2023 Vol. 45, No. 4
Display Method:
2023, 45(4): .
Abstract:
2023, 45(4): 1-16.
doi: 10.12284/hyxb2023035
Abstract:
Using mesoscale eddy trajectory product from 1993 to 2019 provided by the AVISO, this study analyzes the climatology characteristics and seasonal variations of mesoscale eddies in the Andaman Sea (AS). The results show that a total of 328 mesoscale eddies were generated in the AS during the past 27 years, of which anticyclonic eddies (AEs) (171) were more than cyclonic eddies (CEs) (157). The eddies are mainly distributed in the deep waters of the central and western basin of the AS. The average life span of total eddies is 46.4 days, with average eddy radius of 111.8 km, average amplitude of 4.7 cm, rotating and propagating speeds of 24.8 cm/s and 15.0 cm/s, respectively. The AEs have large radius, amplitude, and rotating speed than CEs, but smaller propagating speed. During the eddy life, the composite radius, amplitude, and rotating speed of eddies all increase in the generation stage and then decrease in dissipation stage, while the eddy propagation speed has opposite trend. For the seasonal variation, the comparison of AEs to CEs shows seesaw phenomena in winter and summer, CEs are stronger and larger than AEs in summer, but weaker and smaller in winter. The distribution of AEs and CEs also shows seasonal polarity reversal, a ‘CEs-AEs-CEs’ pattern from north to south in summer, but a reversed ‘AEs-CEs-AEs’ pattern in winter. Dynamic analysis showed that the vorticity of background current may affect the alternating distribution pattern of mesoscale eddies in the AS, in which positive (negative) vorticity favors CEs (AEs). The energy analysis shows that wind forcing is dominant in the eddy kinetic energy (EKE) variation, and the seasonal wind work is coherent to the EKE variation in the AS.
Using mesoscale eddy trajectory product from 1993 to 2019 provided by the AVISO, this study analyzes the climatology characteristics and seasonal variations of mesoscale eddies in the Andaman Sea (AS). The results show that a total of 328 mesoscale eddies were generated in the AS during the past 27 years, of which anticyclonic eddies (AEs) (171) were more than cyclonic eddies (CEs) (157). The eddies are mainly distributed in the deep waters of the central and western basin of the AS. The average life span of total eddies is 46.4 days, with average eddy radius of 111.8 km, average amplitude of 4.7 cm, rotating and propagating speeds of 24.8 cm/s and 15.0 cm/s, respectively. The AEs have large radius, amplitude, and rotating speed than CEs, but smaller propagating speed. During the eddy life, the composite radius, amplitude, and rotating speed of eddies all increase in the generation stage and then decrease in dissipation stage, while the eddy propagation speed has opposite trend. For the seasonal variation, the comparison of AEs to CEs shows seesaw phenomena in winter and summer, CEs are stronger and larger than AEs in summer, but weaker and smaller in winter. The distribution of AEs and CEs also shows seasonal polarity reversal, a ‘CEs-AEs-CEs’ pattern from north to south in summer, but a reversed ‘AEs-CEs-AEs’ pattern in winter. Dynamic analysis showed that the vorticity of background current may affect the alternating distribution pattern of mesoscale eddies in the AS, in which positive (negative) vorticity favors CEs (AEs). The energy analysis shows that wind forcing is dominant in the eddy kinetic energy (EKE) variation, and the seasonal wind work is coherent to the EKE variation in the AS.
2023, 45(4): 17-30.
doi: 10.12284/hyxb2023033
Abstract:
Based on the extreme value theory of non-stationary sequences, this study carried out the quantitative analysis of the effect of sea level rise on the exceedance probability of extreme water levels. A new method for the estimation of extreme water level with sea level rise was proposed by adopting the overall exceedance probability of extreme water level within the design lifetime of coastal facilities as a critical constraint. With the incorporation of sea level rise in the location parameter of Gumbel distribution, the new method allows the adjustment of the annual exceedance probability of extreme water levels along with sea level rise over time. The validity of the proposed method was examined using the long term sea level measurement data at 10 tide gauge stations globally. Using the five global mean sea level rise scenarios projected by IPCC, the extreme water levels for different design lifetime of coastal facilities with sea level rise were estimated, and the return periods of the extreme water levels were also evaluated.
Based on the extreme value theory of non-stationary sequences, this study carried out the quantitative analysis of the effect of sea level rise on the exceedance probability of extreme water levels. A new method for the estimation of extreme water level with sea level rise was proposed by adopting the overall exceedance probability of extreme water level within the design lifetime of coastal facilities as a critical constraint. With the incorporation of sea level rise in the location parameter of Gumbel distribution, the new method allows the adjustment of the annual exceedance probability of extreme water levels along with sea level rise over time. The validity of the proposed method was examined using the long term sea level measurement data at 10 tide gauge stations globally. Using the five global mean sea level rise scenarios projected by IPCC, the extreme water levels for different design lifetime of coastal facilities with sea level rise were estimated, and the return periods of the extreme water levels were also evaluated.
2023, 45(4): 31-45.
doi: 10.12284/hyxb2023023
Abstract:
Ocean fronts variations in strength are key to the terrestrial material transport and global material cycle. Ocean temperature fronts are formed between the branches of West Pacific Boundary Current and the coastal current during the winter and spring seasons in the eastern shelf of China. In order to investigate the multi-time scale variation and main controlling factors of temperature front over the Yellow Sea under the dual influence of winter storms and shelf circulation, we investigate the coupling of low-latitude driven circulation systems and high-latitude driven winter storms on frontal variability with the methods of signal decomposition and explainable deep learning on the decadal and weather scale. On the decadal scale, empirical orthogonal decomposition and ensemble empirical modal decomposition are used to relate temperature changes in the Yellow Sea to the strength of the Yellow Sea Warm Current. The results indicate that the spatial distribution of first sea surface temperature (SST) EOF mode has obvious characteristics of the Yellow Sea Warm Current-coastal current system; the time series of the first SST EOF mode correlates well with the Yellow Sea Warm Current intensity index and is modulated by the low frequency ENSO signal. On the weather scale, this paper trains CNN-LSTM models and uses interpretability metrics to conduct the research. The results show that, in windless or weak wind conditions, the strength of ocean front is maintained by the combination of pressure gradient forces resulted from sea surface height and Coriolis forces caused by flow field. However, in the storm conditions, influenced by Kelvin Wave propagation and shear front fragmentation, the flow field is responsible for the ocean front variation. The results of this study show that big data and machine learning methods are important means to establish connections between many ocean parameters and discover some unique physical ocean processes, which have broad application prospects.
Ocean fronts variations in strength are key to the terrestrial material transport and global material cycle. Ocean temperature fronts are formed between the branches of West Pacific Boundary Current and the coastal current during the winter and spring seasons in the eastern shelf of China. In order to investigate the multi-time scale variation and main controlling factors of temperature front over the Yellow Sea under the dual influence of winter storms and shelf circulation, we investigate the coupling of low-latitude driven circulation systems and high-latitude driven winter storms on frontal variability with the methods of signal decomposition and explainable deep learning on the decadal and weather scale. On the decadal scale, empirical orthogonal decomposition and ensemble empirical modal decomposition are used to relate temperature changes in the Yellow Sea to the strength of the Yellow Sea Warm Current. The results indicate that the spatial distribution of first sea surface temperature (SST) EOF mode has obvious characteristics of the Yellow Sea Warm Current-coastal current system; the time series of the first SST EOF mode correlates well with the Yellow Sea Warm Current intensity index and is modulated by the low frequency ENSO signal. On the weather scale, this paper trains CNN-LSTM models and uses interpretability metrics to conduct the research. The results show that, in windless or weak wind conditions, the strength of ocean front is maintained by the combination of pressure gradient forces resulted from sea surface height and Coriolis forces caused by flow field. However, in the storm conditions, influenced by Kelvin Wave propagation and shear front fragmentation, the flow field is responsible for the ocean front variation. The results of this study show that big data and machine learning methods are important means to establish connections between many ocean parameters and discover some unique physical ocean processes, which have broad application prospects.
2023, 45(4): 46-56.
doi: 10.12284/hyxb2023063
Abstract:
Deep water breaking wave is usually generated by the wave focusing method in laboratory. A wave with a significantly increased height can be generated by the superposition of components so that wave breaks when the steepness exceeds the limit value. However, using this method, the number of wave breaking is usually not unique leading to less obvious field characteristics after breaking and it’s hard to set research cases due to the difficulty in selecting wave-making parameters. As a result, the effect and efficiency of elaborate deep water wave breaking experiments is affected directly. Theoretical wave surface was calculated by the theory of wave focusing method and theoretical wave steepness was calculated using the wave height and wavelength defined by up-cross-zero method in this paper. On the other hand, wave breaking times and intensity were obtained from the physical experiments. The JONSWAP spectrum was used as the input spectrum and the effects of wave-making parameters, such as focusing amplitude, spectrum peak frequency, frequency bandwidth, on wave breaking were discussed so as to establish an approximate quantitative relationship between breaking times and input parameters. The research conclusions can provide a reference for selection of wave-making parameters so that the efficiency of the experiment can be improved.
Deep water breaking wave is usually generated by the wave focusing method in laboratory. A wave with a significantly increased height can be generated by the superposition of components so that wave breaks when the steepness exceeds the limit value. However, using this method, the number of wave breaking is usually not unique leading to less obvious field characteristics after breaking and it’s hard to set research cases due to the difficulty in selecting wave-making parameters. As a result, the effect and efficiency of elaborate deep water wave breaking experiments is affected directly. Theoretical wave surface was calculated by the theory of wave focusing method and theoretical wave steepness was calculated using the wave height and wavelength defined by up-cross-zero method in this paper. On the other hand, wave breaking times and intensity were obtained from the physical experiments. The JONSWAP spectrum was used as the input spectrum and the effects of wave-making parameters, such as focusing amplitude, spectrum peak frequency, frequency bandwidth, on wave breaking were discussed so as to establish an approximate quantitative relationship between breaking times and input parameters. The research conclusions can provide a reference for selection of wave-making parameters so that the efficiency of the experiment can be improved.
2023, 45(4): 57-67.
doi: 10.12284/hyxb2023043
Abstract:
The settling velocity is an important physical parameter of coral sand. Because of the rod coral sand is obviously different from other shapes of coral sand, it is not suitable to apply the settling velocity formula of the existing coral sand for calculation. The rod coral sand was selected to study the settling velocity and its influencing factors for single particle settlement experiment in stagnant water in this study. By analyzing the effects of different equivalent particle sizes and shape coefficients on the settling velocity of rod coral sand, it is found that the settling velocity of rod coral sand is strongly correlated with the diameter of the volume-equivalent sphere and Corey shape coefficient. Based on the experimental data, an empirical formula suitable for calculating the settling velocity of rod coral sand is deduced, which enriches the theory of coastal sediment.
The settling velocity is an important physical parameter of coral sand. Because of the rod coral sand is obviously different from other shapes of coral sand, it is not suitable to apply the settling velocity formula of the existing coral sand for calculation. The rod coral sand was selected to study the settling velocity and its influencing factors for single particle settlement experiment in stagnant water in this study. By analyzing the effects of different equivalent particle sizes and shape coefficients on the settling velocity of rod coral sand, it is found that the settling velocity of rod coral sand is strongly correlated with the diameter of the volume-equivalent sphere and Corey shape coefficient. Based on the experimental data, an empirical formula suitable for calculating the settling velocity of rod coral sand is deduced, which enriches the theory of coastal sediment.
2023, 45(4): 68-81.
doi: 10.12284/hyxb2023037
Abstract:
Estuarine bay is a special geomorphological system, which is often charactered with the combination of shoals and channels. Its evolution and shifting balance of shoal-channel structure are not only the frontier hotspots of estuarine and coastal researches, but also the theoretical cornerstone of estuarine management and port waterway construction. Based on the nautical bathymetry data of different historical ages, using geomorphological information entropy and other analytical methods, this paper studies the phylogenetic evolution characteristics and shifting balance mechanism of the shoal-channel structure in Huangmaohai Estuary Bay (HEB), and the main findings include: (1) The geomorphological evolution of HEB has undergone a transition from siltation to erosion during 1940 to 2007. The average annual siltation rate was 1.4 cm/a. From then on, till 2015, the bay had shifted to erosion period and the average annual erosion rate was 1.2 cm/a. (2) The structure of shoal and channel in HEB was converted, and the structure of "three shoals and two channels" was transformed into the structure of "two shoals and one channel" between 2003 and 2007, and the elevation differentiation between shoals and channels tended to be enlarged due to the impact of reclamation in the shallow coasts and dredging projects in channels. As a result, the shallow shoals became shallower and the channels were deeper. (3) The entropy value of geomorphological information of HEB decreased first and then increased, indicating HEB it changed from the relatively stable mode of slow siltation to the abrupt changing mode, in which the uncertainty of the shoal-channel evolution was induced by human intervention; moreover, the steady states of the shoal and channel are different. The shoals showed higher uncertainty than the deep channel. (4) Human activities disturbed the original steady state of the shoal-channel structure, and the dredging project will enhance the vitality of the East Channel and promote the adaptive reconstruction in the deep channel to evolve in an orderly direction. The West Shoal and the East Shoal have undergone a disturbance balance of human activities such as reclamation, and the shoal instability has shown a disorderly evolution.
Estuarine bay is a special geomorphological system, which is often charactered with the combination of shoals and channels. Its evolution and shifting balance of shoal-channel structure are not only the frontier hotspots of estuarine and coastal researches, but also the theoretical cornerstone of estuarine management and port waterway construction. Based on the nautical bathymetry data of different historical ages, using geomorphological information entropy and other analytical methods, this paper studies the phylogenetic evolution characteristics and shifting balance mechanism of the shoal-channel structure in Huangmaohai Estuary Bay (HEB), and the main findings include: (1) The geomorphological evolution of HEB has undergone a transition from siltation to erosion during 1940 to 2007. The average annual siltation rate was 1.4 cm/a. From then on, till 2015, the bay had shifted to erosion period and the average annual erosion rate was 1.2 cm/a. (2) The structure of shoal and channel in HEB was converted, and the structure of "three shoals and two channels" was transformed into the structure of "two shoals and one channel" between 2003 and 2007, and the elevation differentiation between shoals and channels tended to be enlarged due to the impact of reclamation in the shallow coasts and dredging projects in channels. As a result, the shallow shoals became shallower and the channels were deeper. (3) The entropy value of geomorphological information of HEB decreased first and then increased, indicating HEB it changed from the relatively stable mode of slow siltation to the abrupt changing mode, in which the uncertainty of the shoal-channel evolution was induced by human intervention; moreover, the steady states of the shoal and channel are different. The shoals showed higher uncertainty than the deep channel. (4) Human activities disturbed the original steady state of the shoal-channel structure, and the dredging project will enhance the vitality of the East Channel and promote the adaptive reconstruction in the deep channel to evolve in an orderly direction. The West Shoal and the East Shoal have undergone a disturbance balance of human activities such as reclamation, and the shoal instability has shown a disorderly evolution.
2023, 45(4): 82-94.
doi: 10.12284/hyxb2023039
Abstract:
To explore the source of platinum group elements (PGE) in cobalt-rich crusts, the samples from Caiwei Seamounts in western Pacific were chosen as the research object, for which XRD, ICP-OES and ICP-MS were used to analyze the mineral composition, major elements contents and PGE contents in cobalt-rich crusts. The results showed that, the main crystalline minerals were vernadites in cobalt-rich crusts, and the minor minerals included quartz, plagioclase, potassium feldspar and carbon fluoride apatite. Also many amorphous ferric minerals were contained in cobalt-rich crusts. In addition, Mn and Fe contents were the highest in cobalt-rich crusts, and PGE were enriched in cobalt-rich crusts. PGE contents were 142−1352 ng/g, and Pt contents were 114−1268 ng/g, in which Pt accounted for more than 80%. PGE contents in the old layers were higher than that in the new layers. And the phosphatization appeared in the old crust layers. Moreover, there was an obvious contrast in PGE of cobalt-rich crusts, Pd group (PPGE) contents were more than Ir group (IPGE). PGE diagrams showed the positive Pt anomalies and negative Pd anomalies. And Pt was enriched and Pd was poor in cobalt-rich crusts. Meanwhile, PGE in cobalt-rich crusts were probably derived from the reaction between seamount basalt and seawater during the oceanic shell erosion process. PGE had positive correlation with CaO, P2O5, Ba and Cu, so PGE were probably enriched in the phosphate phase. In addition, the growth profile of cobalt-rich crust was from top to bottom and from new to old, PGE contents increased gradually. Therefore, oxidative marine environment and high marine productivity had a positive impact on phosphatization, which further promoted the enrichment of PGE. This study provided a certain reference value for revealing the source of PGE in cobalt-rich crusts.
To explore the source of platinum group elements (PGE) in cobalt-rich crusts, the samples from Caiwei Seamounts in western Pacific were chosen as the research object, for which XRD, ICP-OES and ICP-MS were used to analyze the mineral composition, major elements contents and PGE contents in cobalt-rich crusts. The results showed that, the main crystalline minerals were vernadites in cobalt-rich crusts, and the minor minerals included quartz, plagioclase, potassium feldspar and carbon fluoride apatite. Also many amorphous ferric minerals were contained in cobalt-rich crusts. In addition, Mn and Fe contents were the highest in cobalt-rich crusts, and PGE were enriched in cobalt-rich crusts. PGE contents were 142−1352 ng/g, and Pt contents were 114−1268 ng/g, in which Pt accounted for more than 80%. PGE contents in the old layers were higher than that in the new layers. And the phosphatization appeared in the old crust layers. Moreover, there was an obvious contrast in PGE of cobalt-rich crusts, Pd group (PPGE) contents were more than Ir group (IPGE). PGE diagrams showed the positive Pt anomalies and negative Pd anomalies. And Pt was enriched and Pd was poor in cobalt-rich crusts. Meanwhile, PGE in cobalt-rich crusts were probably derived from the reaction between seamount basalt and seawater during the oceanic shell erosion process. PGE had positive correlation with CaO, P2O5, Ba and Cu, so PGE were probably enriched in the phosphate phase. In addition, the growth profile of cobalt-rich crust was from top to bottom and from new to old, PGE contents increased gradually. Therefore, oxidative marine environment and high marine productivity had a positive impact on phosphatization, which further promoted the enrichment of PGE. This study provided a certain reference value for revealing the source of PGE in cobalt-rich crusts.
2023, 45(4): 95-108.
doi: 10.12284/hyxb2023019
Abstract:
In order to study the carbon burial rates and sources of early to middle Holocene sediments in the Changjiang River palaeo-valley area, the determination of total organic carbon (TOC), total nitrogen (TN) and δ13C of sediments from ZK1 hole was carried out, and the spatial and temporal distribution characteristics and TOC sources of carbon burial in the Changjiang River palaeo-valley were analyzed by combining AMS14C (plant debris, shells) dating, foraminiferal and grain size data. Using a combination of historical geography and sedimentary geology combined with AMS14C data, the chronostratigraphic classification was carried out from bottom to top as tidal channel (U1), estuarine bay (U2), tidal sand ridge (U3), and pre-delta (U4). Sediments were influenced by the effects or factors of water depth, runoff, estuarine after-circulation, tidal currents, waves, storms and remineralization, and the mean value of TOC was 0.41%, which was lower than the surface layer of the Changjiang River Estuary. The ZK1 hole carbon burial flux (TOCBF) ranged from 7.4 g/(m2·a) to 110.5 g/(m2·a), with large variations. The TOCBF values were mainly controlled by the sedimentation rate. The results of δ13C and TOC/TN (C/N) projection points indicate that there are TOC sources with multi-source characteristics, and the overall performance is partial to terrestrial sources. The linear fit correlation between C/N and δ13C was high, which allowed the quantitative analysis of organic matter sources using C/N and δ13C. The organic carbon source analysis was carried out based on C/N and δ13C using a three-terminal source model. The U2 and U3 depositional periods were in the Holocene Great Warm Period, and the sea-derived and land-derived carbon was higher than that of the U1 and U2 depositional units, which was mainly related to the increase of marine and terrestrial primary productivity. The mean contribution of marine phytoplankton to total organic carbon was 31% in ZK1 hole. The mean contribution of estuarine phytoplankton to total organic carbon was 31%; the mean contribution of terrestrial organic carbon to total organic carbon was 38%. Overall, the contribution of terrestrial organic carbon was greater than that of estuarine phytoplankton and marine phytoplankton, which was basically consistent with the analysis results of the graphical method.
In order to study the carbon burial rates and sources of early to middle Holocene sediments in the Changjiang River palaeo-valley area, the determination of total organic carbon (TOC), total nitrogen (TN) and δ13C of sediments from ZK1 hole was carried out, and the spatial and temporal distribution characteristics and TOC sources of carbon burial in the Changjiang River palaeo-valley were analyzed by combining AMS14C (plant debris, shells) dating, foraminiferal and grain size data. Using a combination of historical geography and sedimentary geology combined with AMS14C data, the chronostratigraphic classification was carried out from bottom to top as tidal channel (U1), estuarine bay (U2), tidal sand ridge (U3), and pre-delta (U4). Sediments were influenced by the effects or factors of water depth, runoff, estuarine after-circulation, tidal currents, waves, storms and remineralization, and the mean value of TOC was 0.41%, which was lower than the surface layer of the Changjiang River Estuary. The ZK1 hole carbon burial flux (TOCBF) ranged from 7.4 g/(m2·a) to 110.5 g/(m2·a), with large variations. The TOCBF values were mainly controlled by the sedimentation rate. The results of δ13C and TOC/TN (C/N) projection points indicate that there are TOC sources with multi-source characteristics, and the overall performance is partial to terrestrial sources. The linear fit correlation between C/N and δ13C was high, which allowed the quantitative analysis of organic matter sources using C/N and δ13C. The organic carbon source analysis was carried out based on C/N and δ13C using a three-terminal source model. The U2 and U3 depositional periods were in the Holocene Great Warm Period, and the sea-derived and land-derived carbon was higher than that of the U1 and U2 depositional units, which was mainly related to the increase of marine and terrestrial primary productivity. The mean contribution of marine phytoplankton to total organic carbon was 31% in ZK1 hole. The mean contribution of estuarine phytoplankton to total organic carbon was 31%; the mean contribution of terrestrial organic carbon to total organic carbon was 38%. Overall, the contribution of terrestrial organic carbon was greater than that of estuarine phytoplankton and marine phytoplankton, which was basically consistent with the analysis results of the graphical method.
2023, 45(4): 109-120.
doi: 10.12284/hyxb2023073
Abstract:
Marginal salt marsh patches play a crucial role in the morphological evolution of salt marsh-tidal flat systems by dissipating hydrodynamics and stabilizing sediment, and the tidal channel can also influence the growth, expansion and erosion of the salt marsh patches. However, the interactions between saltmarsh patch expansion and tidal channel formation are complex and poorly understood. In the study, we established a two-dimensional biomorphodynamic model and introduced a dynamic vegetation module to simulate the spatial-temporal distribution of saltmarsh patches and the geomorphic evolution of the tidal channel system. We explored the two-way feedback between the spatial patterns of the tidal trench system and salt marsh vegetation patches with different initial numbers. Model results showed that the tidal channel extended rapidly to both sides of the sea and land at first, and then developed a large number of creeks, and the salt marsh patches expanded to the periphery and gradually formed a large patch. Besides, the presence of marsh patches can increase the density of tidal channels and promote the development of tidal channels. Further, the orientation of tidal channels was affected by the spatial distribution of marsh patches, which can divert water flow and induce the concentration of tidal flow. Specially, in the early stage of saltmarsh evolution, more tidal channels were formed by the interactions between hydrodynamics and sediment motion with the increase of marsh patch numbers, and in the later stage, the influence of salt marsh clusters gradually changed from promotion to stabilization. However, the expansion and the spatial distribution pattern of salt marsh patches was later limited by the formation of tidal channels reciprocally. Our study extended current understanding of the mechanisms underlying the co-evolution of marsh patches and tidal channels, and can provide scientific basis for future works on coastal protection and restoration.
Marginal salt marsh patches play a crucial role in the morphological evolution of salt marsh-tidal flat systems by dissipating hydrodynamics and stabilizing sediment, and the tidal channel can also influence the growth, expansion and erosion of the salt marsh patches. However, the interactions between saltmarsh patch expansion and tidal channel formation are complex and poorly understood. In the study, we established a two-dimensional biomorphodynamic model and introduced a dynamic vegetation module to simulate the spatial-temporal distribution of saltmarsh patches and the geomorphic evolution of the tidal channel system. We explored the two-way feedback between the spatial patterns of the tidal trench system and salt marsh vegetation patches with different initial numbers. Model results showed that the tidal channel extended rapidly to both sides of the sea and land at first, and then developed a large number of creeks, and the salt marsh patches expanded to the periphery and gradually formed a large patch. Besides, the presence of marsh patches can increase the density of tidal channels and promote the development of tidal channels. Further, the orientation of tidal channels was affected by the spatial distribution of marsh patches, which can divert water flow and induce the concentration of tidal flow. Specially, in the early stage of saltmarsh evolution, more tidal channels were formed by the interactions between hydrodynamics and sediment motion with the increase of marsh patch numbers, and in the later stage, the influence of salt marsh clusters gradually changed from promotion to stabilization. However, the expansion and the spatial distribution pattern of salt marsh patches was later limited by the formation of tidal channels reciprocally. Our study extended current understanding of the mechanisms underlying the co-evolution of marsh patches and tidal channels, and can provide scientific basis for future works on coastal protection and restoration.
2023, 45(4): 121-132.
doi: 10.12284/hyxb2023041
Abstract:
Optically stimulated luminescence (OSL) dating as a absolute dating method for sediments has been widely used in Quaternary studies. Improving the accuracy and precision of OSL dating has been a hot spot in academic research. However, for a long time, there have been numerous studies on equivalent dose measurement procedures and calculation methods, and relatively few studies on environmental dose rates. In this paper, we conducted OSL chronology study on marine sediment samples obtained from the Borehole ZBW in the southwestern of Hainan Province. The contents of uranium, thorium and potassium in the samples were measured by inductively coupled plasma mass spectrometry/optical emission spectrometry (ICP-MS/OES), neutron activation analysis (NAA) and γ-ray spectrometer, respectively. The results show that there are differences in the results measured by the three methods in some strata, and the reasons could be: (1) incomplete dissolution of U in heavy minerals during the ICP-MS/OES pretreatment process; (2) the ICP-MS/OES measurement results are the elemental contents of U, Th, and K, which include some non-radionuclide contents; (3) the small sample size used for NAA, which was subject to chance errors, and the dilution effect of non-radioactive material in the sample affects the measurement results; (4) there is an imbalance of uranium system in the sample. Combined with the sedimentary environment in the study area and the data measured by HPGe γ-ray spectrometer, the results show that the uranium imbalance originates from the autogenous uranium absorption phenomenon, and the effect on the environmental dose rate is about 11%.
Optically stimulated luminescence (OSL) dating as a absolute dating method for sediments has been widely used in Quaternary studies. Improving the accuracy and precision of OSL dating has been a hot spot in academic research. However, for a long time, there have been numerous studies on equivalent dose measurement procedures and calculation methods, and relatively few studies on environmental dose rates. In this paper, we conducted OSL chronology study on marine sediment samples obtained from the Borehole ZBW in the southwestern of Hainan Province. The contents of uranium, thorium and potassium in the samples were measured by inductively coupled plasma mass spectrometry/optical emission spectrometry (ICP-MS/OES), neutron activation analysis (NAA) and γ-ray spectrometer, respectively. The results show that there are differences in the results measured by the three methods in some strata, and the reasons could be: (1) incomplete dissolution of U in heavy minerals during the ICP-MS/OES pretreatment process; (2) the ICP-MS/OES measurement results are the elemental contents of U, Th, and K, which include some non-radionuclide contents; (3) the small sample size used for NAA, which was subject to chance errors, and the dilution effect of non-radioactive material in the sample affects the measurement results; (4) there is an imbalance of uranium system in the sample. Combined with the sedimentary environment in the study area and the data measured by HPGe γ-ray spectrometer, the results show that the uranium imbalance originates from the autogenous uranium absorption phenomenon, and the effect on the environmental dose rate is about 11%.
2023, 45(4): 133-143.
doi: 10.12284/hyxb2023031
Abstract:
Shapes of freak waves are strongly related to the characteristics of their surrounding sea state. The most probable shape of rogue waves obeys NewWave theory under the narrow band assumption in the linear process. Based on the NewWave theory, the largest wave is located in the center of a wave group and the adjacent waves are symmetrical. However, wide spectral widths containing various frequency components are more common in the ocean. There is still a lack of systematic understanding of the shapes of in-situ measured freak waves and the surrounding waves. Furthermore, key parameters that affect the shapes are not clear. In the present study, shapes of 112 freak waves and the related influence factors from the ocean weather station in the Norwegian Sea are investigated. Merely 52% of freak waves are located in the center of the group, and the possibility of other freak waves occurring towards the front of the wave groups is higher. Besides, shapes of the adjacent prior and following waves of freak waves are asymmetry. Generally, the amplitude of the following wave is larger than that of the preceding one. By quantitatively comparing shapes of the averaged measured rogue waves and based on the NewWave theory, it is found that the spectral width is a key parameter for affecting shapes of freak waves. With the spectral width wider, the difference of profiles of sea surface elevations around the freak waves between the measured and using the NewWave theory is exponentially increasing.
Shapes of freak waves are strongly related to the characteristics of their surrounding sea state. The most probable shape of rogue waves obeys NewWave theory under the narrow band assumption in the linear process. Based on the NewWave theory, the largest wave is located in the center of a wave group and the adjacent waves are symmetrical. However, wide spectral widths containing various frequency components are more common in the ocean. There is still a lack of systematic understanding of the shapes of in-situ measured freak waves and the surrounding waves. Furthermore, key parameters that affect the shapes are not clear. In the present study, shapes of 112 freak waves and the related influence factors from the ocean weather station in the Norwegian Sea are investigated. Merely 52% of freak waves are located in the center of the group, and the possibility of other freak waves occurring towards the front of the wave groups is higher. Besides, shapes of the adjacent prior and following waves of freak waves are asymmetry. Generally, the amplitude of the following wave is larger than that of the preceding one. By quantitatively comparing shapes of the averaged measured rogue waves and based on the NewWave theory, it is found that the spectral width is a key parameter for affecting shapes of freak waves. With the spectral width wider, the difference of profiles of sea surface elevations around the freak waves between the measured and using the NewWave theory is exponentially increasing.
2023, 45(4): 144-153.
doi: 10.12284/hyxb2023047
Abstract:
The free-dropping acoustic Doppler current profile (FADCP) samples in a “free-fall” manner, which can observe the full depth current without relying on the cable traction of the ship, and its stability is greatly improved compared with lowered acoustic doppler current profiler (LADCP), effectively reducing the irregular motion in the observations. The FADCP observation experiments conducted in April and September 2021 at Xisha waters in the South China Sea obtained current and CTD data from two sections containing 16 stations. Based on the real bottom current observation during the resting period, the full-depth current profiles at each station were obtained by shear method, and the average deviation of the station profile near a mooring compared with the mooring profile was 3 cm/s. The observation section captured the cyclonic eddies of two periods at Xisha waters with more precise vertical structures than the HYCOM simulation, and the surface flows fitted with the absolute geostrophic currents. This research shows that the FADCP has low vessel requirements, high data quality, easy post-processing and good results, but cannot perform supplementary observations for specific water layers.
The free-dropping acoustic Doppler current profile (FADCP) samples in a “free-fall” manner, which can observe the full depth current without relying on the cable traction of the ship, and its stability is greatly improved compared with lowered acoustic doppler current profiler (LADCP), effectively reducing the irregular motion in the observations. The FADCP observation experiments conducted in April and September 2021 at Xisha waters in the South China Sea obtained current and CTD data from two sections containing 16 stations. Based on the real bottom current observation during the resting period, the full-depth current profiles at each station were obtained by shear method, and the average deviation of the station profile near a mooring compared with the mooring profile was 3 cm/s. The observation section captured the cyclonic eddies of two periods at Xisha waters with more precise vertical structures than the HYCOM simulation, and the surface flows fitted with the absolute geostrophic currents. This research shows that the FADCP has low vessel requirements, high data quality, easy post-processing and good results, but cannot perform supplementary observations for specific water layers.
2023, 45(4): 154-164.
doi: 10.12284/hyxb2023049
Abstract:
Coral reef substrate classification plays a crucial role in marine resource development and marine ecological protection. At present, deep learning semantic segmentation methods are widely used in the field of remote sensing image classification, but less research has been conducted in substrate classification. Due to the high cost of pixel-by-pixel labeling in the fully supervised deep learning-based method, it is not suitable for large-scale and high-frequency substrate classification work. The semi-supervised deep learning-based method can effectively use the labeled labels to generate pseudo-labels for unlabeled data, thus effectively reducing the labor cost, however, the performance of the existing semi-supervised method is vulnerable to the interference of pseudo-label noise. To address the above problems, this paper proposes a semi-supervised substrate classification method based on soft and hard collaborative decision making. First, a high quality Pseudo tag is generated using joint decision making of multiple models; then, a loss function (Collaboration Choice of decision Confidence Loss function, 3CLoss) is proposed to take into account the confidence of Pseudo tag pixels and guide the model for training; finally, a soft and hard collaborative decision making approach is used to obtain accurate substrate classification results. The accuracy of this paper was evaluated on the shallow benthic habitat atlas datasets of Buck Island Reef in the northern part of St. Croix, U.S. Virgin Islands, and Pearl and Hermes Atolls, about 400 km southeast of Midway Island, Hawaiian Islands, and the experimental results show that the accuracy of the proposed method is comparable to that of the fully supervised learning method, and 3.08% higher than that of the mainstream semantic segmentation methods on average, which can effectively serve the coral reef substrate survey.
Coral reef substrate classification plays a crucial role in marine resource development and marine ecological protection. At present, deep learning semantic segmentation methods are widely used in the field of remote sensing image classification, but less research has been conducted in substrate classification. Due to the high cost of pixel-by-pixel labeling in the fully supervised deep learning-based method, it is not suitable for large-scale and high-frequency substrate classification work. The semi-supervised deep learning-based method can effectively use the labeled labels to generate pseudo-labels for unlabeled data, thus effectively reducing the labor cost, however, the performance of the existing semi-supervised method is vulnerable to the interference of pseudo-label noise. To address the above problems, this paper proposes a semi-supervised substrate classification method based on soft and hard collaborative decision making. First, a high quality Pseudo tag is generated using joint decision making of multiple models; then, a loss function (Collaboration Choice of decision Confidence Loss function, 3CLoss) is proposed to take into account the confidence of Pseudo tag pixels and guide the model for training; finally, a soft and hard collaborative decision making approach is used to obtain accurate substrate classification results. The accuracy of this paper was evaluated on the shallow benthic habitat atlas datasets of Buck Island Reef in the northern part of St. Croix, U.S. Virgin Islands, and Pearl and Hermes Atolls, about 400 km southeast of Midway Island, Hawaiian Islands, and the experimental results show that the accuracy of the proposed method is comparable to that of the fully supervised learning method, and 3.08% higher than that of the mainstream semantic segmentation methods on average, which can effectively serve the coral reef substrate survey.
2023, 45(4): 165-178.
doi: 10.12284/hyxb2023027
Abstract:
Water temperature prediction is a key technology to ensure the production of coastal fisheries and environmental safety. The existing numerical models have high development costs with insufficient business applications. This study develops a prediction method of water temperature through integrating differential regression (DR) and transferable long short-term memory (TLSTM). Taking the water temperature of Xiamen Bay (source domain, with a large number of data) and Sansha Bay (target domain, with less data) as the research object, the DR model is established based on the data of monitoring water temperature and forecast temperature in the Sansha Bay, and the TLSTM model is established based on the long-term monitoring data of water temperature in the Xiamen Bay. The pure differential regression model, mixed differential regression model and TLSTM model are integrated into the DR-TLSTM model of Sansha Bay by using variable weight algorithm, and the performance of the model is evaluated, the results are compared with the LSTM model based on only a small amount of monitoring data in the Sansha Bay. The results show that: (1) the prediction accuracy of TLSTM model is better than that of LSTM model based on a small amount of data in the target domain; (2) the DR-TLSTM model has high prediction accuracy, and the root mean square error of prediction in the next 1−7 days is 0.13−0.77℃, and the root mean square error of prediction in the next 1−3 days is less than 0.4℃; (3) the DR-TLSTM model can effectively predict the sudden rise or fall trend of water temperature, and the root mean square error of predicting the sudden change point of water temperature is 0.29−1.09℃. Based on the DR-TLSTM model, the operational information service of water temperature early warning and forecast in the Sansha Bay is realized.
Water temperature prediction is a key technology to ensure the production of coastal fisheries and environmental safety. The existing numerical models have high development costs with insufficient business applications. This study develops a prediction method of water temperature through integrating differential regression (DR) and transferable long short-term memory (TLSTM). Taking the water temperature of Xiamen Bay (source domain, with a large number of data) and Sansha Bay (target domain, with less data) as the research object, the DR model is established based on the data of monitoring water temperature and forecast temperature in the Sansha Bay, and the TLSTM model is established based on the long-term monitoring data of water temperature in the Xiamen Bay. The pure differential regression model, mixed differential regression model and TLSTM model are integrated into the DR-TLSTM model of Sansha Bay by using variable weight algorithm, and the performance of the model is evaluated, the results are compared with the LSTM model based on only a small amount of monitoring data in the Sansha Bay. The results show that: (1) the prediction accuracy of TLSTM model is better than that of LSTM model based on a small amount of data in the target domain; (2) the DR-TLSTM model has high prediction accuracy, and the root mean square error of prediction in the next 1−7 days is 0.13−0.77℃, and the root mean square error of prediction in the next 1−3 days is less than 0.4℃; (3) the DR-TLSTM model can effectively predict the sudden rise or fall trend of water temperature, and the root mean square error of predicting the sudden change point of water temperature is 0.29−1.09℃. Based on the DR-TLSTM model, the operational information service of water temperature early warning and forecast in the Sansha Bay is realized.
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