2017 Vol. 39, No. 3
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2017, 39(3): .
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2017, 39(3): .
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2017, 39(3): 1-13.
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In this study, tsunami generation and propagation model involved trans-Pacific (China's offshore)-local-coastal reef has been established, based on Okada model, nonlinear shallow water equations, and coupled grid with high resolution. The Phoenix Island in Sanya City is selected as research subject. Firstly, the simulation of 2011 Japan Tohoku tsunami has been carried out, and the characteristics of tsunami propagation along the continental shelf of Chinese coasts and the impacts on Phoenix Island are presented, combined with real-time measurements. The impacts of tsunami source along Manila Trench, Ryukyu Trench, and 21 extreme sources around Pacific on Phoenix Island are discussed. According to characteristics of tsunami wave near the Phoenix Island, the amplification effect of tsunami wave near coastal reef is discussed based on Fouriers analysis. It turns out that relatively moderate tsunami near Chinese coasts and extreme trans-Pacific tsunami will have some impacts on Phoenix Island, which may induce tsunami of maximum amplitude reached 1 m. The travel time ranges from 3 h to 27 h. Due to the impact of southeast peninsula Sanya, tsunami from Ryukyu Trench and trans-Pacific tsunami will generate less amplification effect than Manila Trench due to wave diffraction, whose frequency are in the range of 0.8×10-4-2×10-4 Hz. The tsunami from Manila Trench may produce obvious amplification effect, and require more attention.
In this study, tsunami generation and propagation model involved trans-Pacific (China's offshore)-local-coastal reef has been established, based on Okada model, nonlinear shallow water equations, and coupled grid with high resolution. The Phoenix Island in Sanya City is selected as research subject. Firstly, the simulation of 2011 Japan Tohoku tsunami has been carried out, and the characteristics of tsunami propagation along the continental shelf of Chinese coasts and the impacts on Phoenix Island are presented, combined with real-time measurements. The impacts of tsunami source along Manila Trench, Ryukyu Trench, and 21 extreme sources around Pacific on Phoenix Island are discussed. According to characteristics of tsunami wave near the Phoenix Island, the amplification effect of tsunami wave near coastal reef is discussed based on Fouriers analysis. It turns out that relatively moderate tsunami near Chinese coasts and extreme trans-Pacific tsunami will have some impacts on Phoenix Island, which may induce tsunami of maximum amplitude reached 1 m. The travel time ranges from 3 h to 27 h. Due to the impact of southeast peninsula Sanya, tsunami from Ryukyu Trench and trans-Pacific tsunami will generate less amplification effect than Manila Trench due to wave diffraction, whose frequency are in the range of 0.8×10-4-2×10-4 Hz. The tsunami from Manila Trench may produce obvious amplification effect, and require more attention.
2017, 39(3): 14-23.
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A hydrodynamic model that contains six main tidal components (i.e. M2, S2, K1, O1,M4, and MS4) and wet/dry process is developed based on Princeton Ocean Model (POM), and applied for the Qinzhou Bay of China. The simulated water elevations and current agree well with field observations. And on this basis, a dispersion model for water quality is established to invest ability of water exchange in this bay. Our model gives a mean half-life time of 18 days and mean residence time of 45 days, suggesting a relatively strong ability of water exchange. The half-life time is shortest and less than one day in the south of Qinzhou Bonded Port, but prolongs from southwest to northeast, in range of 26-28 days in the central Maowei Sea, and exceeds 50 days in the east, west and north of the Maowei Sea. The numerical experiments suggest that simulation without wet-dry process may underestimate velocity of tidal current and ability of water exchange in the Qinzhou Bay.
A hydrodynamic model that contains six main tidal components (i.e. M2, S2, K1, O1,M4, and MS4) and wet/dry process is developed based on Princeton Ocean Model (POM), and applied for the Qinzhou Bay of China. The simulated water elevations and current agree well with field observations. And on this basis, a dispersion model for water quality is established to invest ability of water exchange in this bay. Our model gives a mean half-life time of 18 days and mean residence time of 45 days, suggesting a relatively strong ability of water exchange. The half-life time is shortest and less than one day in the south of Qinzhou Bonded Port, but prolongs from southwest to northeast, in range of 26-28 days in the central Maowei Sea, and exceeds 50 days in the east, west and north of the Maowei Sea. The numerical experiments suggest that simulation without wet-dry process may underestimate velocity of tidal current and ability of water exchange in the Qinzhou Bay.
2017, 39(3): 24-43.
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One sea breeze circulation process over the Hainan Island is simulated by the WRF model on 25 May, 2014. The impact of topography on the sea breeze circulation is studied by changing the terrain height. The results show that the land-sea thermal difference, which is the trigger mechanism of sea breeze, reaches its top at 15:00 LST in CNTL experiment. In FLAT experiment, the main variations are embodied in two aspects, one is in the horizontal direction:the duration of the sea breeze becomes shorter, and the propagation distance of sea breeze reduces about 1~5 km. At the same time, the intensity of sea breeze weakens more than 1 m/s. Meanwhile, the kinetic energy of sea breeze exists great attenuation area in the coastal and southwest region, and the corresponding range of sea breeze convergence zone narrows down and the sea breeze convergence line also moves to the coastal regions. The other is in the vertical direction:the impacted location of different directions of sea breeze moves to the west and north, the backflow in high altitude and sea breeze thickness become lower. The intensity of the vertical circulation around sea breeze front reduces more than 10 cm/s. Moreover, the effect which the valley wind strengthens the sea breeze disappears. Its Influence mechanism can be summarized as the following two parts:in the dynamical aspect, the updraft and flow caused by mountains disappeared. In the thermal aspect, net radiation absorbed by the earth's surface decreases, which causes the releasing of sensible heat flux and latent heat flux decline about 9%, respectively. Ultimately, land-sea thermal difference and the corresponding air pressure difference all get smaller than CNTL, which weakens the basic characteristics of the sea breeze circulation. In addition, the results of the two experiments which only part of the mountains is removed show that the kinetic energy and convergence zone of sea breeze become weaker in the corresponding regions, and the structure of the vertical circulation also changes, the influence of Limu Mountain (RMLM) on sea breeze is greater than Wuzhi Mountain (RMWZ).
One sea breeze circulation process over the Hainan Island is simulated by the WRF model on 25 May, 2014. The impact of topography on the sea breeze circulation is studied by changing the terrain height. The results show that the land-sea thermal difference, which is the trigger mechanism of sea breeze, reaches its top at 15:00 LST in CNTL experiment. In FLAT experiment, the main variations are embodied in two aspects, one is in the horizontal direction:the duration of the sea breeze becomes shorter, and the propagation distance of sea breeze reduces about 1~5 km. At the same time, the intensity of sea breeze weakens more than 1 m/s. Meanwhile, the kinetic energy of sea breeze exists great attenuation area in the coastal and southwest region, and the corresponding range of sea breeze convergence zone narrows down and the sea breeze convergence line also moves to the coastal regions. The other is in the vertical direction:the impacted location of different directions of sea breeze moves to the west and north, the backflow in high altitude and sea breeze thickness become lower. The intensity of the vertical circulation around sea breeze front reduces more than 10 cm/s. Moreover, the effect which the valley wind strengthens the sea breeze disappears. Its Influence mechanism can be summarized as the following two parts:in the dynamical aspect, the updraft and flow caused by mountains disappeared. In the thermal aspect, net radiation absorbed by the earth's surface decreases, which causes the releasing of sensible heat flux and latent heat flux decline about 9%, respectively. Ultimately, land-sea thermal difference and the corresponding air pressure difference all get smaller than CNTL, which weakens the basic characteristics of the sea breeze circulation. In addition, the results of the two experiments which only part of the mountains is removed show that the kinetic energy and convergence zone of sea breeze become weaker in the corresponding regions, and the structure of the vertical circulation also changes, the influence of Limu Mountain (RMLM) on sea breeze is greater than Wuzhi Mountain (RMWZ).
2017, 39(3): 44-54.
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Based on the magnetic measurement of surficial sediment in the Modaomen Outlet of the Pearl River Estuary in March 2015, we explored spatial distribution of magnetic properties, examined the relationship between magnetic parameters and sediment particle size, and addressed its response to the sedimentary dynamic environment. The values of susceptibility (χ)and saturation isothermal remanent magnetization (SIRM)were low in the sediment bar, and generally displayed a decreasing trend toward the sea outside the ten-meter isobaths. The values of frequency dependent susceptibility (χfd%), anhysteretic remanent magnetization (χARM), χARM/SIRM and χARM/χ were also low in the sediment bar, however, it was high outside the sediment bar. These results revealed that the magnetic properties of study area were dominated by ferrimagnetic mineral, but there were still some antiferromagnetic minerals in the sediment bar. Particle size is an important factor affecting magnetic properties, SIRM/χ shows positive correlation with >63 μm fraction, magnetic parameters such as χfd%、χARM、χARM/SIRM and χARM/χ display significantly positive correlation with <16 μm fraction, these results indicated that χfd%、χARM、χARM/SIRM and χARM/χ could be used as proxies for finer fraction of sediments (<16 μm fraction), and SIRM/χ could be used as proxies for percentages of coarser fraction of sediments (>63 μm fraction). In light of the sediment types, dynamic environment in the Modaomen Outlet, the SIRM, S-300 and SIRM/χ were applied to carry out cluster analysis, and the result has a remarkable consistency with the sedimentary dynamic environment and the dynamic geomorphology pattern. Our study is not only of great significance to understand the new evolution mode of the Modaomen Outlet in new dynamic patterns, but also can enrich the research method of sedimentation dynamics of estuary.
Based on the magnetic measurement of surficial sediment in the Modaomen Outlet of the Pearl River Estuary in March 2015, we explored spatial distribution of magnetic properties, examined the relationship between magnetic parameters and sediment particle size, and addressed its response to the sedimentary dynamic environment. The values of susceptibility (χ)and saturation isothermal remanent magnetization (SIRM)were low in the sediment bar, and generally displayed a decreasing trend toward the sea outside the ten-meter isobaths. The values of frequency dependent susceptibility (χfd%), anhysteretic remanent magnetization (χARM), χARM/SIRM and χARM/χ were also low in the sediment bar, however, it was high outside the sediment bar. These results revealed that the magnetic properties of study area were dominated by ferrimagnetic mineral, but there were still some antiferromagnetic minerals in the sediment bar. Particle size is an important factor affecting magnetic properties, SIRM/χ shows positive correlation with >63 μm fraction, magnetic parameters such as χfd%、χARM、χARM/SIRM and χARM/χ display significantly positive correlation with <16 μm fraction, these results indicated that χfd%、χARM、χARM/SIRM and χARM/χ could be used as proxies for finer fraction of sediments (<16 μm fraction), and SIRM/χ could be used as proxies for percentages of coarser fraction of sediments (>63 μm fraction). In light of the sediment types, dynamic environment in the Modaomen Outlet, the SIRM, S-300 and SIRM/χ were applied to carry out cluster analysis, and the result has a remarkable consistency with the sedimentary dynamic environment and the dynamic geomorphology pattern. Our study is not only of great significance to understand the new evolution mode of the Modaomen Outlet in new dynamic patterns, but also can enrich the research method of sedimentation dynamics of estuary.
2017, 39(3): 55-67.
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Flocculation plays an important role at the behavior of fine sediment in estuary. During 22-29 of July, 2013, the suspended sediment concentration, size of floc, tidal current, salinity and wave were observed in Lingdingyang Estuary by LISST-100 together with other instruments. Based on these situ data and laboratory analysis of dispersed suspended sediment, the characteristics of sediment flocculation and the influences of dynamic factors on flocculation were studied. The results show that there were obvious flocculation at observed filed of Lingdingyang Estuary, which the mean situ floc size is 148.53 μm, larger than the mean size of laboratory dispersed sediment particles (36.74 μm). The settling velocity was positively correlated with effective density and floc size, while the effective density of floc in Lingdingyang Estuary was about 153.49 kg/m3, and the average settling velocity reached 1.13 mm/s; floc size in flood and neap tide was larger than ebb and spring tide, the flocculation in middle water column was greater than upper water and bottom water. The effects of turbulent shear, suspended sediment concentration, salinity stratification and wave on flocculation in Lingdingyang Estuary were considered. The in situ data shows that under low turbulent shear (<5 s-1), low suspended sediment concentration (<50 mg/L) and high volume concentration, promoted the flocculation, and floc would break-up when strength of turbulent shear and particles collision were greater than strength floc can withstand. Salinity stratification result in volume concentration increased rapidly in the middle water column due to sediment trapping, which promote flocculation. The increase of short wind wave also help the flocculation at upper water during in observation period.
Flocculation plays an important role at the behavior of fine sediment in estuary. During 22-29 of July, 2013, the suspended sediment concentration, size of floc, tidal current, salinity and wave were observed in Lingdingyang Estuary by LISST-100 together with other instruments. Based on these situ data and laboratory analysis of dispersed suspended sediment, the characteristics of sediment flocculation and the influences of dynamic factors on flocculation were studied. The results show that there were obvious flocculation at observed filed of Lingdingyang Estuary, which the mean situ floc size is 148.53 μm, larger than the mean size of laboratory dispersed sediment particles (36.74 μm). The settling velocity was positively correlated with effective density and floc size, while the effective density of floc in Lingdingyang Estuary was about 153.49 kg/m3, and the average settling velocity reached 1.13 mm/s; floc size in flood and neap tide was larger than ebb and spring tide, the flocculation in middle water column was greater than upper water and bottom water. The effects of turbulent shear, suspended sediment concentration, salinity stratification and wave on flocculation in Lingdingyang Estuary were considered. The in situ data shows that under low turbulent shear (<5 s-1), low suspended sediment concentration (<50 mg/L) and high volume concentration, promoted the flocculation, and floc would break-up when strength of turbulent shear and particles collision were greater than strength floc can withstand. Salinity stratification result in volume concentration increased rapidly in the middle water column due to sediment trapping, which promote flocculation. The increase of short wind wave also help the flocculation at upper water during in observation period.
2017, 39(3): 68-75.
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Seafloor mound is common in gas hydrate reservoirs. The investigation of seafloor mound can help to understand the pattern of fluid seepage and the occurrence of gas hydrate. This paper investigated a seafloor mound in the Dongsha area, north slope of the South China Sea, where gas hydrate has been sampled. The data used include 3D seismic, multi-beam bathymetric and sub-bottom profiler data. On the multi-beam bathymetric data, seafloor mound manifests itself as an outstanding elevated morphologic feature, with height of ~50 m and diameter of ~300 m. Acoustic blanking zone in the sub-bottom profiler indicates the distribution of gas and the fluid migration pathway. Clearly observable BSR around the seafloor mound suggests the localized occurrence of gas hydrate, which is verified by the drilling program. Though acoustic blanking is also presented in the 3D seismic profiles, enhanced amplitude and continuous reflector directly beneath the mound indicates that the mound is probably not originated from mud volcano. Sediments expansion due to the formation of gas hydrate may be a better explanation.
Seafloor mound is common in gas hydrate reservoirs. The investigation of seafloor mound can help to understand the pattern of fluid seepage and the occurrence of gas hydrate. This paper investigated a seafloor mound in the Dongsha area, north slope of the South China Sea, where gas hydrate has been sampled. The data used include 3D seismic, multi-beam bathymetric and sub-bottom profiler data. On the multi-beam bathymetric data, seafloor mound manifests itself as an outstanding elevated morphologic feature, with height of ~50 m and diameter of ~300 m. Acoustic blanking zone in the sub-bottom profiler indicates the distribution of gas and the fluid migration pathway. Clearly observable BSR around the seafloor mound suggests the localized occurrence of gas hydrate, which is verified by the drilling program. Though acoustic blanking is also presented in the 3D seismic profiles, enhanced amplitude and continuous reflector directly beneath the mound indicates that the mound is probably not originated from mud volcano. Sediments expansion due to the formation of gas hydrate may be a better explanation.
2017, 39(3): 76-84.
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It is necessary to deploy high-resolution topographic surveys in a typical small target in deep-sea areas (e. g. hydrothermal seep, ridge area) to support the future further studies, after the full-covered topography data acquisition of the large study area using a shipborne mutli-beam system. Here, we select PACMANUS hydrothermal area as target area in the Manus Basin and deploy a near-bottom full-covered survey to obtain topography data basing on "FAXIAN" ROV. Results show that Long Baseline provide a reliable high-precision positioning relying on the ship dynamic positioning system and a differential GPS. The resolution of seabed topography which is near-bottom measured by ROV is tens of times better than that obtained by an onboard multi-beam system. High-resolution terrain clearly shows the detailed characters of the terrain in the PACMANUS hydrothermal field, and some cones are corresponding to the locations of the discovered hydrothermal points and volcanic area. Further analysis show that hydrothermal points mainly developed on the steep slopes whose gradients exceed 30°, and the causes are still unknown and need a further study. It is a reliable mean for obtaining high-resolution topography data by deploying near-bottom measurements using ROV, which will promote the development of deep-sea scientific research.
It is necessary to deploy high-resolution topographic surveys in a typical small target in deep-sea areas (e. g. hydrothermal seep, ridge area) to support the future further studies, after the full-covered topography data acquisition of the large study area using a shipborne mutli-beam system. Here, we select PACMANUS hydrothermal area as target area in the Manus Basin and deploy a near-bottom full-covered survey to obtain topography data basing on "FAXIAN" ROV. Results show that Long Baseline provide a reliable high-precision positioning relying on the ship dynamic positioning system and a differential GPS. The resolution of seabed topography which is near-bottom measured by ROV is tens of times better than that obtained by an onboard multi-beam system. High-resolution terrain clearly shows the detailed characters of the terrain in the PACMANUS hydrothermal field, and some cones are corresponding to the locations of the discovered hydrothermal points and volcanic area. Further analysis show that hydrothermal points mainly developed on the steep slopes whose gradients exceed 30°, and the causes are still unknown and need a further study. It is a reliable mean for obtaining high-resolution topography data by deploying near-bottom measurements using ROV, which will promote the development of deep-sea scientific research.
2017, 39(3): 85-95.
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The evolution of tidal limit and its river regime in response to the Three Gorges Project (TGP) is an important issue in the construction of the Yangtze River Economic Belt. However, due to the limitation of the observation method, there has been no report about the comprehensive study on the change of position of the tidal limit and the geomorphic evolution in this area since TGP river closure. In this study, the average location of tidal limit in recent flood season was identified through spectral analysis of water level in Datong station, the evolution characteristics of landform were analyzed by comparison of bathymetric data in 1998 and 2013 and the high resolution micro-geomorphology in typical erosional areas was carried out by the multibeam echo sounding data. The research shows that: (1) From 1998 to 2013, the overall channel erosion in tidal limit reaches was 5 649.7×104m3. The upper segment was all-round eroded with the erosion depth in the main channel up to 5.6 m. Taibaizhou and Taiyangzhou merged into bank and Tonglingsha was scoured aside. The middle segment was deposited with small amplitudes and the main stream line swung. The north side of Tianranzhou, Heishazhou Middle Waterway was silted up while south side eroded up to 8.9 m. The lower segment was generally eroded with strong erosion near the northern shoreline where the max depth was 15.4 m. (2) The grain size of surface sediment was apparently coarsened, which indicates that the river channels are under severe erosional environment in the near future. (3) The erosional channels were mainly distributed in straight reaches, and the depth was 5.4-12.6 m. The scour pits were distributed in braided reaches where the planform suddenly changed, and the max erosion depth was 28.1-30.5 m. The erosional subaqueous bank slope mostly appeared in straight reaches with serious nearshore erosion, and its slope was 0.59-0.62.
The evolution of tidal limit and its river regime in response to the Three Gorges Project (TGP) is an important issue in the construction of the Yangtze River Economic Belt. However, due to the limitation of the observation method, there has been no report about the comprehensive study on the change of position of the tidal limit and the geomorphic evolution in this area since TGP river closure. In this study, the average location of tidal limit in recent flood season was identified through spectral analysis of water level in Datong station, the evolution characteristics of landform were analyzed by comparison of bathymetric data in 1998 and 2013 and the high resolution micro-geomorphology in typical erosional areas was carried out by the multibeam echo sounding data. The research shows that: (1) From 1998 to 2013, the overall channel erosion in tidal limit reaches was 5 649.7×104m3. The upper segment was all-round eroded with the erosion depth in the main channel up to 5.6 m. Taibaizhou and Taiyangzhou merged into bank and Tonglingsha was scoured aside. The middle segment was deposited with small amplitudes and the main stream line swung. The north side of Tianranzhou, Heishazhou Middle Waterway was silted up while south side eroded up to 8.9 m. The lower segment was generally eroded with strong erosion near the northern shoreline where the max depth was 15.4 m. (2) The grain size of surface sediment was apparently coarsened, which indicates that the river channels are under severe erosional environment in the near future. (3) The erosional channels were mainly distributed in straight reaches, and the depth was 5.4-12.6 m. The scour pits were distributed in braided reaches where the planform suddenly changed, and the max erosion depth was 28.1-30.5 m. The erosional subaqueous bank slope mostly appeared in straight reaches with serious nearshore erosion, and its slope was 0.59-0.62.
2017, 39(3): 96-105.
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Based on the measured data and information about tidal current, suspended sediment concentration, surface sediment samples the Zhejiang inner continental shelf in summer, 2014. Material flux decomposition method and Geo-Collins grain size trend analysis was carried out to delineate suspended sediment flux,transport direction and dynamics mechanism and net sediment transport patterns of the study area. The results indicate that the suspended sediment concentration decreases from west to east, increases from south to north, which is well related with tidal current and oscillated with the frequency of semidiurnal tide as well. The suspended sediment flux quickly decreases towards the sea. The net suspended sediment transport is mainly controlled by average current transport, and the second place is gravitational circulation transport. The suspended sediments are primarily transported towards the sea, but in deeper than 30 m water region, under the influence of the Taiwan Warm Current, transport towards northeast direction is found in the study area. The Taiwan Warm Current would also probably block the suspended sediment diffusion towards the sea. Grain size trend analysis result indicates that surface sediments are mostly transported from northeast towards southwest, under the influence of currents and morphology, a weaken trend sedimentary region is founded in the middle study area. The net suspended sediment is estimated at about 1.9×106 t per day with the tide condition in summer, and transports towards northeast.
Based on the measured data and information about tidal current, suspended sediment concentration, surface sediment samples the Zhejiang inner continental shelf in summer, 2014. Material flux decomposition method and Geo-Collins grain size trend analysis was carried out to delineate suspended sediment flux,transport direction and dynamics mechanism and net sediment transport patterns of the study area. The results indicate that the suspended sediment concentration decreases from west to east, increases from south to north, which is well related with tidal current and oscillated with the frequency of semidiurnal tide as well. The suspended sediment flux quickly decreases towards the sea. The net suspended sediment transport is mainly controlled by average current transport, and the second place is gravitational circulation transport. The suspended sediments are primarily transported towards the sea, but in deeper than 30 m water region, under the influence of the Taiwan Warm Current, transport towards northeast direction is found in the study area. The Taiwan Warm Current would also probably block the suspended sediment diffusion towards the sea. Grain size trend analysis result indicates that surface sediments are mostly transported from northeast towards southwest, under the influence of currents and morphology, a weaken trend sedimentary region is founded in the middle study area. The net suspended sediment is estimated at about 1.9×106 t per day with the tide condition in summer, and transports towards northeast.
2017, 39(3): 106-114.
Abstract:
Based on the analysis of 181 grain size testing data which sampled in Chengbei sea area, and combine with the tidal observation data and the elements of wave in 50 years, analyzing the types of surface sediment and the grain size pattern, calculating surface sediment shear stress, the average net transport flux and bed-load transport rate under the interaction of wave and current, the results show that the sediment is mainly composed of silty sand, sandy silt, silt and mud. The grain sizes are all poor sorted and the skewness are objective to symmetrical. In most places of Chengbei area the tidally-induced shear stress is larger than the critical shear stress, it shows that the tide can start and transport the sediment in most places. The average net transport flux per day is 372.32 kg/ (m·d). Under the action of both tide currents and waves in 50 years, the daily sediment bed-load transport rate is approximately equal based on the theory of Bijker and Van Rijn.
Based on the analysis of 181 grain size testing data which sampled in Chengbei sea area, and combine with the tidal observation data and the elements of wave in 50 years, analyzing the types of surface sediment and the grain size pattern, calculating surface sediment shear stress, the average net transport flux and bed-load transport rate under the interaction of wave and current, the results show that the sediment is mainly composed of silty sand, sandy silt, silt and mud. The grain sizes are all poor sorted and the skewness are objective to symmetrical. In most places of Chengbei area the tidally-induced shear stress is larger than the critical shear stress, it shows that the tide can start and transport the sediment in most places. The average net transport flux per day is 372.32 kg/ (m·d). Under the action of both tide currents and waves in 50 years, the daily sediment bed-load transport rate is approximately equal based on the theory of Bijker and Van Rijn.
2017, 39(3): 115-121.
Abstract:
According to the theory of Stokes Law, the test apparatus of flow characteristics of liquefied silt is developed based on the shaking table tests. A steel sphere, embedded in the test box, can be moved in the horizontal direction when the silt liquefaction occurs. Resistance force and velocity of the steel sphere are measured during sphere dragging, then apparent viscosity can be evaluated. Analysis the relationship between apparent viscosity and excess pore pressure ratio during silty liquefaction. The change of apparent viscosity and strain rate after silty liquefaction is researched. The result shows that, during the shaking table test, the pore pressure showed a rapid increase, and silt quickly reached a liquefied state; there was consolidation phenomenon in the soil bed, and vibration had a great influence on consolidation. Analysis found that, when the soil has not reached completely liquefied state (ru<1), the apparent viscosity decreases with increasing of excess pore pressure ratio; when it has reached liquefied state (ru=1), the shear stress decreases with increasing of strain rate, the silt is shear thinning non-Newtonian fluid.
According to the theory of Stokes Law, the test apparatus of flow characteristics of liquefied silt is developed based on the shaking table tests. A steel sphere, embedded in the test box, can be moved in the horizontal direction when the silt liquefaction occurs. Resistance force and velocity of the steel sphere are measured during sphere dragging, then apparent viscosity can be evaluated. Analysis the relationship between apparent viscosity and excess pore pressure ratio during silty liquefaction. The change of apparent viscosity and strain rate after silty liquefaction is researched. The result shows that, during the shaking table test, the pore pressure showed a rapid increase, and silt quickly reached a liquefied state; there was consolidation phenomenon in the soil bed, and vibration had a great influence on consolidation. Analysis found that, when the soil has not reached completely liquefied state (ru<1), the apparent viscosity decreases with increasing of excess pore pressure ratio; when it has reached liquefied state (ru=1), the shear stress decreases with increasing of strain rate, the silt is shear thinning non-Newtonian fluid.
2017, 39(3): 122-134.
Abstract:
The particulate organic carbon (POC) plays an important role in the marine carbon cycle. It transports the organic carbon from the surface layer to the deep sea, and consequently removes the carbon dioxide (CO2) from the air, thus it is an important component of biological pump. To study the temporal and spatial distribution and long-term variation of sea surface POC concentration in the northern South China Sea (nSCS), we used the in situ data of four cruises from June 2009 to May 2011 to validate and calibrate MODIS/AQUA satellite monthly average POC products. The results shown the satellite-derived POC and in situ data had a good linear relationship in the nSCS (R2=0.72), but with a systematic bias. With the validated satellite POC products, we found that POC concentration in the shelf of the bias was high (33.34±8.02) mg/m3; the POC values of the southwest area of Luzon Strait was low (29.25±6.20) mg/m3, and POC had lowest values in the northern basin of SCS (27.02±4.84) mg/m3. The POC concentration was lower in spring and summer than that in winter and autumn; the lowest values generally appeared in May, and it remained a relative low and stable value from June to August, then the POC concentration began to rise in September, and reached the highest value in December. We analyzed the controlling factors on the POC distribution in the nSCS using the satellite-derived chlorophyll a (Chl a) concentration, sea surface temperature (SST), the model-derived mixed layer depth (MLD), as well as the in situ Chl a and total suspended matter concentration (TSM). The results demonstrated that the POC and Chl a in the autumn and winter had a relatively good correlation (R2=0.51), but it was dispersed in the spring and summer, indicating that Chl a had significant influence on POC variation in the nSCS in autumn and winter. The POC, Chl a, MLD and SST had the significant inter-annual variability, but had no significant increase or decrease trend in the period of 2003-2014. The mechanism of controlling POC spatial and temporal variation was complex.
The particulate organic carbon (POC) plays an important role in the marine carbon cycle. It transports the organic carbon from the surface layer to the deep sea, and consequently removes the carbon dioxide (CO2) from the air, thus it is an important component of biological pump. To study the temporal and spatial distribution and long-term variation of sea surface POC concentration in the northern South China Sea (nSCS), we used the in situ data of four cruises from June 2009 to May 2011 to validate and calibrate MODIS/AQUA satellite monthly average POC products. The results shown the satellite-derived POC and in situ data had a good linear relationship in the nSCS (R2=0.72), but with a systematic bias. With the validated satellite POC products, we found that POC concentration in the shelf of the bias was high (33.34±8.02) mg/m3; the POC values of the southwest area of Luzon Strait was low (29.25±6.20) mg/m3, and POC had lowest values in the northern basin of SCS (27.02±4.84) mg/m3. The POC concentration was lower in spring and summer than that in winter and autumn; the lowest values generally appeared in May, and it remained a relative low and stable value from June to August, then the POC concentration began to rise in September, and reached the highest value in December. We analyzed the controlling factors on the POC distribution in the nSCS using the satellite-derived chlorophyll a (Chl a) concentration, sea surface temperature (SST), the model-derived mixed layer depth (MLD), as well as the in situ Chl a and total suspended matter concentration (TSM). The results demonstrated that the POC and Chl a in the autumn and winter had a relatively good correlation (R2=0.51), but it was dispersed in the spring and summer, indicating that Chl a had significant influence on POC variation in the nSCS in autumn and winter. The POC, Chl a, MLD and SST had the significant inter-annual variability, but had no significant increase or decrease trend in the period of 2003-2014. The mechanism of controlling POC spatial and temporal variation was complex.
2017, 39(3): 135-144.
Abstract:
In the last 30 years, the Arctic sea ice is undergoing drastic changes. Sea ice volume is one of the important indicators to quantify the change of sea ice. This paper according to the CryoSat-2 data and OSI SAF sea ice type data in Arctic in 2015. We extracted freeboard, snow depth, sea ice concentration and ice type, and obtained the raster data set in 25 km×25 km spatial resolution through data reprocessing including interpolation, projection transformation, raster conversion, spatial resampling and so on. According to the hydrostatic equilibrium principle calculated the sea ice thickness value in every pixel, multiply ice area in the corresponding pixels thus estimated the sea ice volume of the sea ice concentration exceeds 75%, and analyzed the monthly and seasonal changes characteristics. We used high-accuracy sea ice thickness products from NASA Ice Bridge to verify thickness retrieved from CryoSat-2 Satellite. The results show that there is a high consistency of r=0.72. The sea ice is thickest in spring and thinnest in summer. The thick sea ice concentrated around the north coast of Greenland and Ellesmere Island. Generally the MYI is thicker than the first-year ice FYI. Sea ice volume is largest in winter, about 23.30×103 km3, almost a reduction of 70% after the summer melt. The seasonal fluctuation of the FYI volume is larger than the MYI.
In the last 30 years, the Arctic sea ice is undergoing drastic changes. Sea ice volume is one of the important indicators to quantify the change of sea ice. This paper according to the CryoSat-2 data and OSI SAF sea ice type data in Arctic in 2015. We extracted freeboard, snow depth, sea ice concentration and ice type, and obtained the raster data set in 25 km×25 km spatial resolution through data reprocessing including interpolation, projection transformation, raster conversion, spatial resampling and so on. According to the hydrostatic equilibrium principle calculated the sea ice thickness value in every pixel, multiply ice area in the corresponding pixels thus estimated the sea ice volume of the sea ice concentration exceeds 75%, and analyzed the monthly and seasonal changes characteristics. We used high-accuracy sea ice thickness products from NASA Ice Bridge to verify thickness retrieved from CryoSat-2 Satellite. The results show that there is a high consistency of r=0.72. The sea ice is thickest in spring and thinnest in summer. The thick sea ice concentrated around the north coast of Greenland and Ellesmere Island. Generally the MYI is thicker than the first-year ice FYI. Sea ice volume is largest in winter, about 23.30×103 km3, almost a reduction of 70% after the summer melt. The seasonal fluctuation of the FYI volume is larger than the MYI.
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