Activities of 234Th and nutrient concentrations in the upper 500 m water column were measured at a time-series station in the South China Sea over a time span of 12.3 d. Results showed a reduction of dissolved 234Th a...Activities of 234Th and nutrient concentrations in the upper 500 m water column were measured at a time-series station in the South China Sea over a time span of 12.3 d. Results showed a reduction of dissolved 234Th and an overall increase of particulate 234Th during the period. Meanwhile, activities of total 234Th kept fairly constant, implying rapid transformation of 234Th between the dissolved and particulate forms. Vertical profiles of total 234Th showed evident deficit of 234Th relative to 238U in the upper 500 m water column. Using an irreversible steady-state model of thorium scavenging, export fluxes of particulateorganic carbon (POC) corresponding to time points T1 and T2 were estimated to be 46.5 and 13.1 mmolC .m-2. d-1. It was demonstrated that the estimation of POC export was greatly dependent on the POC/234Thp ratios and the bias caused by the different models of 234Th scavenging, however, was considered to be of minor importance.展开更多
234Th is widely used to quantify the magnitude of upper ocean particulate organic carbon （POC） export in oceans. In the present work, the rates of particulate organic carbon export were measured based on the distrib...234Th is widely used to quantify the magnitude of upper ocean particulate organic carbon （POC） export in oceans. In the present work, the rates of particulate organic carbon export were measured based on the distribution patterns of 234Th/238U disequilibrium in the water column within the continental slope of the East China Sea （ECS） during May 2011. The profiles of particulate and dissolved 234Th activities at all three stations showed a relative deficit with respect to 238U in the upper 100 m of the water column. The dissolved 234Th scavenging rates and the particulate 234Th removal rates and their residence times were calculated by a one-dimensional steady state model. The results showed that the dissolved a34Th scavenging rates and the particulate 234Th removal rates ranged from 12.4-61.4 dpm/（m3.d） and from 3.8-21.8 dpm/（m3.d）, respectively. The residence times of dissolved and particulate 234Th were in the range of 3.4-158 d and 63.7- 96.5 d, respectively. Combined with the measurement of POC/Z34Th ratios of suspended particles, POC export flux （calculated by carbon） from the euphotic zone was estimated in the study region, which ranged from 4.14-14.7 mmol/（m2 .d）, with an average of 8.21 mmol/（m3.d）, occupying 35% of the prime productivity in the study area. The results of this study can provide new information for better understanding the carbon biogeochemical cycle within the continental slope of the ECS.展开更多
To evaluate the particle dynamics and estimate the POC (particulate organic carbon) export flux from the euphotic zone in the western Arctic Ocean,234 Th238 U disequilibrium was applied during the second Chinese Natio...To evaluate the particle dynamics and estimate the POC (particulate organic carbon) export flux from the euphotic zone in the western Arctic Ocean,234 Th238 U disequilibrium was applied during the second Chinese National Arctic Research Expedition (July 15-September 26,2003).The POC export fluxes are estimated from the measured profiles of the 234 Th/238 U activity ratios and the POC/PTh ratios.The average residence times of the particulate and dissolved 234 Th in the euphotic zone are 33 d and 121 d,and their average export fluxes are 480 dpm/m 2 d and 760 dpm/m 2 d,respectively.The scavenging and removal processes of particle reactive elements are active in the upper layer of the Chukchi Sea.The average residence time of 234 Th increases from shelf to basin,while the export fluxes of 234 Th decrease.The estimated POC export fluxes from the euphotic zone vary from 2.1 to 20.3 mmol/m 2 d,indicating that the western Arctic Ocean is an important carbon sink in summer due to efficient biological pump.展开更多
During the Second Chinese National Arctic Expedition （CHINARE） from July to September 2003, depth profiles of dissolved and particulate 234Th in upper water columns were collected at two stations of BR03 and BR24 in...During the Second Chinese National Arctic Expedition （CHINARE） from July to September 2003, depth profiles of dissolved and particulate 234Th in upper water columns were collected at two stations of BR03 and BR24 in the Bering Sea. 234Th was sampled by using a traditional Fe （OH） 3 co-precipitation technique, which is a reliable approach to 234Th measurement. We observed 234 Wh excess at station BR03 below the euphotic zone, which was possibly due to the intensive remineralization of particulate matter. Particulate organic carbon （POC） export fluxes were estimated from a one-dimensional irreversible steady state model of ^234Th fluxes together with measurements of the POC/^234 Th ratio on the suspended particles. The POC export fluxes from the euphotic zone were II. 66 and I1.69 mmol C m^-2 d^- 1 at BR03 and BR24 stations, respectively. The ratios of POC fluxes to primary production at the two stations were about 0.5 and 0.59, respectively, probably due to the presence of large phytoplankton （in particular diatoms）.展开更多
^(234)Th-^(238)U disequilibria were applied to examine the particle dynamics in the euphotic zone of the central South China Sea during the spring 2002 cruise.The particulate organic carbon (POC),^(234)Th (including b...^(234)Th-^(238)U disequilibria were applied to examine the particle dynamics in the euphotic zone of the central South China Sea during the spring 2002 cruise.The particulate organic carbon (POC),^(234)Th (including both dissolved and particulate) and ^(238)U in the water column at three stations were determined. The profiles of ^(234)Th/^(238)U activity ratio at the three stations all showed consistent ^(234)Th deficit as compared to ^(238)U in the upper 100 m water column.Based on the profiles of the dissolved and particulate ^(234)Th and a steady state box model,the dissolved ^(234)Th scavenging rates,the particulate ^(234)Th removal rates and their resident times were quantified.It was found that the POC downward export fluxes out of the upper 100 m euphotic zone ranged from 9.40 to 14.78 mmol·m^(-2)·d^(-1).The results from this study provide new information for our understanding of carbon biogeochemical cycle in the South China Sea.展开更多
A simple model is established to describe the fate of particle-reactive pollutants in the Xiamen Bay. Based on the conditional distribution coefficients (Kd ) of chemicals and residence times of particle and waters, t...A simple model is established to describe the fate of particle-reactive pollutants in the Xiamen Bay. Based on the conditional distribution coefficients (Kd ) of chemicals and residence times of particle and waters, the model can be used to predict the fractions of pollutants which would be scavenged to sediments and would escape from the system. The model is calibrated using scavenging data derived from 234 Th - 238U disequilibrium. The fate of a potential pollutant which will be scavenged is a function of the properties of the chemical, of the particle dynamics, and of the waters dynamics in the environment. It is inappropriate to overlook any factor.展开更多
The spatial and temporal distributions of new production vary largely in different sea areas. To understand the level of new production in the sea area studied better, an estimate of new production must be obtained in...The spatial and temporal distributions of new production vary largely in different sea areas. To understand the level of new production in the sea area studied better, an estimate of new production must be obtained in large spatial and temporal scales. The ~234Th/ ~238U disequilibrium is an effective method for the study of new production. Two sampling strategies, vertically integrated sampling ap proach based on trapezoidal integration principle and discrete layer sampling approach, were compared in the studies of the xiamen Bay and the northern South China Sea. The scavenging fluxes and removal fluxes of ~234Th and the residence times for dissolved and particulate ~234Th were calculated. The coinci dent results from two Sampling approach suggest that vertically integrated sampling approach is not only effective and reliable, but also significantly reduces the number and volume of samples. It allows us to study new production by ba ^(234)Th - ^(238)U disequilibria in large spatial scale.展开更多
基金This work was supported by YPH from the National Science and Technology Research Program of China (Grant No. 97-926-04-02) and the National Natural Science Foundation of China (Grant No. 49676296).
文摘Activities of 234Th and nutrient concentrations in the upper 500 m water column were measured at a time-series station in the South China Sea over a time span of 12.3 d. Results showed a reduction of dissolved 234Th and an overall increase of particulate 234Th during the period. Meanwhile, activities of total 234Th kept fairly constant, implying rapid transformation of 234Th between the dissolved and particulate forms. Vertical profiles of total 234Th showed evident deficit of 234Th relative to 238U in the upper 500 m water column. Using an irreversible steady-state model of thorium scavenging, export fluxes of particulateorganic carbon (POC) corresponding to time points T1 and T2 were estimated to be 46.5 and 13.1 mmolC .m-2. d-1. It was demonstrated that the estimation of POC export was greatly dependent on the POC/234Thp ratios and the bias caused by the different models of 234Th scavenging, however, was considered to be of minor importance.
基金The National Key Basic Research Program from the Ministry of Science and Technology of China under contract Nos 2011CB409801 and 2010DFA24590the National Natural Science Foundation of China under contract No.41240038
文摘234Th is widely used to quantify the magnitude of upper ocean particulate organic carbon （POC） export in oceans. In the present work, the rates of particulate organic carbon export were measured based on the distribution patterns of 234Th/238U disequilibrium in the water column within the continental slope of the East China Sea （ECS） during May 2011. The profiles of particulate and dissolved 234Th activities at all three stations showed a relative deficit with respect to 238U in the upper 100 m of the water column. The dissolved 234Th scavenging rates and the particulate 234Th removal rates and their residence times were calculated by a one-dimensional steady state model. The results showed that the dissolved a34Th scavenging rates and the particulate 234Th removal rates ranged from 12.4-61.4 dpm/（m3.d） and from 3.8-21.8 dpm/（m3.d）, respectively. The residence times of dissolved and particulate 234Th were in the range of 3.4-158 d and 63.7- 96.5 d, respectively. Combined with the measurement of POC/Z34Th ratios of suspended particles, POC export flux （calculated by carbon） from the euphotic zone was estimated in the study region, which ranged from 4.14-14.7 mmol/（m2 .d）, with an average of 8.21 mmol/（m3.d）, occupying 35% of the prime productivity in the study area. The results of this study can provide new information for better understanding the carbon biogeochemical cycle within the continental slope of the ECS.
基金Supported by the National Natural Science Foundation of China (No.40531007)the China Action Plan of the International Polar Year (Nos.2009DFA22920 and 2008Po5040014-03)+1 种基金the International Science and Technology Cooperation (Nos. 2008DFA20420 and 2009DFA22920)the Polar Atmospheric Environment Remote Sensing Monitoring Technique of the National High Technology Research and DevelopmentProgram of China (863 Program) (No. N2008DFA20420)
文摘To evaluate the particle dynamics and estimate the POC (particulate organic carbon) export flux from the euphotic zone in the western Arctic Ocean,234 Th238 U disequilibrium was applied during the second Chinese National Arctic Research Expedition (July 15-September 26,2003).The POC export fluxes are estimated from the measured profiles of the 234 Th/238 U activity ratios and the POC/PTh ratios.The average residence times of the particulate and dissolved 234 Th in the euphotic zone are 33 d and 121 d,and their average export fluxes are 480 dpm/m 2 d and 760 dpm/m 2 d,respectively.The scavenging and removal processes of particle reactive elements are active in the upper layer of the Chukchi Sea.The average residence time of 234 Th increases from shelf to basin,while the export fluxes of 234 Th decrease.The estimated POC export fluxes from the euphotic zone vary from 2.1 to 20.3 mmol/m 2 d,indicating that the western Arctic Ocean is an important carbon sink in summer due to efficient biological pump.
基金supported by the Natural Science Foundation of China (NSFC) through grants 40531007,40676062,10705019by National Key Technology R &D Program for the 11th Five-year Plan Grant(2006BAB18B04)+1 种基金by the commonweal project sponsored by the scientific research foundation of the ministry of science and technology of the people's republic of china(No.2007050228)Chinese IPY Campaign found by MOF and Open Fund of the Key Laboratory of Global Change and Marine-Atmospheric Chemistry(GCMAC),SOA
文摘During the Second Chinese National Arctic Expedition （CHINARE） from July to September 2003, depth profiles of dissolved and particulate 234Th in upper water columns were collected at two stations of BR03 and BR24 in the Bering Sea. 234Th was sampled by using a traditional Fe （OH） 3 co-precipitation technique, which is a reliable approach to 234Th measurement. We observed 234 Wh excess at station BR03 below the euphotic zone, which was possibly due to the intensive remineralization of particulate matter. Particulate organic carbon （POC） export fluxes were estimated from a one-dimensional irreversible steady state model of ^234Th fluxes together with measurements of the POC/^234 Th ratio on the suspended particles. The POC export fluxes from the euphotic zone were II. 66 and I1.69 mmol C m^-2 d^- 1 at BR03 and BR24 stations, respectively. The ratios of POC fluxes to primary production at the two stations were about 0.5 and 0.59, respectively, probably due to the presence of large phytoplankton （in particular diatoms）.
基金Supported by the NSFC (key program No.40531007) and general Programs (No.40406014,40276001 and 10705019)the State Social Commonweal Grant (No.2004DIB5178)+1 种基金and the commonweal project sponsored by the Scientific Research Foundation of the Ministry of Science and Technology of China (No.2007050228)Chinese IPY Campaign found by MOF
文摘^(234)Th-^(238)U disequilibria were applied to examine the particle dynamics in the euphotic zone of the central South China Sea during the spring 2002 cruise.The particulate organic carbon (POC),^(234)Th (including both dissolved and particulate) and ^(238)U in the water column at three stations were determined. The profiles of ^(234)Th/^(238)U activity ratio at the three stations all showed consistent ^(234)Th deficit as compared to ^(238)U in the upper 100 m water column.Based on the profiles of the dissolved and particulate ^(234)Th and a steady state box model,the dissolved ^(234)Th scavenging rates,the particulate ^(234)Th removal rates and their resident times were quantified.It was found that the POC downward export fluxes out of the upper 100 m euphotic zone ranged from 9.40 to 14.78 mmol·m^(-2)·d^(-1).The results from this study provide new information for our understanding of carbon biogeochemical cycle in the South China Sea.
文摘A simple model is established to describe the fate of particle-reactive pollutants in the Xiamen Bay. Based on the conditional distribution coefficients (Kd ) of chemicals and residence times of particle and waters, the model can be used to predict the fractions of pollutants which would be scavenged to sediments and would escape from the system. The model is calibrated using scavenging data derived from 234 Th - 238U disequilibrium. The fate of a potential pollutant which will be scavenged is a function of the properties of the chemical, of the particle dynamics, and of the waters dynamics in the environment. It is inappropriate to overlook any factor.
基金National Natural Science Foundation of China! 49676296National Scientific and Technical Project! 97-926-04-02.
文摘The spatial and temporal distributions of new production vary largely in different sea areas. To understand the level of new production in the sea area studied better, an estimate of new production must be obtained in large spatial and temporal scales. The ~234Th/ ~238U disequilibrium is an effective method for the study of new production. Two sampling strategies, vertically integrated sampling ap proach based on trapezoidal integration principle and discrete layer sampling approach, were compared in the studies of the xiamen Bay and the northern South China Sea. The scavenging fluxes and removal fluxes of ~234Th and the residence times for dissolved and particulate ~234Th were calculated. The coinci dent results from two Sampling approach suggest that vertically integrated sampling approach is not only effective and reliable, but also significantly reduces the number and volume of samples. It allows us to study new production by ba ^(234)Th - ^(238)U disequilibria in large spatial scale.
