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In recent decades, the beaches on both sides of the Jiehe River (hereinafter referred to as Jiehe Beach) in the northeastern part of Laizhou Bay have suffered severe erosion against the backdrop of reduced riverine sediment input to the sea. Additionally, the construction of coastal engineering projects such as Yulong Island (a large artificial offshore island) has made the evolution of the Jiehe Beach shoreline exceptionally complex. This paper utilizes 1,186 satellite images from 1984 to 2024, employing a transect-focused method and sub-pixel shoreline recognition technology to study the evolution of the Jiehe Beach shoreline and assess the impacts of river sediment discharge and coastal engineering. The results show that the early evolution (1984−2004) of Jiehe Beach was primarily controlled by the closure and opening of the Jiehe River estuary, the alongshore movement of sand spits, and the onshore movement of sandbars, with overall erosion occurring. The later evolution (2004−2024) of Jiehe Beach was mainly influenced by the construction of coastal engineering projects such as Yulong Island, with overall accretion occurring. In today's era of intensifying coastal development, the rational layout of coastal engineering is expected to mitigate beach erosion.
In recent decades, the beaches on both sides of the Jiehe River (hereinafter referred to as Jiehe Beach) in the northeastern part of Laizhou Bay have suffered severe erosion against the backdrop of reduced riverine sediment input to the sea. Additionally, the construction of coastal engineering projects such as Yulong Island (a large artificial offshore island) has made the evolution of the Jiehe Beach shoreline exceptionally complex. This paper utilizes 1,186 satellite images from 1984 to 2024, employing a transect-focused method and sub-pixel shoreline recognition technology to study the evolution of the Jiehe Beach shoreline and assess the impacts of river sediment discharge and coastal engineering. The results show that the early evolution (1984−2004) of Jiehe Beach was primarily controlled by the closure and opening of the Jiehe River estuary, the alongshore movement of sand spits, and the onshore movement of sandbars, with overall erosion occurring. The later evolution (2004−2024) of Jiehe Beach was mainly influenced by the construction of coastal engineering projects such as Yulong Island, with overall accretion occurring. In today's era of intensifying coastal development, the rational layout of coastal engineering is expected to mitigate beach erosion.
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Sediment transport is a fundamental issue in the study of coastal and estuarine environments, holding significant scientific importance and practical value for the evolution of estuarine geomorphology, ecological environment, and engineering construction. This paper takes the estuary of the Moyang River as an example, based on the sea current, wave and suspended sediment concentration data measured by ship and bottom tripod, analyzes the alongshore and cross-shore transport trends of suspended sediment on the fixed cross-section of the Moyang River estuary, and calculates the sediment transport flux. It explores the sediment transport mechanisms and patterns in wave-tidal estuaries, with the main findings including: (1) During the flood season at the river mouth, the sediment transport is mainly controlled by the runoff, with the sediment transport rate increasing as the flow rate increases. The alongshore and cross-shore sediment transport reaches the maximum value during the neap tide with the largest flow, which are 111.9 g/m²/s and 269.5 g/m²/s respectively. At the mouth bar in the flood season, the sediment transport is jointly controlled by waves and tides. The alongshore sediment transport is consistently westward along the coast during both spring and neap tides, while the cross-shore sediment transport is dominated by the ebb tide during the spring tide with an offshore transport of 4.0 g/m²/s, and by waves during the neap tide with an onshore transport of 19.0 g/m²/s.(2) During the dry season, the mouth bar is primarily influenced by tidal currents and wave action. Sediment transport along the vertical shore predominantly occurs due to falling tidal currents moving seaward, while coastal transport is governed by wave energy, resulting in an eastward movement under the influence of wave-generated coastal currents. On the eastern side of the mouth bar during this season, tidal currents and waves also play a significant role; vertical shore transport is mainly driven by rising tides during spring tide periods before transitioning to offshore transport as tidal forces diminish. Coastal transport remains affected by wave-induced coastal currents and continues its eastward trajectory. (3) During the flood season observation period, the offshore transport at the river mouth is significant, and the flow direction of each water layer is consistent vertically. During the neap tide, there is a differentiation in the flow direction of the water layers, with the surface layer transporting offshore and the bottom layer onshore. At the mouth bar, the flow direction of each water layer is relatively consistent vertically during both spring and neap tides. Still, after tidal averaging, the spring tide shows offshore transport in all water layers, while the neap tide shows onshore transport in all water layers. During the neap tide, the influence of waves is evident, with the onshore transport ratio reaching 79%. (4) Under the influence of runoff and tidal current, the mouth of Moyang River estuary mainly carries sediment to the sea. The most significant factors affecting sediment transport at the mouth bar are the seaward tidal currents and the alongshore and cross-shore sediment movements driven by waves.
Sediment transport is a fundamental issue in the study of coastal and estuarine environments, holding significant scientific importance and practical value for the evolution of estuarine geomorphology, ecological environment, and engineering construction. This paper takes the estuary of the Moyang River as an example, based on the sea current, wave and suspended sediment concentration data measured by ship and bottom tripod, analyzes the alongshore and cross-shore transport trends of suspended sediment on the fixed cross-section of the Moyang River estuary, and calculates the sediment transport flux. It explores the sediment transport mechanisms and patterns in wave-tidal estuaries, with the main findings including: (1) During the flood season at the river mouth, the sediment transport is mainly controlled by the runoff, with the sediment transport rate increasing as the flow rate increases. The alongshore and cross-shore sediment transport reaches the maximum value during the neap tide with the largest flow, which are 111.9 g/m²/s and 269.5 g/m²/s respectively. At the mouth bar in the flood season, the sediment transport is jointly controlled by waves and tides. The alongshore sediment transport is consistently westward along the coast during both spring and neap tides, while the cross-shore sediment transport is dominated by the ebb tide during the spring tide with an offshore transport of 4.0 g/m²/s, and by waves during the neap tide with an onshore transport of 19.0 g/m²/s.(2) During the dry season, the mouth bar is primarily influenced by tidal currents and wave action. Sediment transport along the vertical shore predominantly occurs due to falling tidal currents moving seaward, while coastal transport is governed by wave energy, resulting in an eastward movement under the influence of wave-generated coastal currents. On the eastern side of the mouth bar during this season, tidal currents and waves also play a significant role; vertical shore transport is mainly driven by rising tides during spring tide periods before transitioning to offshore transport as tidal forces diminish. Coastal transport remains affected by wave-induced coastal currents and continues its eastward trajectory. (3) During the flood season observation period, the offshore transport at the river mouth is significant, and the flow direction of each water layer is consistent vertically. During the neap tide, there is a differentiation in the flow direction of the water layers, with the surface layer transporting offshore and the bottom layer onshore. At the mouth bar, the flow direction of each water layer is relatively consistent vertically during both spring and neap tides. Still, after tidal averaging, the spring tide shows offshore transport in all water layers, while the neap tide shows onshore transport in all water layers. During the neap tide, the influence of waves is evident, with the onshore transport ratio reaching 79%. (4) Under the influence of runoff and tidal current, the mouth of Moyang River estuary mainly carries sediment to the sea. The most significant factors affecting sediment transport at the mouth bar are the seaward tidal currents and the alongshore and cross-shore sediment movements driven by waves.
, Available online ,
doi: 10.12284/hyxb0000-00
Abstract:
Short-term precipitation nowcasting is a critical task in both meteorology and hydrology. However, current deep learning methods often yield ambiguous prediction results and exhibit significant cumulative errors. To address the limitations associated with these predictive methods, particularly the challenges of cumulative error and lack of clarity in prediction sequences, we propose a novel approach based on a Multi-scale Attention Encoding-Dynamic Decoding Network (MAEDDN) for short-term precipitation nowcasting. This method leverages the learning of spatiotemporal features from input data to accurately predict future precipitation scenarios. Within the encoding process, convolutional blocks with spatial and channel attention are utilized for encoding, and a multi-scale fusion module is introduced to address the challenge of capturing both small-scale and large-scale information in precipitation distribution simultaneously. In the short-term precipitation processes to address the generation and dissipation. In the decoding process, a dynamic decoding network is proposed to flexibly select the decoding process based on the learned intensity distribution and change trends from the past input data Experiments are conducted by using the precipitation data from the open-source SEVIR dataset, and comparisons are made with the best methods reported so far. The experimental results reveal that: (1) MAEDDN enhances the forecasting capability in areas with high-intensity precipitation, and (2) MAEDDN outperforms other models in terms of the resolution of predicted image sequences. The constructed multi-scale attention encoding captures the complex relationships in meteorological data more effectively, while the dynamic decoding adapts the decoding process based on different scenarios, resulting in more accurate prediction outcomes.
Short-term precipitation nowcasting is a critical task in both meteorology and hydrology. However, current deep learning methods often yield ambiguous prediction results and exhibit significant cumulative errors. To address the limitations associated with these predictive methods, particularly the challenges of cumulative error and lack of clarity in prediction sequences, we propose a novel approach based on a Multi-scale Attention Encoding-Dynamic Decoding Network (MAEDDN) for short-term precipitation nowcasting. This method leverages the learning of spatiotemporal features from input data to accurately predict future precipitation scenarios. Within the encoding process, convolutional blocks with spatial and channel attention are utilized for encoding, and a multi-scale fusion module is introduced to address the challenge of capturing both small-scale and large-scale information in precipitation distribution simultaneously. In the short-term precipitation processes to address the generation and dissipation. In the decoding process, a dynamic decoding network is proposed to flexibly select the decoding process based on the learned intensity distribution and change trends from the past input data Experiments are conducted by using the precipitation data from the open-source SEVIR dataset, and comparisons are made with the best methods reported so far. The experimental results reveal that: (1) MAEDDN enhances the forecasting capability in areas with high-intensity precipitation, and (2) MAEDDN outperforms other models in terms of the resolution of predicted image sequences. The constructed multi-scale attention encoding captures the complex relationships in meteorological data more effectively, while the dynamic decoding adapts the decoding process based on different scenarios, resulting in more accurate prediction outcomes.
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Abstract:
In recent decades, a newly formed sand bar has developed at the entrance to the North Branch of the Yangtze Estuary, gradually accumulating sediment and showing signs of blocking the entrance to the North Branch. Understanding the hydrodynamics and sediment transport in the North Branch after the formation of the Xinjiangxin Shoal can help to further identify the trend of channel evolution. Based on the synchronised water-sediment observation data from several stations along the North Branch during flood and dry season in January and August 2023, the analysis shows that: (1) The water dynamics in the flood season is stronger than that in the dry season, the water dynamics in the North Branch is stronger than that in the branch point. In the dry season, the water dynamics in the lower part is strong, and that in the middle and upper part is weak. The situation is reversed in the flood saeson. (2) The suspended sediment concentration near the Xinjiangxin Shoal is low, that in the North Branch is high. The suspended sediment concentration along the river gradually increases and then decreases spatially. The suspended sediment concentration in the flood season is significantly greater than that in the dry season. (3) The sediment transport in the North Branch is greater than that near the Xinjiangxin Shoal, and the exchange intensity between the Xinjiangxin Shoal and the surrounding waters is small. (4) With the influence of human activities, the narrow and shallow North Branch intensified the sedimentation and development of the Xinjiangxin Shoal, and the North Branch with high turbidity provided rich material sources for the development of the Xinjiangxin Shoal, and the phase difference of the upflowing tide to the branch point of the North Branch and South Branch provided dynamic conditions for the sedimentation of the Xinjiangxin Shoal, explaining the sediment source and dynamic mechanism of the Xinjiangxin Shoal. The understanding of the hydrodynamics and sediment transport can provide the basis for the treatment of the North Branch.
In recent decades, a newly formed sand bar has developed at the entrance to the North Branch of the Yangtze Estuary, gradually accumulating sediment and showing signs of blocking the entrance to the North Branch. Understanding the hydrodynamics and sediment transport in the North Branch after the formation of the Xinjiangxin Shoal can help to further identify the trend of channel evolution. Based on the synchronised water-sediment observation data from several stations along the North Branch during flood and dry season in January and August 2023, the analysis shows that: (1) The water dynamics in the flood season is stronger than that in the dry season, the water dynamics in the North Branch is stronger than that in the branch point. In the dry season, the water dynamics in the lower part is strong, and that in the middle and upper part is weak. The situation is reversed in the flood saeson. (2) The suspended sediment concentration near the Xinjiangxin Shoal is low, that in the North Branch is high. The suspended sediment concentration along the river gradually increases and then decreases spatially. The suspended sediment concentration in the flood season is significantly greater than that in the dry season. (3) The sediment transport in the North Branch is greater than that near the Xinjiangxin Shoal, and the exchange intensity between the Xinjiangxin Shoal and the surrounding waters is small. (4) With the influence of human activities, the narrow and shallow North Branch intensified the sedimentation and development of the Xinjiangxin Shoal, and the North Branch with high turbidity provided rich material sources for the development of the Xinjiangxin Shoal, and the phase difference of the upflowing tide to the branch point of the North Branch and South Branch provided dynamic conditions for the sedimentation of the Xinjiangxin Shoal, explaining the sediment source and dynamic mechanism of the Xinjiangxin Shoal. The understanding of the hydrodynamics and sediment transport can provide the basis for the treatment of the North Branch.
, Available online ,
doi: 10.12284/hyxb2024000
Abstract:
In real ocean environments, natural reefs typically exhibit complex topography, with reef platforms presenting non-uniform characteristics. Previous extensive research has mainly focused on simplified stepped reef models and has not conducted in-depth studies on the impact of non-uniform reef platforms on the propagation and evolution characteristics of waves. To address the shortcomings of previous research, this paper conducted physical model experiments to systematically study the propagation and evolution characteristics of tsunami-like waves over complex reef platforms. Previous studies did not consider the impact of the non-uniformity of reef platform topography on solitary waves, therefore, this paper also analyzed the effects of incident wave height and reef platform water depth. To investigate the impact of non-uniform reef platform geometric characteristics on the propagation and evolution of tsunami-like waves and the load characteristics of sea walls under different incident wave conditions, this paper further carried out a series of high-resolution numerical calculations. First, physical experiments were used to verify the accuracy of the numerical simulation method, and then numerical calculations were used to study the effects of two wave parameters, incident wave height and reef platform submergence depth, as well as three complex reef topography factors: the height of the second reef platform, the position of the reef platform steps, and the slope of the reef front slope on the maximum wave height along the path, reflection coefficient, maximum run-up height, distribution of the maximum impact pressure on the sea wall, and the variation of the maximum total force and total moment on the sea wall. The research results indicate that the reflection coefficient of solitary waves decreases with increasing incident wave height and increases with increasing reef platform water depth. The maximum run-up height increases with increasing incident wave height and decreases with increasing cotα of the reef front slope. The maximum total force and maximum total moment on the sea wall increase with increasing incident wave height and reef platform water depth, and decrease with increasing height of the second reef platform. The position of the maximum impact pressure on the sea wall rises with increasing incident wave height, increasing reef platform water depth, and decreasing distance between the reef platform steps and the sea wall. The research results can provide a reference for further protecting coastal facilities from the impact of extreme marine environments.
In real ocean environments, natural reefs typically exhibit complex topography, with reef platforms presenting non-uniform characteristics. Previous extensive research has mainly focused on simplified stepped reef models and has not conducted in-depth studies on the impact of non-uniform reef platforms on the propagation and evolution characteristics of waves. To address the shortcomings of previous research, this paper conducted physical model experiments to systematically study the propagation and evolution characteristics of tsunami-like waves over complex reef platforms. Previous studies did not consider the impact of the non-uniformity of reef platform topography on solitary waves, therefore, this paper also analyzed the effects of incident wave height and reef platform water depth. To investigate the impact of non-uniform reef platform geometric characteristics on the propagation and evolution of tsunami-like waves and the load characteristics of sea walls under different incident wave conditions, this paper further carried out a series of high-resolution numerical calculations. First, physical experiments were used to verify the accuracy of the numerical simulation method, and then numerical calculations were used to study the effects of two wave parameters, incident wave height and reef platform submergence depth, as well as three complex reef topography factors: the height of the second reef platform, the position of the reef platform steps, and the slope of the reef front slope on the maximum wave height along the path, reflection coefficient, maximum run-up height, distribution of the maximum impact pressure on the sea wall, and the variation of the maximum total force and total moment on the sea wall. The research results indicate that the reflection coefficient of solitary waves decreases with increasing incident wave height and increases with increasing reef platform water depth. The maximum run-up height increases with increasing incident wave height and decreases with increasing cotα of the reef front slope. The maximum total force and maximum total moment on the sea wall increase with increasing incident wave height and reef platform water depth, and decrease with increasing height of the second reef platform. The position of the maximum impact pressure on the sea wall rises with increasing incident wave height, increasing reef platform water depth, and decreasing distance between the reef platform steps and the sea wall. The research results can provide a reference for further protecting coastal facilities from the impact of extreme marine environments.
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Abstract:
Abstrart: The streamline construction and placement of the marine flow field is of great significance for recognizing and understanding the marine flow field. In the process of streamline drawing, the selection of integration step is very important, which can directly affect the effect of streamline placement. The fixed step size algorithm is often not used because it cannot adapt to the changing curvature. The previous adaptive step size streamline algorithm has the problems of low degree of freedom and poor multi-scale applicability. In view of the above problems, this paper introduces information entropy into the step size calculation for the first time, and proposes an adaptive step size algorithm of marine streamline controlled by information entropy. Firstly, the entropy field is obtained by calculating the information entropy of the flow field, and then the flow field is divided into high entropy region and low entropy region according to the entropy value, and each integration point is given a new step size, so that the flow field can adaptively adjust the step size according to the intensity of change, that is, the step size of the high entropy region (the region with sharp change) is smaller, and the step size of the low entropy region (the region with gentle change) is larger. The experimental results show that the proposed algorithm can significantly increase the number of integration points and streamlines in the rapidly changing region, better draw the details of the streamline at the feature, and reduce the number of integration points and streamlines in the unimportant region without affecting the placement effect to improve the computational efficiency. Compared with the previous adaptive step size algorithm, the proposed algorithm significantly improves the degree of freedom of step size adjustment and the scale applicability, and can be applied to different scales of marine flow field.
Abstrart: The streamline construction and placement of the marine flow field is of great significance for recognizing and understanding the marine flow field. In the process of streamline drawing, the selection of integration step is very important, which can directly affect the effect of streamline placement. The fixed step size algorithm is often not used because it cannot adapt to the changing curvature. The previous adaptive step size streamline algorithm has the problems of low degree of freedom and poor multi-scale applicability. In view of the above problems, this paper introduces information entropy into the step size calculation for the first time, and proposes an adaptive step size algorithm of marine streamline controlled by information entropy. Firstly, the entropy field is obtained by calculating the information entropy of the flow field, and then the flow field is divided into high entropy region and low entropy region according to the entropy value, and each integration point is given a new step size, so that the flow field can adaptively adjust the step size according to the intensity of change, that is, the step size of the high entropy region (the region with sharp change) is smaller, and the step size of the low entropy region (the region with gentle change) is larger. The experimental results show that the proposed algorithm can significantly increase the number of integration points and streamlines in the rapidly changing region, better draw the details of the streamline at the feature, and reduce the number of integration points and streamlines in the unimportant region without affecting the placement effect to improve the computational efficiency. Compared with the previous adaptive step size algorithm, the proposed algorithm significantly improves the degree of freedom of step size adjustment and the scale applicability, and can be applied to different scales of marine flow field.
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Abstract:
In engineering practice, the Morison equation is commonly used to calculate wave loads on slender structures. Traditionally, the Morison equation for wave force calculation is often simplified, assuming the pile as a rigid body and neglecting the elastic deformation of the pile. By employing the Radial Basis Function (RBF), a mesh-free method, this study simultaneously solves the Morison equation, which considers pile elastic deformation, and the dynamic balance equation. This approach obtains the wave force and dynamic response of a single pile under wave load, and compares the results with those from standard methods and previous literature to validate its accuracy. Applying this method to actual engineering cases reveals the dynamic response of the working platform under the most unfavorable conditions. The RBF method is computationally straightforward and easy to master, making it suitable for practical engineering applications and providing a new direction for the calculation of offshore structures in the future.
In engineering practice, the Morison equation is commonly used to calculate wave loads on slender structures. Traditionally, the Morison equation for wave force calculation is often simplified, assuming the pile as a rigid body and neglecting the elastic deformation of the pile. By employing the Radial Basis Function (RBF), a mesh-free method, this study simultaneously solves the Morison equation, which considers pile elastic deformation, and the dynamic balance equation. This approach obtains the wave force and dynamic response of a single pile under wave load, and compares the results with those from standard methods and previous literature to validate its accuracy. Applying this method to actual engineering cases reveals the dynamic response of the working platform under the most unfavorable conditions. The RBF method is computationally straightforward and easy to master, making it suitable for practical engineering applications and providing a new direction for the calculation of offshore structures in the future.
, Available online ,
doi: 10.12284/hyxb2024105
Abstract:
The real-time changes of the internal water structure accompanied by the evolution of eddies have always been one of the important influencing factors to further study the ecological effects of mesoscale eddies. Based on satellite altimeter and Argo profile data, the gradient-dependent optimal interpolation method is used to construct the real-time internal structures of eddies. The reliability and effectiveness of this method in constructing the real-time structures of eddies are systematically evaluated through comparison with satellite observation, in-situ data and numerical simulation data. The results show that the orders of magnitude for the reconstructed velocity of three eddies are consistent with satellite altimetry. Compared with the in-situ data of the ADCP (Acoustic Doppler Current Profiler, ADCP), it is found that the locations of the eddy centers are coincident with the velocity turning position of the ADCP observed sections. The fluctuation shapes and amplitudes of the isodensity lines of the three eddies are consistent with the XCTD (Expendable Conductivity-Temperature-Depth, XCTD) observations. In addition, the eddy center and mean radius of the numerical output are basically consistent with the constructed ones. Therefore, the gradient-dependent OI was a hopeful technique for representing the real-time internal features during eddy evolution.
The real-time changes of the internal water structure accompanied by the evolution of eddies have always been one of the important influencing factors to further study the ecological effects of mesoscale eddies. Based on satellite altimeter and Argo profile data, the gradient-dependent optimal interpolation method is used to construct the real-time internal structures of eddies. The reliability and effectiveness of this method in constructing the real-time structures of eddies are systematically evaluated through comparison with satellite observation, in-situ data and numerical simulation data. The results show that the orders of magnitude for the reconstructed velocity of three eddies are consistent with satellite altimetry. Compared with the in-situ data of the ADCP (Acoustic Doppler Current Profiler, ADCP), it is found that the locations of the eddy centers are coincident with the velocity turning position of the ADCP observed sections. The fluctuation shapes and amplitudes of the isodensity lines of the three eddies are consistent with the XCTD (Expendable Conductivity-Temperature-Depth, XCTD) observations. In addition, the eddy center and mean radius of the numerical output are basically consistent with the constructed ones. Therefore, the gradient-dependent OI was a hopeful technique for representing the real-time internal features during eddy evolution.
, Available online ,
doi: 10.12284/hyxb2024109
Abstract:
A method for the fast calculation of steadily progressing periodic waves by using parameterized expressions is presented. The free surface elevation of steady periodic water waves is approximated by ABR triangular series, and the nonlinear parameter in ABR series is obtained by a numerical calculation of the free surface boundary conditions. The advantage of using ABR series is that it is simple in form and contains only one parameter, so it is convenient to study the relationship between this parameter and wave parameters, and then estimate the wave free surface elevation. For conditions of different wave theories applying (Stokes wave theory and cnoidal wave theory), the results calculated by the new method are compared with the analytical solutions of Stokes wave theory, cnoidal wave theory, and the numerical solutions given by the Fourier method. In addition, the expressions of the nonlinear parameter in the ABR series determined by the wave steepness (in deep water) or the Ursell number (in non-deep water) are given in order to efficiently predict free surface elevations. Finally, the method of calculating time averaged sand transport rates related to wave nonlinearity by using free surface elevation is given for practical engineering applications.
A method for the fast calculation of steadily progressing periodic waves by using parameterized expressions is presented. The free surface elevation of steady periodic water waves is approximated by ABR triangular series, and the nonlinear parameter in ABR series is obtained by a numerical calculation of the free surface boundary conditions. The advantage of using ABR series is that it is simple in form and contains only one parameter, so it is convenient to study the relationship between this parameter and wave parameters, and then estimate the wave free surface elevation. For conditions of different wave theories applying (Stokes wave theory and cnoidal wave theory), the results calculated by the new method are compared with the analytical solutions of Stokes wave theory, cnoidal wave theory, and the numerical solutions given by the Fourier method. In addition, the expressions of the nonlinear parameter in the ABR series determined by the wave steepness (in deep water) or the Ursell number (in non-deep water) are given in order to efficiently predict free surface elevations. Finally, the method of calculating time averaged sand transport rates related to wave nonlinearity by using free surface elevation is given for practical engineering applications.
, Available online ,
doi: 10.12284/hyxb2024089
Abstract:
With the impact of climate change such as rising sea levels and intensified storms, it is particularly important to quickly and accurately predict typhoon wave heights for coastal protection and marine disaster prevention. This article first generates a large number of virtual typhoons based on the TCWiSE model, uses the SWAN numerical model to calculate the significant wave height at the observation station during the typhoon, and constructs a sample database of typhoon waves; Then evaluate and select the input factors and hyperparameters of the BO-LSTM neural network model, and train and test it using a sample database. The results show that the constructed virtual typhoon has good similarity with historical typhoons, which can provide sufficient data basis for the construction of intelligent typhoon wave height prediction models; The BO-LSTM model built can quickly achieve intelligent prediction of typhoon wave height at a single station, and has prediction accuracy comparable to SWAN. Its prediction accuracy in long-term forecasting scenarios is significantly better than RF and BPNN models; Adding future typhoon data to the input of the BO-LSTM model further improves the accuracy and duration of the model’s forecast. Its Bias, RMSE, and R2 for predicting the next 24 h are −0.102 m, 0.494 m, and 0.855, respectively. The research results provide a feasible approach for intelligent forecasting of typhoon waves under extreme weather conditions.
With the impact of climate change such as rising sea levels and intensified storms, it is particularly important to quickly and accurately predict typhoon wave heights for coastal protection and marine disaster prevention. This article first generates a large number of virtual typhoons based on the TCWiSE model, uses the SWAN numerical model to calculate the significant wave height at the observation station during the typhoon, and constructs a sample database of typhoon waves; Then evaluate and select the input factors and hyperparameters of the BO-LSTM neural network model, and train and test it using a sample database. The results show that the constructed virtual typhoon has good similarity with historical typhoons, which can provide sufficient data basis for the construction of intelligent typhoon wave height prediction models; The BO-LSTM model built can quickly achieve intelligent prediction of typhoon wave height at a single station, and has prediction accuracy comparable to SWAN. Its prediction accuracy in long-term forecasting scenarios is significantly better than RF and BPNN models; Adding future typhoon data to the input of the BO-LSTM model further improves the accuracy and duration of the model’s forecast. Its Bias, RMSE, and R2 for predicting the next 24 h are −0.102 m, 0.494 m, and 0.855, respectively. The research results provide a feasible approach for intelligent forecasting of typhoon waves under extreme weather conditions.
, Available online ,
doi: 10.12284/hyxb2024092
Abstract:
Benthic harpacticoid copepods are widely distributed in marine ecosystem, which is particularly abundant in the epilithic algal matrix(EAM) of coral reefs. Due to its unique habitat, there is currently limited research on its developmental process and cultivation methods. In this study, we collected epilithic algal matrix from the coral reef of Luhuitou, Sanya, Hainan in the summer of 2023, from which we isolated one species of Harpacticoida, which was belonging to the genus Robertgurneya based on morphological characteristics. The effects of mono-and mixed-algal cultures on the developmental dynamics of Robertgurneya sp. were observed and recorded. The results showed that the adult body length of the Robertgurneya sp. was 0.5−0.7 mm, with an average life cycle of about 61−68 days. There were no significant differences in egg number per female each time, brood number, reproductive cycle, and life cycle between different feed cultivation techniques. However, under mixed algae culture, the average egg diameter, larval survival rate, and maximum body length of nauplii stage VI in the embryonic development stage of the Robertgurneya sp. were significantly higher than those in the mono-algae culture group (p < 0.05). Moreover, the embryonic development time and cumulative copepodid development time were significantly shorter under mixed-algal culture (p < 0.05). The results indicate that Robertgurneya sp. in EAM have a short life cycle and strong reproductive ability. Considering the abundant benthic microalgae and organic debris in the mats, harpacticoida may be able to provide huge potential food resources for predators such as small fish in coral reefs. Therefore, it may play an important role in the material cycle and energy flow of coral reef ecosystems.
Benthic harpacticoid copepods are widely distributed in marine ecosystem, which is particularly abundant in the epilithic algal matrix(EAM) of coral reefs. Due to its unique habitat, there is currently limited research on its developmental process and cultivation methods. In this study, we collected epilithic algal matrix from the coral reef of Luhuitou, Sanya, Hainan in the summer of 2023, from which we isolated one species of Harpacticoida, which was belonging to the genus Robertgurneya based on morphological characteristics. The effects of mono-and mixed-algal cultures on the developmental dynamics of Robertgurneya sp. were observed and recorded. The results showed that the adult body length of the Robertgurneya sp. was 0.5−0.7 mm, with an average life cycle of about 61−68 days. There were no significant differences in egg number per female each time, brood number, reproductive cycle, and life cycle between different feed cultivation techniques. However, under mixed algae culture, the average egg diameter, larval survival rate, and maximum body length of nauplii stage VI in the embryonic development stage of the Robertgurneya sp. were significantly higher than those in the mono-algae culture group (p < 0.05). Moreover, the embryonic development time and cumulative copepodid development time were significantly shorter under mixed-algal culture (p < 0.05). The results indicate that Robertgurneya sp. in EAM have a short life cycle and strong reproductive ability. Considering the abundant benthic microalgae and organic debris in the mats, harpacticoida may be able to provide huge potential food resources for predators such as small fish in coral reefs. Therefore, it may play an important role in the material cycle and energy flow of coral reef ecosystems.
, Available online ,
doi: 10.12284/hyxb2024103
Abstract:
Pore structure is an important mesoscopic feature of sea ice affecting its mechanical properties. In order to investigate the mesoscopic structure of melting sea ice, a sea ice block was collected during severe ice period in the Bohai Sea. The ice block was put in a low temperature environment (−1.0℃) for 48 h, which was then observed using a CT scanner. The thresholds of CT values among gas, ice, and brine were set to −310 HU and −30 HU for segmentation of the CT image, respectively. The gas and brine inclusions were able to be identified in the CT image, and the two-dimensional morphological characteristics of the pores in ice were analyzed. On the basis of image segmentation, the three-dimensional reconstruction of the ice pores was carried out, and the three-dimensional morphological characteristics of the pores were analyzed. It was found that along the ice thickness, the gas area fraction was 5.00%～35.93%, and the brine distribution was discontinuous with maximum area fraction of 0.06%. The cross-sectional shape of the gas and brine pores parallel to the ice surface was approximately circular, with a roundness more than 0.60. The equivalent circle diameter of gas pore was 1.1～3.2 mm, and that of brine was 0.2～2.0 mm. The equivalent circle diameter of pores was positively correlated with the area fraction and negatively correlated with the roundness. In terms of three-dimensional structure, 4 types of gas pores were divided according to sphericity (Rsph) into coronary pores (Rsph ≤ 0.25), irregular pores (0.25 < Rsph ≤ 0.45), strip pores (0.45 < Rsph ≤ 0.60), and spherical bubbles (0.60 < Rsph ≤ 1.00). The coronary pore was the largest (average volume (11522.8 ± 5610.2 ) mm3) with smallest amount, and the spherical bubble was the smallest (average diameter (2.0 ± 1.1) mm) with the largest amount. The brine pores were divided into brine channels (0.45 < Rsph ≤ 0.60) and brine cells (0.60 < Rsph ≤ 1.00). The average length of the brine channel was (17.1 ± 12.1) mm, and the average diameter of the brine cell was (1.5 ± 0.9) mm. The amount of brine channels was less, but the volume proportion was comparable to that of brine cells.
Pore structure is an important mesoscopic feature of sea ice affecting its mechanical properties. In order to investigate the mesoscopic structure of melting sea ice, a sea ice block was collected during severe ice period in the Bohai Sea. The ice block was put in a low temperature environment (−1.0℃) for 48 h, which was then observed using a CT scanner. The thresholds of CT values among gas, ice, and brine were set to −310 HU and −30 HU for segmentation of the CT image, respectively. The gas and brine inclusions were able to be identified in the CT image, and the two-dimensional morphological characteristics of the pores in ice were analyzed. On the basis of image segmentation, the three-dimensional reconstruction of the ice pores was carried out, and the three-dimensional morphological characteristics of the pores were analyzed. It was found that along the ice thickness, the gas area fraction was 5.00%～35.93%, and the brine distribution was discontinuous with maximum area fraction of 0.06%. The cross-sectional shape of the gas and brine pores parallel to the ice surface was approximately circular, with a roundness more than 0.60. The equivalent circle diameter of gas pore was 1.1～3.2 mm, and that of brine was 0.2～2.0 mm. The equivalent circle diameter of pores was positively correlated with the area fraction and negatively correlated with the roundness. In terms of three-dimensional structure, 4 types of gas pores were divided according to sphericity (Rsph) into coronary pores (Rsph ≤ 0.25), irregular pores (0.25 < Rsph ≤ 0.45), strip pores (0.45 < Rsph ≤ 0.60), and spherical bubbles (0.60 < Rsph ≤ 1.00). The coronary pore was the largest (average volume (
, Available online ,
doi: 10.12284/hyxb2024101
Abstract:
Both the southeastern Tropical Indian Ocean and the northern South China Sea are similar in topography and background circulation characteristics, and both have active mesoscale eddy motion. Based on satellite altimeter data, the seasonal and interannual variations of mesoscale eddies in these two sea areas are compared. The results show that the number of mesoscale eddies generated in the southeastern Tropical Indian Ocean and the northern South China Sea decay exponentially with the growth of their life cycle. Mesoscale eddies in these two sea areas move to the west or southwest with an average speed of 0.2 m/s, but the average radius of the former is larger and the average amplitude of the latter is stronger. In terms of seasonal variation, the eddy kinetic energy is smallest in spring and largest in autumn in the northern hemisphere, but the eddy generation number in the southeastern Tropical Indian Ocean is largest in summer-autumn and the northern South China Sea is largest in winter-spring. In interannual variation, the eddy activity in the southeastern Tropical Indian Ocean and the northern South China Sea is affected by El Niño-Southern Oscillation (ENSO). The eddy kinetic energy is stronger In El Niño year and weaker in La Niña year, but the mechanism of ENSO affecting the mesoscale eddy in these two areas is slightly different. The former is mainly achieved by modulating Indonesian Throughflow to suppress or enhance the baroclinic instability energy in this area, while the latter is mainly achieved by changing the local wind field in the northern South China Sea to produce wind stress curl anomaly. In addition, the mesoscale eddy in the southeastern Tropical Indian Ocean is also affected by the Indian Ocean Dipole, while the correlation between the mesoscale eddy in the northern South China Sea and the Indian Ocean Dipole is weak.
Both the southeastern Tropical Indian Ocean and the northern South China Sea are similar in topography and background circulation characteristics, and both have active mesoscale eddy motion. Based on satellite altimeter data, the seasonal and interannual variations of mesoscale eddies in these two sea areas are compared. The results show that the number of mesoscale eddies generated in the southeastern Tropical Indian Ocean and the northern South China Sea decay exponentially with the growth of their life cycle. Mesoscale eddies in these two sea areas move to the west or southwest with an average speed of 0.2 m/s, but the average radius of the former is larger and the average amplitude of the latter is stronger. In terms of seasonal variation, the eddy kinetic energy is smallest in spring and largest in autumn in the northern hemisphere, but the eddy generation number in the southeastern Tropical Indian Ocean is largest in summer-autumn and the northern South China Sea is largest in winter-spring. In interannual variation, the eddy activity in the southeastern Tropical Indian Ocean and the northern South China Sea is affected by El Niño-Southern Oscillation (ENSO). The eddy kinetic energy is stronger In El Niño year and weaker in La Niña year, but the mechanism of ENSO affecting the mesoscale eddy in these two areas is slightly different. The former is mainly achieved by modulating Indonesian Throughflow to suppress or enhance the baroclinic instability energy in this area, while the latter is mainly achieved by changing the local wind field in the northern South China Sea to produce wind stress curl anomaly. In addition, the mesoscale eddy in the southeastern Tropical Indian Ocean is also affected by the Indian Ocean Dipole, while the correlation between the mesoscale eddy in the northern South China Sea and the Indian Ocean Dipole is weak.
, Available online ,
doi: 10.12284/hyxb2024097
Abstract:
The sea ice in Bohai Sea in winter affects the safety production activities of oil platform and ship navigation, as well as the safety of offshore engineering and construction. Spaceborne SAR is not affected by weather and has high resolution, which can be used for sea ice disaster monitoring in Bohai Sea. Based on deep learning model UNet++, this paper introduces Convolutional attention module (CBAM) and uses cross loss function to optimize the model, and establishes a high-precision sea ice detection model for Sentinel-1 SAR data in the Liaodong Bay (AUNet++). And compared with PSPNet, Deeplabv3+, DAU-Net and other deep learning methods. The experimental results show that AUNet++ sea ice detection method achieves 97.56%, 97.53%, 95.19% and 95.07% in OA, AA, MIoU and Kappa coefficients, respectively, which is superior to other deep learning methods. This method can extract accurate sea ice information from sea ice edge and smooth ice under the interference of high wind speed, and can provide technical support for large-scale and high-precision sea ice detection in Liaodong Bay area.
The sea ice in Bohai Sea in winter affects the safety production activities of oil platform and ship navigation, as well as the safety of offshore engineering and construction. Spaceborne SAR is not affected by weather and has high resolution, which can be used for sea ice disaster monitoring in Bohai Sea. Based on deep learning model UNet++, this paper introduces Convolutional attention module (CBAM) and uses cross loss function to optimize the model, and establishes a high-precision sea ice detection model for Sentinel-1 SAR data in the Liaodong Bay (AUNet++). And compared with PSPNet, Deeplabv3+, DAU-Net and other deep learning methods. The experimental results show that AUNet++ sea ice detection method achieves 97.56%, 97.53%, 95.19% and 95.07% in OA, AA, MIoU and Kappa coefficients, respectively, which is superior to other deep learning methods. This method can extract accurate sea ice information from sea ice edge and smooth ice under the interference of high wind speed, and can provide technical support for large-scale and high-precision sea ice detection in Liaodong Bay area.
, Available online ,
doi: 10.12284/hyxb2024113
Abstract:
As a natural barrier to the coast, coral reefs have caused irreversible damage in recent years due to the influence of human activities. How to resist the erosion of extreme waves has become an urgent problem for islands that have lost their natural barriers. Based on the physical model test of wave flume, this paper studies the complex hydrodynamic characteristics of solitary waves near coral reef topography from the parameters of incident wave height, reef flat water depth and pore radius, and reveals the wave dissipation mechanism of artificial reefs from the perspective of energy. The test results show that the permeable artificial reef can significantly weaken the wave energy, and the ability of the artificial reef group to weaken the wave energy has a certain limit. Under the influence of the reef, the wave is partially reduced after passing through the reef, and the effective water depth of the subsequent propagation on the reef flat can be reduced. The transmission coefficient and reflection coefficient increase with the increase of incident wave height. With the increase of reef flat water depth, the reflection coefficient decreases and the transmission coefficient increases. The reflection coefficient decreases with the increase of pore radius, and the transmission coefficient has no obvious law. The permeable trapezoidal reef can effectively reduce the transmission intensity of waves and realize the protection of islands. The permeable trapezoidal reef can not only weaken the wave energy, but also take into account the ecological friendliness, reduce the force of structures and provide space for water exchange.
As a natural barrier to the coast, coral reefs have caused irreversible damage in recent years due to the influence of human activities. How to resist the erosion of extreme waves has become an urgent problem for islands that have lost their natural barriers. Based on the physical model test of wave flume, this paper studies the complex hydrodynamic characteristics of solitary waves near coral reef topography from the parameters of incident wave height, reef flat water depth and pore radius, and reveals the wave dissipation mechanism of artificial reefs from the perspective of energy. The test results show that the permeable artificial reef can significantly weaken the wave energy, and the ability of the artificial reef group to weaken the wave energy has a certain limit. Under the influence of the reef, the wave is partially reduced after passing through the reef, and the effective water depth of the subsequent propagation on the reef flat can be reduced. The transmission coefficient and reflection coefficient increase with the increase of incident wave height. With the increase of reef flat water depth, the reflection coefficient decreases and the transmission coefficient increases. The reflection coefficient decreases with the increase of pore radius, and the transmission coefficient has no obvious law. The permeable trapezoidal reef can effectively reduce the transmission intensity of waves and realize the protection of islands. The permeable trapezoidal reef can not only weaken the wave energy, but also take into account the ecological friendliness, reduce the force of structures and provide space for water exchange.
, Available online ,
doi: 10.12284/hyxb2024093
Abstract:
Under the backdrop of climate change, mass sea level change rates are varied across regions. Therein, underthe combined effect ofthe self-attraction and loading effect andpolar motion feedback, freshwater transported from land to searesulted in the spatiotemporal heterogeneous change of mass sea level, termed sea level fingerprints. The sea level fingerprints are important components of mass sea level. This study utilized three terrestrial water storage anomalies datasets to simulate sea level fingerprints under three scenarios, following a sea level equation that incorporated the self-attraction and loading effect along with polar motion feedback. The simulated scenarios were: (1) aligning with the actual glacial mass balance; (2) consistent with the recent climate change rates; and (3) considering climate natural variability alone. Based on simulation results, this study analyzed the evolution ofsea level fingerprints under multiple scenarios and assessed their contribution to observed mass sea level anomalies.The study revealed that glacier melting in regions such as Greenland, Alaska, the Caucasus and Middle East, the Southern Andes, and Antarctica dominated the trendterm of sea level fingerprints. The sea level fingerprints, which align with the actual glacier mass balance, better replicated the global distribution pattern of the observed mass sea level anomalies trend term,as shown by the spatial similarity coefficients of 0.31 with the GRACE/GRACE-FO results and 0.71 with the altimetry satellite results. Non-glacial regional terrestrial water storage anomalies better captured the amplitude term of the observed mass sea level anomalies, as shown by sea level fingerprints, which consider climate natural variability alone, having spatial similarity coefficients of 0.67 with the GRACE/GRACE-FO results and 0.84 with the altimetry satellite results. The sea level fingerprints were the primary contributing source to mass sea level anomalies in low-latitude regions.
Under the backdrop of climate change, mass sea level change rates are varied across regions. Therein, underthe combined effect ofthe self-attraction and loading effect andpolar motion feedback, freshwater transported from land to searesulted in the spatiotemporal heterogeneous change of mass sea level, termed sea level fingerprints. The sea level fingerprints are important components of mass sea level. This study utilized three terrestrial water storage anomalies datasets to simulate sea level fingerprints under three scenarios, following a sea level equation that incorporated the self-attraction and loading effect along with polar motion feedback. The simulated scenarios were: (1) aligning with the actual glacial mass balance; (2) consistent with the recent climate change rates; and (3) considering climate natural variability alone. Based on simulation results, this study analyzed the evolution ofsea level fingerprints under multiple scenarios and assessed their contribution to observed mass sea level anomalies.The study revealed that glacier melting in regions such as Greenland, Alaska, the Caucasus and Middle East, the Southern Andes, and Antarctica dominated the trendterm of sea level fingerprints. The sea level fingerprints, which align with the actual glacier mass balance, better replicated the global distribution pattern of the observed mass sea level anomalies trend term,as shown by the spatial similarity coefficients of 0.31 with the GRACE/GRACE-FO results and 0.71 with the altimetry satellite results. Non-glacial regional terrestrial water storage anomalies better captured the amplitude term of the observed mass sea level anomalies, as shown by sea level fingerprints, which consider climate natural variability alone, having spatial similarity coefficients of 0.67 with the GRACE/GRACE-FO results and 0.84 with the altimetry satellite results. The sea level fingerprints were the primary contributing source to mass sea level anomalies in low-latitude regions.
, Available online
Abstract:
Rapid changes in the Arctic environment significantly impact the characteristics of water masses in the Arctic Ocean, potentially affecting the ocean’s physical and biogeochemical processes. This study utilizes the latest MOSAiC observation data (from October 2019 to August 2020) and high-resolution reanalysis data (GLORYS12V1) to analyze the variations in temperature and salinity of water masses across the Eurasian Basin along the MOSAiC drift trajectory, and to explore the influence of the Atlantic inflow on these variations. The results show that: (1) Both temperature and salinity within the upper 100 m layer along the drift trajectory exhibit an overall pattern of initially increasing and then decreasing from the Amundsen Basin to the Nansen Basin. The spatial variation in salinity is greatest within the 0－20 m layer, with highly saline surface water (S >34) present in Nansen Basin. In contrast, the variation in temperature is greatest at the 100 m layer, with the depth of 0℃ isothermal less than 100 m in parts of the Nansen Basin. Although GLORYS12V1 simulates the higher temperature in the upper Nansen Basin, it reasonably captures the main features of horizontal and vertical variations in temperature and salinity along the drift trajectory. (2) The warm and saline Atlantic water generally flows anticlockwise in the Eurasian Basin, with its depth gradually deepening during transport, which predominantly determines the overall variations in temperature and salinity in intermedia and upper layers in the Eurasian Basin. The high salinity of surface water in the Nansen Basin is due to the drift trajectory involved into the regions influenced by deep winter convection in northern Svalbard. Strong wind events play a limited role in the distributional differences of temperature and salinity along the drift trajectory. (3) In the western Nansen Basin, GLORYS12V1 indicates a northward extension of Atlantic Water beyond what is observed, with its northern boundary nearing the Gakkel Ridge. This discrepancy results in an overestimation of temperature compared to in-situ observations. To improve the accuracy of the GLORYS12V1 simulated results, refining the setting of Atlantic inflow flux at the open boundary is suggested.
Rapid changes in the Arctic environment significantly impact the characteristics of water masses in the Arctic Ocean, potentially affecting the ocean’s physical and biogeochemical processes. This study utilizes the latest MOSAiC observation data (from October 2019 to August 2020) and high-resolution reanalysis data (GLORYS12V1) to analyze the variations in temperature and salinity of water masses across the Eurasian Basin along the MOSAiC drift trajectory, and to explore the influence of the Atlantic inflow on these variations. The results show that: (1) Both temperature and salinity within the upper 100 m layer along the drift trajectory exhibit an overall pattern of initially increasing and then decreasing from the Amundsen Basin to the Nansen Basin. The spatial variation in salinity is greatest within the 0－20 m layer, with highly saline surface water (S >34) present in Nansen Basin. In contrast, the variation in temperature is greatest at the 100 m layer, with the depth of 0℃ isothermal less than 100 m in parts of the Nansen Basin. Although GLORYS12V1 simulates the higher temperature in the upper Nansen Basin, it reasonably captures the main features of horizontal and vertical variations in temperature and salinity along the drift trajectory. (2) The warm and saline Atlantic water generally flows anticlockwise in the Eurasian Basin, with its depth gradually deepening during transport, which predominantly determines the overall variations in temperature and salinity in intermedia and upper layers in the Eurasian Basin. The high salinity of surface water in the Nansen Basin is due to the drift trajectory involved into the regions influenced by deep winter convection in northern Svalbard. Strong wind events play a limited role in the distributional differences of temperature and salinity along the drift trajectory. (3) In the western Nansen Basin, GLORYS12V1 indicates a northward extension of Atlantic Water beyond what is observed, with its northern boundary nearing the Gakkel Ridge. This discrepancy results in an overestimation of temperature compared to in-situ observations. To improve the accuracy of the GLORYS12V1 simulated results, refining the setting of Atlantic inflow flux at the open boundary is suggested.
, Available online
Abstract:
Iron oxides play a significant role in the global soil (sediment) organic carbon (OC) storage. Mangrove wetlands, receiving both terrestrial and marine inputs, provide a unique habitat for the preservation of organic carbon by reactive iron oxides (FeR). However, the impact of FeR in the surface sediments of mangroves on the preservation process of OC, as well as the selectivity of FeR towards different OC components, is still unclear. The surface sediments in the present work was collected in the natural mangrove areas around the estuaries of the Dafeng River and Maowei Sea in Guangxi, which are highly influenced by tides and rivers. The research was focused on the changes in the content and composition of iron-bound organic carbon (Fe-OC) in sediments. The results indicated that the average content of Fe-OC in surface sediments in the estuaries of Dafeng River and Maowei Sea was 0.16 ± 0.07% and 0.17 ± 0.07%, respectively. These values represented 16.2 ± 5.04% and 10.9 ± 5.63% of the total organic carbon (TOC) content in the respective sediments, which were primarily preserved through adsorption. Furthermore, the preservation of OC by FeR was influenced by the sediment particle size, the content and form of FeR, and the source and composition of TOC. TOC, FeR and Fe-OC were mainly distributed in the smaller grain size sediment fractions. The predominant form of iron in surface sediments was Fe3+, accounting for 87.42% of the total iron, and is relatively higher in high salinity sediments. FeR selectively preserved OC with higher δ13C (stable carbon isotope natural abundance) and aromatic OC. Compared with the Maowei Sea, the proportion of protein-like fluorescent components in Fe-OC of surface sediments from the Dafeng River estuary was higher and the proportion of protein-like fluorescent components increased as the molar ratio of Fe-OC:Fe increased. This study helps to clarify the selective preservation mechanism of OC by FeR in mangrove surface sediments in Guangxi, and deepen our understanding of the preservation process of OC in land-sea interface sediments.
Iron oxides play a significant role in the global soil (sediment) organic carbon (OC) storage. Mangrove wetlands, receiving both terrestrial and marine inputs, provide a unique habitat for the preservation of organic carbon by reactive iron oxides (FeR). However, the impact of FeR in the surface sediments of mangroves on the preservation process of OC, as well as the selectivity of FeR towards different OC components, is still unclear. The surface sediments in the present work was collected in the natural mangrove areas around the estuaries of the Dafeng River and Maowei Sea in Guangxi, which are highly influenced by tides and rivers. The research was focused on the changes in the content and composition of iron-bound organic carbon (Fe-OC) in sediments. The results indicated that the average content of Fe-OC in surface sediments in the estuaries of Dafeng River and Maowei Sea was 0.16 ± 0.07% and 0.17 ± 0.07%, respectively. These values represented 16.2 ± 5.04% and 10.9 ± 5.63% of the total organic carbon (TOC) content in the respective sediments, which were primarily preserved through adsorption. Furthermore, the preservation of OC by FeR was influenced by the sediment particle size, the content and form of FeR, and the source and composition of TOC. TOC, FeR and Fe-OC were mainly distributed in the smaller grain size sediment fractions. The predominant form of iron in surface sediments was Fe3+, accounting for 87.42% of the total iron, and is relatively higher in high salinity sediments. FeR selectively preserved OC with higher δ13C (stable carbon isotope natural abundance) and aromatic OC. Compared with the Maowei Sea, the proportion of protein-like fluorescent components in Fe-OC of surface sediments from the Dafeng River estuary was higher and the proportion of protein-like fluorescent components increased as the molar ratio of Fe-OC:Fe increased. This study helps to clarify the selective preservation mechanism of OC by FeR in mangrove surface sediments in Guangxi, and deepen our understanding of the preservation process of OC in land-sea interface sediments.
, Available online
Abstract:
Based on analyses of solid-phase and porewater chemistry of sediment cores at four sites collected from Laizhou Bay of the Bohai Sea, we revealed diagenetic cycles of iron, manganese and sulfur and their responses to terrestrial inputs and anthropogenic perturbations. Results suggest that water eutrophication of the bay has not given rise to organic carbon (OC) enrichment in the sediments. Actually, contents and lability of sediment OC are generally low, largely due to the inputs of terrestrial refractory OC and intense sediment resuspension induced by natural processes and anthropogenic perturbations in the river-dominated area. This feature greatly dampens sulfate reduction, resulting in low accumulation of total reduced inorganic sulfide (0.28～88 μmol/g). Porewater Mn2+ is mainly from reductive dissolution of amorphous and poorly crystalline Mn oxides, while precipitation of MnCO3 is mainly responsible for Mn2+ consumption in sediment below 10 cm depth. Intense sediment resuspension and refractory nature of sediment OC encourage dissimilatory iron reduction, with relative contribution of this pathway to total anaerobic OC mineralization of about 51%, on average. At the site (S6) heavily influenced by the Yellow River input, dynamic depositional regime facilitates reductive dissolution of manganese oxides, but dampens reduction of iron oxides and sulfate to some extent. Upward diffusive fluxes of porewater Mn2+ and Fe2+ in the sediments are at the lower end for sediments of other areas dominated by major river inputs, which is attributable to overall low lability of sediment OC.
Based on analyses of solid-phase and porewater chemistry of sediment cores at four sites collected from Laizhou Bay of the Bohai Sea, we revealed diagenetic cycles of iron, manganese and sulfur and their responses to terrestrial inputs and anthropogenic perturbations. Results suggest that water eutrophication of the bay has not given rise to organic carbon (OC) enrichment in the sediments. Actually, contents and lability of sediment OC are generally low, largely due to the inputs of terrestrial refractory OC and intense sediment resuspension induced by natural processes and anthropogenic perturbations in the river-dominated area. This feature greatly dampens sulfate reduction, resulting in low accumulation of total reduced inorganic sulfide (0.28～88 μmol/g). Porewater Mn2+ is mainly from reductive dissolution of amorphous and poorly crystalline Mn oxides, while precipitation of MnCO3 is mainly responsible for Mn2+ consumption in sediment below 10 cm depth. Intense sediment resuspension and refractory nature of sediment OC encourage dissimilatory iron reduction, with relative contribution of this pathway to total anaerobic OC mineralization of about 51%, on average. At the site (S6) heavily influenced by the Yellow River input, dynamic depositional regime facilitates reductive dissolution of manganese oxides, but dampens reduction of iron oxides and sulfate to some extent. Upward diffusive fluxes of porewater Mn2+ and Fe2+ in the sediments are at the lower end for sediments of other areas dominated by major river inputs, which is attributable to overall low lability of sediment OC.
, Available online
Abstract:
To analysis the suitability of using wind field data for forecasting Pacific saury habitat in the northwest Pacific, this paper use the generalized additive model to fit the habitat suitability index (HSI) for Pacific saury in summer and autumn, based on the Chinese fishery data, environmental data and four types of wind field data included the China-France oceanography satellite (CFOSAT) during June to November in 2019−2020.Result indicates that, (1) Weighted analysis shows distinct seasonal variation of environmental variables on catch per unit effort, with chlorophyll concentration and sea surface temperature having the highest weights in summer and autumn, respectively, while wind speed had the lowest weight and directly proportional to the weight. (2) The average accuracy of the four data in summer and autumn is 68.37% and 76.65%, respectively, and CFOSAT reaching the highest accuracy of 80.94% in autumn. (3) The high-HSI areas are consistent with the fishing grounds of Pacific saury, while the high-value regions of scatter meter in autumn show clear and focus. The advantages of using wind speed on the forecast model in autumn, which can explain the influence of transient variation factors on the migration and aggregation of Pacific saury.
To analysis the suitability of using wind field data for forecasting Pacific saury habitat in the northwest Pacific, this paper use the generalized additive model to fit the habitat suitability index (HSI) for Pacific saury in summer and autumn, based on the Chinese fishery data, environmental data and four types of wind field data included the China-France oceanography satellite (CFOSAT) during June to November in 2019−2020.Result indicates that, (1) Weighted analysis shows distinct seasonal variation of environmental variables on catch per unit effort, with chlorophyll concentration and sea surface temperature having the highest weights in summer and autumn, respectively, while wind speed had the lowest weight and directly proportional to the weight. (2) The average accuracy of the four data in summer and autumn is 68.37% and 76.65%, respectively, and CFOSAT reaching the highest accuracy of 80.94% in autumn. (3) The high-HSI areas are consistent with the fishing grounds of Pacific saury, while the high-value regions of scatter meter in autumn show clear and focus. The advantages of using wind speed on the forecast model in autumn, which can explain the influence of transient variation factors on the migration and aggregation of Pacific saury.
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Abstract:
Phosphonates in the ocean are a kind of potential phosphorus (P) source which could be utilized by phytoplankton. Although dinoflagellates cannot directly utilize phosphonates themselves, their symbiotic bacteria have the capability to degrade phosphonates into phosphate, thereby promoting the growth of algal cells. However, no studies focusing on a specific bacteria strain have been conducted thus far. In this study, Prorocentrum donghaiense was cultured under conditions with 2-Aminoethylphosphonic acid (2-AEP) as the sole P source. Isolation and purification of the symbiotic bacteria from the culture was conducted and five kinds of bacteria were obtained. Genome sequencing results revealed the presence of two types of C-P lyase pathways in the bacterial strain designated as Yoonia sp. PD-AEP-1. The function of the bacteira strain was verified through the co-culture of bacteria and algal cells. The results demonstrated that after the algal cells were treated to phosphorus-starved condition, when 2-AEP and the bacteria suspension were added together, as compared to conditions which only 2-AEP or the bacterial suspension of PD-AEP-1 was introduced, both the growth rate of algal cells and the phosphate concentration in the cultures showed a significant increase. Meanwhile, alkaline phosphatase activity and non-photochemical quenching of the algal cells decreased significantly, indicating that PD-AEP-1 has the ability to degrade 2-AEP into phosphate, thereby alleviating phosphorus limitation for P. donghaiense cells and effectively promoting the growth of algal cells. The study suggests that symbiotic bacteria of P. donghaiense might play a part in providing P sources to the algal cells through the degradation of phosphonates. This process could probably contribute to the outbreak of P. donghaiense bloom, highlighting the importance of algae-bacteira interactions in marine ecosystems.
Phosphonates in the ocean are a kind of potential phosphorus (P) source which could be utilized by phytoplankton. Although dinoflagellates cannot directly utilize phosphonates themselves, their symbiotic bacteria have the capability to degrade phosphonates into phosphate, thereby promoting the growth of algal cells. However, no studies focusing on a specific bacteria strain have been conducted thus far. In this study, Prorocentrum donghaiense was cultured under conditions with 2-Aminoethylphosphonic acid (2-AEP) as the sole P source. Isolation and purification of the symbiotic bacteria from the culture was conducted and five kinds of bacteria were obtained. Genome sequencing results revealed the presence of two types of C-P lyase pathways in the bacterial strain designated as Yoonia sp. PD-AEP-1. The function of the bacteira strain was verified through the co-culture of bacteria and algal cells. The results demonstrated that after the algal cells were treated to phosphorus-starved condition, when 2-AEP and the bacteria suspension were added together, as compared to conditions which only 2-AEP or the bacterial suspension of PD-AEP-1 was introduced, both the growth rate of algal cells and the phosphate concentration in the cultures showed a significant increase. Meanwhile, alkaline phosphatase activity and non-photochemical quenching of the algal cells decreased significantly, indicating that PD-AEP-1 has the ability to degrade 2-AEP into phosphate, thereby alleviating phosphorus limitation for P. donghaiense cells and effectively promoting the growth of algal cells. The study suggests that symbiotic bacteria of P. donghaiense might play a part in providing P sources to the algal cells through the degradation of phosphonates. This process could probably contribute to the outbreak of P. donghaiense bloom, highlighting the importance of algae-bacteira interactions in marine ecosystems.
, Available online
Abstract:
The phenomenon of marine phytoplankton bloom in ocean refers to the annual cycle increase in biomass caused by rapid reproduction, which plays an important role in the biochemical cycles of marine organisms. However, the spatiotemporal variation characteristics of global phytoplankton blooms and their response mechanisms to the environment still require further exploration. Based on the chlorophyll-a products of the MODIS-Aqua (Moderate Resolution Imaging Spectroradiometer) from 2003 to 2022, we extracted the bloom indexes of global ocean phytoplankton (the ratio of bloom duration and bloom intensity). Then, we analyzed their spatiotemporal characteristics, trends, and correlations with environmental factors. The results indicated that there are significant seasonal and latitudinal difference in the distribution of the bloom indexes. Blooms in high latitudes of the Northern Hemisphere mainly occurring from April to October, while in mid-low latitudes, blooms mainly occur from November to March of the following year. In the Southern Hemisphere, blooms develop in the month of November and persist until March of the following year in high latitudes, while those in low and middle latitudes occur from May to September. The ratio of bloom duration and bloom intensity shows a decreasing trend mainly in the mid-low latitude regions of the North Pacific, while increasing trends are observed in mid-high latitude regions of the Southern Hemisphere. The distribution and trends changes of blooms are both regulated by environmental factors. Sea surface temperature and photosynthetically active radiation promote blooms intensity in high latitude waters, but inhibit them in low latitude waters. Meanwhile, the wind speed plays a restraining role in the high latitude sea area and a promoting role in the low latitude sea area.
The phenomenon of marine phytoplankton bloom in ocean refers to the annual cycle increase in biomass caused by rapid reproduction, which plays an important role in the biochemical cycles of marine organisms. However, the spatiotemporal variation characteristics of global phytoplankton blooms and their response mechanisms to the environment still require further exploration. Based on the chlorophyll-a products of the MODIS-Aqua (Moderate Resolution Imaging Spectroradiometer) from 2003 to 2022, we extracted the bloom indexes of global ocean phytoplankton (the ratio of bloom duration and bloom intensity). Then, we analyzed their spatiotemporal characteristics, trends, and correlations with environmental factors. The results indicated that there are significant seasonal and latitudinal difference in the distribution of the bloom indexes. Blooms in high latitudes of the Northern Hemisphere mainly occurring from April to October, while in mid-low latitudes, blooms mainly occur from November to March of the following year. In the Southern Hemisphere, blooms develop in the month of November and persist until March of the following year in high latitudes, while those in low and middle latitudes occur from May to September. The ratio of bloom duration and bloom intensity shows a decreasing trend mainly in the mid-low latitude regions of the North Pacific, while increasing trends are observed in mid-high latitude regions of the Southern Hemisphere. The distribution and trends changes of blooms are both regulated by environmental factors. Sea surface temperature and photosynthetically active radiation promote blooms intensity in high latitude waters, but inhibit them in low latitude waters. Meanwhile, the wind speed plays a restraining role in the high latitude sea area and a promoting role in the low latitude sea area.
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In order to understand the long−term variations in the nutritional environment and the key influencing factors of Bohai Bay, two sediment cores from the mouth of the bay (BH15) and the outer area of the bay (BH47) were collected in April and June 2018 separately. The contents of total organic carbon (TOC), total nitrogen (TN), phosphorus (P), biogenic silica (BSi), and stable isotopes of carbon and nitrogen (\begin{document}$ \mathrm{\delta } $\end{document} ![]()
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In order to understand the long−term variations in the nutritional environment and the key influencing factors of Bohai Bay, two sediment cores from the mouth of the bay (BH15) and the outer area of the bay (BH47) were collected in April and June 2018 separately. The contents of total organic carbon (TOC), total nitrogen (TN), phosphorus (P), biogenic silica (BSi), and stable isotopes of carbon and nitrogen (
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Abstract:
The coast of Hainan Island is dominated by embayed beaches, which is an important coastal tourist destination in China and also has a high incidence of drowning accidents caused by rip currents. To investigate the distribution characteristics of rip currents on embayed beaches, the occurrence and distribution characteristics of rip currents are interpreted from the satellite images of 54 embayed beaches around Hainan Island over the past 20 years, and compared with the field survey results. The results show that, in terms of regional distribution, the occurrence probability of rip currents on the eastern and southern coasts is significantly higher than that on the western and northern coasts of Hainan Island. In terms of location distribution, the number of rip currents in the middle of the headland bays is higher than that on the two sides. In terms of geometric characteristics, the average rip length was positively correlated with the average rip width, and the average rip spacing. The distribution density of rip currents is negatively correlated with significant wave height, average wave period, incident wave power, and wave energy. The scale of the headland has a significant effect on the number of rips, which is positively correlated with the bay width, the maximum bay indentation, and length of the headland, but the curvature of the shoreline has no significant correlation with the average number of rips. The results of satellite image interpretation for the occurrence of rips are consistent with the results of the field survey and the evaluation of the Ω-RTR model. These conclusions can provide useful references for the beach safety management and rip current warning work on Hainan Island.
The coast of Hainan Island is dominated by embayed beaches, which is an important coastal tourist destination in China and also has a high incidence of drowning accidents caused by rip currents. To investigate the distribution characteristics of rip currents on embayed beaches, the occurrence and distribution characteristics of rip currents are interpreted from the satellite images of 54 embayed beaches around Hainan Island over the past 20 years, and compared with the field survey results. The results show that, in terms of regional distribution, the occurrence probability of rip currents on the eastern and southern coasts is significantly higher than that on the western and northern coasts of Hainan Island. In terms of location distribution, the number of rip currents in the middle of the headland bays is higher than that on the two sides. In terms of geometric characteristics, the average rip length was positively correlated with the average rip width, and the average rip spacing. The distribution density of rip currents is negatively correlated with significant wave height, average wave period, incident wave power, and wave energy. The scale of the headland has a significant effect on the number of rips, which is positively correlated with the bay width, the maximum bay indentation, and length of the headland, but the curvature of the shoreline has no significant correlation with the average number of rips. The results of satellite image interpretation for the occurrence of rips are consistent with the results of the field survey and the evaluation of the Ω-RTR model. These conclusions can provide useful references for the beach safety management and rip current warning work on Hainan Island.
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doi: 10.12284/hyxb2024-04
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In order to investigate the characteristics and spatial-temporal variations of the phytoplankton community in artificial reef areas, as well as to elucidate the relationship between phytoplankton abundance and environmental factors associated with artificial reef construction, four surveys were conducted in 2021 (May, August, November) and 2022 (January) at two artificial reef areas and a control area in Xiangyun Bay. A total of 70 phytoplankton taxa belonging to 39 genera and 3 classes were identified in this study. The annual average abundance of phytoplankton in the artificial reef areas was recorded as 313.5×104 cells/m3, which were 1.4 times higher than that observed in the control area. The succession rate of dominant phytoplankton species ranged from 0.75 to 1.00, with an overall trend indicating lower values for both reef areas relative to control area, suggesting greater stability of community structure within artificial reef areas compared to the control area. The biological increment index for each phytoplankton taxon ranged from 0.9 to 3.6; notably, Bacillariophyta displayed an average biological increment index value of 1.8. Pearson correlation analysis revealed that phytoplankton abundance was primarily influenced by TP, TN, NH4-N, NO2-N and DIP; significant seasonal differences were observed among these variables. These findings demonstrate that artificial reef construction has a positive conservation effect on phytoplankton communities closely related to temporal and spatial changes in nutrient availability.
In order to investigate the characteristics and spatial-temporal variations of the phytoplankton community in artificial reef areas, as well as to elucidate the relationship between phytoplankton abundance and environmental factors associated with artificial reef construction, four surveys were conducted in 2021 (May, August, November) and 2022 (January) at two artificial reef areas and a control area in Xiangyun Bay. A total of 70 phytoplankton taxa belonging to 39 genera and 3 classes were identified in this study. The annual average abundance of phytoplankton in the artificial reef areas was recorded as 313.5×104 cells/m3, which were 1.4 times higher than that observed in the control area. The succession rate of dominant phytoplankton species ranged from 0.75 to 1.00, with an overall trend indicating lower values for both reef areas relative to control area, suggesting greater stability of community structure within artificial reef areas compared to the control area. The biological increment index for each phytoplankton taxon ranged from 0.9 to 3.6; notably, Bacillariophyta displayed an average biological increment index value of 1.8. Pearson correlation analysis revealed that phytoplankton abundance was primarily influenced by TP, TN, NH4-N, NO2-N and DIP; significant seasonal differences were observed among these variables. These findings demonstrate that artificial reef construction has a positive conservation effect on phytoplankton communities closely related to temporal and spatial changes in nutrient availability.
, Available online ,
doi: 10.12284/hyxb2024-03
Abstract:
In order to investigate the impact of climate change on the catch of bigeye tuna, we utilized the annual Pacific bigeye tuna catch data from 1960 to 2021, which was statistically compiled by the Western and Central Pacific Fisheries Commission. We also employed corresponding monthly climate indices, including Niño1+2, Niño3, Niño4, Niño3.4, Southern Oscillation Index (SOI), North Atlantic Oscillation (NAO), Pacific Decadal Oscillation (PDO), North Pacific Index (NPI), and global sea-air temperature anomaly (dT). By using a BP neural network and variable sensitivity analysis, we examined the relationship between these low-frequency climate factors and bigeye tuna catch. Our findings revealed that Niño1+2, SOI, NAO, PDO, NPI, and dT are relatively independent climate factors that have an impact on bigeye tuna catch. The optimal lag orders for these climate factors were determined to be 8 years for Niño1+2, 2 years for SOI, 9 years for NAO, 0 years for PDO, 9 years for NPI, and 3 years for dT. Among these factors, Niño1+2, SOI, and NAO were identified as the key climate factors influencing bigeye tuna catch. We constructed an optimal BP neural network model with a structure of 6-8-1, and the ratio of the difference between the predicted and actual bigeye tuna catch to the actual catch has been maintained within 15% since 1971. Additionally, the trend of the predicted and actual catch was found to be basically consistent, indicating a satisfactory level of model fit.
In order to investigate the impact of climate change on the catch of bigeye tuna, we utilized the annual Pacific bigeye tuna catch data from 1960 to 2021, which was statistically compiled by the Western and Central Pacific Fisheries Commission. We also employed corresponding monthly climate indices, including Niño1+2, Niño3, Niño4, Niño3.4, Southern Oscillation Index (SOI), North Atlantic Oscillation (NAO), Pacific Decadal Oscillation (PDO), North Pacific Index (NPI), and global sea-air temperature anomaly (dT). By using a BP neural network and variable sensitivity analysis, we examined the relationship between these low-frequency climate factors and bigeye tuna catch. Our findings revealed that Niño1+2, SOI, NAO, PDO, NPI, and dT are relatively independent climate factors that have an impact on bigeye tuna catch. The optimal lag orders for these climate factors were determined to be 8 years for Niño1+2, 2 years for SOI, 9 years for NAO, 0 years for PDO, 9 years for NPI, and 3 years for dT. Among these factors, Niño1+2, SOI, and NAO were identified as the key climate factors influencing bigeye tuna catch. We constructed an optimal BP neural network model with a structure of 6-8-1, and the ratio of the difference between the predicted and actual bigeye tuna catch to the actual catch has been maintained within 15% since 1971. Additionally, the trend of the predicted and actual catch was found to be basically consistent, indicating a satisfactory level of model fit.
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doi: 10.12284/hyxb2024-02
Abstract:
Recognition of reef-building corals is important for protecting and monitoring coral reef ecosystems. Deep learning, as an advanced technology in image recognition, has been increasingly applied in coral recognition. However, its performance is still challenged by several issues, such as the imbalance of samples among different coral categories within a dataset and the limitation of data diversity. The former makes the deep learning model more likely to extract features from classes with a large number of samples and, therefore, decreases its ability to recognize small-sample-size corals, which often refer to endangered ones needing to be protected. The latter further reduces the performance of deep learning in recognizing corals with different appearances and are captured in variant environments. To solve these two problems, this study develops a reef-building coral recognition method by integrating a category-quantity adaptive deep data augmentation algorithm and transfer learning. To address the first problem, a category-quantity adaptive deep data augmentation algorithm named DeepSMOTE-F1 is proposed. This algorithm improves the existing DeepSMOTE by introducing a sample-size determination stagey using an F1-score based evaluation metric. It can adaptively augment the number of samples of each category of corals according to its recognition performance so that the deep learning model can fully learn features from each class of corals. For the second problem, transfer learning is used to further enhance the model's ability to extract features. The experimental results on three widely used public coral recognition datasets, RSMAS, EILAT, and EILAT2 show that the recognition accuracy of the proposed DeepSMOTE-F1 is improved by 2.88%, 0.39%, and 1.54%, respectively, compared with the traditional DeepSMOTE; and the accuracy of the integrated method is improved by 0.76%, 1.40% and 1.30% compared with the existing deep learning methods for coral recognition.
Recognition of reef-building corals is important for protecting and monitoring coral reef ecosystems. Deep learning, as an advanced technology in image recognition, has been increasingly applied in coral recognition. However, its performance is still challenged by several issues, such as the imbalance of samples among different coral categories within a dataset and the limitation of data diversity. The former makes the deep learning model more likely to extract features from classes with a large number of samples and, therefore, decreases its ability to recognize small-sample-size corals, which often refer to endangered ones needing to be protected. The latter further reduces the performance of deep learning in recognizing corals with different appearances and are captured in variant environments. To solve these two problems, this study develops a reef-building coral recognition method by integrating a category-quantity adaptive deep data augmentation algorithm and transfer learning. To address the first problem, a category-quantity adaptive deep data augmentation algorithm named DeepSMOTE-F1 is proposed. This algorithm improves the existing DeepSMOTE by introducing a sample-size determination stagey using an F1-score based evaluation metric. It can adaptively augment the number of samples of each category of corals according to its recognition performance so that the deep learning model can fully learn features from each class of corals. For the second problem, transfer learning is used to further enhance the model's ability to extract features. The experimental results on three widely used public coral recognition datasets, RSMAS, EILAT, and EILAT2 show that the recognition accuracy of the proposed DeepSMOTE-F1 is improved by 2.88%, 0.39%, and 1.54%, respectively, compared with the traditional DeepSMOTE; and the accuracy of the integrated method is improved by 0.76%, 1.40% and 1.30% compared with the existing deep learning methods for coral recognition.
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Oil spill is one of the critical target of marine environmental monitoring. Synthetic Aperture Radar (SAR), thermal infrared remote sensing, and optical remote sensing for monitoring of marine oil spills have been elucidated, and it is crucial for marine environmental protection to utilize the features and advantages of multi-source remote sensing to achieve accurate monitoring and quantitative assessment of marine oil spills. On April 27, 2021, the collision between the Panamanian vessel Sea Justice and the Liberian oil tanker A Symphony resulted in an estimated 9,400 tons of cargo oil seeping into the sea. Here, we monitor and analyze the oil spill pollution coverage and emulsified oil spill characteristics in this accident using multi-source satellite remote sensing data. Based on the response mechanism and characteristics of oil spill multi-source remote sensing, the processing of multi-source data is optimized to realize the identification of oil spill and the classification of multiple oil spill types. The findings indicate that from May 1 to May 22, 2021, the cumulative pixel coverage area of oil spills from A Symphony tanker was2368.7 km2, of which the emulsified oil pixel coverage area was 1019.3 km2, accounting for 43.0%. The maximum daily oil spill pixel area reached 734 km2. The results of multi- remote sensing monitoring mutually validated each other, and optical remote sensing is more capable of identifying different oil spill pollution, in which the emulsified oil represents the key of pollution hazards. It improves the accuracy of monitoring and assessment of marine oil spill pollution, and provides reliable technical and methodological references for the hazard assessment and refined monitoring of oil pollution events.
Oil spill is one of the critical target of marine environmental monitoring. Synthetic Aperture Radar (SAR), thermal infrared remote sensing, and optical remote sensing for monitoring of marine oil spills have been elucidated, and it is crucial for marine environmental protection to utilize the features and advantages of multi-source remote sensing to achieve accurate monitoring and quantitative assessment of marine oil spills. On April 27, 2021, the collision between the Panamanian vessel Sea Justice and the Liberian oil tanker A Symphony resulted in an estimated 9,400 tons of cargo oil seeping into the sea. Here, we monitor and analyze the oil spill pollution coverage and emulsified oil spill characteristics in this accident using multi-source satellite remote sensing data. Based on the response mechanism and characteristics of oil spill multi-source remote sensing, the processing of multi-source data is optimized to realize the identification of oil spill and the classification of multiple oil spill types. The findings indicate that from May 1 to May 22, 2021, the cumulative pixel coverage area of oil spills from A Symphony tanker was
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Abstract:
Against the backdrop of global warming, the Arctic has experienced a series of changes, including permafrost degradation, reduced summer sea ice, increased land runoff, and intensified coastal erosion. With global warming, organic carbon (OC) stored in permafrost is accelerating its migration and release to the sea, which will affect the pattern of carbon cycling in the Arctic Ocean. However, there is currently little evidence to directly confirm this inference. This article analyzes the lignin and carbon isotopes of two hundred year scale sedimentary cores in the Chukchi Sea, and discusses the sources and profile changes of the buried organic matter. The results showed that the organic carbon in the columnar sediments of the Chukchi Sea came from a mixed contribution of herbaceous tissue of terrestrial C3 plants and marine source production. The absolute content of lignin Σ8 in sediment shows an overall upward trend, indicating that with global warming, more terrestrial materials are being transported to the Chukchi Sea. This study indicates that global warming caused by human activities has indeed increased the migration of organic carbon from permafrost to the sea, and the increase in lignin content due to enhanced terrestrial inputs is direct evidence of the enhanced melting of permafrost caused by global warming on a century scale.
Against the backdrop of global warming, the Arctic has experienced a series of changes, including permafrost degradation, reduced summer sea ice, increased land runoff, and intensified coastal erosion. With global warming, organic carbon (OC) stored in permafrost is accelerating its migration and release to the sea, which will affect the pattern of carbon cycling in the Arctic Ocean. However, there is currently little evidence to directly confirm this inference. This article analyzes the lignin and carbon isotopes of two hundred year scale sedimentary cores in the Chukchi Sea, and discusses the sources and profile changes of the buried organic matter. The results showed that the organic carbon in the columnar sediments of the Chukchi Sea came from a mixed contribution of herbaceous tissue of terrestrial C3 plants and marine source production. The absolute content of lignin Σ8 in sediment shows an overall upward trend, indicating that with global warming, more terrestrial materials are being transported to the Chukchi Sea. This study indicates that global warming caused by human activities has indeed increased the migration of organic carbon from permafrost to the sea, and the increase in lignin content due to enhanced terrestrial inputs is direct evidence of the enhanced melting of permafrost caused by global warming on a century scale.
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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.
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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.
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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.
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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.
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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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2024, 46(8): 1-18.
doi: 10.12284/hyxb2024081
Abstract:
It prevails southwesterly monsoon in summer in the northern South China Sea. Consequently, the seasonal coastal upwellings are frequently driven up in summer off the southeastern coast of the Hainan Island, the eastern coast of the Leizhou Peninsula and the eastern coast of Guangdong Province, and these upwellings have attracted common research attention. The present paper revisits the historic hydrologic survey data in the northern South China Sea. It is found that, besides the coastal upwellings frequently reaching the sea surface in the above-mentioned zones, there are more subsurface upwelling patterns in the northern South China Sea: namely, (1) the subsurface upwelling throughout the eastern coastal zones of Hainan Province and all the western and eastern coastal zones of Guangdong Province under strong overlying southwesterly monsoon; (2) the subsurface one over the wide continental shelf off the western coast of Guangdong Province; (3) the subsurface one driven by the diluted Pearl River runoff off the river mouth; and (4) the bottom continental water invasion into the bays of eastern Guangdong Province and the cyclonic eddies in the bays. These four upwelling patterns have not been reported in the existing research papers, or little attention has been paid to them. Besides the Ekman’s transport due to strong summer southwesterly monsoon and Ekman’s pumping due to overlying wind stress curl, the bottom Ekman’s effect due to the basin-scale South China Sea circulation is possibly the non-negligible driving mechanism for the subsurface upwelling throughout all the coastal zones. In the light of the simultaneous atmospheric circulation over the northern South China Sea, Ekman’s pumping due to positive wind stress curl seems to be the major driving force for the subsurface upwelling over the continental shelf off western Guangdong coast. The positive wind stress curl as well as the diluted Pearl River runoff drives a cyclonic circulation off western Guangdong coast. The seawater divengence in the cyclonic circulation is favorable to the formation and maintenance of the subsurface upwelling. The vertical circulations driven by southwesterly monsoon and horizontal cyclonic ones in the coastal bays of eastern Guangdong Province are the major driving forces for the bottom continental water intruding into the bays. In the Daya Bay, the thermal plume due to the unclear power plants is favorable to strengthen the horizontal cyclonic circulations. The western and eastern capes of the Honghai Bay are favorable to the formation of horizontal cyclonic circulations in the bay. So we need attach more importance to the other driving mechanisms of the upwelling but to surface Ekman’s effect in the northern South China Sea.
It prevails southwesterly monsoon in summer in the northern South China Sea. Consequently, the seasonal coastal upwellings are frequently driven up in summer off the southeastern coast of the Hainan Island, the eastern coast of the Leizhou Peninsula and the eastern coast of Guangdong Province, and these upwellings have attracted common research attention. The present paper revisits the historic hydrologic survey data in the northern South China Sea. It is found that, besides the coastal upwellings frequently reaching the sea surface in the above-mentioned zones, there are more subsurface upwelling patterns in the northern South China Sea: namely, (1) the subsurface upwelling throughout the eastern coastal zones of Hainan Province and all the western and eastern coastal zones of Guangdong Province under strong overlying southwesterly monsoon; (2) the subsurface one over the wide continental shelf off the western coast of Guangdong Province; (3) the subsurface one driven by the diluted Pearl River runoff off the river mouth; and (4) the bottom continental water invasion into the bays of eastern Guangdong Province and the cyclonic eddies in the bays. These four upwelling patterns have not been reported in the existing research papers, or little attention has been paid to them. Besides the Ekman’s transport due to strong summer southwesterly monsoon and Ekman’s pumping due to overlying wind stress curl, the bottom Ekman’s effect due to the basin-scale South China Sea circulation is possibly the non-negligible driving mechanism for the subsurface upwelling throughout all the coastal zones. In the light of the simultaneous atmospheric circulation over the northern South China Sea, Ekman’s pumping due to positive wind stress curl seems to be the major driving force for the subsurface upwelling over the continental shelf off western Guangdong coast. The positive wind stress curl as well as the diluted Pearl River runoff drives a cyclonic circulation off western Guangdong coast. The seawater divengence in the cyclonic circulation is favorable to the formation and maintenance of the subsurface upwelling. The vertical circulations driven by southwesterly monsoon and horizontal cyclonic ones in the coastal bays of eastern Guangdong Province are the major driving forces for the bottom continental water intruding into the bays. In the Daya Bay, the thermal plume due to the unclear power plants is favorable to strengthen the horizontal cyclonic circulations. The western and eastern capes of the Honghai Bay are favorable to the formation of horizontal cyclonic circulations in the bay. So we need attach more importance to the other driving mechanisms of the upwelling but to surface Ekman’s effect in the northern South China Sea.
2024, 46(8): 19-36.
doi: 10.12284/hyxb2024083
Abstract:
Using temperature-salinity profiles and current measurements, satellite data and reanalysis data in April 2018, this study analyses the acoustic field characteristics and effects of an abnormal anticyclonic eddy (AAE) on acoustic propagation on the continental slope area in the northwestern South China Sea (SCS). The results show that the AAE has a lens-shaped structure with a surface cold core, a shallower mixed layer, and subsurface intensified velocities. Unlike the concave sound-speed contours in the normal anticyclonic eddy (NAE), the sound-speed distribution in the abnormal anticyclonic eddy (AAE) exhibits a lens-shaped structure with an upward convexity and downward concavity. The surface sound speed within the eddy is lower than that outside, showing a negative anomaly (<−2 m/s). Conversely, the sound speed in the subsurface layer of the eddy is higher than that outside, showing a positive anomaly (>11 m/s). This results in the thickness of the original double thermocline extending up and down by a total of 47 meters in the presence of the eddy. As the sound propagates from the eddy outside on the shelf to the deep sea, the surface sound channel disappears as the propagation distances decreasing in the AAE, contrast to the increased distance in the NAE. As the sound propagates from the eddy outside in the deep ocean to the shelf, the location of the sound energy convergence zone moves backward and downward in the AAE, with the maximum distance exceeding 24 km and 0.3 km, respectively. This is similar to the situation in the NAE. As the sound propagates from the eddy core to outside in the deep sea, the turning depth of the sound deepens and the distance between the sound energy convergence zones doubles in the AAE, while no changes in the NAE.
Using temperature-salinity profiles and current measurements, satellite data and reanalysis data in April 2018, this study analyses the acoustic field characteristics and effects of an abnormal anticyclonic eddy (AAE) on acoustic propagation on the continental slope area in the northwestern South China Sea (SCS). The results show that the AAE has a lens-shaped structure with a surface cold core, a shallower mixed layer, and subsurface intensified velocities. Unlike the concave sound-speed contours in the normal anticyclonic eddy (NAE), the sound-speed distribution in the abnormal anticyclonic eddy (AAE) exhibits a lens-shaped structure with an upward convexity and downward concavity. The surface sound speed within the eddy is lower than that outside, showing a negative anomaly (<−2 m/s). Conversely, the sound speed in the subsurface layer of the eddy is higher than that outside, showing a positive anomaly (>11 m/s). This results in the thickness of the original double thermocline extending up and down by a total of 47 meters in the presence of the eddy. As the sound propagates from the eddy outside on the shelf to the deep sea, the surface sound channel disappears as the propagation distances decreasing in the AAE, contrast to the increased distance in the NAE. As the sound propagates from the eddy outside in the deep ocean to the shelf, the location of the sound energy convergence zone moves backward and downward in the AAE, with the maximum distance exceeding 24 km and 0.3 km, respectively. This is similar to the situation in the NAE. As the sound propagates from the eddy core to outside in the deep sea, the turning depth of the sound deepens and the distance between the sound energy convergence zones doubles in the AAE, while no changes in the NAE.
2024, 46(8): 37-49.
doi: 10.12284/hyxb2024073
Abstract:
Based on the Acoustic Doppler Current Profiler carried by deep-sea moorings, we investigated the diel vertical migration of the acoustic scattering layer and the impact of internal solitary waves on it in the northern South China Sea. The observational results reveal that the acoustic scattering layer, influenced by zooplankton, ascends to shallower depth within approximately an hour after sunset, remains there throughout the night, then migrates to the deeper depth within about an hour before sunrise. The average migration velocities are 4.7 cm/s (upward) and 5.8 cm/s (downward). Additionally, internal solitary waves observed in the region induce a pair of downward and upward currents, with maximum vertical velocities exceeding 50 cm/s, leading to fluctuations of tens to hundreds of meters in the acoustic scattering layer. The acoustic backscattering strength of the ocean’s upper layer reaches its maximum value at the troughs of internal solitary waves. Further research indicates that the daytime internal solitary waves exhibit a stronger correlation between the vertical velocity and the depth-averaged backscattering strength variation compared to the nighttime internal solitary waves. When the vertical velocities induced by both types of waves are equal, the depth-averaged backscattering strength variations during the day are typically greater than those at night.
Based on the Acoustic Doppler Current Profiler carried by deep-sea moorings, we investigated the diel vertical migration of the acoustic scattering layer and the impact of internal solitary waves on it in the northern South China Sea. The observational results reveal that the acoustic scattering layer, influenced by zooplankton, ascends to shallower depth within approximately an hour after sunset, remains there throughout the night, then migrates to the deeper depth within about an hour before sunrise. The average migration velocities are 4.7 cm/s (upward) and 5.8 cm/s (downward). Additionally, internal solitary waves observed in the region induce a pair of downward and upward currents, with maximum vertical velocities exceeding 50 cm/s, leading to fluctuations of tens to hundreds of meters in the acoustic scattering layer. The acoustic backscattering strength of the ocean’s upper layer reaches its maximum value at the troughs of internal solitary waves. Further research indicates that the daytime internal solitary waves exhibit a stronger correlation between the vertical velocity and the depth-averaged backscattering strength variation compared to the nighttime internal solitary waves. When the vertical velocities induced by both types of waves are equal, the depth-averaged backscattering strength variations during the day are typically greater than those at night.
2024, 46(8): 50-62.
doi: 10.12284/hyxb2024071
Abstract:
The analysis of the changes in the path of the Kuroshio south of Japan has always been a hot topic. Previous studies have pointed out that the changes in the Kuroshio path south of Japan are influenced by various factors, such as upstream transport, mesoscale eddies, climate signals etc. However, the causal relationship between these influencing factors is not fully understood. The paper first obtains the time series of the Kuroshio path south of Japan based on the 50 year (1958−2007) China Ocean Reanalysis dataset (CORA) and 14 year (2008−2021) satellite altimeter data, and uses the Complex Empirical Orthogonal Function (CEOF) analysis method to analyze its spatiotemporal characteristics. The results show that the first two main modes obtained by CEOF analysis can describe the main characteristics of the space-time variation of the Kuroshio path in the south of Japan and represent the related eastward and westward signals, respectively. Furthermore, the causal analysis results based on information flow theory indicate that: on the one hand, PDO affects the eddy kinetic energy in the subtropical countercurrent (STCC) region through changes in wind stress, thus affecting the changes of Kuroshio transport in the Tokara Strait, and then has a direct impact on the eastward signal, and finally affects the changes of the Kuroshio path in the southern region of Japan. On the other hand, the eddy kinetic energy of the Kuroshio extension is influenced by the NPGO signal, which affects the westward movement of the mesoscale eddies in the region, thereby directly affecting the westward signal and ultimately affecting the Kuroshio path changes in the region south of Japan. In addition, the experimental results also indicate that the relative vorticity and recirculation gyre strength in the southern region of Japan are responses to the changes in the Kuroshio path, rather than factors affecting the changes in the Kuroshio path.
The analysis of the changes in the path of the Kuroshio south of Japan has always been a hot topic. Previous studies have pointed out that the changes in the Kuroshio path south of Japan are influenced by various factors, such as upstream transport, mesoscale eddies, climate signals etc. However, the causal relationship between these influencing factors is not fully understood. The paper first obtains the time series of the Kuroshio path south of Japan based on the 50 year (1958−2007) China Ocean Reanalysis dataset (CORA) and 14 year (2008−2021) satellite altimeter data, and uses the Complex Empirical Orthogonal Function (CEOF) analysis method to analyze its spatiotemporal characteristics. The results show that the first two main modes obtained by CEOF analysis can describe the main characteristics of the space-time variation of the Kuroshio path in the south of Japan and represent the related eastward and westward signals, respectively. Furthermore, the causal analysis results based on information flow theory indicate that: on the one hand, PDO affects the eddy kinetic energy in the subtropical countercurrent (STCC) region through changes in wind stress, thus affecting the changes of Kuroshio transport in the Tokara Strait, and then has a direct impact on the eastward signal, and finally affects the changes of the Kuroshio path in the southern region of Japan. On the other hand, the eddy kinetic energy of the Kuroshio extension is influenced by the NPGO signal, which affects the westward movement of the mesoscale eddies in the region, thereby directly affecting the westward signal and ultimately affecting the Kuroshio path changes in the region south of Japan. In addition, the experimental results also indicate that the relative vorticity and recirculation gyre strength in the southern region of Japan are responses to the changes in the Kuroshio path, rather than factors affecting the changes in the Kuroshio path.
2024, 46(8): 63-73.
doi: 10.12284/hyxb2024091
Abstract:
Tides act an important role in the transfer of ocean energy and mixing, and provide the main energy to maintain the global thermohaline circulation and influence the global ocean circulation. Previous work has explored the sensitivity of ocean circulation states to tidal forcing within an individual ocean model at a low resolution. To further investigate the influence of tidal forcing on ocean circulation and climate states, it is imperative to incorporate the tidal forcing into a coupled climate model. In this paper, the eight major equilibrium constituents are included into the coupled climate model FGOALS-g3 explicitly, and we evaluate its ability to simulate global ocean tides, which lays the basic for the further research on the influence of tidal forcing on large-scale circulation and climate states.We apply tidal harmonic analysis on the sea surface height data to obtain the harmonic constants of each constituent, and compare the model results with the global tidal models TPXO9 and FES2014, and the open ocean tide dataset from st102. The results show that the coupled model FGOALS-g3 can effectively simulate the barotropic tides in the global ocean, with relatively small errors compared to the global tidal models and the observation dataset. Compared with these two global tidal models, the mean square error is relatively small, and the errors are mostly distributed in the region of larger amplitudes. And compared with st102 dataset, the average amplitude relative errors of the eight major equilibrium constituents simulated by FGOALS-g3 are all less than 10%, and the total mean square errors are all less than 10 cm.
Tides act an important role in the transfer of ocean energy and mixing, and provide the main energy to maintain the global thermohaline circulation and influence the global ocean circulation. Previous work has explored the sensitivity of ocean circulation states to tidal forcing within an individual ocean model at a low resolution. To further investigate the influence of tidal forcing on ocean circulation and climate states, it is imperative to incorporate the tidal forcing into a coupled climate model. In this paper, the eight major equilibrium constituents are included into the coupled climate model FGOALS-g3 explicitly, and we evaluate its ability to simulate global ocean tides, which lays the basic for the further research on the influence of tidal forcing on large-scale circulation and climate states.We apply tidal harmonic analysis on the sea surface height data to obtain the harmonic constants of each constituent, and compare the model results with the global tidal models TPXO9 and FES2014, and the open ocean tide dataset from st102. The results show that the coupled model FGOALS-g3 can effectively simulate the barotropic tides in the global ocean, with relatively small errors compared to the global tidal models and the observation dataset. Compared with these two global tidal models, the mean square error is relatively small, and the errors are mostly distributed in the region of larger amplitudes. And compared with st102 dataset, the average amplitude relative errors of the eight major equilibrium constituents simulated by FGOALS-g3 are all less than 10%, and the total mean square errors are all less than 10 cm.
2024, 46(8): 74-88.
doi: 10.12284/hyxb2024053
Abstract:
Sea ice leads in the Arctic, accounting for only 1%−10% area of the whole ice area, play a crucial role in the exchange of energy and moisture between the ocean and the atmosphere. Currently, the analysis of the numerical simulation of the leads mainly focuses on the spatial distribution of the occurrence frequency and the spatio-temporal variations of the lead area proportion within the cell, while few analysis concerns the simulated lead morphology (length, width and orientation). This article is based on the high-resolution (2 km) ice sea coupling model using visual plastic rheologies to simulate sea ice thickness to extract leads, and the lead morphology is compared to three MODIS lead products respectly. The results show that the spatial distribution of simulated leads occurrence frequency in Beaufort Sea is basically consistent with WH2015 and H2019 products. The number density and total length of leads with a width greater than 6 km follow the power law distribution as presented in remote sensing products, while that of the narrow (2−4 km) leads are underestimated due to limited model’s resolution. The correlation between the total length of simulated leads and remote sensed products is high in January and March, but the model fails to reproduce the trends in February and April shown in the remote sensing products. The overall orientation of the simulated leads aligns with the remote sensing products, both show that leads along the north of the Canadian archipelago and the southeast of Beaufort sea are almost parallel to the coastline and the ice drift direction, while the orientation of the simulated leads is more restricted by the continent than that of remote sensing products, and the location of the lead and ice speed turning is not consistent in the middle of the Beaufort Sea. This study highlights the capability of the state-of-the-art high-resolution sea ice-ocean coupled models in simulating various morphological characteristics of sea ice lead, and provides insights for further model improvements.
Sea ice leads in the Arctic, accounting for only 1%−10% area of the whole ice area, play a crucial role in the exchange of energy and moisture between the ocean and the atmosphere. Currently, the analysis of the numerical simulation of the leads mainly focuses on the spatial distribution of the occurrence frequency and the spatio-temporal variations of the lead area proportion within the cell, while few analysis concerns the simulated lead morphology (length, width and orientation). This article is based on the high-resolution (2 km) ice sea coupling model using visual plastic rheologies to simulate sea ice thickness to extract leads, and the lead morphology is compared to three MODIS lead products respectly. The results show that the spatial distribution of simulated leads occurrence frequency in Beaufort Sea is basically consistent with WH2015 and H2019 products. The number density and total length of leads with a width greater than 6 km follow the power law distribution as presented in remote sensing products, while that of the narrow (2−4 km) leads are underestimated due to limited model’s resolution. The correlation between the total length of simulated leads and remote sensed products is high in January and March, but the model fails to reproduce the trends in February and April shown in the remote sensing products. The overall orientation of the simulated leads aligns with the remote sensing products, both show that leads along the north of the Canadian archipelago and the southeast of Beaufort sea are almost parallel to the coastline and the ice drift direction, while the orientation of the simulated leads is more restricted by the continent than that of remote sensing products, and the location of the lead and ice speed turning is not consistent in the middle of the Beaufort Sea. This study highlights the capability of the state-of-the-art high-resolution sea ice-ocean coupled models in simulating various morphological characteristics of sea ice lead, and provides insights for further model improvements.
2024, 46(8): 89-107.
doi: 10.12284/hyxb2024077
Abstract:
When black carbon deposits on snow/ice surface, it can reduce the albedo and increase the absorption of shortwave radiation. The changes in black carbon and their impact on the sea ice melting process are worth investigating. Study of the influence of black carbon in the Arctic Ocean was conducted using the CICE sea ice model. The results indicates that under the impact of black carbon deposition from different sources, from 1980 to 2014, the simulated summer albedo of the Arctic Ocean decreased by 0.82% to 1.71%, ultimately causing a decrease in sea ice extent by 0.97%−1.93%. In the Barents Sea, Kara Sea, and Laptev Sea, the summer sea ice area reduction caused by black carbon is approximately 2–3 times greater than the overall reduction in the Arctic Ocean. The simulation results under different black carbon deposition all show that from 1980 to 1995, the impact of black carbon on albedo in the Arctic exhibited a decreasing trend. However, from 1996 to 2014, the black carbon effect shifted to an increasing trend. In low-latitude regions, due to the retreat of sea ice, the effect of black carbon showed a decreasing trend, while in high-latitude regions, due to the cumulative effect of black carbon in multi-year ice, the radiative impact of black carbon showed an enhancing effect.
When black carbon deposits on snow/ice surface, it can reduce the albedo and increase the absorption of shortwave radiation. The changes in black carbon and their impact on the sea ice melting process are worth investigating. Study of the influence of black carbon in the Arctic Ocean was conducted using the CICE sea ice model. The results indicates that under the impact of black carbon deposition from different sources, from 1980 to 2014, the simulated summer albedo of the Arctic Ocean decreased by 0.82% to 1.71%, ultimately causing a decrease in sea ice extent by 0.97%−1.93%. In the Barents Sea, Kara Sea, and Laptev Sea, the summer sea ice area reduction caused by black carbon is approximately 2–3 times greater than the overall reduction in the Arctic Ocean. The simulation results under different black carbon deposition all show that from 1980 to 1995, the impact of black carbon on albedo in the Arctic exhibited a decreasing trend. However, from 1996 to 2014, the black carbon effect shifted to an increasing trend. In low-latitude regions, due to the retreat of sea ice, the effect of black carbon showed a decreasing trend, while in high-latitude regions, due to the cumulative effect of black carbon in multi-year ice, the radiative impact of black carbon showed an enhancing effect.
2024, 46(8): 108-120.
doi: 10.12284/hyxb2024087
Abstract:
Antarctic sea ice is a crucial component of the polar climate system, with profound implications for global climate. Sea ice thickness, as one of the key properties of sea ice, holds significant importance for understanding and predicting the influences of climate change by revealing its spatial and temporal distribution patterns and variation trends. However, current monitoring of Antarctic sea ice thickness is constrained by limited ground observations with restricted spatial and temporal coverage or short-term satellite observations, long-term sea ice thickness data remains elusive. To address this issue, this study utilized the continuous satellite radar altimetry data from Envisat and CryoSat-2 and constructed a consistent dataset of radar freeboard of Antarctic sea ice. Then, the penetration depth of radar signals through the snow covers over Antarctic sea ice was quantitatively estimated, and a method applicable to various sea ice-snow scenarios for estimating Antarctic sea ice thickness was developed. The estimated sea ice thickness shows an average absolute bias of approximately 0.28 m compared to in situ measurements from the Australian Antarctic Data Centre, and an average absolute bias of approximately 0.65 m compared to ICESat laser altimeter with a high correlation coefficient of 0.71. Analysis of the spatiotemporal variations of Antarctic sea ice thickness from 2002 to 2023 reveals that thick ice is predominantly concentrated in the western Weddell Sea and Bellingshuan/Amundsen Seas, while ice in other sea sectors is relatively thin. Antarctic sea ice thickness exhibited a slight decreasing trend before 2011, followed by an accelerated decline after 2011 (−0.03 m/a). The distribution and trends of Antarctic sea ice thickness exhibit distinct seasonal and regional characteristics.
Antarctic sea ice is a crucial component of the polar climate system, with profound implications for global climate. Sea ice thickness, as one of the key properties of sea ice, holds significant importance for understanding and predicting the influences of climate change by revealing its spatial and temporal distribution patterns and variation trends. However, current monitoring of Antarctic sea ice thickness is constrained by limited ground observations with restricted spatial and temporal coverage or short-term satellite observations, long-term sea ice thickness data remains elusive. To address this issue, this study utilized the continuous satellite radar altimetry data from Envisat and CryoSat-2 and constructed a consistent dataset of radar freeboard of Antarctic sea ice. Then, the penetration depth of radar signals through the snow covers over Antarctic sea ice was quantitatively estimated, and a method applicable to various sea ice-snow scenarios for estimating Antarctic sea ice thickness was developed. The estimated sea ice thickness shows an average absolute bias of approximately 0.28 m compared to in situ measurements from the Australian Antarctic Data Centre, and an average absolute bias of approximately 0.65 m compared to ICESat laser altimeter with a high correlation coefficient of 0.71. Analysis of the spatiotemporal variations of Antarctic sea ice thickness from 2002 to 2023 reveals that thick ice is predominantly concentrated in the western Weddell Sea and Bellingshuan/Amundsen Seas, while ice in other sea sectors is relatively thin. Antarctic sea ice thickness exhibited a slight decreasing trend before 2011, followed by an accelerated decline after 2011 (−0.03 m/a). The distribution and trends of Antarctic sea ice thickness exhibit distinct seasonal and regional characteristics.
2024, 46(8): 121-130.
doi: 10.12284/hyxb2024079
Abstract:
Coastal Acoustic Tomography (CAT) is an effective tool to observe the flow field in the large offshore range using high-frequency acoustic signals, of which direct observation range is still limited. The numerical ocean model provides a large-scale ocean background field with simulation errors, and the resolution and accuracy of the flow field results can be improved by assimilating the CAT data with the ocean background results. In this paper, we applied a method to obtain a larger range of two-dimensional ocean flow field results by fitting ocean-mode flow field results using Stream Function and assimilating CAT data using the Ensemble Kalman Filtering algorithm. The assimilation study used the unstructured grid Finite-Volume Community Ocean Model (FVCOM) as the background field, and the four CAT stations experiment conducted in Bali Strait, Indonesia, from 1st to 3rd June 2016 as the observational data. After fitting background field by Stream Function and assimilating CAT data, the two-dimensional flow field in Bali Strait is obtained. The assimilation results were compared with those of the same period of observation and tide level data, which is found that the flow function fitted and assimilated flow field can more accurately describe the high and low tides and flow conditions in the Bali Strait. By introducing the functional relationship between the CAT data and the flow field it can effectively reduce the error of the ocean model and the sparsity of the original observation data.
Coastal Acoustic Tomography (CAT) is an effective tool to observe the flow field in the large offshore range using high-frequency acoustic signals, of which direct observation range is still limited. The numerical ocean model provides a large-scale ocean background field with simulation errors, and the resolution and accuracy of the flow field results can be improved by assimilating the CAT data with the ocean background results. In this paper, we applied a method to obtain a larger range of two-dimensional ocean flow field results by fitting ocean-mode flow field results using Stream Function and assimilating CAT data using the Ensemble Kalman Filtering algorithm. The assimilation study used the unstructured grid Finite-Volume Community Ocean Model (FVCOM) as the background field, and the four CAT stations experiment conducted in Bali Strait, Indonesia, from 1st to 3rd June 2016 as the observational data. After fitting background field by Stream Function and assimilating CAT data, the two-dimensional flow field in Bali Strait is obtained. The assimilation results were compared with those of the same period of observation and tide level data, which is found that the flow function fitted and assimilated flow field can more accurately describe the high and low tides and flow conditions in the Bali Strait. By introducing the functional relationship between the CAT data and the flow field it can effectively reduce the error of the ocean model and the sparsity of the original observation data.
2024, 46(8): 131-142.
doi: 10.12284/hyxb2024075
Abstract:
Sea ice is an indicator of global climate change, and the change of Arctic sea ice is related to global warming and sea level rise. Aiming at the problems such as inaccuracy and slow speed of extracting details from sea ice by traditional semantic segmentation model, an improved DeepLabV3+ sea ice extraction method was constructed. Firstly, we replaced the Xception backbone network with MobileNetV2, which significantly reduces the network’s parameter count and save time while maintaining the accuracy of sea ice extraction. Secondly, we enhanced the ASPP module to DenseASPP, further expanding the receptive field during multi-scale feature extraction for sea ice, resulting in denser features. Lastly, we introduced a coordinate attention mechanism to strengthen the focus on both channel and spatial features, enhancing the extraction of fine edge details in sea ice. The Greenland Sea in the Arctic is selected as the experimental area, and 10 Sentinel-1A dual-polarization SAR images from the winter of 2020 to 2022 in the sea area are processed and labeled to form a data set for the experiment, we compared our method with classic models such as U-Net, PSPNet and DeepLabV3+. The results showed that our method achieved anmIoU of 88.46% and an mPA of 94.16%. Compared to the traditional DeepLabV3+, mIoU increased by 2.35%, mPA increased by 2.90%, and the parameter count and GFLOPs decreased 45.08 M and 106.01 G, respectively. Meanwhile, the training time and sea ice extraction time decreased by 68% and 30%, respectively. Compared to U-Net、PSPNet and other models, the optimal results are also obtained. Compared with other models, the new model constructed in this paper has a stronger learning ability about sea ice characteristics, can obtain more detailed information of sea ice and greatly saves time, and can provide technical support for the study of sea ice degradation monitoring under global warming environment.
Sea ice is an indicator of global climate change, and the change of Arctic sea ice is related to global warming and sea level rise. Aiming at the problems such as inaccuracy and slow speed of extracting details from sea ice by traditional semantic segmentation model, an improved DeepLabV3+ sea ice extraction method was constructed. Firstly, we replaced the Xception backbone network with MobileNetV2, which significantly reduces the network’s parameter count and save time while maintaining the accuracy of sea ice extraction. Secondly, we enhanced the ASPP module to DenseASPP, further expanding the receptive field during multi-scale feature extraction for sea ice, resulting in denser features. Lastly, we introduced a coordinate attention mechanism to strengthen the focus on both channel and spatial features, enhancing the extraction of fine edge details in sea ice. The Greenland Sea in the Arctic is selected as the experimental area, and 10 Sentinel-1A dual-polarization SAR images from the winter of 2020 to 2022 in the sea area are processed and labeled to form a data set for the experiment, we compared our method with classic models such as U-Net, PSPNet and DeepLabV3+. The results showed that our method achieved anmIoU of 88.46% and an mPA of 94.16%. Compared to the traditional DeepLabV3+, mIoU increased by 2.35%, mPA increased by 2.90%, and the parameter count and GFLOPs decreased 45.08 M and 106.01 G, respectively. Meanwhile, the training time and sea ice extraction time decreased by 68% and 30%, respectively. Compared to U-Net、PSPNet and other models, the optimal results are also obtained. Compared with other models, the new model constructed in this paper has a stronger learning ability about sea ice characteristics, can obtain more detailed information of sea ice and greatly saves time, and can provide technical support for the study of sea ice degradation monitoring under global warming environment.
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