2021 Vol. 43, No. 11
Display Method:
2021, 43(11): 105-115.
doi: 10.12284/hyxb2021140
Abstract:
Tuna is an important fishing target in China’s pelagic fishery. Its morphological indexes are of great significance for the study of the growth, development and life history of tunas. Manual measurement of morphological index is a very tedious and inefficient measurement method, while computer vision is an efficient and objective automatic measurement method. Therefore, in this paper, images of three Thunnus species are preprocessed by the computer vision library (OpenCV). It mainly uses image processing techniques such as bilateral filter, gray transformation, image binarization and contour extraction to obtain the contour image of tuna. According to the pre-selected feature points, the computer vision technology is used to traversal all the pixel points on the contour image, and 17 pre-selected feature points of each contour image are automatically located. By using the computer vision technology, the pixel length of the morphological index of the three species of tuna is automatically measured and the actual length of the morphological index is calculated. The absolute error and relative error between automatic measurement and manual measurement are compared and analyzed. The results show that the computer vision technique is effective in the automatic measurement of the morphological indexes of the three Thunnus species. The absolute error ranges of 12 morphological indices of Thunnus obesus, Thunnus albacores and Thunnus alalunga are 0.00−1.46 cm, 0−1.73 cm and 0−1.32 cm, respectively, and the relative error ranges are 0.01%−5.84%, 0%−6.17% and 0%−6.89%, respectively. It is expected to provide a basis for intelligent identification of tuna and a basic reference for automatic measurement of other fish.
Tuna is an important fishing target in China’s pelagic fishery. Its morphological indexes are of great significance for the study of the growth, development and life history of tunas. Manual measurement of morphological index is a very tedious and inefficient measurement method, while computer vision is an efficient and objective automatic measurement method. Therefore, in this paper, images of three Thunnus species are preprocessed by the computer vision library (OpenCV). It mainly uses image processing techniques such as bilateral filter, gray transformation, image binarization and contour extraction to obtain the contour image of tuna. According to the pre-selected feature points, the computer vision technology is used to traversal all the pixel points on the contour image, and 17 pre-selected feature points of each contour image are automatically located. By using the computer vision technology, the pixel length of the morphological index of the three species of tuna is automatically measured and the actual length of the morphological index is calculated. The absolute error and relative error between automatic measurement and manual measurement are compared and analyzed. The results show that the computer vision technique is effective in the automatic measurement of the morphological indexes of the three Thunnus species. The absolute error ranges of 12 morphological indices of Thunnus obesus, Thunnus albacores and Thunnus alalunga are 0.00−1.46 cm, 0−1.73 cm and 0−1.32 cm, respectively, and the relative error ranges are 0.01%−5.84%, 0%−6.17% and 0%−6.89%, respectively. It is expected to provide a basis for intelligent identification of tuna and a basic reference for automatic measurement of other fish.
2021, 43(11): 116-122.
doi: 10.12284/hyxb2021122
Abstract:
In order to explore the effects of low temperature stress on the expression of genes related to lipid synthesis and catabolism in cobia (Rachycentron canadum), the experiment set up a normal temperature group (30.5±1.0)°C and a low temperature group (20.0±0.5)°C, and used real-time fluorescent quantitative PCR (qRT-PCR) to analyze the expression levels of 5 target genes in liver, muscle and intraperitoneal fat (IPF). The results showed that at 1 d, the expression of
In order to explore the effects of low temperature stress on the expression of genes related to lipid synthesis and catabolism in cobia (Rachycentron canadum), the experiment set up a normal temperature group (30.5±1.0)°C and a low temperature group (20.0±0.5)°C, and used real-time fluorescent quantitative PCR (qRT-PCR) to analyze the expression levels of 5 target genes in liver, muscle and intraperitoneal fat (IPF). The results showed that at 1 d, the expression of
2021, 43(11): 123-135.
doi: 10.12284/hyxb2021150
Abstract:
The community structure of scleractinian corals in the southwest seawaters the of the Weizhou Island was analyzed with the data collected in a survey conducted with the method of line intercept transect from May 14 to 22, 2019. The results showed that 38 species of scleractinian corals in 9 families were found, dominated by mass corals such as porites sp., favites abdita, goniopora stutchburyi etc. The coverage of the living scleractinian corals ranged from 5.20% to 31.20%, the average coverage were 16.66%, higher at the sites far from or close to the shore but with deeper water. The living scleractinian coral had low recruitment rate, few diseases and low mortality rate. Species diversity, dominance and evenness of the scleractinian coral communities were positively correlated one another (p<0.05). The coverage and biodiversity of the living scleractinian corals were higher at the sites where anthropogenic disturbance was less, i.e. closer to the cliff, deeper water, fewer boating and diving etc. The living scleractinian corals closer to sandy beach influenced severely by suspended sediment on eroded coast and diving had the lowest coverage, the highest dominance of the dominant species and relatively lower diversity. Human activities, southwest monsoon, storm surge, suspended sediment on eroded coast and extreme weather are the main influential factors on the coral reef ecosystem in the southwest seawaters of the Weizhou Island.
The community structure of scleractinian corals in the southwest seawaters the of the Weizhou Island was analyzed with the data collected in a survey conducted with the method of line intercept transect from May 14 to 22, 2019. The results showed that 38 species of scleractinian corals in 9 families were found, dominated by mass corals such as porites sp., favites abdita, goniopora stutchburyi etc. The coverage of the living scleractinian corals ranged from 5.20% to 31.20%, the average coverage were 16.66%, higher at the sites far from or close to the shore but with deeper water. The living scleractinian coral had low recruitment rate, few diseases and low mortality rate. Species diversity, dominance and evenness of the scleractinian coral communities were positively correlated one another (p<0.05). The coverage and biodiversity of the living scleractinian corals were higher at the sites where anthropogenic disturbance was less, i.e. closer to the cliff, deeper water, fewer boating and diving etc. The living scleractinian corals closer to sandy beach influenced severely by suspended sediment on eroded coast and diving had the lowest coverage, the highest dominance of the dominant species and relatively lower diversity. Human activities, southwest monsoon, storm surge, suspended sediment on eroded coast and extreme weather are the main influential factors on the coral reef ecosystem in the southwest seawaters of the Weizhou Island.
2021, 43(11): 136-145.
doi: 10.12284/hyxb2021168
Abstract:
Numerous engineering projects show that beach nourishment is a common method against coastal erosion. Beach nourishment is an artificial process of adding sediment to a beach to increase beach width and protect it from erosion. In this paper, a 1D numerical model for beach profile was established and verified by the results of physical model experiment. In addition, the rates of profile change to equilibrium profile on different positions and different sand volume schemes were calculated, and the efficiency was compared and analyzed. To analyze the protection effects of beach nourishment, the profiles in nourishment schemes and no nourishment schemes after storm condition were compared. It turned out that when the nourishment volume was large the efficiency of bar nourishment under the calm condition was higher than of berm nourishment, and the nourishment effect under the storm condition was better. This study has important implications to save construction costs and raise working efficiency during the practical nourishment engineering. In the meantime, it sheds light on evaluating the effect of beach nourishment.
Numerous engineering projects show that beach nourishment is a common method against coastal erosion. Beach nourishment is an artificial process of adding sediment to a beach to increase beach width and protect it from erosion. In this paper, a 1D numerical model for beach profile was established and verified by the results of physical model experiment. In addition, the rates of profile change to equilibrium profile on different positions and different sand volume schemes were calculated, and the efficiency was compared and analyzed. To analyze the protection effects of beach nourishment, the profiles in nourishment schemes and no nourishment schemes after storm condition were compared. It turned out that when the nourishment volume was large the efficiency of bar nourishment under the calm condition was higher than of berm nourishment, and the nourishment effect under the storm condition was better. This study has important implications to save construction costs and raise working efficiency during the practical nourishment engineering. In the meantime, it sheds light on evaluating the effect of beach nourishment.
2021, 43(11): 146-156.
doi: 10.12284/hyxb2021176
Abstract:
Tropical cyclone disaster is one of the most serious natural disasters, and its impact mainly depends on the center location and the intensity. Monitoring the location and the intensity of tropical cyclones is of great significance for improving the accuracy of tropical cyclone forecast and for reducing the impact of tropical cyclone disasters. In this paper, the characteristics of the HY-2B scatterometer wind field, as well as its divergence and curl, are analyzed. It is found that the divergence or curl of the wind field near the cyclone center shows remarkable signatures, such that a new method is proposed to identify the cyclone center, and then the results are compared with the conventional method. Moreover, a method for estimating the size of the tropical cyclone is introduced to evaluate the cyclone intensity. Finally, the remote sensing data of Typhoon Francisco and Typhoon Bualoi are used to verify the proposed methods. The results show that the difference between the cyclone center position determined by the scatterometer and the one of the optimal path is generally less than 20 km. Meanwhile, the determined wind radii correspond well with the development of the tropical cyclone.
Tropical cyclone disaster is one of the most serious natural disasters, and its impact mainly depends on the center location and the intensity. Monitoring the location and the intensity of tropical cyclones is of great significance for improving the accuracy of tropical cyclone forecast and for reducing the impact of tropical cyclone disasters. In this paper, the characteristics of the HY-2B scatterometer wind field, as well as its divergence and curl, are analyzed. It is found that the divergence or curl of the wind field near the cyclone center shows remarkable signatures, such that a new method is proposed to identify the cyclone center, and then the results are compared with the conventional method. Moreover, a method for estimating the size of the tropical cyclone is introduced to evaluate the cyclone intensity. Finally, the remote sensing data of Typhoon Francisco and Typhoon Bualoi are used to verify the proposed methods. The results show that the difference between the cyclone center position determined by the scatterometer and the one of the optimal path is generally less than 20 km. Meanwhile, the determined wind radii correspond well with the development of the tropical cyclone.
On the wind inversion characteristics of China-France Oceanography Satellite microwave scatterometer
2021, 43(11): 157-165.
doi: 10.12284/hyxb2021164
Abstract:
China-France Oceanography Satellite scatterometer (CSCAT) is the first rotating fan beam scatterometer internationally, which was flown onboard China-France Oceanography Satellite (CFOSAT) on October 2018. Based on the maximum likelihood estimation wind inversion algorithm, the residual characteristics of the CSCAT sea surface wind inversion cost function in detail, focuses on the influence of the new observation geometry on the wind inversion residual and wind quality is analyzed in this article, we establish the likelihood probability model function of the ambiguous solutions. The results show that the residual characteristic of the CSCAT wind inversion varies with the position of the wind vector cell (WVC) across the swath. The exponential distribution of the ambiguous solution likelihood probability model function is between −0.4 and −1.8. The results provide an important reference for the quality control of CSCAT and the refinement adjustment of the two dimensional variational ambiguity removal algorithm.
China-France Oceanography Satellite scatterometer (CSCAT) is the first rotating fan beam scatterometer internationally, which was flown onboard China-France Oceanography Satellite (CFOSAT) on October 2018. Based on the maximum likelihood estimation wind inversion algorithm, the residual characteristics of the CSCAT sea surface wind inversion cost function in detail, focuses on the influence of the new observation geometry on the wind inversion residual and wind quality is analyzed in this article, we establish the likelihood probability model function of the ambiguous solutions. The results show that the residual characteristic of the CSCAT wind inversion varies with the position of the wind vector cell (WVC) across the swath. The exponential distribution of the ambiguous solution likelihood probability model function is between −0.4 and −1.8. The results provide an important reference for the quality control of CSCAT and the refinement adjustment of the two dimensional variational ambiguity removal algorithm.
2021, 43(11): 166-180.
doi: 10.12284/hyxb2021158
Abstract:
Sea fog is a kind of disastrous weather phenomenon which occurs on the sea surface. Mastering the distribution and dynamic changes of sea fog can effectively reduce the disasters caused by sea fog. Satellite remote sensing observation has the characteristics of near real time, wide coverage, continuous observation and so on. Especially the geostationary satellite remote sensing observation with high time resolution, which can continuously and dynamically track the occurrence, development and extinction of sea fog. The sea fog events in the Yellow Sea and Bohai Sea are taken from 2018 to 2019 as examples in this paper. Based on the analysis of the multi-channel bright temperature radiation characteristics of sea fog in the Yellow Sea and Bohai Sea by using Himawari-8 (H-8) geostationary satellite data, the separation index of sea fog and cloud, the separation index of sea fog and water, the slope index of multi-band brightness temperature difference and texture index of mid-infrared bright temperature are defined through the difference and ratio combination of different bands, and the night sea fog monitoring algorithm based on multi-exponential probability distribution is proposed to realize the automatic identification of sea fog at night. The algorithm is applied to H-8 and GEO-KOMPSAT2A (GK-2A) geostationary satellite data respectively. The position distribution and coverage area of sea fog identify by multi-time satellite observations of six sea fog events from February to June 2020 are compared to achieve mutual verification. The results show that the algorithm proposed in this paper can effectively recognize sea fog at night. The monitoring results every 10 minutes of continuous observations of H-8 and GK-2A at night on April 29, 2020 are selected to follow up and analyze the area where sea fog occurred, it shows the occurrence, development and evolution of the sea fog event clearly. It indicates that the algorithm can monitor the distribution of sea fog and track the development and change of fog. It can provide scientific basis and decision-making basis for the prevention and mitigation of sea fog.
Sea fog is a kind of disastrous weather phenomenon which occurs on the sea surface. Mastering the distribution and dynamic changes of sea fog can effectively reduce the disasters caused by sea fog. Satellite remote sensing observation has the characteristics of near real time, wide coverage, continuous observation and so on. Especially the geostationary satellite remote sensing observation with high time resolution, which can continuously and dynamically track the occurrence, development and extinction of sea fog. The sea fog events in the Yellow Sea and Bohai Sea are taken from 2018 to 2019 as examples in this paper. Based on the analysis of the multi-channel bright temperature radiation characteristics of sea fog in the Yellow Sea and Bohai Sea by using Himawari-8 (H-8) geostationary satellite data, the separation index of sea fog and cloud, the separation index of sea fog and water, the slope index of multi-band brightness temperature difference and texture index of mid-infrared bright temperature are defined through the difference and ratio combination of different bands, and the night sea fog monitoring algorithm based on multi-exponential probability distribution is proposed to realize the automatic identification of sea fog at night. The algorithm is applied to H-8 and GEO-KOMPSAT2A (GK-2A) geostationary satellite data respectively. The position distribution and coverage area of sea fog identify by multi-time satellite observations of six sea fog events from February to June 2020 are compared to achieve mutual verification. The results show that the algorithm proposed in this paper can effectively recognize sea fog at night. The monitoring results every 10 minutes of continuous observations of H-8 and GK-2A at night on April 29, 2020 are selected to follow up and analyze the area where sea fog occurred, it shows the occurrence, development and evolution of the sea fog event clearly. It indicates that the algorithm can monitor the distribution of sea fog and track the development and change of fog. It can provide scientific basis and decision-making basis for the prevention and mitigation of sea fog.
2021, 43(11): 1-21.
doi: 10.12284/hyxb2021127
Abstract:
Based on the outputs of eight earth system models involved in the Coupled Model Intercomparison Project Phase 6 (CMIP6), this study assessed the simulation skill of the Southeast Indian subantarctic mode water (SEISAMW) of these models by comparing with observations. Moreover, this study investigated the projected long-term trends in subduction rate, volume and properties of the SEISAMW under medium and high greenhouse gas emission scenarios (i.e., SSP245, SSP585). The results show that the CMIP6 models generally have produced artificially greater mixed layer depth and smaller upper layer potential density in comparison with those of the Argo observation. Consequently, the simulated SEISAMW in the CMIP6 models are generally with larger subduction rate and smaller potential density. Meanwhile, the subduction regions of the SEISAMWs show significant differences among the analyzed CMIP6 models, which are attribute to lateral induction in the mixed layer. Furthermore, in the historical, SSP245 and SSP585 outputs, the SEISAMWs show consistent decreasing trends in subduction rate and volume, increasing trend in temperature, and decreasing trends in salinity and potential density. The long-term trends of the SEISAMWs are largest under SSP585 scenario, followed by the SSP245 scenario and historical simulation. The projected trends of SEISAMW can be explained by the following mechanism: the temperature and freshwater flux in the southeastern Indian Ocean upper layer tend to increase under enhanced radioactive forcing, resulting in shoaling in mixed layer and flattening of the mixed layer gradient. As a result, the trends of SEISAMWs in subduction rate, volume and water properties show larger values in accordance with stronger radioactive forcing.
Based on the outputs of eight earth system models involved in the Coupled Model Intercomparison Project Phase 6 (CMIP6), this study assessed the simulation skill of the Southeast Indian subantarctic mode water (SEISAMW) of these models by comparing with observations. Moreover, this study investigated the projected long-term trends in subduction rate, volume and properties of the SEISAMW under medium and high greenhouse gas emission scenarios (i.e., SSP245, SSP585). The results show that the CMIP6 models generally have produced artificially greater mixed layer depth and smaller upper layer potential density in comparison with those of the Argo observation. Consequently, the simulated SEISAMW in the CMIP6 models are generally with larger subduction rate and smaller potential density. Meanwhile, the subduction regions of the SEISAMWs show significant differences among the analyzed CMIP6 models, which are attribute to lateral induction in the mixed layer. Furthermore, in the historical, SSP245 and SSP585 outputs, the SEISAMWs show consistent decreasing trends in subduction rate and volume, increasing trend in temperature, and decreasing trends in salinity and potential density. The long-term trends of the SEISAMWs are largest under SSP585 scenario, followed by the SSP245 scenario and historical simulation. The projected trends of SEISAMW can be explained by the following mechanism: the temperature and freshwater flux in the southeastern Indian Ocean upper layer tend to increase under enhanced radioactive forcing, resulting in shoaling in mixed layer and flattening of the mixed layer gradient. As a result, the trends of SEISAMWs in subduction rate, volume and water properties show larger values in accordance with stronger radioactive forcing.
2021, 43(11): 22-31.
doi: 10.12284/hyxb2021172
Abstract:
Using the direct observation data of the MSS90L turbulence profiler obtained in the summer cruise of the Changjiang River Estuary scientific investigation and experimental study (NORC2019-03-02) in July 2019, in this paper, the distribution of the turbulent kinetic energy dissipation rate ε and the vertical turbulent diffusion coefficient Kz are calculated and analyzed. The turbulent kinetic energy dissipation rate is 1.72×10−10 W/kg to 2.95×10−5 W/kg, and the vertical turbulent diffusion coefficient is 3.24×10−7 m2/s to 4.55×10−2 m2/s. The distribution of the turbulent kinetic energy dissipation rate and the vertical turbulent diffusion coefficient are similar, both of which are the strongest in the upper layer, the next in the bottom layer and the weakest in the middle layer. In the upper layer, due to wind stress, the turbulent kinetic energy dissipation rate and vertical turbulent diffusion coefficient are larger; the stratification is stronger at the thermocline, which suppresses the dissipation of turbulent kinetic energy and vertical turbulent mixing. The secondary circulation of the salinity front will promote the separation of the low salt water mass, and the vertical circulation caused by the front will enhance the turbulent mixing of the ocean. The energy exchange between the low salt water mass and the outside world is less, and the turbulent kinetic energy dissipation rate is weaker. There are obvious upwelling and downwelling in the Changjiang River Estuary, which are produced by the secondary circulation of the front; the existence of upwelling and downwelling promotes the dissipation of turbulent kinetic energy and turbulent mixing.
Using the direct observation data of the MSS90L turbulence profiler obtained in the summer cruise of the Changjiang River Estuary scientific investigation and experimental study (NORC2019-03-02) in July 2019, in this paper, the distribution of the turbulent kinetic energy dissipation rate ε and the vertical turbulent diffusion coefficient Kz are calculated and analyzed. The turbulent kinetic energy dissipation rate is 1.72×10−10 W/kg to 2.95×10−5 W/kg, and the vertical turbulent diffusion coefficient is 3.24×10−7 m2/s to 4.55×10−2 m2/s. The distribution of the turbulent kinetic energy dissipation rate and the vertical turbulent diffusion coefficient are similar, both of which are the strongest in the upper layer, the next in the bottom layer and the weakest in the middle layer. In the upper layer, due to wind stress, the turbulent kinetic energy dissipation rate and vertical turbulent diffusion coefficient are larger; the stratification is stronger at the thermocline, which suppresses the dissipation of turbulent kinetic energy and vertical turbulent mixing. The secondary circulation of the salinity front will promote the separation of the low salt water mass, and the vertical circulation caused by the front will enhance the turbulent mixing of the ocean. The energy exchange between the low salt water mass and the outside world is less, and the turbulent kinetic energy dissipation rate is weaker. There are obvious upwelling and downwelling in the Changjiang River Estuary, which are produced by the secondary circulation of the front; the existence of upwelling and downwelling promotes the dissipation of turbulent kinetic energy and turbulent mixing.
2021, 43(11): 32-45.
doi: 10.12284/hyxb2021162
Abstract:
In this study, we quantify the mixed-layer salinity (MLS) budget in the Indian Ocean using the salinity budget equation along with Argo salinity, SODA ocean current, evaporation, and precipitation data. The results show that the distribution and seasonal variability for the terms of freshwater flux, advection and entrainment in the Indian Ocean, and their contributions to the variations of MLS. Regarding the climatological annual mean, the negative contribution (15.14%) of the horizontal advection term to MLS is much larger than its positive contribution (9.89%). This implies that the horizontal advection transports low-salinity water to the salty regions, resulting in a decrease in MLS there. The distribution and seasonal variability of the freshwater flux term are generally consistent with those of precipitation, with a positive contribution (13.70%) higher than negative contribution (7.81%). It suggests that the freshwater flux term increases MLS in the Indian Ocean because of the evaporation overwhelming the precipitation. Analysis on the regions with significant seasonal variations of MLS indicates that from June to November, the Southwest Monsoon Current transports low-salinity water from the western equatorial Indian Ocean to the western Arabian Sea, causing salinity in that region to decrease. The advection of high-salinity water from the southern and central to the northern of Bengal Bay is the main reason for the increase in salinity there.
In this study, we quantify the mixed-layer salinity (MLS) budget in the Indian Ocean using the salinity budget equation along with Argo salinity, SODA ocean current, evaporation, and precipitation data. The results show that the distribution and seasonal variability for the terms of freshwater flux, advection and entrainment in the Indian Ocean, and their contributions to the variations of MLS. Regarding the climatological annual mean, the negative contribution (15.14%) of the horizontal advection term to MLS is much larger than its positive contribution (9.89%). This implies that the horizontal advection transports low-salinity water to the salty regions, resulting in a decrease in MLS there. The distribution and seasonal variability of the freshwater flux term are generally consistent with those of precipitation, with a positive contribution (13.70%) higher than negative contribution (7.81%). It suggests that the freshwater flux term increases MLS in the Indian Ocean because of the evaporation overwhelming the precipitation. Analysis on the regions with significant seasonal variations of MLS indicates that from June to November, the Southwest Monsoon Current transports low-salinity water from the western equatorial Indian Ocean to the western Arabian Sea, causing salinity in that region to decrease. The advection of high-salinity water from the southern and central to the northern of Bengal Bay is the main reason for the increase in salinity there.
2021, 43(11): 46-60.
doi: 10.12284/hyxb2021156
Abstract:
Using in-situ hydrographic observations from January to December 2017, 3D thermohaline structure and seasonal variation in the Zhanjiang Bay is investigated in this study. The results show that: (1) In 2017, the annual mean temperature is 23−27℃, the mean salinity is 19−27, the mean potential density is between 11−17 kg/m3, and the mean buoyancy frequency (N2) is about 7×10−5−5×10−3 s−2 in the Zhanjiang Bay. The vertical structure and horizontal distribution of N2 are similar to that of the temperature, while the distributions of potential density and salinity are similar. (2) The temperature has significant seasonality with the highest value in summer, followed by autumn, and the lowest in winter. The maximum temperature difference between winter and summer reaches 15℃, while the seasonal mean of the salinity varies slightly. The ebb and flood have less influence on temperature and salinity, comparing with their seasonal variations. The thermocline is the strongest in summer with the maximum gradient reaches 0.7℃/m at 10 m, whereas it shallows to 5 m in spring and fall, and the water well mixed in winter. The halocline is prominent in summer and fall, with the maximum gradient 1.1 m−1. The seasonal variation of the thermohaline in the upper layer and lower layer are consistent. (3) For the horizontal distribution, the temperature decreases and the salinity increases from the bay head, the mid bay, the bank region, the shoal region to the bay mouth. The average temperature difference between the bay head and the bay mouth is 2.3℃, and the salinity difference is 2.7. The temperature-salinity (θ-S) diagram shows banding distributions with one end as the low-temperature and high-salinity water in the bay mouth, one end as the high-temperature and low-salinity water in the bay head, and the other water masses are between them. Different bands are shown in different seasons.
Using in-situ hydrographic observations from January to December 2017, 3D thermohaline structure and seasonal variation in the Zhanjiang Bay is investigated in this study. The results show that: (1) In 2017, the annual mean temperature is 23−27℃, the mean salinity is 19−27, the mean potential density is between 11−17 kg/m3, and the mean buoyancy frequency (N2) is about 7×10−5−5×10−3 s−2 in the Zhanjiang Bay. The vertical structure and horizontal distribution of N2 are similar to that of the temperature, while the distributions of potential density and salinity are similar. (2) The temperature has significant seasonality with the highest value in summer, followed by autumn, and the lowest in winter. The maximum temperature difference between winter and summer reaches 15℃, while the seasonal mean of the salinity varies slightly. The ebb and flood have less influence on temperature and salinity, comparing with their seasonal variations. The thermocline is the strongest in summer with the maximum gradient reaches 0.7℃/m at 10 m, whereas it shallows to 5 m in spring and fall, and the water well mixed in winter. The halocline is prominent in summer and fall, with the maximum gradient 1.1 m−1. The seasonal variation of the thermohaline in the upper layer and lower layer are consistent. (3) For the horizontal distribution, the temperature decreases and the salinity increases from the bay head, the mid bay, the bank region, the shoal region to the bay mouth. The average temperature difference between the bay head and the bay mouth is 2.3℃, and the salinity difference is 2.7. The temperature-salinity (θ-S) diagram shows banding distributions with one end as the low-temperature and high-salinity water in the bay mouth, one end as the high-temperature and low-salinity water in the bay head, and the other water masses are between them. Different bands are shown in different seasons.
2021, 43(11): 61-69.
doi: 10.12284/hyxb2021174
Abstract:
Ocean waves can affect the roughness of the ocean surface, and the waves generated by tropical cyclones impact the momentum and energy fluxes across the air-sea interface. In this study, the impacts of ocean waves on the momentum and energy fluxes under tropical cyclones is examined by using the tropical cyclone observation dataset IBTrACS (International Best Track Archive for Climate Stewardship) and the simulations from wave model WW III (WAVEWATCH III). It is found that the intensity of tropical cyclones increased by about 1 m/s every decade in the past 30 years, but the change of translation speed is not obvious. For the stronger tropical cyclones, the difference for momentum flux and the energy flux between the air-sea interface can be significantly increased by the waves. Owing to the asymmetry of wind and surface wave fields under tropical cyclones, momentum difference and energy difference also demonstrate asymmetric distribution: the area with larger momentum difference is behind the moving direction of tropical cyclone, while energy difference is the largest in the right-rear quadrant, and both are relatively smaller in the left front quadrant. The inverse wave age is highly correlated with momentum difference and energy difference, and the correlation coefficient is about 0.95, indicating that the younger the surface wave, the more momentum and energy absorbed and stored by surface wave field. The inverse wave age increases with the increase of tropical cyclone translation speed, and the speed is positively correlated with momentum difference and energy difference according to the correlation coefficient above 0.8. Therefore, the surface waves affect the distribution and magnitude of momentum and energy input from the atmosphere to the ocean under tropical cyclones. In the future study of ocean boundary dynamics and thermodynamics, especially the study of tropical cyclones, considering the influence of ocean wave evolution is necessary.
Ocean waves can affect the roughness of the ocean surface, and the waves generated by tropical cyclones impact the momentum and energy fluxes across the air-sea interface. In this study, the impacts of ocean waves on the momentum and energy fluxes under tropical cyclones is examined by using the tropical cyclone observation dataset IBTrACS (International Best Track Archive for Climate Stewardship) and the simulations from wave model WW III (WAVEWATCH III). It is found that the intensity of tropical cyclones increased by about 1 m/s every decade in the past 30 years, but the change of translation speed is not obvious. For the stronger tropical cyclones, the difference for momentum flux and the energy flux between the air-sea interface can be significantly increased by the waves. Owing to the asymmetry of wind and surface wave fields under tropical cyclones, momentum difference and energy difference also demonstrate asymmetric distribution: the area with larger momentum difference is behind the moving direction of tropical cyclone, while energy difference is the largest in the right-rear quadrant, and both are relatively smaller in the left front quadrant. The inverse wave age is highly correlated with momentum difference and energy difference, and the correlation coefficient is about 0.95, indicating that the younger the surface wave, the more momentum and energy absorbed and stored by surface wave field. The inverse wave age increases with the increase of tropical cyclone translation speed, and the speed is positively correlated with momentum difference and energy difference according to the correlation coefficient above 0.8. Therefore, the surface waves affect the distribution and magnitude of momentum and energy input from the atmosphere to the ocean under tropical cyclones. In the future study of ocean boundary dynamics and thermodynamics, especially the study of tropical cyclones, considering the influence of ocean wave evolution is necessary.
2021, 43(11): 70-76.
doi: 10.12284/hyxb2021138
Abstract:
The radionuclides 7Be, 210Po and 210Pb transported by the atmosphere can be used as important tracers for studying the material deposition flux of the Arctic Ocean’s atmosphere, modern ocean sedimentation and the transport of materials into the sea ice. They have been widely used in the study of air mass movement, soil erosion, and particle circulation processes in water systems. This paper reports the activities of 7Be, 210Po and 210Pb in the surface snow of the high-latitude ice floes of the Arctic Ocean in 2018. The activity concentrations of 7Be, 210Po and 210Pb are 33.6−632.68 mBq/L, 36.2−87.5 mBq/L, and 30.9−194.49 mBq/L, respectively. The activity concentrations of 7Be and 210Pb in the surface snow of the Arctic Ocean are lower than those in the mid-latitude continental areas. The results show that the activity concentrations of 7Be in snow increased with the increase of latitude. The activity ratio of 210Po/210Pb ranged from 0.70 to 1.48 (with an average of 0.93), 210Po is almost in equilibrium with 210Pb. It indicates that the age of the surface snow is “older”.
The radionuclides 7Be, 210Po and 210Pb transported by the atmosphere can be used as important tracers for studying the material deposition flux of the Arctic Ocean’s atmosphere, modern ocean sedimentation and the transport of materials into the sea ice. They have been widely used in the study of air mass movement, soil erosion, and particle circulation processes in water systems. This paper reports the activities of 7Be, 210Po and 210Pb in the surface snow of the high-latitude ice floes of the Arctic Ocean in 2018. The activity concentrations of 7Be, 210Po and 210Pb are 33.6−632.68 mBq/L, 36.2−87.5 mBq/L, and 30.9−194.49 mBq/L, respectively. The activity concentrations of 7Be and 210Pb in the surface snow of the Arctic Ocean are lower than those in the mid-latitude continental areas. The results show that the activity concentrations of 7Be in snow increased with the increase of latitude. The activity ratio of 210Po/210Pb ranged from 0.70 to 1.48 (with an average of 0.93), 210Po is almost in equilibrium with 210Pb. It indicates that the age of the surface snow is “older”.
2021, 43(11): 77-87.
doi: 10.12284/hyxb2021194
Abstract:
The geochemistry, occurrence phase and enrichment mechanism of REE and PGE were studied in cobalt-rich crusts from the Seamount Xufu in the Pacific by ICP-OES, ICP-MS and phase analysis methods. The results showed that, REE and PGE were enriched in cobalt-rich crusts, REE contents were 1 842−2854 μg/g, and PGE contents were 144−1180 ng/g. REE and PGE contents in the old layers were higher than that in the new layers, and the phosphatization in the old layers might play an active role in the REE and PGE enrichment. Moreover, LREE contents were more than HREE contents, and REE diagrams showed the positive Ce anomalies and no Eu anomalies, so Ce was enriched in cobalt-rich crusts. Meanwhile, there was an obvious contrast between PGE, and PPGE contents were more than IPGE contents. PGE diagrams showed the positive Pt anomalies and negative Pd anomalies, so Pt was enriched and Pd was poor in cobalt-rich crusts. In addition, REE in the new layers were mainly enriched in the iron oxide phase, and the enrichment ratios were 65.40%−70.05%. While REE in the old layers were mainly enriched in the residual phase, and the enrichment ratios were 62.27%−65.77%, because it might be related to the phosphate. Meanwhile, PGE in the new or old layers were mainly enriched in the iron oxide phase, and the enrichment ratios were 63.66%−69.51%, and also the residual phase ranged from 29.20% to 34.68% had an impact on PGE enrichment. Therefore, REE and PGE enrichment were presumed to the iron oxide colloid particles adsorption. In the marine oxidative environment, the soluble Ce3+ and Pt2+ were oxidized to insoluble Ce4+ and Pt4+ respectively, and the precipitates were adsorbed into the iron oxide phase, so REE and PGE were enriched in cobalt-rich crusts.
The geochemistry, occurrence phase and enrichment mechanism of REE and PGE were studied in cobalt-rich crusts from the Seamount Xufu in the Pacific by ICP-OES, ICP-MS and phase analysis methods. The results showed that, REE and PGE were enriched in cobalt-rich crusts, REE contents were 1 842−2854 μg/g, and PGE contents were 144−1180 ng/g. REE and PGE contents in the old layers were higher than that in the new layers, and the phosphatization in the old layers might play an active role in the REE and PGE enrichment. Moreover, LREE contents were more than HREE contents, and REE diagrams showed the positive Ce anomalies and no Eu anomalies, so Ce was enriched in cobalt-rich crusts. Meanwhile, there was an obvious contrast between PGE, and PPGE contents were more than IPGE contents. PGE diagrams showed the positive Pt anomalies and negative Pd anomalies, so Pt was enriched and Pd was poor in cobalt-rich crusts. In addition, REE in the new layers were mainly enriched in the iron oxide phase, and the enrichment ratios were 65.40%−70.05%. While REE in the old layers were mainly enriched in the residual phase, and the enrichment ratios were 62.27%−65.77%, because it might be related to the phosphate. Meanwhile, PGE in the new or old layers were mainly enriched in the iron oxide phase, and the enrichment ratios were 63.66%−69.51%, and also the residual phase ranged from 29.20% to 34.68% had an impact on PGE enrichment. Therefore, REE and PGE enrichment were presumed to the iron oxide colloid particles adsorption. In the marine oxidative environment, the soluble Ce3+ and Pt2+ were oxidized to insoluble Ce4+ and Pt4+ respectively, and the precipitates were adsorbed into the iron oxide phase, so REE and PGE were enriched in cobalt-rich crusts.
2021, 43(11): 88-95.
doi: 10.12284/hyxb2021160
Abstract:
The seabed soil layer will gradually accumulate pore pressure under the action of wave cyclic load, reduce the stability of the soil layer, and threaten offshore engineering. In order to study the accumulation mechanism of pore water pressure, the discrete element pore density flow method was proposed, and the discrete element analysis software MatDEM was improved to realize the simulation of the accumulation process of seabed sediment pore pressure. Based on the field test device and the mechanical parameters of the soil body, a discrete element model was established. By comparing field test and numerical simulation results, it was found that after applying the wave load to the seabed sediment, a higher pore pressure was generated in the surface soil body and gradually transferred to the deep layer. Under the action of cyclic wave load, the cumulative range of pore pressure between soil particles gradually increased. When the pore pressure accumulation time was long enough, the pore pressure in the soil layer converged to the average of the maximum and minimum loads applied. As the number of load cycles increased, the pore pressure at all depths increased cumulatively until the soil body liquefied and the internal soil particles became resuspended sediments. Under the action of periodic wave loads, the soil particles moved after being liquefied and suspended, and the shallow particles had a large displacement, and the overall performance of the soil was circular arc movement.
The seabed soil layer will gradually accumulate pore pressure under the action of wave cyclic load, reduce the stability of the soil layer, and threaten offshore engineering. In order to study the accumulation mechanism of pore water pressure, the discrete element pore density flow method was proposed, and the discrete element analysis software MatDEM was improved to realize the simulation of the accumulation process of seabed sediment pore pressure. Based on the field test device and the mechanical parameters of the soil body, a discrete element model was established. By comparing field test and numerical simulation results, it was found that after applying the wave load to the seabed sediment, a higher pore pressure was generated in the surface soil body and gradually transferred to the deep layer. Under the action of cyclic wave load, the cumulative range of pore pressure between soil particles gradually increased. When the pore pressure accumulation time was long enough, the pore pressure in the soil layer converged to the average of the maximum and minimum loads applied. As the number of load cycles increased, the pore pressure at all depths increased cumulatively until the soil body liquefied and the internal soil particles became resuspended sediments. Under the action of periodic wave loads, the soil particles moved after being liquefied and suspended, and the shallow particles had a large displacement, and the overall performance of the soil was circular arc movement.
2021, 43(11): 96-104.
doi: 10.12284/hyxb2021154
Abstract:
The storage pressure and reconstruction of the mesostructure of gas-bearing sediments are key factors in the study of shallow gas geohazards. Using an industrial CT scanning test system, vertical rotational (SR) scanning is used, with the position of the microfocus X-ray source fixed and the sample rotated at a constant speed of 360° along the XY plane, with a set rotation step of 0.3° per second, the gas-bearing samples in the reactor are pressurized to 2 MPa, 4 MPa, and 6 MPa, taking into account the best resolution of the sample imaging, the best detection range and other. The results show that the slices and reconstructed images obtained from the CT scan have good experimental results; the greyscale values of small bubbles increase when pressurized to 2 MPa; the overall greyscale values of gas increase significantly when pressurized to 6 MPa; the number of bubbles decrease with increasing bubble radius during the pressurization process; the pressurization process lead to local changes in the solid-liquid-gas phase, which show that the volume of pore gas and pore water changes more than that of the soil skeleton. The overall change is greater than that of the soil skeleton, and the microscopic local location will have a greater rise or decrease. When the gas content at different locations rises and dominates, it will drive the reduction of pore water and the movement of the soil skeleton.
The storage pressure and reconstruction of the mesostructure of gas-bearing sediments are key factors in the study of shallow gas geohazards. Using an industrial CT scanning test system, vertical rotational (SR) scanning is used, with the position of the microfocus X-ray source fixed and the sample rotated at a constant speed of 360° along the XY plane, with a set rotation step of 0.3° per second, the gas-bearing samples in the reactor are pressurized to 2 MPa, 4 MPa, and 6 MPa, taking into account the best resolution of the sample imaging, the best detection range and other. The results show that the slices and reconstructed images obtained from the CT scan have good experimental results; the greyscale values of small bubbles increase when pressurized to 2 MPa; the overall greyscale values of gas increase significantly when pressurized to 6 MPa; the number of bubbles decrease with increasing bubble radius during the pressurization process; the pressurization process lead to local changes in the solid-liquid-gas phase, which show that the volume of pore gas and pore water changes more than that of the soil skeleton. The overall change is greater than that of the soil skeleton, and the microscopic local location will have a greater rise or decrease. When the gas content at different locations rises and dominates, it will drive the reduction of pore water and the movement of the soil skeleton.
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