The program described herein （LEADAT） serves to calculate sediment date and sedimentation rate using the ^210pb method for the studies of environmental processes and pollution history on a time scale of 100 - 150 a....The program described herein （LEADAT） serves to calculate sediment date and sedimentation rate using the ^210pb method for the studies of environmental processes and pollution history on a time scale of 100 - 150 a. The program written in MATLAB （ Version7.0） permits the user to select the principal models of ^210pb method, i. e. , the constant fluxes of sediment and lead-210 （ CF- SL） model, the constant flux of lead-210 （CFL） model, the constant initial concentration of lead-210 （CICL） model and the twolayer mixing （TLM） model. Although appropriate model selection is essentially based on understanding of the sedimentary processes, the pattern of the excess ^210pb profile is also helpful for model selection. The excess ^210pb profiles for two sediment cores collected from a brackish lake and an embayment respectively are used to demonstrate the application of the program. With a graphical user interface, the program can be easily executed. Not only ASCII but also graphical output can be generated by means of the program. Meanwhile, the code can be modified easily for extension.展开更多
The radionuclide ^（210） Pb is suitable for century-scale dating and has been used to calculate the sedimentation rate in a variety of environments. However, two common ways to apply 210 Pb dating techniques may give...The radionuclide ^（210） Pb is suitable for century-scale dating and has been used to calculate the sedimentation rate in a variety of environments. However, two common ways to apply 210 Pb dating techniques may give misleading results. One is ＂prolonging of age＂, i.e., using the calculated sedimentation rate to date back to 200 or 300 years.This practice must be treated with caution because the 210 Pb dating techniques do not guarantee direct dating for ages much older than 100 years. Another is ＂loss of age＂, i.e., the calculated time span between the topmost layer and the 210 Pb background layer in cores is less than 100 years when an apparent sedimentation rate is used in the calculation. Here, we propose that based on the principle of 210 Pb dating, the upper limit of age suitable for direct210 Pb dating is between 110 and 155 years. The ＂prolonging＂ application is acceptable only if the sedimentary environment in the past several hundred years was stable and the sedimentation rate was generally constant, and verification with independent evidence（such as historical records or biomarker methodology） is needed.Furthermore, after analyzing many published and collected data, we found four possible reasons for the ＂loss of age＂. First, the compaction effect of sediment should be corrected in laboratory analysis or else the calculated age will be underestimated. Second, the accuracy and uncertainty of 210 Pb activity measurement affect the judgment of the background. To be cautious, researchers are apt to choose a background activity with a younger age. Third,use of a slightly smaller value of supported 210 Pb activity in a calculation will lead to considerable underestimation of the time span. Finally, later-stage erosion and migration are common for sedimentation, which lead to loss of sedimentary records and are often reflected as a ＂loss of age＂ in cores. We believe that proper use of 210 Pb dating data may provide helpful information on our understanding of sediment records and recent environmental changes.展开更多
Deposition of organic carbon forms the final net effect of the ocean carbon sink at a certain time scale. Organic carbon deposition on the Arctic shelves plays a particularly important role in the global carbon cycle ...Deposition of organic carbon forms the final net effect of the ocean carbon sink at a certain time scale. Organic carbon deposition on the Arctic shelves plays a particularly important role in the global carbon cycle because of the broad shelf area and rich nutrient concentration. To determine the organic carbon deposition flux at the northern margin of the Chukchi Sea shelf, the 210pb dating method was used to analyze the age and deposition rate of sediment samples from station R17 of the third Chinese National Arctic Research Expedition. The results showed that the deposition rate was 0.6 mm＇aI, the apparent deposition mass flux was 0.72 kg.m2a1, and the organic carbon deposition flux was 517 mmol C.m2.al. It was estimated that at least 16% of the export organic carbon flux out of the euphoric zone was transferred and chronically buried into the sediment, a value which was much higher than the average ratio （-10%） for low- to mid-latitude regions, indicating a highly effective carbon sink at the northern mar- gin of the Chukchi Sea shelf. With the decrease of sea ice coverage caused by warming in the Arctic Ocean, it could be inferred that the Arctic shelves will play an increasingly important role in the global carbon cycle.展开更多
Seven cores were collected from different sediment zones of tidal flats at Xin- yanggang in north Jiangsu province in August 2007. Sediment grain-size distribution and radioisotopes of ^137Cs and ^210Ppb analysis were...Seven cores were collected from different sediment zones of tidal flats at Xin- yanggang in north Jiangsu province in August 2007. Sediment grain-size distribution and radioisotopes of ^137Cs and ^210Ppb analysis were carried out for these cores. Sediment rates of the cores and radioisotopes distribution in surface sediment in different zones of the tidal flat were calculated from the ^137Cs and ^210Ppb activities in sediments cores. The results indicated that each tidal zone had experienced different evolution phases, hydrological dynamics in the tidal flats made the grain-size of the surface sediment change gradually. ^137Cs and ^210Ppb activities on the superficial layer of the cores varied spatially and the reason was discussed. On tidal flats, the fluctuation of ^137Cs and ^210Ppb activities in the cores reflected the special sedimentary characteristics. Vegetation affects the grain-size distribution and the vertical profiles of ^137Cs and ^210Ppb in the upper depths. ^137Cs and ^210Ppb chronology got the comparable average sediment rates on the tidal flat. The characteristics of ^137Cs and ^210Ppb in the cores reflected various depositional dynamical environments in different tidal zones and gave information on the different evolvement phases of the tidal zones. Based on the information of grain-size distribution, texture of the cores, sediment rates and topography, the evolution lines of the tidal flat were reconstructed.展开更多
The time scale of transport and reaction processes in the ocean can be evaluated using natural radionuclides of different half-lives.In the present study,we evaluated the residence times of particulate reactive radion...The time scale of transport and reaction processes in the ocean can be evaluated using natural radionuclides of different half-lives.In the present study,we evaluated the residence times of particulate reactive radionuclides 7 Be,210 Pb xs and 234 Th in the Changjiang (Yangtze River) estuary,which is a high turbidity estuary,in June,2006.The residence times of particulate 7 Be,234 Th xs and 210 Pb xs in the Changjiang estuary were calculated to be 0.7-20.4,0.18-4.1 and 0.6-89.8 d,respectively.The obtained residence times of those nuclides are comparable with those of other estuaries and bays.For 234 Th xs and 7 Be,the residence times decreased with increasing concentrations of suspended particulate matter (SPM);however,those of 210 Pb xs increased.Moreover,scavenging residence times of 234 Th and 7 Be increased from coast to offshore,while those of 210 Pb xs decreased.展开更多
文摘The program described herein （LEADAT） serves to calculate sediment date and sedimentation rate using the ^210pb method for the studies of environmental processes and pollution history on a time scale of 100 - 150 a. The program written in MATLAB （ Version7.0） permits the user to select the principal models of ^210pb method, i. e. , the constant fluxes of sediment and lead-210 （ CF- SL） model, the constant flux of lead-210 （CFL） model, the constant initial concentration of lead-210 （CICL） model and the twolayer mixing （TLM） model. Although appropriate model selection is essentially based on understanding of the sedimentary processes, the pattern of the excess ^210pb profile is also helpful for model selection. The excess ^210pb profiles for two sediment cores collected from a brackish lake and an embayment respectively are used to demonstrate the application of the program. With a graphical user interface, the program can be easily executed. Not only ASCII but also graphical output can be generated by means of the program. Meanwhile, the code can be modified easily for extension.
基金The National Natural Science Foundation of China under contract Nos 41376068 and 41776068
文摘The radionuclide ^（210） Pb is suitable for century-scale dating and has been used to calculate the sedimentation rate in a variety of environments. However, two common ways to apply 210 Pb dating techniques may give misleading results. One is ＂prolonging of age＂, i.e., using the calculated sedimentation rate to date back to 200 or 300 years.This practice must be treated with caution because the 210 Pb dating techniques do not guarantee direct dating for ages much older than 100 years. Another is ＂loss of age＂, i.e., the calculated time span between the topmost layer and the 210 Pb background layer in cores is less than 100 years when an apparent sedimentation rate is used in the calculation. Here, we propose that based on the principle of 210 Pb dating, the upper limit of age suitable for direct210 Pb dating is between 110 and 155 years. The ＂prolonging＂ application is acceptable only if the sedimentary environment in the past several hundred years was stable and the sedimentation rate was generally constant, and verification with independent evidence（such as historical records or biomarker methodology） is needed.Furthermore, after analyzing many published and collected data, we found four possible reasons for the ＂loss of age＂. First, the compaction effect of sediment should be corrected in laboratory analysis or else the calculated age will be underestimated. Second, the accuracy and uncertainty of 210 Pb activity measurement affect the judgment of the background. To be cautious, researchers are apt to choose a background activity with a younger age. Third,use of a slightly smaller value of supported 210 Pb activity in a calculation will lead to considerable underestimation of the time span. Finally, later-stage erosion and migration are common for sedimentation, which lead to loss of sedimentary records and are often reflected as a ＂loss of age＂ in cores. We believe that proper use of 210 Pb dating data may provide helpful information on our understanding of sediment records and recent environmental changes.
基金supported by the Scientific Research Foundation of the Third Institute of Oceanography, SOA (Grant nos. 2011024 and 2011025)the Marine Science Youth Fund of SOA (Grant no. 2012107)
文摘Deposition of organic carbon forms the final net effect of the ocean carbon sink at a certain time scale. Organic carbon deposition on the Arctic shelves plays a particularly important role in the global carbon cycle because of the broad shelf area and rich nutrient concentration. To determine the organic carbon deposition flux at the northern margin of the Chukchi Sea shelf, the 210pb dating method was used to analyze the age and deposition rate of sediment samples from station R17 of the third Chinese National Arctic Research Expedition. The results showed that the deposition rate was 0.6 mm＇aI, the apparent deposition mass flux was 0.72 kg.m2a1, and the organic carbon deposition flux was 517 mmol C.m2.al. It was estimated that at least 16% of the export organic carbon flux out of the euphoric zone was transferred and chronically buried into the sediment, a value which was much higher than the average ratio （-10%） for low- to mid-latitude regions, indicating a highly effective carbon sink at the northern mar- gin of the Chukchi Sea shelf. With the decrease of sea ice coverage caused by warming in the Arctic Ocean, it could be inferred that the Arctic shelves will play an increasingly important role in the global carbon cycle.
基金National Basic Research Program of China, No.2002CB412401 Scientific Research Foundation of Graduate School of Nanjing University National Natural Science Foundation of China, No.40776023
文摘Seven cores were collected from different sediment zones of tidal flats at Xin- yanggang in north Jiangsu province in August 2007. Sediment grain-size distribution and radioisotopes of ^137Cs and ^210Ppb analysis were carried out for these cores. Sediment rates of the cores and radioisotopes distribution in surface sediment in different zones of the tidal flat were calculated from the ^137Cs and ^210Ppb activities in sediments cores. The results indicated that each tidal zone had experienced different evolution phases, hydrological dynamics in the tidal flats made the grain-size of the surface sediment change gradually. ^137Cs and ^210Ppb activities on the superficial layer of the cores varied spatially and the reason was discussed. On tidal flats, the fluctuation of ^137Cs and ^210Ppb activities in the cores reflected the special sedimentary characteristics. Vegetation affects the grain-size distribution and the vertical profiles of ^137Cs and ^210Ppb in the upper depths. ^137Cs and ^210Ppb chronology got the comparable average sediment rates on the tidal flat. The characteristics of ^137Cs and ^210Ppb in the cores reflected various depositional dynamical environments in different tidal zones and gave information on the different evolvement phases of the tidal zones. Based on the information of grain-size distribution, texture of the cores, sediment rates and topography, the evolution lines of the tidal flat were reconstructed.
基金Supported by the National Natural Science Foundation of China (No.40976054)the State Key Laboratory of Estuarine and Coastal Research of China (No. 2008KYYW08)the National Basic Research Program of China (973 Program) (Nos. 2002CB412405 and 2006CB400601)
文摘The time scale of transport and reaction processes in the ocean can be evaluated using natural radionuclides of different half-lives.In the present study,we evaluated the residence times of particulate reactive radionuclides 7 Be,210 Pb xs and 234 Th in the Changjiang (Yangtze River) estuary,which is a high turbidity estuary,in June,2006.The residence times of particulate 7 Be,234 Th xs and 210 Pb xs in the Changjiang estuary were calculated to be 0.7-20.4,0.18-4.1 and 0.6-89.8 d,respectively.The obtained residence times of those nuclides are comparable with those of other estuaries and bays.For 234 Th xs and 7 Be,the residence times decreased with increasing concentrations of suspended particulate matter (SPM);however,those of 210 Pb xs increased.Moreover,scavenging residence times of 234 Th and 7 Be increased from coast to offshore,while those of 210 Pb xs decreased.
