A large area hypoxia has been already reported respectively by two interdisciplinary surveys off the Changjiang Estuary since summer of 1999 and 2006. The bypoxic zone shows distinct year-to-year variations. Observed ...A large area hypoxia has been already reported respectively by two interdisciplinary surveys off the Changjiang Estuary since summer of 1999 and 2006. The bypoxic zone shows distinct year-to-year variations. Observed oceanographic data are first analysized and reveal a big difference for the Changjiang Diluted Water （CDW） between these two periods. These great changes are related to the tremendous reduction of the freshwater discharge and variations of wind fields between these two years. It is also found that the monthly mean intrusion of Kuroshio and its branches has increased in the northern East China Sea （ECS）, but decreased in the southern ECS in August of 2006 as compared with 1999 on the base of general circulation models. Then, the Regional Ocean Modelling Systems is applied to the East China Sea to evaluate the contributions and relative importance of impacts from the river discharge, wind forcing and open boundary data. Our simulations reproduce the phenomena that more fresh water extends northeastward in 2006 and forms a negative SSS anomaly to the northeast of the river mouth as compared with 1999, which is consistent with observations. The five group numerical tests suggest that the wind forcing dominates the CDW variations followed by the Kuroshio and its branches. The study implies important roles played by hydrodynamic processes on the variability of hypoxic zone in the study areas.展开更多
The barotropic processes of tides, tidal currents, wind-driven currents and the interaction of winds andtides in the Bobai Sea are investigated with a three-dimensional shelf sea model. The tides and tidal currents ar...The barotropic processes of tides, tidal currents, wind-driven currents and the interaction of winds andtides in the Bobai Sea are investigated with a three-dimensional shelf sea model. The tides and tidal currents are wellsimulated. The main characteristics of tides and tidal currents, such as the types of tides and tidal currents, co-tidaland co-range charts, co-current charts, tidal ellipses, mean tidal currents and tidal residual currents are presented. Apair Of cyclonic and anticyclonic headland eddies in the northern Bohai Straits is discovered. The tidal currents have little vertical structure except close to the sea bottom. Driven by strong winds, the currents have a significant three-dimensional structure. In response to coastal geometry and bottom friction, the wind drift in the upper layers is in the direction of the wind or slightly to the right. In depth, considerable compensating currents maintain a circulation balance. The interaction of winds and tides is locally strong. The oscillating tidal currents play a role of dissipating energy. Thus the usual purely wind-driven currents in the area of weak residual tidal currents are often overestimated in theabsence of tides.展开更多
The seasonal thermal structure in the Bobal Sea are examined with a three-dimensional boroclinic primitiveequation model for shelf sea. The evolution of the seasonal thermal stratification is well simulated. The strat...The seasonal thermal structure in the Bobal Sea are examined with a three-dimensional boroclinic primitiveequation model for shelf sea. The evolution of the seasonal thermal stratification is well simulated. The stratification ap pears early in April, first in the area off Qinhuangdao and it is well developed in the middle of May. It intensifies withsynoptic and neap-spring nuctuations throughout the summer and reaches its maximum in the middle of July. Eventually,it is destroyed at the end of September. There are cold water belts between well-mixed and stratified regions. They are lo cated on the mixed side of tidal fronts, and coincide with the isolines for a temperature difference of 1-2℃ between surface and bottom. The sea surface temperature(SST)distribution shows local maxima at the head of three bays and to thesouth of Qinhuangdao during the summer. The Bobal Sea responds to the variability in the atmospheric forcing and intides with the synoptic and neap-spring variations of SST, as well as in the stratification and in variable positions of tidalfronts展开更多
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 ...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.展开更多
In a survey on the Yellow Sea and the East China Sea on August 20-30 of 1999,we found a hypoxic zone(<2 mg/L)of 13700 km2 with an average thickness of 20m at the bottom of the Changjiang(Yangtze River)Estuary,with ...In a survey on the Yellow Sea and the East China Sea on August 20-30 of 1999,we found a hypoxic zone(<2 mg/L)of 13700 km2 with an average thickness of 20m at the bottom of the Changjiang(Yangtze River)Estuary,with an oxygen minimum value of 1 mg/L.The extension of the dissolved oxygen deficiency extended to the 100m isobath in a southeastward direction along the bottom of the continental shelf of the East China Sea.During the last two decades,the minimum dissolved oxygen values in the low oxygen region of the Changjiang Estuary have decreased from 2.85 mg/L to 1 mg/L.In the hypoxic zone,the apparent oxygen utilization(AOU)was 5.8 mg/L and the total oxygen depletion approximately 1.59×10^(6) t.The strong halocline above the hypoxic zone,as a result of affluent water from the Changjiang,Taiwan Warm Current(TWC),and the high concentrations of particle organic carbon(POC)and nitrogen(PON)are the major factors causing the formation of the hypoxic zone.The POC:PON ratios and nutrient concentration distributions in the hypoxic zone suggest that the oxygen deficiency in the bottom water during the summer in the East China Sea off the Changjiang is the result of organic carbon production enhanced by nutrients from the Changjiang and fluvial organic matter input,followed by a shift in regeneration of nutrients in the East China Sea.展开更多
Regional Ocean Modeling Systems (ROMS 3.0) and the κ-ε turbulence closure scheme has been applied to investigating the seasonal evolution of the thermsocline in the Bohai Sea. The simulation reproduces the stratific...Regional Ocean Modeling Systems (ROMS 3.0) and the κ-ε turbulence closure scheme has been applied to investigating the seasonal evolution of the thermsocline in the Bohai Sea. The simulation reproduces the stratifications lasting from early April to early September and reveals the existence of marked Asymmetric Dual-Core Cold Bottom Water (ADCCBW) in the south and north depression basin respectively under the thermocline. The bottom temperature in the north depression is about 1―4℃ lower than that in the south depression basin which is in good agreement with observations. Model results suggest that the local bathymetry characteristics and inhomogeneous net heat flux due to the latitude difference are the major cause for the early formation of the ADCCBW. Numerical Lagrangian drifter experiments support the finding that the ADCCBW is maintained throughout the stratification periods by the inflow of cold bottom water from the northern Yellow Sea and deep channel in the western side of Liaodong Peninsula. The inflow cold water contributes to the north depression basin distinctively larger than to the south one. Tidal mixing enhances the bottom temperature asymmetry between the two basins.展开更多
Inverse calculations using data from 16 repeat hydrographic transects collected from April 2003 to June 2007 have yielded velocity structures and volume transports(VTs) of the Ryukyu Current in the region east of the ...Inverse calculations using data from 16 repeat hydrographic transects collected from April 2003 to June 2007 have yielded velocity structures and volume transports(VTs) of the Ryukyu Current in the region east of the northern Ryukyu Islands.The inverse calculation results show that the Ryukyu Current is dominated by a subsurface velocity core with maximum velocities from 15.1 to 80.0 cm/s,whose positions vary between 110 and 600 dbar and 27.2°-28.2°N along the transect.The mean velocity exhibits a subsurface velocity core with a maximum value of 24.6 cm/s at 326 dbar depth,a VT of 14.0 Sv(1 Sv≡106 m3/s),a vertical dimension of 800 m,and a horizontal dimension of 60 km.The seasonal mean velocities show that the Ryukyu Current is stronger in autumn than in other seasons.It is suggested that this seasonal variation is coincident with the intensification of the anticyclonic eddy south of Shikoku,Japan.展开更多
基金The Ministry of Science and Technology of China under contract Nos 2006CB400603 and 2008BAC42B02the National Natural Science Foundation of China under contract Nos 40706018 and 40776021+1 种基金the National Natural Science Foundation of Zhejiang Province under contract No.Y507229"908" project under contract Nos 908-01-BC06 and 908-ZC-I-01
文摘A large area hypoxia has been already reported respectively by two interdisciplinary surveys off the Changjiang Estuary since summer of 1999 and 2006. The bypoxic zone shows distinct year-to-year variations. Observed oceanographic data are first analysized and reveal a big difference for the Changjiang Diluted Water （CDW） between these two periods. These great changes are related to the tremendous reduction of the freshwater discharge and variations of wind fields between these two years. It is also found that the monthly mean intrusion of Kuroshio and its branches has increased in the northern East China Sea （ECS）, but decreased in the southern ECS in August of 2006 as compared with 1999 on the base of general circulation models. Then, the Regional Ocean Modelling Systems is applied to the East China Sea to evaluate the contributions and relative importance of impacts from the river discharge, wind forcing and open boundary data. Our simulations reproduce the phenomena that more fresh water extends northeastward in 2006 and forms a negative SSS anomaly to the northeast of the river mouth as compared with 1999, which is consistent with observations. The five group numerical tests suggest that the wind forcing dominates the CDW variations followed by the Kuroshio and its branches. The study implies important roles played by hydrodynamic processes on the variability of hypoxic zone in the study areas.
文摘The barotropic processes of tides, tidal currents, wind-driven currents and the interaction of winds andtides in the Bobai Sea are investigated with a three-dimensional shelf sea model. The tides and tidal currents are wellsimulated. The main characteristics of tides and tidal currents, such as the types of tides and tidal currents, co-tidaland co-range charts, co-current charts, tidal ellipses, mean tidal currents and tidal residual currents are presented. Apair Of cyclonic and anticyclonic headland eddies in the northern Bohai Straits is discovered. The tidal currents have little vertical structure except close to the sea bottom. Driven by strong winds, the currents have a significant three-dimensional structure. In response to coastal geometry and bottom friction, the wind drift in the upper layers is in the direction of the wind or slightly to the right. In depth, considerable compensating currents maintain a circulation balance. The interaction of winds and tides is locally strong. The oscillating tidal currents play a role of dissipating energy. Thus the usual purely wind-driven currents in the area of weak residual tidal currents are often overestimated in theabsence of tides.
文摘The seasonal thermal structure in the Bobal Sea are examined with a three-dimensional boroclinic primitiveequation model for shelf sea. The evolution of the seasonal thermal stratification is well simulated. The stratification ap pears early in April, first in the area off Qinhuangdao and it is well developed in the middle of May. It intensifies withsynoptic and neap-spring nuctuations throughout the summer and reaches its maximum in the middle of July. Eventually,it is destroyed at the end of September. There are cold water belts between well-mixed and stratified regions. They are lo cated on the mixed side of tidal fronts, and coincide with the isolines for a temperature difference of 1-2℃ between surface and bottom. The sea surface temperature(SST)distribution shows local maxima at the head of three bays and to thesouth of Qinhuangdao during the summer. The Bobal Sea responds to the variability in the atmospheric forcing and intides with the synoptic and neap-spring variations of SST, as well as in the stratification and in variable positions of tidalfronts
基金The Public Science and Technology Research Funds Projects of Ocean under contract Nos 200905001 and 201005019the Germany-China Cooperation in Marine Science and Technology under contract No.CHN 04/009+4 种基金the State Basic Research Program of China under contract No.2011CB409803the State Key Technology Research and Development Program of China under contract No.2008BAC42B03the Hi-tech Research Development Program of China under Grant No.2007AA09Z117the National Natural Science Foundation of China under contract No.40706018the Scientific Research Fund of the Second Institute of Oceanography,the State Oceanic Administration of China under contract Nos JT1105 and JT0903
文摘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.
基金This study was made under the auspices of the National Key Basic Research Program of the Ministry of Science and Technology,P.R.China(Grant No.G1999043705)and the Shanghai Priority Academic Discipline.
文摘In a survey on the Yellow Sea and the East China Sea on August 20-30 of 1999,we found a hypoxic zone(<2 mg/L)of 13700 km2 with an average thickness of 20m at the bottom of the Changjiang(Yangtze River)Estuary,with an oxygen minimum value of 1 mg/L.The extension of the dissolved oxygen deficiency extended to the 100m isobath in a southeastward direction along the bottom of the continental shelf of the East China Sea.During the last two decades,the minimum dissolved oxygen values in the low oxygen region of the Changjiang Estuary have decreased from 2.85 mg/L to 1 mg/L.In the hypoxic zone,the apparent oxygen utilization(AOU)was 5.8 mg/L and the total oxygen depletion approximately 1.59×10^(6) t.The strong halocline above the hypoxic zone,as a result of affluent water from the Changjiang,Taiwan Warm Current(TWC),and the high concentrations of particle organic carbon(POC)and nitrogen(PON)are the major factors causing the formation of the hypoxic zone.The POC:PON ratios and nutrient concentration distributions in the hypoxic zone suggest that the oxygen deficiency in the bottom water during the summer in the East China Sea off the Changjiang is the result of organic carbon production enhanced by nutrients from the Changjiang and fluvial organic matter input,followed by a shift in regeneration of nutrients in the East China Sea.
基金Supported by "973" Project from the Ministry of Science and Technology of China (Grant No. 2006CB400603)National Natural Science Foundation of China (Grant No. 40706018)+1 种基金National Natural Science Foundation of Zhejiang Province (Grant No. Y507229)Youth Marine Science Foundation of State Oceanic Administration (Grant No. 2007204)
文摘Regional Ocean Modeling Systems (ROMS 3.0) and the κ-ε turbulence closure scheme has been applied to investigating the seasonal evolution of the thermsocline in the Bohai Sea. The simulation reproduces the stratifications lasting from early April to early September and reveals the existence of marked Asymmetric Dual-Core Cold Bottom Water (ADCCBW) in the south and north depression basin respectively under the thermocline. The bottom temperature in the north depression is about 1―4℃ lower than that in the south depression basin which is in good agreement with observations. Model results suggest that the local bathymetry characteristics and inhomogeneous net heat flux due to the latitude difference are the major cause for the early formation of the ADCCBW. Numerical Lagrangian drifter experiments support the finding that the ADCCBW is maintained throughout the stratification periods by the inflow of cold bottom water from the northern Yellow Sea and deep channel in the western side of Liaodong Peninsula. The inflow cold water contributes to the north depression basin distinctively larger than to the south one. Tidal mixing enhances the bottom temperature asymmetry between the two basins.
基金supported by National Natural Science Foundation of China (Grant Nos.40776021,40706018)National Basic Research Program of China (Grant No.2006CB400603)+1 种基金National High Technology Research and Development Program of China (Grant No.2006AA09Z102)JSPS KAKENHI (Grant No.21310012)
文摘Inverse calculations using data from 16 repeat hydrographic transects collected from April 2003 to June 2007 have yielded velocity structures and volume transports(VTs) of the Ryukyu Current in the region east of the northern Ryukyu Islands.The inverse calculation results show that the Ryukyu Current is dominated by a subsurface velocity core with maximum velocities from 15.1 to 80.0 cm/s,whose positions vary between 110 and 600 dbar and 27.2°-28.2°N along the transect.The mean velocity exhibits a subsurface velocity core with a maximum value of 24.6 cm/s at 326 dbar depth,a VT of 14.0 Sv(1 Sv≡106 m3/s),a vertical dimension of 800 m,and a horizontal dimension of 60 km.The seasonal mean velocities show that the Ryukyu Current is stronger in autumn than in other seasons.It is suggested that this seasonal variation is coincident with the intensification of the anticyclonic eddy south of Shikoku,Japan.
