234Th was utilized as a tracer of particulate organic carbon （POC） export in the northwestern South China Sea （SCS） on the basis of the data collected at four stations during a spring cruise. Depth profiles of dis...234Th was utilized as a tracer of particulate organic carbon （POC） export in the northwestern South China Sea （SCS） on the basis of the data collected at four stations during a spring cruise. Depth profiles of dissolved and particulate 234Th activities were measured in the upper 60m, showing a significant deficit relative to 23Su over the investigated stations. A stratified structure of 234Th-23su disequilibrium was in general observed in the upper 60 m water column, indicating that the euphotic zone of the northwestern SCS in this reason can be divided into two layers, an upper and lower layer, with different export rates. POC export fluxes were estimated from a one-dimensional steady state model of 234Th fluxes in combination with the measurement of POC/234Th ratios on suspended particles. The POC export in this region ranged from 8.2 to 20.0 mmol/（m2.d）, with an average of 16.0 mmol/（m2-d）, and was slightly higher than those previously reported in the southern SCS.展开更多
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
基金The National Natural Science Foundation of China under grant Nos 40531007,40676062 and 10705019the scientific research foundation of the Ministry of Science and Technology of China through commonweal grant No.2007050228+3 种基金International Cooperation Program No.2009DFA22920Open Fund of the Key Laboratory of Global Change and Marine-Atmospheric ChemistryState Oceanic Administration under grant Nos 0807 and 0902Tsinghua University Initiative Scientific Research Program
文摘234Th was utilized as a tracer of particulate organic carbon （POC） export in the northwestern South China Sea （SCS） on the basis of the data collected at four stations during a spring cruise. Depth profiles of dissolved and particulate 234Th activities were measured in the upper 60m, showing a significant deficit relative to 23Su over the investigated stations. A stratified structure of 234Th-23su disequilibrium was in general observed in the upper 60 m water column, indicating that the euphotic zone of the northwestern SCS in this reason can be divided into two layers, an upper and lower layer, with different export rates. POC export fluxes were estimated from a one-dimensional steady state model of 234Th fluxes in combination with the measurement of POC/234Th ratios on suspended particles. The POC export in this region ranged from 8.2 to 20.0 mmol/（m2.d）, with an average of 16.0 mmol/（m2-d）, and was slightly higher than those previously reported in the southern SCS.
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.
