2011 Vol. 30, No. 5
Display Method:
2011, (5): 1-13.
doi: 10.1007/s13131-011-0142-3
Abstract:
The computer model for near shore wave propagation, SWAN, was used to study wave climates in Liverpool Bay, northwest England with various input parameters, including bottom friction factor, white capping, wind drag formulation and effects of tidal modulations. Results were compared with in-situ measurements and reveal the impacts from these inputs on the predictions of wave height and propagation distributions. In particular, the model results were found very sensitive to different input formulations, and tend to underestimate the wave parameters under storm conditions in comparison with the observations. It is therefore important to further validate the model against detailed field measurements, particularly under large storms that are often of the primary concern.
The computer model for near shore wave propagation, SWAN, was used to study wave climates in Liverpool Bay, northwest England with various input parameters, including bottom friction factor, white capping, wind drag formulation and effects of tidal modulations. Results were compared with in-situ measurements and reveal the impacts from these inputs on the predictions of wave height and propagation distributions. In particular, the model results were found very sensitive to different input formulations, and tend to underestimate the wave parameters under storm conditions in comparison with the observations. It is therefore important to further validate the model against detailed field measurements, particularly under large storms that are often of the primary concern.
2011, (5): 14-22.
doi: 10.1007/s13131-011-0143-2
Abstract:
Analysis of tidal current and sea level has been made based on the observations from the summer of 2006 to the winter of 2007, respectively. The result indicates that a two-layer structure of residual current exists in summer, with its upper layer going northwestward and the lower layer southeastward. In addition, some strong residuals exist in the neighboring depth of the pycnocline during the current period of astronomical tide. In winter, except some individual layersthe residual currents mostly direct to the northwest, from which we can see the fluctuation of abnormal sea-level and the appearance of associated current because of the changes of the wind field. The analysis of tidal ellipse indicates that the direction of the maximum semidiurnal component is clockwise from summer to winter, with an angle of 16°-18°. Moreover, in summer the semidiurnal component rotates with depth clockwise while the diurnal component counterclockwise. However, the vertical structure is almost homogeneous in winter.
Analysis of tidal current and sea level has been made based on the observations from the summer of 2006 to the winter of 2007, respectively. The result indicates that a two-layer structure of residual current exists in summer, with its upper layer going northwestward and the lower layer southeastward. In addition, some strong residuals exist in the neighboring depth of the pycnocline during the current period of astronomical tide. In winter, except some individual layersthe residual currents mostly direct to the northwest, from which we can see the fluctuation of abnormal sea-level and the appearance of associated current because of the changes of the wind field. The analysis of tidal ellipse indicates that the direction of the maximum semidiurnal component is clockwise from summer to winter, with an angle of 16°-18°. Moreover, in summer the semidiurnal component rotates with depth clockwise while the diurnal component counterclockwise. However, the vertical structure is almost homogeneous in winter.
2011, (5): 23-32.
doi: 10.1007/s13131-011-0144-1
Abstract:
Based on the z-coordinate ocean model HAMSOM, we introduced the internal-tide viscosity term and applied the model to numerically investigate the M2 internal tide generation and propagation in the Luzon Strait (LS). The results show that (1) in the upper 250 m depth, at the thermocline, the maximum amplitude of the generated internal tides in the LS can reach 40 m; (2) the major internal tides are generated to the northwest of Itbayat Island, the southwest of Batan Island and the northwest of the Babuyan Islands; (3) during the propagation the baroclinic energy scattering and reflection is obvious, which exists under the effect of the specific topography in the South China Sea (SCS); (4) the westward-propagating internal tides are divided into two branches entering the SCS. While passing through 118°E, the major branch is divided into two branches again. The strongest internal tides in the LS are generated to the northwest of Itbayat Island and propagate northeastward to the Pacific. However, to the east of 122°E, most of the internal tides propagate southeastward to the Pacific as a beam.
Based on the z-coordinate ocean model HAMSOM, we introduced the internal-tide viscosity term and applied the model to numerically investigate the M2 internal tide generation and propagation in the Luzon Strait (LS). The results show that (1) in the upper 250 m depth, at the thermocline, the maximum amplitude of the generated internal tides in the LS can reach 40 m; (2) the major internal tides are generated to the northwest of Itbayat Island, the southwest of Batan Island and the northwest of the Babuyan Islands; (3) during the propagation the baroclinic energy scattering and reflection is obvious, which exists under the effect of the specific topography in the South China Sea (SCS); (4) the westward-propagating internal tides are divided into two branches entering the SCS. While passing through 118°E, the major branch is divided into two branches again. The strongest internal tides in the LS are generated to the northwest of Itbayat Island and propagate northeastward to the Pacific. However, to the east of 122°E, most of the internal tides propagate southeastward to the Pacific as a beam.
2011, (5): 33-44.
doi: 10.1007/s13131-011-0145-0
Abstract:
A 30-d current numerical simulation is running for the Yangshan Port, the Changjiang Estuary, the Hangzhou Bay and their adjacent seas using a finite volume coastal ocean model (FVCOM), with Changjiang River runoff and wind effect being considered. At the open boundary, this model is driven by the water level obtained from prediction including eight main partial tides. After the harmonic analysis, the cotidal chart and the iso-amplitude line as well as the current ellipse distribution map are displayed to illustrate the propagation property of a tidal wave. Horizontal velocity of both the U and V components coincides with the actual measurement, which shows that the model result is credible to describe the hydrodynamic pattern in this sea area. On this basis, real-time current data from high-frequency radar is assimilated with the implementation of quick ensemble Kalman filter, which takes the variation tendency of the state vector to compute the analysis field, instead of integrating the field for N (the number of ensemble) times as it used to in the standard EnKF, aiming at raising the efficiency of computation, reducing the error of prediction and at the same time, improving the forecast effect.
A 30-d current numerical simulation is running for the Yangshan Port, the Changjiang Estuary, the Hangzhou Bay and their adjacent seas using a finite volume coastal ocean model (FVCOM), with Changjiang River runoff and wind effect being considered. At the open boundary, this model is driven by the water level obtained from prediction including eight main partial tides. After the harmonic analysis, the cotidal chart and the iso-amplitude line as well as the current ellipse distribution map are displayed to illustrate the propagation property of a tidal wave. Horizontal velocity of both the U and V components coincides with the actual measurement, which shows that the model result is credible to describe the hydrodynamic pattern in this sea area. On this basis, real-time current data from high-frequency radar is assimilated with the implementation of quick ensemble Kalman filter, which takes the variation tendency of the state vector to compute the analysis field, instead of integrating the field for N (the number of ensemble) times as it used to in the standard EnKF, aiming at raising the efficiency of computation, reducing the error of prediction and at the same time, improving the forecast effect.
2011, (5): 45-55.
doi: 10.1007/s13131-011-0146-z
Abstract:
A fine resolution model has been applied to get more insight into the effects of a modified runoff due to the Three-Gorges-Dam (TGD) on the East China Sea (ECS). The region of interest was confined to the offshore area in the vicinity of the Changjiang River. To the east, it extended up to the area southwest of Cheju Island. The model was used to evaluate the effect of a modified runoff on the water properties of the adjacent regions like the Changjiang diluted water (CDW) and the Zhoushan Fishing Ground. The sensitivity of the ECS to a modified Changjiang runoff was explored firstly by sensitivity studies and secondly by experiments based on historical runoff records and water management plans of the TGD. These experiments led to the general conclusion that the most affected area by runoff is located close to the Changjiang River mouth. The area of influence has an extension of about 150 km×150 km. In the realistic experiment, the related anomalies reached their maximum value in early summer (May). In normal years the related salinity anomalies can get to as large as 2.
A fine resolution model has been applied to get more insight into the effects of a modified runoff due to the Three-Gorges-Dam (TGD) on the East China Sea (ECS). The region of interest was confined to the offshore area in the vicinity of the Changjiang River. To the east, it extended up to the area southwest of Cheju Island. The model was used to evaluate the effect of a modified runoff on the water properties of the adjacent regions like the Changjiang diluted water (CDW) and the Zhoushan Fishing Ground. The sensitivity of the ECS to a modified Changjiang runoff was explored firstly by sensitivity studies and secondly by experiments based on historical runoff records and water management plans of the TGD. These experiments led to the general conclusion that the most affected area by runoff is located close to the Changjiang River mouth. The area of influence has an extension of about 150 km×150 km. In the realistic experiment, the related anomalies reached their maximum value in early summer (May). In normal years the related salinity anomalies can get to as large as 2.
2011, (5): 56-63.
doi: 10.1007/s13131-011-0147-y
Abstract:
Four sources of surface heat flux (SHF) and the satellite remote sensing sea surface temperature (SST) data are combined to investigate the heat budget closure of the Huanghai Sea (HS) in winter. It is found that heat loss occurs all over the HS during winter and the area averaged heat content change decreases with a rate of -106 W/m2. Comparing with the area averaged SHF of -150 W/m-2 from the four SHF data sets, it can be concluded that the SHF plays a dominant role in the HS heat budget during winter. In contrast, the heat advection transported by the Huanghai Warm Current (Yellow Sea Warm Current, HWC) accounted for up to 29% of the HS heat content change. Close correlation, especially in February, between the storm events and the SST increase demonstrates that the HWC behaves strongly as a wind-driven compensation current.
Four sources of surface heat flux (SHF) and the satellite remote sensing sea surface temperature (SST) data are combined to investigate the heat budget closure of the Huanghai Sea (HS) in winter. It is found that heat loss occurs all over the HS during winter and the area averaged heat content change decreases with a rate of -106 W/m2. Comparing with the area averaged SHF of -150 W/m-2 from the four SHF data sets, it can be concluded that the SHF plays a dominant role in the HS heat budget during winter. In contrast, the heat advection transported by the Huanghai Warm Current (Yellow Sea Warm Current, HWC) accounted for up to 29% of the HS heat content change. Close correlation, especially in February, between the storm events and the SST increase demonstrates that the HWC behaves strongly as a wind-driven compensation current.
2011, (5): 64-70.
doi: 10.1007/s13131-011-0148-x
Abstract:
A numerical study of sea waves generated by tropical cyclone Jelawat is carried out using the cycle 4 version of the WAM. The model domain currently covers the latitudes 20°-45°N and longitudes 115°-135°E, and the model spatial resolution reaches 0.25°×0.25°. Comparison of the model results with buoy observations reveals that the model can fairly reproduce the temporal variation of observed waves. Two-dimensional comparison is also made against the satellite altimeter significant wave heights derived from TOPEX/POSEIDON and ERS-2 data, showing high quality of the model performance.
A numerical study of sea waves generated by tropical cyclone Jelawat is carried out using the cycle 4 version of the WAM. The model domain currently covers the latitudes 20°-45°N and longitudes 115°-135°E, and the model spatial resolution reaches 0.25°×0.25°. Comparison of the model results with buoy observations reveals that the model can fairly reproduce the temporal variation of observed waves. Two-dimensional comparison is also made against the satellite altimeter significant wave heights derived from TOPEX/POSEIDON and ERS-2 data, showing high quality of the model performance.
2011, (5): 71-83.
doi: 10.1007/s13131-011-0149-9
Abstract:
This paper analyzed the distribution of thermohaline and circulation characteristics of Zhejiang and Fujian waters, based on the cross-sectional thermohaline data and on current data (up to 30 d duration) at fixed-point moorings, collected in the summer of 2006. We also performed low-pass filtering and spectrum analysis on the mooring submersible buoy data. Based on that analysis, we discussed the characteristics of low frequency currents and time-variations in these waters. The main conclusions are as follows. (1) There is a low salinity pinnate area near the Hangzhou Bay in summer, and outside the low salinity area, an obvious salinity front is present from surface to bottom near 123°E. There is also a temperature front below the surface at a corresponding position. (2) Bottom water of the Taiwan Warm Current comes from the subsurface of Kuroshio. (3) The direction of low frequency current at fixed anchor stations is N-NE or S, which mainly depends on the interaction of control currents in this waters. (4) Significant spectral peaks at all mooring stations are typically semidiurnal and diurnal tides. Semidiurnal tidal waves are the main ones in these waters, and have more energy closer to the shore. (5) Significant energy spectral peaks of middle period (3 to 8 d) of currents are responses to weather frequency. (6) Significant energy spectral peaks of long periods at the surface or bottom are probably responses to seasonal wind or bottom friction, while, the long period peaks of other depths can reflect cyclical changes of interactions between currents. We conclude that the pulsation period of the Taiwan Warm Current in these waters is 10-17 d.
This paper analyzed the distribution of thermohaline and circulation characteristics of Zhejiang and Fujian waters, based on the cross-sectional thermohaline data and on current data (up to 30 d duration) at fixed-point moorings, collected in the summer of 2006. We also performed low-pass filtering and spectrum analysis on the mooring submersible buoy data. Based on that analysis, we discussed the characteristics of low frequency currents and time-variations in these waters. The main conclusions are as follows. (1) There is a low salinity pinnate area near the Hangzhou Bay in summer, and outside the low salinity area, an obvious salinity front is present from surface to bottom near 123°E. There is also a temperature front below the surface at a corresponding position. (2) Bottom water of the Taiwan Warm Current comes from the subsurface of Kuroshio. (3) The direction of low frequency current at fixed anchor stations is N-NE or S, which mainly depends on the interaction of control currents in this waters. (4) Significant spectral peaks at all mooring stations are typically semidiurnal and diurnal tides. Semidiurnal tidal waves are the main ones in these waters, and have more energy closer to the shore. (5) Significant energy spectral peaks of middle period (3 to 8 d) of currents are responses to weather frequency. (6) Significant energy spectral peaks of long periods at the surface or bottom are probably responses to seasonal wind or bottom friction, while, the long period peaks of other depths can reflect cyclical changes of interactions between currents. We conclude that the pulsation period of the Taiwan Warm Current in these waters is 10-17 d.
2011, (5): 84-93.
doi: 10.1007/s13131-011-0150-3
Abstract:
Power spectrum and cross-wavelet transform analysis was adopted to study the time-frequency characteristics and multiscale correlations between runoff, tidal range and salinity in the Changjiang Estuary based on the runoff data collected at the Datong Station, the tidal range measured at the Baozhen Station, and the salinity at the Baogang Station from 2008 to 2009. The variations of the salinity showed significant periodicity at scales of 2-3, 7-8, 14-15 and 26-30 d. The correlation between the salinity and the runoff and the tidal range were found to be significantly related to shock at scales of 5-7, 14-15, 26-30 d and 0.5 a. The correlation between the runoff and the salinity was mainly in the same phase, while the correlation between the tidal range and the salinity was in the antiphase. Different frequency bands were related to different degrees, and their relevance increased as the resonance frequency decreased. In addition, changes of the seasonal runoff were obvious. Specifically, a point of discontinuity was reached in early June with a cycle of 7-8 d, which coincided with the periodicity of plum rains in the Changjiang-Huaihe region. High-frequency changes (8-16 d period) of the salinity corresponded to the time domain in January-April 2008, February-April 2009 and October-December 2009 and exhibited an approximately 0.5 a (184 d) long frequency oscillation. Short-period changes were found to be stronger than long-period changes. Cross-wavelet transforms for the salinity, the runoff and the tidal range revealed local features in the time domain, while the significant levels of different periodic oscillations were observed in the frequency domain. The correlation characteristics of the salinity and the runoff were significant in the 80-90 d frequency domain, indicating that the major impact of the runoff on the salinity was reflected in seasonal changes. The tidal range on the small scale of 14-15 and 30-32 d was more obvious than the runoff.
Power spectrum and cross-wavelet transform analysis was adopted to study the time-frequency characteristics and multiscale correlations between runoff, tidal range and salinity in the Changjiang Estuary based on the runoff data collected at the Datong Station, the tidal range measured at the Baozhen Station, and the salinity at the Baogang Station from 2008 to 2009. The variations of the salinity showed significant periodicity at scales of 2-3, 7-8, 14-15 and 26-30 d. The correlation between the salinity and the runoff and the tidal range were found to be significantly related to shock at scales of 5-7, 14-15, 26-30 d and 0.5 a. The correlation between the runoff and the salinity was mainly in the same phase, while the correlation between the tidal range and the salinity was in the antiphase. Different frequency bands were related to different degrees, and their relevance increased as the resonance frequency decreased. In addition, changes of the seasonal runoff were obvious. Specifically, a point of discontinuity was reached in early June with a cycle of 7-8 d, which coincided with the periodicity of plum rains in the Changjiang-Huaihe region. High-frequency changes (8-16 d period) of the salinity corresponded to the time domain in January-April 2008, February-April 2009 and October-December 2009 and exhibited an approximately 0.5 a (184 d) long frequency oscillation. Short-period changes were found to be stronger than long-period changes. Cross-wavelet transforms for the salinity, the runoff and the tidal range revealed local features in the time domain, while the significant levels of different periodic oscillations were observed in the frequency domain. The correlation characteristics of the salinity and the runoff were significant in the 80-90 d frequency domain, indicating that the major impact of the runoff on the salinity was reflected in seasonal changes. The tidal range on the small scale of 14-15 and 30-32 d was more obvious than the runoff.
2011, (5): 94-100.
doi: 10.1007/s13131-011-0151-2
Abstract:
Water temperature, turbidity, chlorophyll-a and suspended sediment concentration (SSC) were investigated at 61 stations of eight sections in the southern Huanghai Sea (HS) and the East China Sea (ECS) during the summer (28 June to 15 July) of 2006. The horizontal distribution of suspended parti culate matter (SPM) displayed a high concentration inshore and a low value offshore. The maximum value can reach 10.4 mg/dm3, which can be found at the Changjiang River mouth. For the same site, the SSC was generally higher at the bottom than on the surface. In the vertical direction, distribution characteristics of turbidity can be divided into two types:in the southern HS high values at the bottom while low values on the surface, and in the ECS high values inshore with low values offshore. The thermocline in the HS and the Taiwan Warm Current in the ECS could be important factors preventing the SPM from diffusing upward and seaward. Even the typhoon Ewiniar was not able to work on the major sediment transport under the thermocline during the observation.
Water temperature, turbidity, chlorophyll-a and suspended sediment concentration (SSC) were investigated at 61 stations of eight sections in the southern Huanghai Sea (HS) and the East China Sea (ECS) during the summer (28 June to 15 July) of 2006. The horizontal distribution of suspended parti culate matter (SPM) displayed a high concentration inshore and a low value offshore. The maximum value can reach 10.4 mg/dm3, which can be found at the Changjiang River mouth. For the same site, the SSC was generally higher at the bottom than on the surface. In the vertical direction, distribution characteristics of turbidity can be divided into two types:in the southern HS high values at the bottom while low values on the surface, and in the ECS high values inshore with low values offshore. The thermocline in the HS and the Taiwan Warm Current in the ECS could be important factors preventing the SPM from diffusing upward and seaward. Even the typhoon Ewiniar was not able to work on the major sediment transport under the thermocline during the observation.
2011, (5): 101-107.
doi: 10.1007/s13131-011-0152-1
Abstract:
The rotary ring flume is used to study the silty sand movement in a periodic alternating current. Characteristics of sediment movement of different coasts in the tidal current are summarized. More detailed analysis of erosion-sedimentation function in a numerical simulation is made. The equilibrium sediment concentration is advanced. Based on the equilibrium sediment concentration, the seabed erosion-sedimentation index is derived and the seabed erosion-sedimentation calculation is analyzed. The seabed erosion-sedimentation index is used to calculate the seabed evolution of Yangshan sea area and a good agreement with field measurements is obtained.
The rotary ring flume is used to study the silty sand movement in a periodic alternating current. Characteristics of sediment movement of different coasts in the tidal current are summarized. More detailed analysis of erosion-sedimentation function in a numerical simulation is made. The equilibrium sediment concentration is advanced. Based on the equilibrium sediment concentration, the seabed erosion-sedimentation index is derived and the seabed erosion-sedimentation calculation is analyzed. The seabed erosion-sedimentation index is used to calculate the seabed evolution of Yangshan sea area and a good agreement with field measurements is obtained.
2011, (5): 108-113.
doi: 10.1007/s13131-011-0153-0
Abstract:
The influence of density, foliage and stem flexibility on the roughness coefficients under unsubmerged conditions, such as Manning's n, is investigated experimentally. An instrumentation system has been developed for measuring the flow rate ranging from 0.1 to 0.3 L/s under the condition of different artificial foliated reeds. Based on the experimental results, the influence on the relationship between n with different density, foliage, flexibility and flow depth is discussed. It is found that the foliage and the density are the important factors affecting Manning's n. At a range of relatively low velocity and relatively large bending stiffness of stem, Manning's n is not influenced significanthy by the flexibility of stem.
The influence of density, foliage and stem flexibility on the roughness coefficients under unsubmerged conditions, such as Manning's n, is investigated experimentally. An instrumentation system has been developed for measuring the flow rate ranging from 0.1 to 0.3 L/s under the condition of different artificial foliated reeds. Based on the experimental results, the influence on the relationship between n with different density, foliage, flexibility and flow depth is discussed. It is found that the foliage and the density are the important factors affecting Manning's n. At a range of relatively low velocity and relatively large bending stiffness of stem, Manning's n is not influenced significanthy by the flexibility of stem.
2011, (5): 114-124.
doi: 10.1007/s13131-011-0136-1
Abstract:
The Philippine Basin, surrounded by a series of oceanic trenches, is an independent deep ocean basin in the West Pacific Ocean. Its middle part is divided into three marginal sea sub-basins by the Kyushu-Palau and West Mariana Ridges, namely, the West Philippine Basin, the Shikoku and Parece Vela Basins and the Mariana Trough. This paper, through the analysis of the geomorphologic features and gravity and magnetic characteristics of the basin and identification of striped magnetic anomalies, suggests that the entire Philippine Basin developed magnetic lineation of oceanic nature, and therefore, the entire basin is of the nature of oceanic crust. The basin has developed a series of special geomorphic units with different shapes. The KPR runs through the entire Philippine Basin. From the view of geomorphologic features, the KPR is a discontinuous seamount chain (chain-shaped seamounts) and subduction beneath the Japanese Island arc at the Nankai Trough which is the natural boundary between the basin and the Japanese Island arc. At the positions of 25°N, 24°N, 23°N and 18°N, obvious discontinuity is shown, which belongs to natural topographic discontinuity. Therefore, the KPR is topographically discontinuous.
The Philippine Basin, surrounded by a series of oceanic trenches, is an independent deep ocean basin in the West Pacific Ocean. Its middle part is divided into three marginal sea sub-basins by the Kyushu-Palau and West Mariana Ridges, namely, the West Philippine Basin, the Shikoku and Parece Vela Basins and the Mariana Trough. This paper, through the analysis of the geomorphologic features and gravity and magnetic characteristics of the basin and identification of striped magnetic anomalies, suggests that the entire Philippine Basin developed magnetic lineation of oceanic nature, and therefore, the entire basin is of the nature of oceanic crust. The basin has developed a series of special geomorphic units with different shapes. The KPR runs through the entire Philippine Basin. From the view of geomorphologic features, the KPR is a discontinuous seamount chain (chain-shaped seamounts) and subduction beneath the Japanese Island arc at the Nankai Trough which is the natural boundary between the basin and the Japanese Island arc. At the positions of 25°N, 24°N, 23°N and 18°N, obvious discontinuity is shown, which belongs to natural topographic discontinuity. Therefore, the KPR is topographically discontinuous.
2011, (5): 125-140.
doi: 10.1007/s13131-011-0154-z
Abstract:
The ridge like seafloor highs with various geological origins can be classed into mid-ocean ridges, transverse ridges related to transform faults, hot spot/mantle plume originated ridges, microcontinent rifted from major continent, intra-plate arc formed by interaction of two oceanic plates, and tectonic ridges uplifted by later tectonic activity. Those ridges moved towards the convergent continental margins along with the underlain plate drifting and formed so-called accreted ridges commonly trending at a high angle to the continental margins. At divergent continental margins, the continental crusts were extended and thinned accompanying with magmatism, which formed high terrains protruding or parallel to the coastal line. The ridges worldwide have various origins and the crustal thicknesses and structures of them are diversity. The crusts beneath the microcontinents, and the transverse ridges along the transform margin, and the seafloor highs beside the passive continental margins are continental, while the crusts of other ridges are oceanic. Article 76 of the United Nations Convention on the Law of the Sea (UNCLOS) has classed the seafloor highs worldwide into three legal categories, namely oceanic ridges, submarine ridges and submarine elevations, for the purpose to delineate the outer limit of the coastal States' continental shelf beyond 200 nautical miles. To define the categories of the legal seafloor highs to which the ridges with various geological origins belong, the continuities in morphology and geology including the rock types, crustal structures, origins and tectonic setting of the ridges and the coastal States' land mass with its submerged prolongation should be taken into account. If a ridge is continuous both in morphology and geology with the coastal States' land mass and its submerged prolongation, it is a submarine elevation stipulated in Article 76. If it is discontinuous in morphology, the ridge should be regarded as oceanic ridges. If a ridge is continuous in morphology but discontinuous in geology with the coastal States' land mass and its submerged prolongation, then it is a submarine ridge as stipulated in Article 76.
The ridge like seafloor highs with various geological origins can be classed into mid-ocean ridges, transverse ridges related to transform faults, hot spot/mantle plume originated ridges, microcontinent rifted from major continent, intra-plate arc formed by interaction of two oceanic plates, and tectonic ridges uplifted by later tectonic activity. Those ridges moved towards the convergent continental margins along with the underlain plate drifting and formed so-called accreted ridges commonly trending at a high angle to the continental margins. At divergent continental margins, the continental crusts were extended and thinned accompanying with magmatism, which formed high terrains protruding or parallel to the coastal line. The ridges worldwide have various origins and the crustal thicknesses and structures of them are diversity. The crusts beneath the microcontinents, and the transverse ridges along the transform margin, and the seafloor highs beside the passive continental margins are continental, while the crusts of other ridges are oceanic. Article 76 of the United Nations Convention on the Law of the Sea (UNCLOS) has classed the seafloor highs worldwide into three legal categories, namely oceanic ridges, submarine ridges and submarine elevations, for the purpose to delineate the outer limit of the coastal States' continental shelf beyond 200 nautical miles. To define the categories of the legal seafloor highs to which the ridges with various geological origins belong, the continuities in morphology and geology including the rock types, crustal structures, origins and tectonic setting of the ridges and the coastal States' land mass with its submerged prolongation should be taken into account. If a ridge is continuous both in morphology and geology with the coastal States' land mass and its submerged prolongation, it is a submarine elevation stipulated in Article 76. If it is discontinuous in morphology, the ridge should be regarded as oceanic ridges. If a ridge is continuous in morphology but discontinuous in geology with the coastal States' land mass and its submerged prolongation, then it is a submarine ridge as stipulated in Article 76.
