended to deflect at a large angle in summer. The annual mean wind speed maintained a basically flat linear trend, and the abnormal high or low in some years was related to the occurrence of El Niño-Southern Oscillation(ENSO). When the diurnal variation characteristics were studied, it was found that the wind speed and direction fluctuated most at 20 PM. The wind speed varied periodically within a day. The diurnal variation of wind direction deflection was most obvious in summer.
, Available online , doi: 10.12284/hyxb2024031
Abstract:
The buried hill oil and gas reservoirs have become an important exploration field in China’s marine basins. The northwestern area of Shaleitian area of Bohai Bay Basin is a typical carbonate buried hill zone. Due to the lack of research on the reservoir control effect of multiple stage fractures and their related karstification, the oil and gas exploration of carbonate buried hills is restricted. This paper conducts a detailed analysis of the development characteristics of the fracture-cave system in carbonate buried hill reservoirs in the northwestern Shaleitian Uplift, and studies the reservoir control effects of fractures and karst. The results indicate that the lower Paleozoic carbonate buried hills in the northwestern area of Shaleitian Uplift belong to fracture related karst reservoirs. The reservoir space includes dissolution pores, structural fractures, and expansion pores along the structural fractures. High quality reservoirs have lithological selectivity, and fractures and dissolution pores developed in microlite crystalline dolomite and fine crystalline dolomite are better. The reservoir mainly develops three sets of fractures, with NW and NEE oriented shear fractures mainly related to two tectonic compressions during the Indosinian and Late Yanshanian . The third set of WE oriented tensile fractures is related to the intracratonic movement during the Himalayan orogeny, and compression is the main mechanism for forming high-density fractures. The later stage of extension is a necessary condition for the relaxation of fractures to form reservoir spaces. The Lower Paleozoic carbonate buried hill reservoirs have undergone three stages ofkarstification, which are karstification in the steady Caledonian tectonic background, karstification in the Indosinian compressive background, and fault block-horst karstification in the Yanshanian-Himalayan extensional background. In summary, the carbonate buried hill reservoirs in the northwestern Shaleitian Uplift are formed by multiple stages and multiple types of tectonic-karst processes, and the analysis of the differences in the degree of recombination in different structural parts is an important factor in understanding the reservoir formation mechanism.
The buried hill oil and gas reservoirs have become an important exploration field in China’s marine basins. The northwestern area of Shaleitian area of Bohai Bay Basin is a typical carbonate buried hill zone. Due to the lack of research on the reservoir control effect of multiple stage fractures and their related karstification, the oil and gas exploration of carbonate buried hills is restricted. This paper conducts a detailed analysis of the development characteristics of the fracture-cave system in carbonate buried hill reservoirs in the northwestern Shaleitian Uplift, and studies the reservoir control effects of fractures and karst. The results indicate that the lower Paleozoic carbonate buried hills in the northwestern area of Shaleitian Uplift belong to fracture related karst reservoirs. The reservoir space includes dissolution pores, structural fractures, and expansion pores along the structural fractures. High quality reservoirs have lithological selectivity, and fractures and dissolution pores developed in microlite crystalline dolomite and fine crystalline dolomite are better. The reservoir mainly develops three sets of fractures, with NW and NEE oriented shear fractures mainly related to two tectonic compressions during the Indosinian and Late Yanshanian . The third set of WE oriented tensile fractures is related to the intracratonic movement during the Himalayan orogeny, and compression is the main mechanism for forming high-density fractures. The later stage of extension is a necessary condition for the relaxation of fractures to form reservoir spaces. The Lower Paleozoic carbonate buried hill reservoirs have undergone three stages ofkarstification, which are karstification in the steady Caledonian tectonic background, karstification in the Indosinian compressive background, and fault block-horst karstification in the Yanshanian-Himalayan extensional background. In summary, the carbonate buried hill reservoirs in the northwestern Shaleitian Uplift are formed by multiple stages and multiple types of tectonic-karst processes, and the analysis of the differences in the degree of recombination in different structural parts is an important factor in understanding the reservoir formation mechanism.
, Available online , doi: 10.12284/hyxb2024027
Abstract:
This study focuses on the physical process of a sea fog event during Typhoon Lekima(1909) in the northern Yellow Sea by using observation data, reanalysis data and backward trajectory model. The analysis indicates that the typhoon circulation was the decisive factor determining whether fog formed offshore and developed inland. The warm and humid southerlies from the South Yellow Sea condensed into fog on the colder sea surface besides the typhoon center, which not only provided sufficient moisture for the formation and development of the sea fog but also formed a significant inversion layer over the fog area with the downdraft in the center of the typhoon. The “stable up and turbulent down” structure in the atmospheric boundary layer improved the development of sea fog on the coast and inland area. However, the horizontal wind steering and the strengthening wind speed behind the typhoon strengthened the wind shear in the atmospheric boundary layer, resulting in the enhanced turbulent mixing and the decrease of the stability in the bottom atmospheric boundary layer, which was the main cause of the fog dissipation.
This study focuses on the physical process of a sea fog event during Typhoon Lekima(1909) in the northern Yellow Sea by using observation data, reanalysis data and backward trajectory model. The analysis indicates that the typhoon circulation was the decisive factor determining whether fog formed offshore and developed inland. The warm and humid southerlies from the South Yellow Sea condensed into fog on the colder sea surface besides the typhoon center, which not only provided sufficient moisture for the formation and development of the sea fog but also formed a significant inversion layer over the fog area with the downdraft in the center of the typhoon. The “stable up and turbulent down” structure in the atmospheric boundary layer improved the development of sea fog on the coast and inland area. However, the horizontal wind steering and the strengthening wind speed behind the typhoon strengthened the wind shear in the atmospheric boundary layer, resulting in the enhanced turbulent mixing and the decrease of the stability in the bottom atmospheric boundary layer, which was the main cause of the fog dissipation.
, Available online
Abstract:
Plastic floating objects have a profound impact on the marine environment. The nearshore process of the floating objects is mainly influenced by the action of waves. On the kinetic characteristics of plastic floating objects, previous studies were not thorough for the nearshore regime. In this paper, laboratory experimentswere used to study the drift-law of plastic-floating objects under finite-water-depth waves. The relationship between the horizontal drift velocity of a weakly inertial plastic blocks and their characteristics, along with the wave steepness were discussed. The experimental results show that the drift of plastic blocks is affected by Stokes drift and Euler return flow, which is in good agreement with the second-order Lagrange drift theory. As the floating object’s size is much smaller than the wave length, size or density of the floating objects has no significant effect on drift. The drift of floating objects is proportional to the square of wave steepness. Based on the experiments conducted in this study and previously published experimental data, the empirical formula is revised to provide useful reference for the nearshore migration law of plastic floating objects and so for the relevant prediction.
Plastic floating objects have a profound impact on the marine environment. The nearshore process of the floating objects is mainly influenced by the action of waves. On the kinetic characteristics of plastic floating objects, previous studies were not thorough for the nearshore regime. In this paper, laboratory experimentswere used to study the drift-law of plastic-floating objects under finite-water-depth waves. The relationship between the horizontal drift velocity of a weakly inertial plastic blocks and their characteristics, along with the wave steepness were discussed. The experimental results show that the drift of plastic blocks is affected by Stokes drift and Euler return flow, which is in good agreement with the second-order Lagrange drift theory. As the floating object’s size is much smaller than the wave length, size or density of the floating objects has no significant effect on drift. The drift of floating objects is proportional to the square of wave steepness. Based on the experiments conducted in this study and previously published experimental data, the empirical formula is revised to provide useful reference for the nearshore migration law of plastic floating objects and so for the relevant prediction.
, Available online
Abstract:
Submesoscale processes associated with strong vertical velocities play significant roles in the vertical transport of tracers between the ocean surface and the interior, including heat, buoyancy, and mass. Based on the results of the 1/48° LLC4320 model, this study investigates the seasonal variations ofsubmesoscale vertical heat transport in the Kuroshio Extension. The results show that submesoscale vertical heat transport in the Kuroshio Extension exhibits distinct seasonal variations, with strong transport in spring and winter, and weaker transport in summer and autumn. The variation of net submesoscale vertical heat flux in the upper ocean is consistent with the trend of mixed layer depth, which shows overall upward submesoscale heat transport above the mixed layer and strong alternating positive and negative submesoscale vertical heat transport below the mixed layer, resulting in relatively small net submesoscale vertical heat transport. Coherent spectral analysis of vertical heat flux wavenumber-frequency suggests that submesoscale vertical heat transport below the mixed layer may be caused by linear internal waves, but the upward and downward vertical heat transports induced by linear internal waves counteract each other, leading to a reduced net vertical heat transport after averaging over the season.
Submesoscale processes associated with strong vertical velocities play significant roles in the vertical transport of tracers between the ocean surface and the interior, including heat, buoyancy, and mass. Based on the results of the 1/48° LLC4320 model, this study investigates the seasonal variations ofsubmesoscale vertical heat transport in the Kuroshio Extension. The results show that submesoscale vertical heat transport in the Kuroshio Extension exhibits distinct seasonal variations, with strong transport in spring and winter, and weaker transport in summer and autumn. The variation of net submesoscale vertical heat flux in the upper ocean is consistent with the trend of mixed layer depth, which shows overall upward submesoscale heat transport above the mixed layer and strong alternating positive and negative submesoscale vertical heat transport below the mixed layer, resulting in relatively small net submesoscale vertical heat transport. Coherent spectral analysis of vertical heat flux wavenumber-frequency suggests that submesoscale vertical heat transport below the mixed layer may be caused by linear internal waves, but the upward and downward vertical heat transports induced by linear internal waves counteract each other, leading to a reduced net vertical heat transport after averaging over the season.
, Available online , doi: 10.12284/hyxb2024066
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Oil and plastic pollutants are a serious threat to marine ecosystems and have even been found in the Ross Sea of the Southern Ocean. In order to obtain low-temperature alkane degrading bacteria and plastic-degrading bacteria in the region, a total of twelve sediment samples were collected in the Ross Sea area for enrichment and isolation of alkane-degrading bacteria at low-temperature, and the diversity analyses of the tetradecane-enriched communities showed that the most dominant genera were Pseudomonas, Alcanivorax, Marinomonas, Pseudoalteromonas. The polyethylene terephthalate(PET)and polyethylene(PE)was further validated using the dominant alkane-degrading bacteria. Scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (ATR-FTIR) demonstrated that the four pure cultures of Pseudomonas pelagia R1-05-CR3, Pseudomonas taeanensis A11-04-CA4, Halomonas titanicae A11-02-7C2 and Rhodococcus cerastii R1-05-7C3 could degrade PE effectively. The results of UPLC-MS and SEM confirmed the PET degradation by isolates of R. cerastii R1-05-7C3, Microbacterium maritypicum RA1-00-CA1, and H. titanicae A11-02-7C2. In conclusion, this study reports the diversity of the tetradecane-enriched consortia at low-temperature in the Southern Ocean and the pure culture isolated from tetradecane-enriched consortia possessing PET and PE degrading potential, providing a basis for the presence of plastic-degrading bacteria in polar environment.
Oil and plastic pollutants are a serious threat to marine ecosystems and have even been found in the Ross Sea of the Southern Ocean. In order to obtain low-temperature alkane degrading bacteria and plastic-degrading bacteria in the region, a total of twelve sediment samples were collected in the Ross Sea area for enrichment and isolation of alkane-degrading bacteria at low-temperature, and the diversity analyses of the tetradecane-enriched communities showed that the most dominant genera were Pseudomonas, Alcanivorax, Marinomonas, Pseudoalteromonas. The polyethylene terephthalate(PET)and polyethylene(PE)was further validated using the dominant alkane-degrading bacteria. Scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (ATR-FTIR) demonstrated that the four pure cultures of Pseudomonas pelagia R1-05-CR3, Pseudomonas taeanensis A11-04-CA4, Halomonas titanicae A11-02-7C2 and Rhodococcus cerastii R1-05-7C3 could degrade PE effectively. The results of UPLC-MS and SEM confirmed the PET degradation by isolates of R. cerastii R1-05-7C3, Microbacterium maritypicum RA1-00-CA1, and H. titanicae A11-02-7C2. In conclusion, this study reports the diversity of the tetradecane-enriched consortia at low-temperature in the Southern Ocean and the pure culture isolated from tetradecane-enriched consortia possessing PET and PE degrading potential, providing a basis for the presence of plastic-degrading bacteria in polar environment.
, Available online , doi: 10.12284/hyxb2024074
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Sediment oxygen consumption (SOC) is an important parameter of marine sediments and an important characterization parameter of the rate of organic carbon mineralization in seafloor sediments, and the study of SOC can help us to understand the carbon cycling process in the whole ocean. As one of the most important and active sites for organic carbon mineralization and burial, marginal seas have received widespread attention and research around the world, but there is still a lack of relevant attention to the Chinese marginal sea region with typical seasonal variations of the marine environment, especially the Yellow Sea and Bohai Sea. In this paper, the intact core incubation was used to study the SOC in the Yellow Sea and Bohai Sea in April, July and October 2022, and the results showed that the rates of SOC ranged from 7.11 mmol/(m2·d) to 17.33 mmol/(m2·d). There was no significant difference between the SOC of the Yellow Sea and the Bohai Sea in spring (ANOVA, p > 0.05), and the SOC of the Yellow Sea was lower than Bohai Sea in summer (ANOVA, p < 0.01) and autumn (ANOVA, p < 0.01); the SOC of the Yellow Sea was the largest in spring and the smallest in summer, and there was no significant difference between the SOC of the Bohai Sea in summer and autumn, which were significantly higher than that of spring (ANOVA, p < 0.05). Temperature and sediment Chl a concentration were the influencing factors. Meanwhile, the SOC was used to assess the rate of benthic organic carbon mineralization. When compared with the primary productivity, the results indicated that the contribution of benthic organic carbon mineralization to primary productivity in the Bohai Sea ranged from 42.8% to 74.5%, which was one of the key links in the carbon cycle of the Bohai Sea, while the benthic organic carbon mineralization in Yellow Sea plays a less significant role in the carbon cycle of the Yellow Sea carbon cycle than Bohai Sea. This paper systematically studied the SOC in the Yellow Sea and Bohai Sea and its spatial and temporal distribution characteristics, exploring the contribution of organic carbon mineralization to primary productivity in the Yellow Sea and Bohai Sea, which provided theoretical support for the understanding of organic carbon mineralization and burial in the Yellow Sea and Bohai Sea.
Sediment oxygen consumption (SOC) is an important parameter of marine sediments and an important characterization parameter of the rate of organic carbon mineralization in seafloor sediments, and the study of SOC can help us to understand the carbon cycling process in the whole ocean. As one of the most important and active sites for organic carbon mineralization and burial, marginal seas have received widespread attention and research around the world, but there is still a lack of relevant attention to the Chinese marginal sea region with typical seasonal variations of the marine environment, especially the Yellow Sea and Bohai Sea. In this paper, the intact core incubation was used to study the SOC in the Yellow Sea and Bohai Sea in April, July and October 2022, and the results showed that the rates of SOC ranged from 7.11 mmol/(m2·d) to 17.33 mmol/(m2·d). There was no significant difference between the SOC of the Yellow Sea and the Bohai Sea in spring (ANOVA, p > 0.05), and the SOC of the Yellow Sea was lower than Bohai Sea in summer (ANOVA, p < 0.01) and autumn (ANOVA, p < 0.01); the SOC of the Yellow Sea was the largest in spring and the smallest in summer, and there was no significant difference between the SOC of the Bohai Sea in summer and autumn, which were significantly higher than that of spring (ANOVA, p < 0.05). Temperature and sediment Chl a concentration were the influencing factors. Meanwhile, the SOC was used to assess the rate of benthic organic carbon mineralization. When compared with the primary productivity, the results indicated that the contribution of benthic organic carbon mineralization to primary productivity in the Bohai Sea ranged from 42.8% to 74.5%, which was one of the key links in the carbon cycle of the Bohai Sea, while the benthic organic carbon mineralization in Yellow Sea plays a less significant role in the carbon cycle of the Yellow Sea carbon cycle than Bohai Sea. This paper systematically studied the SOC in the Yellow Sea and Bohai Sea and its spatial and temporal distribution characteristics, exploring the contribution of organic carbon mineralization to primary productivity in the Yellow Sea and Bohai Sea, which provided theoretical support for the understanding of organic carbon mineralization and burial in the Yellow Sea and Bohai Sea.
, Available online
Abstract:
Near-inertial motion is a type of motion in the ocean that is ubiquitous and has a frequency close to the local inertial frequency. Tropical cyclones are one of the mainmechanisms that generate near-inertial motion. This study established a three-dimensional hydrodynamic model based on COAWST (Coupled Ocean-Atmosphere-Wave-Sediment Transport) numerical model system, which couples waves and currents, covers the northern shelf of the South China Sea, and was fully verified. The model was used to simulate the near-inertial motion triggered by Typhoon Cempaka, the No.7 typhoon of 2021, on the shelf of western Guangdong. The results indicate that there are spatially two peaks of near-inertial kinetic energy, one in the coastal area with the highest typhoon wind speed, and the other at 130 km offshore, with the second energy peak lasting longer. In the coastal area with water depth shallower than 40 m, the near-inertialmotion is mainly in a barotropic mode. As the water depth gradually increasesoffshore, we found that the near-inertial motions exhibit a clear two-layer structure inthe regions with depths ranging from 70-100 m, with opposite directions of near-inertialflow in the surface and bottom layers, and two energy peaks in the vertical direction, showing the characteristics of the first baroclinic mode. Through dynamic modedecomposition, we found that some areas with obvious two-layer structures are composed of the first and secondbaroclinic modes. As the water depth continues to increase, higher modes of near-inertialflow account for an increasing proportion of the total near-inertial kinetic energy. Momentum balance analysis shows that in the coastal area with shallow water depth and high wind speed, the balance of momentum equation in the entire water layer is dominated by the vertical turbulent viscous force and pressure gradient force. In offshore areas with deeper water depths and lower wind speeds, vertical turbulent viscous forces are concentrated in the surface and bottom layers, and the balance of momentum equation in the intermediate water body is mainly dominated by the pressure gradient forces, Coriolis forces, and local acceleration. This indicates that the near-inertialmotion in the coastal area is mainly driven by barotropicwave caused bywind stress, while in the continental shelf area, the near-inertial motion in the uppermixed layer is driven by wind stress, and the near-inertial motion below the mixed layeris driven by barotropic pressure gradient force.
Near-inertial motion is a type of motion in the ocean that is ubiquitous and has a frequency close to the local inertial frequency. Tropical cyclones are one of the mainmechanisms that generate near-inertial motion. This study established a three-dimensional hydrodynamic model based on COAWST (Coupled Ocean-Atmosphere-Wave-Sediment Transport) numerical model system, which couples waves and currents, covers the northern shelf of the South China Sea, and was fully verified. The model was used to simulate the near-inertial motion triggered by Typhoon Cempaka, the No.7 typhoon of 2021, on the shelf of western Guangdong. The results indicate that there are spatially two peaks of near-inertial kinetic energy, one in the coastal area with the highest typhoon wind speed, and the other at 130 km offshore, with the second energy peak lasting longer. In the coastal area with water depth shallower than 40 m, the near-inertialmotion is mainly in a barotropic mode. As the water depth gradually increasesoffshore, we found that the near-inertial motions exhibit a clear two-layer structure inthe regions with depths ranging from 70-100 m, with opposite directions of near-inertialflow in the surface and bottom layers, and two energy peaks in the vertical direction, showing the characteristics of the first baroclinic mode. Through dynamic modedecomposition, we found that some areas with obvious two-layer structures are composed of the first and secondbaroclinic modes. As the water depth continues to increase, higher modes of near-inertialflow account for an increasing proportion of the total near-inertial kinetic energy. Momentum balance analysis shows that in the coastal area with shallow water depth and high wind speed, the balance of momentum equation in the entire water layer is dominated by the vertical turbulent viscous force and pressure gradient force. In offshore areas with deeper water depths and lower wind speeds, vertical turbulent viscous forces are concentrated in the surface and bottom layers, and the balance of momentum equation in the intermediate water body is mainly dominated by the pressure gradient forces, Coriolis forces, and local acceleration. This indicates that the near-inertialmotion in the coastal area is mainly driven by barotropicwave caused bywind stress, while in the continental shelf area, the near-inertial motion in the uppermixed layer is driven by wind stress, and the near-inertial motion below the mixed layeris driven by barotropic pressure gradient force.
, Available online , doi: 10.12284/hyxb2024050
Abstract:
Planktonic copepods is an important group of zooplankton. It is of great significance to study the distribution characteristics of planktonic copepods abundance and its correlation with various environmental indicators. In this study, we analyzed environmental monitoring data of Haizhou Bay, Lianyungang, Jiangsu Province, from 2003 to 2022 using generalized additive model (GAM), to investigate the spatiotemporal variation of planktonic copepods and its correlation with other sea water indicators. The results showed that the abundance of planktonic copepods varied significantly different between seasons (p < 0.01), and the mean value of copepods was greater in spring than in summer than in autumn. The spatial distribution of abundance was generally low in the artificial reef area and high in the southern coastal area. GAM analysis showed that the main influencing factors were different between seasons. The main influencing factors in spring were dissolved oxygen, Chlorophyll a concentration,\begin{document}${\mathrm{SiO}}_3^- $\end{document} ![]()
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Planktonic copepods is an important group of zooplankton. It is of great significance to study the distribution characteristics of planktonic copepods abundance and its correlation with various environmental indicators. In this study, we analyzed environmental monitoring data of Haizhou Bay, Lianyungang, Jiangsu Province, from 2003 to 2022 using generalized additive model (GAM), to investigate the spatiotemporal variation of planktonic copepods and its correlation with other sea water indicators. The results showed that the abundance of planktonic copepods varied significantly different between seasons (p < 0.01), and the mean value of copepods was greater in spring than in summer than in autumn. The spatial distribution of abundance was generally low in the artificial reef area and high in the southern coastal area. GAM analysis showed that the main influencing factors were different between seasons. The main influencing factors in spring were dissolved oxygen, Chlorophyll a concentration,
, Available online , doi: 10.12284/hyxb2024052
Abstract:
Based on the survey data of fishery resources and environment of four voyages from April 2021 to January 2022, the spatial and temporal distribution of Portunus trituberculatus and its relationship with influencing factors in the Ruian Sea area were studied, including its marine dominance, community structure and resource density distribution. At the same time, generalized additive model (GAM) is used to analyze the relationship between resource density and influencing factors. The results showed that: in the Ruian Sea area, P. trituberculatus is an important species (100 ≤ IRI < 1 000) in spring and summer and a dominant species (IRI ≥ 1 000) in autumn and winter. The average carapace length and body weight of P. trituberculatus ranged from 33.9 mm to 60.4 mm, and 22.9 g to 126.1 g. The carapace length and body weight of P. trituberculatus were the highest in summer and the lowest in autumn. There were significant differences between different seasons. P. trituberculatus showed negative allometric growth in spring, summer and winter (b < 3), and positive allometric growth in autumn (b > 3). The average resource density of P. trituberculatus ranged from 16.57 kg/km2 to 422.60 kg/km2, with the highest in autumn and the lowest in spring, and the average resource density in autumn was 25.5 times of that in spring. GAM analysis showed that the interpretation rate of the model was 80.2%. Season, surface water temperature, bottom water temperature, bottom salinity and surface chlorophyll a concentration had significant effects on the resource density of P. trituberculatus (p < 0.05), among which season had the greatest effect. Through this study, it provides reference for grasping the dynamic change law of P. trituberculatus resources in Ruian Sea area, and further provides theoretical support for the proliferation and release of P. trituberculatus.
Based on the survey data of fishery resources and environment of four voyages from April 2021 to January 2022, the spatial and temporal distribution of Portunus trituberculatus and its relationship with influencing factors in the Ruian Sea area were studied, including its marine dominance, community structure and resource density distribution. At the same time, generalized additive model (GAM) is used to analyze the relationship between resource density and influencing factors. The results showed that: in the Ruian Sea area, P. trituberculatus is an important species (100 ≤ IRI < 1 000) in spring and summer and a dominant species (IRI ≥ 1 000) in autumn and winter. The average carapace length and body weight of P. trituberculatus ranged from 33.9 mm to 60.4 mm, and 22.9 g to 126.1 g. The carapace length and body weight of P. trituberculatus were the highest in summer and the lowest in autumn. There were significant differences between different seasons. P. trituberculatus showed negative allometric growth in spring, summer and winter (b < 3), and positive allometric growth in autumn (b > 3). The average resource density of P. trituberculatus ranged from 16.57 kg/km2 to 422.60 kg/km2, with the highest in autumn and the lowest in spring, and the average resource density in autumn was 25.5 times of that in spring. GAM analysis showed that the interpretation rate of the model was 80.2%. Season, surface water temperature, bottom water temperature, bottom salinity and surface chlorophyll a concentration had significant effects on the resource density of P. trituberculatus (p < 0.05), among which season had the greatest effect. Through this study, it provides reference for grasping the dynamic change law of P. trituberculatus resources in Ruian Sea area, and further provides theoretical support for the proliferation and release of P. trituberculatus.
, Available online , doi: 10.12284/hyxb2024038
Abstract:
To understand the characteristics and distribution of benthic shellfish communities in the vicinity of the Nanji Islands, we conducted bottom trawl surveys in the surrounding waters during October 2022 (autumn) and March 2023 (spring). The findings reveal that a total of 49 benthic shellfish species were captured, spanning 2 classes, 6 orders, and 17 families. During spring, the average abundance of benthic shellfish was (2 429 ± 2 038) ind./Agt, with an average biomass of (4 849.79 ± 2 513.84) g/Agt. In autumn, the average abundance was (1 149 ± 1 589) ind./Agt, with an average biomass of (4 985.30 ± 2 159.23) g/Agt. The primary dominant species comprised Turritella bacillum, Murex trapa, Tegillarca nodifera, Inquisitor jeffreysii, Bufonaria rana, Cancellaria sinensis and Trigonaphera bocageana. Notably, Turritella bacillum emerged as a dominant species in both spring and autumn, with dominance significantly surpassing that of other species. The dominance of benthic shellfish communities in this marine area appears relatively stable, with the community’s functionality and nature being primarily governed by a select few species. This study provides a reference basis for the dynamic changes in the marine ecosystem of the Nansha Islands and offers foundational data for the protection of marine ecological environments.
To understand the characteristics and distribution of benthic shellfish communities in the vicinity of the Nanji Islands, we conducted bottom trawl surveys in the surrounding waters during October 2022 (autumn) and March 2023 (spring). The findings reveal that a total of 49 benthic shellfish species were captured, spanning 2 classes, 6 orders, and 17 families. During spring, the average abundance of benthic shellfish was (2 429 ± 2 038) ind./Agt, with an average biomass of (4 849.79 ± 2 513.84) g/Agt. In autumn, the average abundance was (1 149 ± 1 589) ind./Agt, with an average biomass of (4 985.30 ± 2 159.23) g/Agt. The primary dominant species comprised Turritella bacillum, Murex trapa, Tegillarca nodifera, Inquisitor jeffreysii, Bufonaria rana, Cancellaria sinensis and Trigonaphera bocageana. Notably, Turritella bacillum emerged as a dominant species in both spring and autumn, with dominance significantly surpassing that of other species. The dominance of benthic shellfish communities in this marine area appears relatively stable, with the community’s functionality and nature being primarily governed by a select few species. This study provides a reference basis for the dynamic changes in the marine ecosystem of the Nansha Islands and offers foundational data for the protection of marine ecological environments.
, Available online
Abstract:
In recent years, natural processes and human activities have significantly altered the Huanghe River channel and the coastal geomorphic pattern, while the impact of the dramatic geomorphic evolution on the coastal hydrodynamics has not been fully studied. Based on series images captured by the Landsat satellites and bathymetric measurements, this paper analyzed the shorelines and topography changes of the Huanghe River Delta from 1992 to 2020. Several sets of numerical models covering the entire Bohai Sea were established by TELEMAC-2D to investigate the response of tidal dynamics to geomorphic evolution and its depositional effects in the Huanghe River Delta. The results show that the erosion and deposition had significant spatial and temporal heterogeneity, and there were multiple siltation and erosion centers. The erosion center outside the old Qingshuigou Estuary moved 9.6 km to the south during 2000–2020, and the one outside the Diaokou Estuary moved 6.4 km to the east during 1992–2015. The tidal dynamics were dominated by the coastline and terrain changes on the medium and long time scales. The tidal range of the Diaokou estuary decreased, while the old and the new estuary increased. And the tidal range at 5 m depth had a maximum variation of 0.27 m. The K1 tidal amplitude increased significantly, while the M2 tidal amplitude was considerably reduced, and the amphidromic point near Dongying port eastward migration of 3.8 km. The high velocity outside the Diaokou Estuary and the old estuary continued to weaken, and another high velocity area gradually developed outside the current estuary. The continuous and stable high velocity area caused the erosion of the subaqueous delta and the coarsening of sediment.
In recent years, natural processes and human activities have significantly altered the Huanghe River channel and the coastal geomorphic pattern, while the impact of the dramatic geomorphic evolution on the coastal hydrodynamics has not been fully studied. Based on series images captured by the Landsat satellites and bathymetric measurements, this paper analyzed the shorelines and topography changes of the Huanghe River Delta from 1992 to 2020. Several sets of numerical models covering the entire Bohai Sea were established by TELEMAC-2D to investigate the response of tidal dynamics to geomorphic evolution and its depositional effects in the Huanghe River Delta. The results show that the erosion and deposition had significant spatial and temporal heterogeneity, and there were multiple siltation and erosion centers. The erosion center outside the old Qingshuigou Estuary moved 9.6 km to the south during 2000–2020, and the one outside the Diaokou Estuary moved 6.4 km to the east during 1992–2015. The tidal dynamics were dominated by the coastline and terrain changes on the medium and long time scales. The tidal range of the Diaokou estuary decreased, while the old and the new estuary increased. And the tidal range at 5 m depth had a maximum variation of 0.27 m. The K1 tidal amplitude increased significantly, while the M2 tidal amplitude was considerably reduced, and the amphidromic point near Dongying port eastward migration of 3.8 km. The high velocity outside the Diaokou Estuary and the old estuary continued to weaken, and another high velocity area gradually developed outside the current estuary. The continuous and stable high velocity area caused the erosion of the subaqueous delta and the coarsening of sediment.
, Available online
Abstract:
The impact of the El Niño-Southern Oscillation (ENSO) on the climate of the low-latitude tropical region of the Malay Peninsula, particularly with regard to precipitation, remains a topic of debate. This study focuses on the NTT-3 drill core from Setiu Lagoon in Terengganu, northeastern Malay Peninsula. By employing analyses such as grain size, total organic carbon/nitrogen content, C/N ratio, and XRF core scanning, this research investigates the sedimentary environmental changes in the drill core and their response to ENSO. The results reveal two distinct trends in the drill core record, appearing around 1970 (at 84 cm depth). Sediment characteristics such as grain size and geochemical features of both organic and inorganic components suggest the possible occurrence of episodic sedimentation or sedimentary interruptions, with exceptionally slow sedimentation rates observed in the lower part of the core before 1970. Since 1970, the organic components in the lagoon sediment primarily originate from mangroves, accompanied by contributions from freshwater phytoplankton associated with river inputs. Spectral analysis indicates a pronounced ENSO periodic variation in the upper part of the drill core since 1970. The variations in Zr/Rb and Zr/Ti ratios correlate well with the occurrences of strong El Niño and La Niña events. This conclusion not only supports contemporary observations of climate change in the eastern coastal region of the Malay Peninsula but also provides direct geological evidence of ENSO variations in the sedimentary record. This discovery holds significant practical implications for a comprehensive understanding of the impact of ENSO on climate change in Asia, regional land-sea interaction processes, and environmental responses.
The impact of the El Niño-Southern Oscillation (ENSO) on the climate of the low-latitude tropical region of the Malay Peninsula, particularly with regard to precipitation, remains a topic of debate. This study focuses on the NTT-3 drill core from Setiu Lagoon in Terengganu, northeastern Malay Peninsula. By employing analyses such as grain size, total organic carbon/nitrogen content, C/N ratio, and XRF core scanning, this research investigates the sedimentary environmental changes in the drill core and their response to ENSO. The results reveal two distinct trends in the drill core record, appearing around 1970 (at 84 cm depth). Sediment characteristics such as grain size and geochemical features of both organic and inorganic components suggest the possible occurrence of episodic sedimentation or sedimentary interruptions, with exceptionally slow sedimentation rates observed in the lower part of the core before 1970. Since 1970, the organic components in the lagoon sediment primarily originate from mangroves, accompanied by contributions from freshwater phytoplankton associated with river inputs. Spectral analysis indicates a pronounced ENSO periodic variation in the upper part of the drill core since 1970. The variations in Zr/Rb and Zr/Ti ratios correlate well with the occurrences of strong El Niño and La Niña events. This conclusion not only supports contemporary observations of climate change in the eastern coastal region of the Malay Peninsula but also provides direct geological evidence of ENSO variations in the sedimentary record. This discovery holds significant practical implications for a comprehensive understanding of the impact of ENSO on climate change in Asia, regional land-sea interaction processes, and environmental responses.
, Available online , doi: 10.12284/hyxb2023040
Abstract:
Spaceborne synthetic aperture radar (SAR) is able to collect observations under all kinds of weather during day and night. Such measurements have been proven to provide significant data support for the ocean dynamics study. While SAR imaging of ocean waves is a highly nonlinear process, leading the wave signal missing along the azimuth direction. The image cross-spectrum provides a way to help investigate the ocean wave features particularly for their propagation direction. In this study, we extended a recently defined parameter based on SAR image cross-spectrum and analyzed the correlation of different wave scales with the local wind speed. The range peak wavenumber (wavelength) extracted from the range spectral profile is also demonstrated at the global scale based on about 4 million SAR images. It is found that this new spectral parameter could to some extent reflect the coupling between wind and waves. The global pattern of range peak wavenumber also illustrates evident seasonality.
Spaceborne synthetic aperture radar (SAR) is able to collect observations under all kinds of weather during day and night. Such measurements have been proven to provide significant data support for the ocean dynamics study. While SAR imaging of ocean waves is a highly nonlinear process, leading the wave signal missing along the azimuth direction. The image cross-spectrum provides a way to help investigate the ocean wave features particularly for their propagation direction. In this study, we extended a recently defined parameter based on SAR image cross-spectrum and analyzed the correlation of different wave scales with the local wind speed. The range peak wavenumber (wavelength) extracted from the range spectral profile is also demonstrated at the global scale based on about 4 million SAR images. It is found that this new spectral parameter could to some extent reflect the coupling between wind and waves. The global pattern of range peak wavenumber also illustrates evident seasonality.
, Available online , doi: 10.12284/hyxb2024004
Abstract:
Natural gas hydrates have received widespread attention due to their enormous resource potential, but previous researches have focused mostly on the passive continental margin in the northern South China Sea, while rarely on the active continental margin in the eastern South China Sea. Based on the analysis of multi-channel seismic profiles in the active continental margin area of the Manila Trench in northeast of the South China Sea, this paper identified typical gas hydrate indicators such as bottom simulating reflector, blanking zone, polarity-reversal, and fluid migration channels, such as reverse fault and mud diapir are identified in this paper. The Orogenic Belt in southwestern Taiwan is an extension of the accretionary wedge of the Manila Trench. The associated gas of mud volcano is mainly CH4 and minorly showing high nitrogen anomaly. The geochemical characteristics of the associated gas show that natural gas in this area is mainly mature hydrocarbon gas of pyrolysis origin, and is mainly the contribution of Neogene thick marine sedimentary source rock. According to the analysis, the cause is that the plate subduction brought deep hydrocarbon into the accretionary wedge and formed a high-pressure environment. The thermally generated hydrocarbon gas migrated upward along mud diapir and reverse fault. During the migration, some natural gas was gradually transformed by decomposition of microorganisms and mixed with in-situ microbial gas. The thermogenic and biogenic methane eventually mixed in the suitable stable zone to form a mixed gas hydrate reservoir dominated by thermogenic and partly biogenic. In addition, with the change of external environment and the continuous activities of subduction movement, the stability of natural gas hydrate is damaged and decomposition leakage occurs, which may cause landslide. In the further exploration and development of natural gas hydrate resources in this area, we must pay attention to the potential geological disaster risk.
Natural gas hydrates have received widespread attention due to their enormous resource potential, but previous researches have focused mostly on the passive continental margin in the northern South China Sea, while rarely on the active continental margin in the eastern South China Sea. Based on the analysis of multi-channel seismic profiles in the active continental margin area of the Manila Trench in northeast of the South China Sea, this paper identified typical gas hydrate indicators such as bottom simulating reflector, blanking zone, polarity-reversal, and fluid migration channels, such as reverse fault and mud diapir are identified in this paper. The Orogenic Belt in southwestern Taiwan is an extension of the accretionary wedge of the Manila Trench. The associated gas of mud volcano is mainly CH4 and minorly showing high nitrogen anomaly. The geochemical characteristics of the associated gas show that natural gas in this area is mainly mature hydrocarbon gas of pyrolysis origin, and is mainly the contribution of Neogene thick marine sedimentary source rock. According to the analysis, the cause is that the plate subduction brought deep hydrocarbon into the accretionary wedge and formed a high-pressure environment. The thermally generated hydrocarbon gas migrated upward along mud diapir and reverse fault. During the migration, some natural gas was gradually transformed by decomposition of microorganisms and mixed with in-situ microbial gas. The thermogenic and biogenic methane eventually mixed in the suitable stable zone to form a mixed gas hydrate reservoir dominated by thermogenic and partly biogenic. In addition, with the change of external environment and the continuous activities of subduction movement, the stability of natural gas hydrate is damaged and decomposition leakage occurs, which may cause landslide. In the further exploration and development of natural gas hydrate resources in this area, we must pay attention to the potential geological disaster risk.
, Available online
Abstract:
Submarine fans developed in the middle Miocene Meishan formation possess significant potential for natural gas exploration. Most of scholars believed that these Miocene submarine fans were formed primarily by turbidity currents. However, drilling cores reveal the presence of pebbles with a particle size of up to 5 cm in the sandy conglomerates. These sandy conglomerates exhibit good roundness and poor sorting, indicating that the traditional turbidity formation mechanism cannot fully explain the origin of this type of sandy conglomerates. Furthermore, the classic submarine fan model has limitations in predicting the distribution of sand bodies. Through a comprehensive study involving core, thin section observation, and grain size analysis, we have conducted a systematic investigation of the petrological characteristics and sedimentary structures of submarine fan in the study area. Our findings suggest that submarine fans in the study area resulted from the interaction of turbidity and hyperpycnal flow deposits. We have identified distinct sequences of turbidites and hyperpycnalites within the submarine fan. Based on the paleogeomorphlogy of the study area, we have established a genetic evolution model for the submarine fan in Meishan Formation. This model reveals that the hyperpycnites dominated by feldspathic litharenite, exhibit low compositional maturity. Poor sorting and subangular-circular of the rocks indicate middle-to-high structural maturity. Typical features of hyperpycnal flow include orientated gravel within block sandy conglomerates, reverse-to-normal grain order bedding, parallel bedding, carbonaceous debris, and biological fossil fragments. Multi stage superimposed turbidite sequence and hyperpycnites sequence developed in submarine fan in the study area. The early Meishan period is primarily composed of turbidite submarine fan lobes, while the middle Meishan period is dominated by hyperpycnites submarine fan channels. The late Meishan period, on the other hand, is mainly composed of turbidite submarine fan channels. We predict that more favorable submarine fan sand bodies could be found in the southern part of the study area. The results can serve as a basis for predicting the distribution of favorable submarine fan reservoirs of the Qiongdongnan Basin, and they hold significance for selecting exploration and development targets for hydrocarbon exploration.
Submarine fans developed in the middle Miocene Meishan formation possess significant potential for natural gas exploration. Most of scholars believed that these Miocene submarine fans were formed primarily by turbidity currents. However, drilling cores reveal the presence of pebbles with a particle size of up to 5 cm in the sandy conglomerates. These sandy conglomerates exhibit good roundness and poor sorting, indicating that the traditional turbidity formation mechanism cannot fully explain the origin of this type of sandy conglomerates. Furthermore, the classic submarine fan model has limitations in predicting the distribution of sand bodies. Through a comprehensive study involving core, thin section observation, and grain size analysis, we have conducted a systematic investigation of the petrological characteristics and sedimentary structures of submarine fan in the study area. Our findings suggest that submarine fans in the study area resulted from the interaction of turbidity and hyperpycnal flow deposits. We have identified distinct sequences of turbidites and hyperpycnalites within the submarine fan. Based on the paleogeomorphlogy of the study area, we have established a genetic evolution model for the submarine fan in Meishan Formation. This model reveals that the hyperpycnites dominated by feldspathic litharenite, exhibit low compositional maturity. Poor sorting and subangular-circular of the rocks indicate middle-to-high structural maturity. Typical features of hyperpycnal flow include orientated gravel within block sandy conglomerates, reverse-to-normal grain order bedding, parallel bedding, carbonaceous debris, and biological fossil fragments. Multi stage superimposed turbidite sequence and hyperpycnites sequence developed in submarine fan in the study area. The early Meishan period is primarily composed of turbidite submarine fan lobes, while the middle Meishan period is dominated by hyperpycnites submarine fan channels. The late Meishan period, on the other hand, is mainly composed of turbidite submarine fan channels. We predict that more favorable submarine fan sand bodies could be found in the southern part of the study area. The results can serve as a basis for predicting the distribution of favorable submarine fan reservoirs of the Qiongdongnan Basin, and they hold significance for selecting exploration and development targets for hydrocarbon exploration.
, Available online , doi: 10.12284/hyxb2024014
Abstract:
Reliable assessment of the impact and risk of typhoons on coastal areas is very important for scientific resistance to typhoon disasters. China has a detailed typhoon observation record with a history of only 60 years, which makes it limited in estimating extreme wind speed with a long recurrence period and corresponding extreme wave height and tide level. The insufficient records also limits the application of data-driven models in typhoon disaster prediction. Therefore, it is necessary to construct synthetic typhoons based on the actual typhoon travel law to overcome the problem of insufficient historical observations. In this paper, 18 671 synthetic typhoons were constructed in the Northwest Pacific Ocean by using the Empirical Path Model based on kernel density estimation, and the parameters such as the start and end position, frequency of occurrence, travel speed and direction of the synthetic typhoons were statistically compared and analyzed with historical typhoons. The results show that the synthetic typhoon constructed based on the proposed method is generally consistent with the traveling characteristics of historical typhoons in the Northwest Pacific Ocean. Through the construction of these synthetic typhoons, a synthetic typhoon database with sufficient data and reliable performance can be provided for the study of extreme wave and storm surge along the coast of China.
Reliable assessment of the impact and risk of typhoons on coastal areas is very important for scientific resistance to typhoon disasters. China has a detailed typhoon observation record with a history of only 60 years, which makes it limited in estimating extreme wind speed with a long recurrence period and corresponding extreme wave height and tide level. The insufficient records also limits the application of data-driven models in typhoon disaster prediction. Therefore, it is necessary to construct synthetic typhoons based on the actual typhoon travel law to overcome the problem of insufficient historical observations. In this paper, 18 671 synthetic typhoons were constructed in the Northwest Pacific Ocean by using the Empirical Path Model based on kernel density estimation, and the parameters such as the start and end position, frequency of occurrence, travel speed and direction of the synthetic typhoons were statistically compared and analyzed with historical typhoons. The results show that the synthetic typhoon constructed based on the proposed method is generally consistent with the traveling characteristics of historical typhoons in the Northwest Pacific Ocean. Through the construction of these synthetic typhoons, a synthetic typhoon database with sufficient data and reliable performance can be provided for the study of extreme wave and storm surge along the coast of China.
, Available online
Abstract:
Using multiple observational subsurface temperature and salinity datasets based on Argo, we analyze the trend of 0–1 500 m ocean heat content in the Pacific between 2004 and 2020. It was found that the long-term trend of the Pacific ocean heat content showed a shift in 2013. The ocean heat content in 2013–2020 increased rapidly compared with that in 2004–2012. The linear trend of the former reaches about 0.50 × 1022 J/a, which is significantly higher than that of the latter. The Pacific has recently experienced rapid warming. During 2013–2020, the largest linear trend of the ocean heat content in the Pacific appeared in the western North Pacific, followed by the Tropical Pacific and eastern North Pacific. While the ocean heat content in the entire South Pacific showed a slightly decreasing trend. In the western North Pacific, the rapid increase of ocean heat content was concentrated in the Kuroshio Extension areas, and this warming trend is likely to be caused by the northward shift of the Kuroshio Extension main axis. It is worth mentioning that there was a local decreasing trend of ocean heat content in the south of Japan, and this cooling trend is associated with the strengthening of the Kuroshio large meander. In the Tropical Pacific where the warming trend is the second largest, the rapid increase of ocean heat content is likely to be induced by the thermocline deepening. In addition, we point out that the rapid warming in the Pacific is reflected by the rapid rise of sea level. The linear trend of sea level per 1 cm/a corresponds to the linear trend of ocean heat content of 0.11 × 109 J/(m2·a). This study elucidates the rapid warming of the Pacific since the end of the global warming hiatus, deepening our understanding of recent thermal conditions in the Pacific.
Using multiple observational subsurface temperature and salinity datasets based on Argo, we analyze the trend of 0–1 500 m ocean heat content in the Pacific between 2004 and 2020. It was found that the long-term trend of the Pacific ocean heat content showed a shift in 2013. The ocean heat content in 2013–2020 increased rapidly compared with that in 2004–2012. The linear trend of the former reaches about 0.50 × 1022 J/a, which is significantly higher than that of the latter. The Pacific has recently experienced rapid warming. During 2013–2020, the largest linear trend of the ocean heat content in the Pacific appeared in the western North Pacific, followed by the Tropical Pacific and eastern North Pacific. While the ocean heat content in the entire South Pacific showed a slightly decreasing trend. In the western North Pacific, the rapid increase of ocean heat content was concentrated in the Kuroshio Extension areas, and this warming trend is likely to be caused by the northward shift of the Kuroshio Extension main axis. It is worth mentioning that there was a local decreasing trend of ocean heat content in the south of Japan, and this cooling trend is associated with the strengthening of the Kuroshio large meander. In the Tropical Pacific where the warming trend is the second largest, the rapid increase of ocean heat content is likely to be induced by the thermocline deepening. In addition, we point out that the rapid warming in the Pacific is reflected by the rapid rise of sea level. The linear trend of sea level per 1 cm/a corresponds to the linear trend of ocean heat content of 0.11 × 109 J/(m2·a). This study elucidates the rapid warming of the Pacific since the end of the global warming hiatus, deepening our understanding of recent thermal conditions in the Pacific.
, Available online , doi: 10.12284/hyxb0000-00
Abstract:
Quantitative studies on the spatial distribution of geometric parameters of complex submarine sand waves in the developmental area are rare, and the correlation between the complex geometric parameters of sand waves and environmental variables has not been clarified. Based on measured data of water depth, sediment grain size, and flow velocity in the western area of Hainan Island, the environmental variables of the study area were quantified and extracted. The morphological parameters of complex submarine sand waves were calculated using an automated extraction and analysis method, and the correlation between sand wave geometric parameters and environmental variables was analyzed. The results show that the morphological characteristics of submarine sand waves in the study area are complex and variable, with an average wavelength ranging from 64 to 340 m and an average wave height ranging from 0.39 to 4.13 m. There is a strong positive correlation between wave height and steepness, as well as between wave height and the average angle of the lee side. There is also a strong positive correlation between wavelength and symmetry, and a strong positive correlation between median sediment grain size and the average angle of the lee side and wave height. The development of submarine sand waves in the study area is less influenced by water depth. Under the action of tidal currents, sediment transport is mainly by traction, and the erosion of submarine sand waves is relatively weak. The evolution of sand waves is mainly characterized by vertical growth and migration, with wave height growth prioritized over wavelength increase. Under stable tidal flow conditions, regional sediment supply and sediment grain size can both affect the scale of submarine sand waves.
Quantitative studies on the spatial distribution of geometric parameters of complex submarine sand waves in the developmental area are rare, and the correlation between the complex geometric parameters of sand waves and environmental variables has not been clarified. Based on measured data of water depth, sediment grain size, and flow velocity in the western area of Hainan Island, the environmental variables of the study area were quantified and extracted. The morphological parameters of complex submarine sand waves were calculated using an automated extraction and analysis method, and the correlation between sand wave geometric parameters and environmental variables was analyzed. The results show that the morphological characteristics of submarine sand waves in the study area are complex and variable, with an average wavelength ranging from 64 to 340 m and an average wave height ranging from 0.39 to 4.13 m. There is a strong positive correlation between wave height and steepness, as well as between wave height and the average angle of the lee side. There is also a strong positive correlation between wavelength and symmetry, and a strong positive correlation between median sediment grain size and the average angle of the lee side and wave height. The development of submarine sand waves in the study area is less influenced by water depth. Under the action of tidal currents, sediment transport is mainly by traction, and the erosion of submarine sand waves is relatively weak. The evolution of sand waves is mainly characterized by vertical growth and migration, with wave height growth prioritized over wavelength increase. Under stable tidal flow conditions, regional sediment supply and sediment grain size can both affect the scale of submarine sand waves.
, Available online , doi: 10.12284/hyxb2024008
Abstract:
There are also obvious inter-annual variations of the North Equatorial Countercurrent (NECC) during the occurrence and development of the El Niño-Southern Oscillation (ENSO), but its changing process in hydroecological conditions and response mechanism influenced by ENSO cycle are still unclear. Taking the NECC affected area in the tropical western Pacific as the study area, this paper analyzes the characteristics of the changes of hydroecoclimatic conditions at different stages during the ENSO cycle during autumn and winter transition period from 2006 to 2022. Results reveal that there are high chlorophyll concentration bands in the NECC source area and its path, which are formed by the combined influence of nutrients carried by the NECC from its source area and the New Guinea coastal Undercurrent. The upwelling of the Mindanao Dome also has a great influence on the nutrient supply. When El Niño events occurred, the westerly wind events in the tropical western Pacific increased, the NECC strengthened, a large amount of surface water moved eastward, the sea level in the study area decreased, the deep water recharge to the shallow layer increased, and the deep cold water rose. The jointly enhanced NECC, New Guinea Coastal Current, New Guinea Coastal Undercurrent and Mindanao Dome upwelling transport more nutrients to the sea surface from both horizontal and vertical levels, resulting in significant increases in surface chlorophyll concentration and primary organic carbon production by all types of phytoplankton. When La Niña events occurred, the changes of ecohydroclimatic conditions in the NECC affected area are almost opposite to those during El Niño events, but the degree of change is weaker than that during El Nino events. The combined weakening of the NECC, the New Guinea coastal undercurrent and the Mindanao Dome upwelling significantly reduce the nutrients delivered to the sea surface from the horizontal and vertical levels. The chlorophyll concentration and primary organic carbon production by all types of phytoplankton decreased significantly. This paper proposes a model of the response mechanism of the evolution of hydroecoclimatic conditions in the NECC affected area to El Niño and La Niña events, which is conducive to further analysis of the role of ENSO cycle in local ecological effects and hydroclimatic evolution. It has important significance for understanding the impact of global climate change on the material cycle.
There are also obvious inter-annual variations of the North Equatorial Countercurrent (NECC) during the occurrence and development of the El Niño-Southern Oscillation (ENSO), but its changing process in hydroecological conditions and response mechanism influenced by ENSO cycle are still unclear. Taking the NECC affected area in the tropical western Pacific as the study area, this paper analyzes the characteristics of the changes of hydroecoclimatic conditions at different stages during the ENSO cycle during autumn and winter transition period from 2006 to 2022. Results reveal that there are high chlorophyll concentration bands in the NECC source area and its path, which are formed by the combined influence of nutrients carried by the NECC from its source area and the New Guinea coastal Undercurrent. The upwelling of the Mindanao Dome also has a great influence on the nutrient supply. When El Niño events occurred, the westerly wind events in the tropical western Pacific increased, the NECC strengthened, a large amount of surface water moved eastward, the sea level in the study area decreased, the deep water recharge to the shallow layer increased, and the deep cold water rose. The jointly enhanced NECC, New Guinea Coastal Current, New Guinea Coastal Undercurrent and Mindanao Dome upwelling transport more nutrients to the sea surface from both horizontal and vertical levels, resulting in significant increases in surface chlorophyll concentration and primary organic carbon production by all types of phytoplankton. When La Niña events occurred, the changes of ecohydroclimatic conditions in the NECC affected area are almost opposite to those during El Niño events, but the degree of change is weaker than that during El Nino events. The combined weakening of the NECC, the New Guinea coastal undercurrent and the Mindanao Dome upwelling significantly reduce the nutrients delivered to the sea surface from the horizontal and vertical levels. The chlorophyll concentration and primary organic carbon production by all types of phytoplankton decreased significantly. This paper proposes a model of the response mechanism of the evolution of hydroecoclimatic conditions in the NECC affected area to El Niño and La Niña events, which is conducive to further analysis of the role of ENSO cycle in local ecological effects and hydroclimatic evolution. It has important significance for understanding the impact of global climate change on the material cycle.
, Available online
Abstract:
Tidal flats maintain a complex ecosystem, while its formation is driven by multi-factor interaction, including hydrodynamics, sediment transport, and biological processes. In particular, investigating tidal flat biological processes and elucidating their biological-physical effects are current research hotspots and challenges in the field of marine science. This study focused on intertidal biofilms, constructed a two-dimensional biomorphodynamic model which coupled biofilms with hydrodynamics, sediment transport, and bed level change, to explore the role of biofilms in sediment transport and geomorphological evolution. The biomorphodynamic model was validated using literature data, indicating that the constructed model can simulate the growth pattern and interannual variation of biofilms well. Model results show that tidal creeks with biofilm attachment are more fully extended towards the landward side, showing a branching distribution when hydrodynamics are weak, and biofilms were distributed on both sides of the intertidal zone. Through quantitative analysis of tidal creek morphology, it is found that the presence of biofilms promoted an increase in the number of tidal creek and their development in the vertical direction, while limiting the increase in their width. Compared to tidal flats without the influence of biofilms, the average depth of tidal creeks increases, the total area decreases, the total length increases, the average width decreases, and the overall volume increases. The research outcome of this study deepens the understanding of the role of biofilms on tidal flat evolution and provides a scientific basis for coastal zone protection and ecological restoration projects.
Tidal flats maintain a complex ecosystem, while its formation is driven by multi-factor interaction, including hydrodynamics, sediment transport, and biological processes. In particular, investigating tidal flat biological processes and elucidating their biological-physical effects are current research hotspots and challenges in the field of marine science. This study focused on intertidal biofilms, constructed a two-dimensional biomorphodynamic model which coupled biofilms with hydrodynamics, sediment transport, and bed level change, to explore the role of biofilms in sediment transport and geomorphological evolution. The biomorphodynamic model was validated using literature data, indicating that the constructed model can simulate the growth pattern and interannual variation of biofilms well. Model results show that tidal creeks with biofilm attachment are more fully extended towards the landward side, showing a branching distribution when hydrodynamics are weak, and biofilms were distributed on both sides of the intertidal zone. Through quantitative analysis of tidal creek morphology, it is found that the presence of biofilms promoted an increase in the number of tidal creek and their development in the vertical direction, while limiting the increase in their width. Compared to tidal flats without the influence of biofilms, the average depth of tidal creeks increases, the total area decreases, the total length increases, the average width decreases, and the overall volume increases. The research outcome of this study deepens the understanding of the role of biofilms on tidal flat evolution and provides a scientific basis for coastal zone protection and ecological restoration projects.
, Available online , doi: 10.12284/hyxb2024028
Abstract:
The Chukchi Borderland served as the critical gateway for the inflow of Atlantic Water (AW, which is the most important heat storage layer in the Arctic Ocean) into the Canada Basin in the western Arctic Ocean. One of the key issues is how the AW and Pacific Winter Water (PWW) interacts in this complex topography region. The answer to this question will shed light on the important role of AW in the Arctic Ocean. In this study, based on the multi-sources’ quality controlled hydrographic data during 1999−2021, the variation of AW, PWW and the double-diffusive staircases in the Chukchi Borderland are studied in details. We identified three anomalous warm events of AW that occurred in year 2000, 2012 and 2018 with the maximum potential temperature over 1°C. The vertical averaged heat content between the PWW and AW shows a warming trend in the central and eastern region of the Chukchi Borderland. The major reason for this is the warming of PWW. The depth of PWW is more sensitive to the shifting of the Beaufort Gyre (BG) than that of the AW. The combined changes of PWW and AW lead to the variation of double-diffusive staircases, which show a regime shift from large to small thickness and to largely decayed in the Canada Basin. Our results suggest that the major mechanism for this transition is the cooling of AW along with the stronger stratification that restricts the vertical mixing for all.
The Chukchi Borderland served as the critical gateway for the inflow of Atlantic Water (AW, which is the most important heat storage layer in the Arctic Ocean) into the Canada Basin in the western Arctic Ocean. One of the key issues is how the AW and Pacific Winter Water (PWW) interacts in this complex topography region. The answer to this question will shed light on the important role of AW in the Arctic Ocean. In this study, based on the multi-sources’ quality controlled hydrographic data during 1999−2021, the variation of AW, PWW and the double-diffusive staircases in the Chukchi Borderland are studied in details. We identified three anomalous warm events of AW that occurred in year 2000, 2012 and 2018 with the maximum potential temperature over 1°C. The vertical averaged heat content between the PWW and AW shows a warming trend in the central and eastern region of the Chukchi Borderland. The major reason for this is the warming of PWW. The depth of PWW is more sensitive to the shifting of the Beaufort Gyre (BG) than that of the AW. The combined changes of PWW and AW lead to the variation of double-diffusive staircases, which show a regime shift from large to small thickness and to largely decayed in the Canada Basin. Our results suggest that the major mechanism for this transition is the cooling of AW along with the stronger stratification that restricts the vertical mixing for all.
Evaluation of benthic ecological quality status in the Yalu River estuary based on environmental DNA
, Available online , doi: 10.12284/hyxb2024058
Abstract:
Investigating the potential for application of environmental DNA to identify benthic organisms for evaluating ecological quality status collection of 17 benthic samples from the Yalu River estuary, environmental DNA and morphological identification and comparative analyses of the resulting ecological quality assessment indices (AMBI, BENTIX, Shannon-Wiener H', M-AMBI) were used, respectively. The results show: environmental DNA identification of organisms belonging to 10 class, 16 orders, 19 families, 20 genera and 22 species, morphological identification of organisms belonging to 9 class, 27 orders, 43 families, 55 genera and 57 species, with a total of 10 organisms; the two methods of identification yielded AMBI inter-index (R = 0.428, p = 0.043, y = 0.32x + 1.08), BENTIX inter-exponential (R = 0.430, p = 0.043, y = 0.28x + 3.59) significant consistency exists, while there was significant difference between the Shannon-Wiener H' indices; the two methods of identification yielded AMBI intergrade,M-AMBI intergrade higher similarity, 51.02 per cent, 44.90 per cent, respectively; the AMBI and M-AMBI grades from the two identification methods were more in line with the actual situation and evaluated the overall ecological quality status of the Yalu River estuary as good. This study demonstrates that the identification of benthic organisms based on environmental DNA to evaluate the ecological quality status has a high potential for application in marine environmental monitoring surveys.
Investigating the potential for application of environmental DNA to identify benthic organisms for evaluating ecological quality status collection of 17 benthic samples from the Yalu River estuary, environmental DNA and morphological identification and comparative analyses of the resulting ecological quality assessment indices (AMBI, BENTIX, Shannon-Wiener H', M-AMBI) were used, respectively. The results show: environmental DNA identification of organisms belonging to 10 class, 16 orders, 19 families, 20 genera and 22 species, morphological identification of organisms belonging to 9 class, 27 orders, 43 families, 55 genera and 57 species, with a total of 10 organisms; the two methods of identification yielded AMBI inter-index (R = 0.428, p = 0.043, y = 0.32x + 1.08), BENTIX inter-exponential (R = 0.430, p = 0.043, y = 0.28x + 3.59) significant consistency exists, while there was significant difference between the Shannon-Wiener H' indices; the two methods of identification yielded AMBI intergrade,M-AMBI intergrade higher similarity, 51.02 per cent, 44.90 per cent, respectively; the AMBI and M-AMBI grades from the two identification methods were more in line with the actual situation and evaluated the overall ecological quality status of the Yalu River estuary as good. This study demonstrates that the identification of benthic organisms based on environmental DNA to evaluate the ecological quality status has a high potential for application in marine environmental monitoring surveys.
, Available online
Abstract:
In this paper, a high spatial-temporal resolution sea ice concentration estimation method for the Arctic melting season is proposed, aiming to improve the overestimation of sea ice concentration in seawater by the Global Navigation Satellite System-Reflectometry (GNSS-R). The method utilizes machine learning algorithms to extract feature parameters from the Delay Doppler Maps (DDM) obtained through GNSS-R and combines them with sea surface temperature data to establish a LightGBM model. The inversion results are then subjected to correlation analysis and evaluation against reference sea ice concentration values. The model's performance is compared with the sea ice concentration product from OSI SAF, demonstrating good consistency, with correlation coefficient, mean absolute error, and root mean square error being 0.965, 0.061, and 0.090, respectively. This approach enables high-precision estimation of sea ice concentration in the Arctic marginal ice zone.
In this paper, a high spatial-temporal resolution sea ice concentration estimation method for the Arctic melting season is proposed, aiming to improve the overestimation of sea ice concentration in seawater by the Global Navigation Satellite System-Reflectometry (GNSS-R). The method utilizes machine learning algorithms to extract feature parameters from the Delay Doppler Maps (DDM) obtained through GNSS-R and combines them with sea surface temperature data to establish a LightGBM model. The inversion results are then subjected to correlation analysis and evaluation against reference sea ice concentration values. The model's performance is compared with the sea ice concentration product from OSI SAF, demonstrating good consistency, with correlation coefficient, mean absolute error, and root mean square error being 0.965, 0.061, and 0.090, respectively. This approach enables high-precision estimation of sea ice concentration in the Arctic marginal ice zone.
, Available online , doi: 10.12284/hyxb2024042
Abstract:
In order to explore the relationship between zooplankton community structure and environmental factors in Oujiang River Estuary, four voyages were conducted in March (winter), May (spring), August (summer) and November (autumn) in 2021 to investigate the zooplankton and other environmental factors such as sea temperature, salinity and chlorophyll-a in Oujiang River Estuary sea area. The results showed that 78 species of zooplankton were identified, including 16 species of larva, it belongs to 8 classes and 14 categories , with the highest number of species in summer (47 species) and the lowest number in winter (23 species). The dominant species (Y ≥ 0.02) include Calanus sinicus, Sinocalanus sinensis, Acartia pacifica, and Centropages dorsispinatus, 17 species. The average annual abundance of zooplankton was (162.95 ± 310.96) ind./m3, and the average annual biomass was (118.85 ± 62.80) mg/m3. The abundance and biomass of zooplankton were the highest in spring and the lowest in autumn. The abundance in winter was higher than that in summer, and the biomass was lower than that in summer. The average annual Shannon-Wiener diversity index (H'), Pielou evenness index (J') and Margalef richness index (D) were 1.500 ± 0.702, 0.656 ± 0.270 and 2.301 ± 1.087, respectively. Spearman correlation analysis and CCA canonical correspondence analysis showed that sea temperature, salinity, Chl a concentration and phytoplankton abundance were important environmental factors affecting the dominant abundance of zooplankton in the Oujiang River Estuary. It provides scientific reference for the study on the influence of seasonal environmental changes on zooplankton in Oujiang River Estuary, and provides basic data and theoretical basis for the sustainable development of biological resources in Oujiang River Estuary.
In order to explore the relationship between zooplankton community structure and environmental factors in Oujiang River Estuary, four voyages were conducted in March (winter), May (spring), August (summer) and November (autumn) in 2021 to investigate the zooplankton and other environmental factors such as sea temperature, salinity and chlorophyll-a in Oujiang River Estuary sea area. The results showed that 78 species of zooplankton were identified, including 16 species of larva, it belongs to 8 classes and 14 categories , with the highest number of species in summer (47 species) and the lowest number in winter (23 species). The dominant species (Y ≥ 0.02) include Calanus sinicus, Sinocalanus sinensis, Acartia pacifica, and Centropages dorsispinatus, 17 species. The average annual abundance of zooplankton was (162.95 ± 310.96) ind./m3, and the average annual biomass was (118.85 ± 62.80) mg/m3. The abundance and biomass of zooplankton were the highest in spring and the lowest in autumn. The abundance in winter was higher than that in summer, and the biomass was lower than that in summer. The average annual Shannon-Wiener diversity index (H'), Pielou evenness index (J') and Margalef richness index (D) were 1.500 ± 0.702, 0.656 ± 0.270 and 2.301 ± 1.087, respectively. Spearman correlation analysis and CCA canonical correspondence analysis showed that sea temperature, salinity, Chl a concentration and phytoplankton abundance were important environmental factors affecting the dominant abundance of zooplankton in the Oujiang River Estuary. It provides scientific reference for the study on the influence of seasonal environmental changes on zooplankton in Oujiang River Estuary, and provides basic data and theoretical basis for the sustainable development of biological resources in Oujiang River Estuary.
, Available online , doi: 10.12284/hyxb2024000
Abstract:
Beach nourishment, as a widely-adopted soft solution to coastal erosion, can effectively alleviate the beach erosion induced by the construction of artificial islands. This paper takes the nourished beaches on both sides of the wave shadow zone of an artificial island in Haikou Bay as an example. Based on the bimonthly surveys of beach profiles and shorelines since nourishment, the characteristics of beach erosion and accretion and the associated driving factors were analyzed by using Empirical Orthogonal Function (EOF) and Digital Shoreline Analysis System methods. The EOF results showed that the first two eigenvalues accounted for more than 90% of the total variance, which could reflect the main spatio-temporal changes of the beaches. The area with conspicuous changes, corresponding to the first spatial mode, was located between the outer edge of the beach berm to the mean sea level, in which there were significant differences between the nourished beaches on both sides of the wave shadow zone and the natural beach in the wave shadow zone. The temporal mode showed that the most significant changes of the nourished beaches occurred in the initial four months after nourishment, followed by mild profile changes. The second spatial mode demonstrated the impact of typhoons on the beaches, resulting in the accumulation and leveling of some low-lying sites on the beach berms in the wave shadow zone. This study found that the evolution of nourished beaches under the influence of an artificial island in Haikou Bay could be divided into two stages. The first stage was the adaptation period, during which the artificially designed beach profile adjusted to the equilibrium state for adapting to the local hydrodynamics. The equilibrium time of nourished profiles was approximately 4 months, during which beach changes were dominated by cross-shore sediment transport. The second stage was dominated by the longshore sediment transport induced by the artificial island, resulting in sediment transport from the eastern and western sides of the artificial island to the wave shadow zone. At that time, the nourished beach shoreline in Haikou Bay had not reached the equilibrium state. The beaches on both sides of the wave shadow zone would continue to retreat in the future, while the shoreline in the wave shadow zone would advance into the sea for about 690 m until it reaches the equilibrium. This study would be helpful for the analysis of the beach evolution and beach restoration of similar cases.
Beach nourishment, as a widely-adopted soft solution to coastal erosion, can effectively alleviate the beach erosion induced by the construction of artificial islands. This paper takes the nourished beaches on both sides of the wave shadow zone of an artificial island in Haikou Bay as an example. Based on the bimonthly surveys of beach profiles and shorelines since nourishment, the characteristics of beach erosion and accretion and the associated driving factors were analyzed by using Empirical Orthogonal Function (EOF) and Digital Shoreline Analysis System methods. The EOF results showed that the first two eigenvalues accounted for more than 90% of the total variance, which could reflect the main spatio-temporal changes of the beaches. The area with conspicuous changes, corresponding to the first spatial mode, was located between the outer edge of the beach berm to the mean sea level, in which there were significant differences between the nourished beaches on both sides of the wave shadow zone and the natural beach in the wave shadow zone. The temporal mode showed that the most significant changes of the nourished beaches occurred in the initial four months after nourishment, followed by mild profile changes. The second spatial mode demonstrated the impact of typhoons on the beaches, resulting in the accumulation and leveling of some low-lying sites on the beach berms in the wave shadow zone. This study found that the evolution of nourished beaches under the influence of an artificial island in Haikou Bay could be divided into two stages. The first stage was the adaptation period, during which the artificially designed beach profile adjusted to the equilibrium state for adapting to the local hydrodynamics. The equilibrium time of nourished profiles was approximately 4 months, during which beach changes were dominated by cross-shore sediment transport. The second stage was dominated by the longshore sediment transport induced by the artificial island, resulting in sediment transport from the eastern and western sides of the artificial island to the wave shadow zone. At that time, the nourished beach shoreline in Haikou Bay had not reached the equilibrium state. The beaches on both sides of the wave shadow zone would continue to retreat in the future, while the shoreline in the wave shadow zone would advance into the sea for about 690 m until it reaches the equilibrium. This study would be helpful for the analysis of the beach evolution and beach restoration of similar cases.
, Available online , doi: 10.12284/hyxb2024054
Abstract:
The deposition fluxes of 210Po, 210Bi and 210Pb in atmosphere are the basis for the application of radionuclide tracing in the ocean. In order to reveal the spatio-temporal variation of the activity of 210Po, 210Bi and 210Pb in nearshore areas and estimate their deposition fluxes into the sea, In this paper, sampling observation and analysis of two typical areas near the East China Sea in Shanghai and Xiamen in different periods are carried out.A time series study was conducted on the activity of 210Po, 210Pb and 210Bi in Shanghai and Xiamen from September 2016 to February 2017 and from September to December 2021, respectively. The residence time of particulate matter was calculated based on 210Po/210Pb and 210Bi/210Pb. Deposition fluxes of three nuclides were also estimated. This paper reported the activity of 210Po, 210Bi and 210Pb in Shanghai in autumn and winter of 2016.The activity ranges of 210Po, 210Pb and 210Bi were 0.11-1.27 mBq/m3, 0.45-1.83 mBq/m3 and 1.12-6.10 mBq/m3, respectively. In the fall of 2021, the activity ranges of 210Po, 210Bi and 210Pb in Xiamen were 0.05-0.85mBq/m3, 0.61-2.42mBq/m3 and 0.18-1.32mBq/m3, respectively.The activity of each nuclide in Shanghai was higher than that in Xiamen. The aerosol residence time (τPo-Pb) over Shanghai and Xiamen are 28-202d and 19-355d, respectively. In this paper, based on a one-dimensional simple aerosol deposition rate model, the atmospheric deposition fluxes of 210Pb, 210Bi and 210Po over Shanghai area into the East China Sea are estimated, and their variation ranges are 0.1-26.35Bq /m2/d, 0.04-7.91Bq /m2/d and 0.01-5.49 Bq /m2/d, respectively. The sedimentation fluxes of 210Po, 210Bi and 210Pb estimated based on the model are close to the actual observed values in the study area during the same period in winter within a certain range. The feasibility of estimating the deposition flux of nuclide into the sea with a simple one dimensional aerosol deposition rate model is verified.
The deposition fluxes of 210Po, 210Bi and 210Pb in atmosphere are the basis for the application of radionuclide tracing in the ocean. In order to reveal the spatio-temporal variation of the activity of 210Po, 210Bi and 210Pb in nearshore areas and estimate their deposition fluxes into the sea, In this paper, sampling observation and analysis of two typical areas near the East China Sea in Shanghai and Xiamen in different periods are carried out.A time series study was conducted on the activity of 210Po, 210Pb and 210Bi in Shanghai and Xiamen from September 2016 to February 2017 and from September to December 2021, respectively. The residence time of particulate matter was calculated based on 210Po/210Pb and 210Bi/210Pb. Deposition fluxes of three nuclides were also estimated. This paper reported the activity of 210Po, 210Bi and 210Pb in Shanghai in autumn and winter of 2016.The activity ranges of 210Po, 210Pb and 210Bi were 0.11-1.27 mBq/m3, 0.45-1.83 mBq/m3 and 1.12-6.10 mBq/m3, respectively. In the fall of 2021, the activity ranges of 210Po, 210Bi and 210Pb in Xiamen were 0.05-0.85mBq/m3, 0.61-2.42mBq/m3 and 0.18-1.32mBq/m3, respectively.The activity of each nuclide in Shanghai was higher than that in Xiamen. The aerosol residence time (τPo-Pb) over Shanghai and Xiamen are 28-202d and 19-355d, respectively. In this paper, based on a one-dimensional simple aerosol deposition rate model, the atmospheric deposition fluxes of 210Pb, 210Bi and 210Po over Shanghai area into the East China Sea are estimated, and their variation ranges are 0.1-26.35Bq /m2/d, 0.04-7.91Bq /m2/d and 0.01-5.49 Bq /m2/d, respectively. The sedimentation fluxes of 210Po, 210Bi and 210Pb estimated based on the model are close to the actual observed values in the study area during the same period in winter within a certain range. The feasibility of estimating the deposition flux of nuclide into the sea with a simple one dimensional aerosol deposition rate model is verified.
, Available online , doi: 10.12284/hyxb2024048
Abstract:
The “fairy circle” represents a unique form of spatial self-organization found within coastal salt marsh ecosystems, profoundly influencing the productivity, stability, and resilience of these wetlands. Unmanned Aerial Vehicle (UAV) imagery plays a pivotal role in precisely pinpointing the “fairy circle” locations and deciphering their temporal and spatial development trends. However, identifying “fairy circle” pixels within two-dimensional images poses a considerable technical challenge due to the subtle differences in color and shape characteristics between these pixels and their surroundings. Therefore, intelligently and accurately identify “fairy circle” pixels from two-dimensional images and form individual “fairy circle” for the identified pixels are the current technical difficulties. This paper introduces an innovative approach to extract “fairy circle” from UAV images by integrating the SAM (Segment Anything Model) visual segmentation model with random forest machine learning. This novel method accomplishes the recognition and extraction of individual “fairy circle” through a two-step process: segmentation followed by classification. Initially, we establish Dice (Sørensen-Dice coefficient) and IOU (Intersection Over Union) evaluation metrics, and optimize SAM’s pre-trained model parameters, which produces segmentation mask devoid of attribute information by fully automated image segmentation. Subsequently, we align the segmentation mask with the original image, and utilizes RGB (red, green, and blue) color channels and spatial coordinates to construct a feature index for the segmentation mask. These features undergo analysis and selection based on Out-of-Bag (OOB) error reduction and feature distribution patterns. Ultimately, the refined features are employed to train a random forest model, enabling the automatic identification and classification of “fairy circle” vegetation, common vegetation, and bare flat areas. The experimental results show that the average correct extraction rate of "fairy circle" is 96.1%, and the average wrong extraction rate is 9.5%, which provides methodological and technological support for the accurate depiction of the spatial and temporal pattern of "fairy circle" as well as the processing of coastal remote sensing images by UAVs.
The “fairy circle” represents a unique form of spatial self-organization found within coastal salt marsh ecosystems, profoundly influencing the productivity, stability, and resilience of these wetlands. Unmanned Aerial Vehicle (UAV) imagery plays a pivotal role in precisely pinpointing the “fairy circle” locations and deciphering their temporal and spatial development trends. However, identifying “fairy circle” pixels within two-dimensional images poses a considerable technical challenge due to the subtle differences in color and shape characteristics between these pixels and their surroundings. Therefore, intelligently and accurately identify “fairy circle” pixels from two-dimensional images and form individual “fairy circle” for the identified pixels are the current technical difficulties. This paper introduces an innovative approach to extract “fairy circle” from UAV images by integrating the SAM (Segment Anything Model) visual segmentation model with random forest machine learning. This novel method accomplishes the recognition and extraction of individual “fairy circle” through a two-step process: segmentation followed by classification. Initially, we establish Dice (Sørensen-Dice coefficient) and IOU (Intersection Over Union) evaluation metrics, and optimize SAM’s pre-trained model parameters, which produces segmentation mask devoid of attribute information by fully automated image segmentation. Subsequently, we align the segmentation mask with the original image, and utilizes RGB (red, green, and blue) color channels and spatial coordinates to construct a feature index for the segmentation mask. These features undergo analysis and selection based on Out-of-Bag (OOB) error reduction and feature distribution patterns. Ultimately, the refined features are employed to train a random forest model, enabling the automatic identification and classification of “fairy circle” vegetation, common vegetation, and bare flat areas. The experimental results show that the average correct extraction rate of "fairy circle" is 96.1%, and the average wrong extraction rate is 9.5%, which provides methodological and technological support for the accurate depiction of the spatial and temporal pattern of "fairy circle" as well as the processing of coastal remote sensing images by UAVs.
, Available online , doi: 10.12284/hyxb2024056
Abstract:
To clarify the composition and distribution characteristics of macrobenthic communities in Yantai Changdao Island marine ranch and evaluate the impact of marine ranching on these macrobenthos, sampling stations were set up inside and outside the marine ranch in October 2022. Surveys of macrobenthic animals and the characteristics of macrobenthic communities were analyzed. A total of 88 species of macrobenthic animals were collected and identified during this voyage. Although the number of species in the pasture and control area was similar, the dominant groups differed. In the pasture, 70 species were identified, with mollusks being the dominant group; whereas, in the control area, 69 species were identified, with annelids as the dominant group. Eight dominant species were found, including 3 mollusk species in the pasture and 6 species in the control area, comprising 2 mollusk species, 1 echinoderm species, and 3 annelid species. The average abundance and biomass of macrobenthic animals in the pasture were significantly higher than those in the control area. However, Margalef species richness index (d), Pielou evenness index (J'), and Shannon Wiener diversity index (H') values showed little difference between the pasture and the outside. The results of Cluster analysis (CLUSTER) and non-metric multidimensional scaling (NMDS) analysis indicated that relatively low similarity among each station inside and outside the marine ranch. The AMBI and m-AMBI analyses revealed that the overall pollution disturbance in the studied water area was relatively small, indicating good benthic ecological health. Combined with historical data, the analysis revealed a significant increase in species abundance and biomass of macrobenthic communities in the surveyed area. These results suggest that the development of marine pastures has a certain degree of impact on the growth and development of macrobenthic communities.
To clarify the composition and distribution characteristics of macrobenthic communities in Yantai Changdao Island marine ranch and evaluate the impact of marine ranching on these macrobenthos, sampling stations were set up inside and outside the marine ranch in October 2022. Surveys of macrobenthic animals and the characteristics of macrobenthic communities were analyzed. A total of 88 species of macrobenthic animals were collected and identified during this voyage. Although the number of species in the pasture and control area was similar, the dominant groups differed. In the pasture, 70 species were identified, with mollusks being the dominant group; whereas, in the control area, 69 species were identified, with annelids as the dominant group. Eight dominant species were found, including 3 mollusk species in the pasture and 6 species in the control area, comprising 2 mollusk species, 1 echinoderm species, and 3 annelid species. The average abundance and biomass of macrobenthic animals in the pasture were significantly higher than those in the control area. However, Margalef species richness index (d), Pielou evenness index (J'), and Shannon Wiener diversity index (H') values showed little difference between the pasture and the outside. The results of Cluster analysis (CLUSTER) and non-metric multidimensional scaling (NMDS) analysis indicated that relatively low similarity among each station inside and outside the marine ranch. The AMBI and m-AMBI analyses revealed that the overall pollution disturbance in the studied water area was relatively small, indicating good benthic ecological health. Combined with historical data, the analysis revealed a significant increase in species abundance and biomass of macrobenthic communities in the surveyed area. These results suggest that the development of marine pastures has a certain degree of impact on the growth and development of macrobenthic communities.
, Available online , doi: 10.12284/hyxb2024030
Abstract:
Coastal wetlands have important economic and ecological value. Rapid and accurate monitoring of the status of coastal wetlands is of great significance for the protection and management of coastal wetland resources. Due to factors such as the variability of the tide-level changes, similarity of vegetation spectra, and frequent cloud cover, remote sensing monitoring of coastal wetlands faced certain challenges. In this paper, we proposed a multi-technology coupled remote sensing classification method of coastal wetlands that considers tide-level changes and vegetation phenological characteristics. Based on the Google Earth Engine (GEE) platform, the Fmask (Function of mask) algorithm was first performed for cloud testing and cloud removal processing. Then, the S-G (Savitzky-Golay) filtering algorithm was used to reconstruct NDVI time series data and extract vegetation phenological characteristic parameters. In this phase, the random forest algorithm was applied for the classification of four vegetation types namely Phragmites australi (PA), Suaeda salsa (SS), Spartina alterniflora (SA), and Imperata cylindrical (IC). Finally, the Maximum Spectral Index Composite (MSIC) algorithm was used to generate composite images of the highest and lowest tide levels. The tidal flats and seawater were precisely extracted using the Otsu algorithm based on these two composite images. Combining these feature types, the refined remote sensing classification of coastal wetlands was ideally obtained. The results showed that start-of-season time, end-of-season time, length of season, base value, amplitude, and small seasonal integral were the six key vegetation phenological characteristic parameters for distinguishing different types of coastal wetland vegetation. Applying this method to classify coastal wetlands on the Yancheng coast, the overall classification accuracy was 96.50%, and the Kappa coefficient reached 0.957 1. Among the wetland vegetation, the highest user accuracy was 96.59% for SA, followed by PA and SS, and the lowest was 93.55% for IC. Compared with object-oriented methods, our method can extract the complete range of tidal flats, and the overall accuracy is improved by 10.25%, reflecting the potential application of vegetation phenological characteristics in remote sensing monitoring of dynamic changes in coastal wetlands.
Coastal wetlands have important economic and ecological value. Rapid and accurate monitoring of the status of coastal wetlands is of great significance for the protection and management of coastal wetland resources. Due to factors such as the variability of the tide-level changes, similarity of vegetation spectra, and frequent cloud cover, remote sensing monitoring of coastal wetlands faced certain challenges. In this paper, we proposed a multi-technology coupled remote sensing classification method of coastal wetlands that considers tide-level changes and vegetation phenological characteristics. Based on the Google Earth Engine (GEE) platform, the Fmask (Function of mask) algorithm was first performed for cloud testing and cloud removal processing. Then, the S-G (Savitzky-Golay) filtering algorithm was used to reconstruct NDVI time series data and extract vegetation phenological characteristic parameters. In this phase, the random forest algorithm was applied for the classification of four vegetation types namely Phragmites australi (PA), Suaeda salsa (SS), Spartina alterniflora (SA), and Imperata cylindrical (IC). Finally, the Maximum Spectral Index Composite (MSIC) algorithm was used to generate composite images of the highest and lowest tide levels. The tidal flats and seawater were precisely extracted using the Otsu algorithm based on these two composite images. Combining these feature types, the refined remote sensing classification of coastal wetlands was ideally obtained. The results showed that start-of-season time, end-of-season time, length of season, base value, amplitude, and small seasonal integral were the six key vegetation phenological characteristic parameters for distinguishing different types of coastal wetland vegetation. Applying this method to classify coastal wetlands on the Yancheng coast, the overall classification accuracy was 96.50%, and the Kappa coefficient reached 0.957 1. Among the wetland vegetation, the highest user accuracy was 96.59% for SA, followed by PA and SS, and the lowest was 93.55% for IC. Compared with object-oriented methods, our method can extract the complete range of tidal flats, and the overall accuracy is improved by 10.25%, reflecting the potential application of vegetation phenological characteristics in remote sensing monitoring of dynamic changes in coastal wetlands.
, Available online
Abstract:
As a national key construction sea area, the trend of offshore wind power construction in the Jiangsu sea area towards the open sea is the main trend of future development. The open sea areas have more surge components, and the wave spectrum often appears in the form of bimodal spectrum. Therefore, the wave characteristics of bimodal spectrum waves need further in-depth research to provide reference basis for offshore construction. Based on the observation data of the buoy station throughout 2018, 1223 bimodal spectral data were obtained through outlier testing and bimodal spectral identification. The bimodal spectral characteristics of waves in the Jiangsu sea area were studied, and different typical bimodal spectral types were compared. The fitting of the measured bimodal spectra was carried out, and the corrected spectral width parameters were proposed. The dependency relationship between the correction coefficient, peak rise factor, and spectral width parameters was explored, and the bimodal spectral fitting expression was obtained. The results indicate that the Ochi Hubble spectrum proposed based on the North Atlantic sea area and the Torsethaugen spectrum proposed based on the Norwegian sea area are not applicable to the bimodal spectrum type in the Jiangsu sea area. The bimodal JONSWAP fitting spectrum proposed in this paper has adaptability and can scientifically and reasonably describe the bimodal spectrum in the Jiangsu sea area, and is widely applied to different wind and terrain conditions in the sea area.
As a national key construction sea area, the trend of offshore wind power construction in the Jiangsu sea area towards the open sea is the main trend of future development. The open sea areas have more surge components, and the wave spectrum often appears in the form of bimodal spectrum. Therefore, the wave characteristics of bimodal spectrum waves need further in-depth research to provide reference basis for offshore construction. Based on the observation data of the buoy station throughout 2018, 1223 bimodal spectral data were obtained through outlier testing and bimodal spectral identification. The bimodal spectral characteristics of waves in the Jiangsu sea area were studied, and different typical bimodal spectral types were compared. The fitting of the measured bimodal spectra was carried out, and the corrected spectral width parameters were proposed. The dependency relationship between the correction coefficient, peak rise factor, and spectral width parameters was explored, and the bimodal spectral fitting expression was obtained. The results indicate that the Ochi Hubble spectrum proposed based on the North Atlantic sea area and the Torsethaugen spectrum proposed based on the Norwegian sea area are not applicable to the bimodal spectrum type in the Jiangsu sea area. The bimodal JONSWAP fitting spectrum proposed in this paper has adaptability and can scientifically and reasonably describe the bimodal spectrum in the Jiangsu sea area, and is widely applied to different wind and terrain conditions in the sea area.
, Available online
Abstract:
Based on the non-hydrostatic model SWASH, a numerical wave flume was established to systematically investigate the hydrodynamic characteristics of the interaction between waves, mangroves, and vertical sea dikes through a comparative experiment with and without mangroves. The study analyzed the influence of factors such as wave steepness, relative water depth, Ursell number, mangrove length, density, and characteristic diameter on the wave height in front of the sea dike and the maximum wave pressure on the windward side of the sea dike. The results indicate that in the absence of mangroves, the Goda formula cannot accurately estimate the impact load on the vertical sea dike. In a numerical experiment with a model scale of 1:10, a 2-meter wide mangroves in front of the dike was observed to reduce wave height by 6% to 45% and wave pressure by 11% to 74%. However, in conditions with relatively large wave heights and smaller characteristic parameters of the mangrove, an increase in the wave height in front of the dike by approximately 4% to 26% was noted. In the hydraulic conditions considered in this study, the maximum wave pressure decreased by 58% to 93% with a decrease in wave steepness, by 42% to 72% with an increase in relative water depth, and by 87% to 96% with a decrease in the Ursell number. The attenuation rates of wave height and wave pressure in front of the dike non-linearly increased with the increase in the width, density, and characteristic diameter of the mangroves. These findings provide a scientific basis for a deeper understanding of the wave-damping effects of mangroves, as well as for the design and planning of coastal protection projects combining mangrove ecosystems with sea dikes.
Based on the non-hydrostatic model SWASH, a numerical wave flume was established to systematically investigate the hydrodynamic characteristics of the interaction between waves, mangroves, and vertical sea dikes through a comparative experiment with and without mangroves. The study analyzed the influence of factors such as wave steepness, relative water depth, Ursell number, mangrove length, density, and characteristic diameter on the wave height in front of the sea dike and the maximum wave pressure on the windward side of the sea dike. The results indicate that in the absence of mangroves, the Goda formula cannot accurately estimate the impact load on the vertical sea dike. In a numerical experiment with a model scale of 1:10, a 2-meter wide mangroves in front of the dike was observed to reduce wave height by 6% to 45% and wave pressure by 11% to 74%. However, in conditions with relatively large wave heights and smaller characteristic parameters of the mangrove, an increase in the wave height in front of the dike by approximately 4% to 26% was noted. In the hydraulic conditions considered in this study, the maximum wave pressure decreased by 58% to 93% with a decrease in wave steepness, by 42% to 72% with an increase in relative water depth, and by 87% to 96% with a decrease in the Ursell number. The attenuation rates of wave height and wave pressure in front of the dike non-linearly increased with the increase in the width, density, and characteristic diameter of the mangroves. These findings provide a scientific basis for a deeper understanding of the wave-damping effects of mangroves, as well as for the design and planning of coastal protection projects combining mangrove ecosystems with sea dikes.
, Available online
Abstract:
This study focuses on the physical process of a sea fog event during Typhoon Lekima in the Northern Yellow Sea by using observation data, reanalysis data and backward trajectory model. The analysis indicates that the typhoon circulation was the decisive factor determining whether fog formed offshore and developed inland. The warm and humid southerlies from the south Yellow Sea condensed into fog on the colder sea surface besides the typhoon center, which not only provided sufficient moisture for the formation and development of the sea fog but also formed a significant inversion layer over the fog area with the downdraft in the center of the typhoon. The "stable up and turbulent down" structure in the atmospheric boundary layer improved the development of sea fog on the coast and inland area. However, the horizontal wind steering and the strengthening wind speed behind the typhoon strengthened the wind shear in the atmospheric boundary layer, resulting in the enhanced turbulent mixing and the decrease of the stability in the bottom atmospheric boundary layer, which was the main cause of the fog dissipation.
This study focuses on the physical process of a sea fog event during Typhoon Lekima in the Northern Yellow Sea by using observation data, reanalysis data and backward trajectory model. The analysis indicates that the typhoon circulation was the decisive factor determining whether fog formed offshore and developed inland. The warm and humid southerlies from the south Yellow Sea condensed into fog on the colder sea surface besides the typhoon center, which not only provided sufficient moisture for the formation and development of the sea fog but also formed a significant inversion layer over the fog area with the downdraft in the center of the typhoon. The "stable up and turbulent down" structure in the atmospheric boundary layer improved the development of sea fog on the coast and inland area. However, the horizontal wind steering and the strengthening wind speed behind the typhoon strengthened the wind shear in the atmospheric boundary layer, resulting in the enhanced turbulent mixing and the decrease of the stability in the bottom atmospheric boundary layer, which was the main cause of the fog dissipation.
, Available online
Abstract:
The possibility of the Indonesian submarine wreck on 20 April 2021 was analyzed based on satellite remote sensing observation and numerical simulation. The results indicate that large-amplitude oceanic internal waves, estimated to be approximately 50 m using satellite images, originate from the Lombok Strait. They are widely distributed to the north of the Bali Island and are suggested to cause an abrupt sinking of the Indonesian submarine.
The possibility of the Indonesian submarine wreck on 20 April 2021 was analyzed based on satellite remote sensing observation and numerical simulation. The results indicate that large-amplitude oceanic internal waves, estimated to be approximately 50 m using satellite images, originate from the Lombok Strait. They are widely distributed to the north of the Bali Island and are suggested to cause an abrupt sinking of the Indonesian submarine.
, Available online
Abstract:
Abstract：The potential fish production was controlled largely by ocean primary production (OPP) and there were a lot of research findings of estimating fish production by using OPP in China. The relationships between the biomass of fishery stock and OPP were often complicated by the varieties of trophic control in the ecosystem. In this paper, we examined the relationship between biomass of chub mackerel (Scomber japonicus) and net primary production (NPP) and discussed mechanism of trophic control in the ecosystem of chub mackerel fishing ground in south East China Sea by using catch and effort data from the large purse sense of China fishery and NPP derived from remote sensing. The results showed there was a significant non-linear relationship between NPP and standardized CPUE (Catch Per Unit Effort) (P<0.05) instead of the linear trend. The non-linear relationship could be described by a reversed parabolic curve, which meant the biomass of chub mackerel increased with NPP and then decreased when the NPP exceeded a point. The results implied there were other trophic controls in addition to bottom-up control occurred in the ecosystem in south East China Sea. We speculated the change of abundance of the key species at intermediate trophic levels or/and interspecific competitions contribute to the relationship.
Abstract：The potential fish production was controlled largely by ocean primary production (OPP) and there were a lot of research findings of estimating fish production by using OPP in China. The relationships between the biomass of fishery stock and OPP were often complicated by the varieties of trophic control in the ecosystem. In this paper, we examined the relationship between biomass of chub mackerel (Scomber japonicus) and net primary production (NPP) and discussed mechanism of trophic control in the ecosystem of chub mackerel fishing ground in south East China Sea by using catch and effort data from the large purse sense of China fishery and NPP derived from remote sensing. The results showed there was a significant non-linear relationship between NPP and standardized CPUE (Catch Per Unit Effort) (P<0.05) instead of the linear trend. The non-linear relationship could be described by a reversed parabolic curve, which meant the biomass of chub mackerel increased with NPP and then decreased when the NPP exceeded a point. The results implied there were other trophic controls in addition to bottom-up control occurred in the ecosystem in south East China Sea. We speculated the change of abundance of the key species at intermediate trophic levels or/and interspecific competitions contribute to the relationship.
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