Dissolved and particulate thorium-234, particulate organic carbon in the upper 150 m of water columns from five stations in the Prydz Bay, the Southern Ocean were determined during the 22nd Chinese National Antarctic ...Dissolved and particulate thorium-234, particulate organic carbon in the upper 150 m of water columns from five stations in the Prydz Bay, the Southern Ocean were determined during the 22nd Chinese National Antarctic Research Expedition （from November 2005 to March 2006 ）. The disequilibria between thorium-234 and its parent uranium-238 in upper layer was used to derive the averaged residence time of thorium-234, which decreased along with the latitude to the south and a minimum value, 1 - 8 d for particulate thorium-234 and 29 - 48 d for dissolved thorium-234, appeared at the medium latitude station, and the export fluxes of thorium-234 were calculated too and ＇a maximum value, 0. 35 -0. 63 Bq/（m^3 · d） for the particulate thorium-234 and 0. 44 -0. 65 Bq/ （m^3 ·d） for the dissolved thorium-234, appeared at the same station. The export fluxes of particulate organic carbon at different water columns were derived by two methods with irreversible scavenging model, and the averaged values were 104. 7 mmol/ （ m2 · d ） （ E method） and 120. 6 mmol/（ m2·d ） （ B method ）, respectively, indicating that a relatively high new production would exist in summer in the Prydz Bay where it will play a potential significant role in sequestering the absorption CO2 to deeper ocean.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
^(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
Seawater samples were collected around Prydz Bay in summer of 2014,dissolved and particulate^(210)Po and^(210)Pb were measured to reveal the disequilibrium characteristics and particle dynamics.Our results show that t...Seawater samples were collected around Prydz Bay in summer of 2014,dissolved and particulate^(210)Po and^(210)Pb were measured to reveal the disequilibrium characteristics and particle dynamics.Our results show that the distribution of^(210)Po and^(210)Po/^(210)Pb activity ratio in the upper water is mainly affected by biological absorption or particle adsorption.An abnormal excess of^(210)Po relative to^(210)Pb was observed in the surface water at stations P1-2 and P2-2,which is likely to be the horizontal transport of water mass with high DPo/DPb)_(A.R.)and TPo/TPb)_(A.R.).In this study,the removal of particulate^(210)Po is mainly controlled by the scavenging of dissolved^(210)Po and the two have a linear positive correlation with the salinity,a negative linear correlation with the content of dissolved oxygen and a reciprocal relationship with the content of POC.The export flux of POC at 100 m is estimated to be 1.8-4.4 mmol·m^(−2)·d^(−1)(avg.2.9 mmol·m^(−2)·d^(−1))based on^(210)Po/^(210)Pb disequilibria,with the highest value in the shelf,which is consistent with the distribution of biological productivity.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
Activities of the naturally occurring radionuclides, ^(210)Pb and ^(210)Po,were measured in both dissolved ( 【 0.45 μm) and particulate ( 】 0.45 μm) phases from surfacewaters of the southern South China Sea. The a...Activities of the naturally occurring radionuclides, ^(210)Pb and ^(210)Po,were measured in both dissolved ( 【 0.45 μm) and particulate ( 】 0.45 μm) phases from surfacewaters of the southern South China Sea. The average activity of particulate ^(210)Pb, 0.23 Bq/m^3 (n= 23), accounted for about 12% of the total ^(210)Pb, which corresponds with values of open oceans.Particulate ^(210)Po, with an average activity of 0.43 Bq/m^3, accounted for about 40% of the total^(210)Po, which was much higher than those of open and eutrophic oceans. The residence times oftotal ^(210)Po and ^(210)Pb in surface waters estimated from an irreversible steady-state model were0.82 a and 1.16 a, respectively. The consistently high fractionation factor calculated either byscavenging rate constants (5.42) or K_d values (6.69) suggested that a significant fractionationoccurred between ^(210)Po and ^(210)Pb during their removal from solution to particles and that thetwo radionuclides had different biogeochemical cycling pathways in the oligotrophic South China Sea.Furthermore, our results indicated that there exist different fractionation mechanisms between^(210)Po and ^(210)Pb in different marine environments: in eutrophic ocean, plankton detritus andfecal pellets are the main carrier of ^(210)Po and ^(210)Pb, by which ^(210)Po and ^(210)Pb havebeen scavenged and removed; while in oligotrophic ocean, microbes could become the main carrier of^(210)Po and fractionate ^(210)Po and ^(210)Pb significantly as a result of scarce plankton detritusand fecal pellets. These results suggest the use of ^(210)Po to trace marine biogeochemicalprocesses relating to microbial activities and the cycling of sulfur group elements (S, Se, Te andPo).展开更多
Disequilibria between 210Po and 210Pb in the upper water and their potential applications as a proxy of particle export and remineralization were examined in the Southern Ocean (station IV3) and the South China Sea (N...Disequilibria between 210Po and 210Pb in the upper water and their potential applications as a proxy of particle export and remineralization were examined in the Southern Ocean (station IV3) and the South China Sea (NS44). 210Po was deficit in surface waters but excessive relative to 210Pb in subsurface waters. Good positive correlation between 210Po and particulate organic carbon (POC) indicated deficits and excess of 210Po resulted from particulate organic matter (POM) export and remineralization respectively, which was also supported by the decreased δ 13C and increased δ 15N downwards as a result of particle remineralization. On the basis of 210Po/210Pb box-model, POC export flux out of the surface waters were 1.2 mmol C·m-2·d-1 and 2.3 mmol C·m-2·d-1 for station NS44 and IV3, respectively. In the subsurface waters, remineralization fluxes of 210Po were 0.062 Bq·m-2·d-1 and 0.566 Bq·m-2·d-1 for station NS44 and IV3 along with the recycle efficiency of 52±26% and 119±52%, respectively. Remineralized fluxes of POM derived from 210Po and exported POC were 0.6 mmol C·m-2·d-1 and 2.7 mmol C·m-2·d-1 for NS44 and IV3. This study suggested that 210Po was a powerful tracer of particle export and remineralization.展开更多
基金The Scientific Research Foundation of Third Institute of Oceanography,State Oceanic Administration under contract NoTIO2007003the Natural Science Foundation of Fujian Province of China under contract No2006J0287+1 种基金the National Natural Science Foundation of China fromkey program under contract No 40531007 and from general program under contract Nos40406014 and 40276001the State Social Commonweal Foundationof China under contract No 2004DIB5178
文摘Dissolved and particulate thorium-234, particulate organic carbon in the upper 150 m of water columns from five stations in the Prydz Bay, the Southern Ocean were determined during the 22nd Chinese National Antarctic Research Expedition （from November 2005 to March 2006 ）. The disequilibria between thorium-234 and its parent uranium-238 in upper layer was used to derive the averaged residence time of thorium-234, which decreased along with the latitude to the south and a minimum value, 1 - 8 d for particulate thorium-234 and 29 - 48 d for dissolved thorium-234, appeared at the medium latitude station, and the export fluxes of thorium-234 were calculated too and ＇a maximum value, 0. 35 -0. 63 Bq/（m^3 · d） for the particulate thorium-234 and 0. 44 -0. 65 Bq/ （m^3 ·d） for the dissolved thorium-234, appeared at the same station. The export fluxes of particulate organic carbon at different water columns were derived by two methods with irreversible scavenging model, and the averaged values were 104. 7 mmol/ （ m2 · d ） （ E method） and 120. 6 mmol/（ m2·d ） （ B method ）, respectively, indicating that a relatively high new production would exist in summer in the Prydz Bay where it will play a potential significant role in sequestering the absorption CO2 to deeper ocean.
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.
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.
基金financially supported by National Polar Special Program “Impact and Response of Antarctic Seas to Climate Change” (Grant nos. IRASCC 01-01-02C, 02-01-01)supported by National Natural Science Foundation of China (Grant no. 41721005)the program funded by China Ocean Mineral Resources R & D Association (Grant no. DY135-13-E2-03)。
文摘Seawater samples were collected around Prydz Bay in summer of 2014,dissolved and particulate^(210)Po and^(210)Pb were measured to reveal the disequilibrium characteristics and particle dynamics.Our results show that the distribution of^(210)Po and^(210)Po/^(210)Pb activity ratio in the upper water is mainly affected by biological absorption or particle adsorption.An abnormal excess of^(210)Po relative to^(210)Pb was observed in the surface water at stations P1-2 and P2-2,which is likely to be the horizontal transport of water mass with high DPo/DPb)_(A.R.)and TPo/TPb)_(A.R.).In this study,the removal of particulate^(210)Po is mainly controlled by the scavenging of dissolved^(210)Po and the two have a linear positive correlation with the salinity,a negative linear correlation with the content of dissolved oxygen and a reciprocal relationship with the content of POC.The export flux of POC at 100 m is estimated to be 1.8-4.4 mmol·m^(−2)·d^(−1)(avg.2.9 mmol·m^(−2)·d^(−1))based on^(210)Po/^(210)Pb disequilibria,with the highest value in the shelf,which is consistent with the distribution of biological productivity.
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supported by the grants to YPH and Mchen from the National Natural Science Foundation of China(Grant Nos.40576037,90411016 and 40376021)the Chinese National Nansha Special Project(Grant No.2001DIA 50041-4-303).
文摘Activities of the naturally occurring radionuclides, ^(210)Pb and ^(210)Po,were measured in both dissolved ( 【 0.45 μm) and particulate ( 】 0.45 μm) phases from surfacewaters of the southern South China Sea. The average activity of particulate ^(210)Pb, 0.23 Bq/m^3 (n= 23), accounted for about 12% of the total ^(210)Pb, which corresponds with values of open oceans.Particulate ^(210)Po, with an average activity of 0.43 Bq/m^3, accounted for about 40% of the total^(210)Po, which was much higher than those of open and eutrophic oceans. The residence times oftotal ^(210)Po and ^(210)Pb in surface waters estimated from an irreversible steady-state model were0.82 a and 1.16 a, respectively. The consistently high fractionation factor calculated either byscavenging rate constants (5.42) or K_d values (6.69) suggested that a significant fractionationoccurred between ^(210)Po and ^(210)Pb during their removal from solution to particles and that thetwo radionuclides had different biogeochemical cycling pathways in the oligotrophic South China Sea.Furthermore, our results indicated that there exist different fractionation mechanisms between^(210)Po and ^(210)Pb in different marine environments: in eutrophic ocean, plankton detritus andfecal pellets are the main carrier of ^(210)Po and ^(210)Pb, by which ^(210)Po and ^(210)Pb havebeen scavenged and removed; while in oligotrophic ocean, microbes could become the main carrier of^(210)Po and fractionate ^(210)Po and ^(210)Pb significantly as a result of scarce plankton detritusand fecal pellets. These results suggest the use of ^(210)Po to trace marine biogeochemicalprocesses relating to microbial activities and the cycling of sulfur group elements (S, Se, Te andPo).
基金Supported by National Natural Science Foundation of China(Grant Nos.40576037and90411016)National Key Technology Research and Development Program(Grant No.2006BAB19B03)COMRA project(Grant No.DYXM-115-01-3-04)
文摘Disequilibria between 210Po and 210Pb in the upper water and their potential applications as a proxy of particle export and remineralization were examined in the Southern Ocean (station IV3) and the South China Sea (NS44). 210Po was deficit in surface waters but excessive relative to 210Pb in subsurface waters. Good positive correlation between 210Po and particulate organic carbon (POC) indicated deficits and excess of 210Po resulted from particulate organic matter (POM) export and remineralization respectively, which was also supported by the decreased δ 13C and increased δ 15N downwards as a result of particle remineralization. On the basis of 210Po/210Pb box-model, POC export flux out of the surface waters were 1.2 mmol C·m-2·d-1 and 2.3 mmol C·m-2·d-1 for station NS44 and IV3, respectively. In the subsurface waters, remineralization fluxes of 210Po were 0.062 Bq·m-2·d-1 and 0.566 Bq·m-2·d-1 for station NS44 and IV3 along with the recycle efficiency of 52±26% and 119±52%, respectively. Remineralized fluxes of POM derived from 210Po and exported POC were 0.6 mmol C·m-2·d-1 and 2.7 mmol C·m-2·d-1 for NS44 and IV3. This study suggested that 210Po was a powerful tracer of particle export and remineralization.
