冲绳海槽海底热液喷出口附近海水中210Pb和210Po的行为
210Pb and210Po in sea water around the hydrothermal vents in the Okinawa Trough
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摘要: 讨论了在冲绳海槽伊平屋海岭和南奄西海丘两处海底热液喷出口附近海水中的铀系子体放射性核素210Pb和210Po浓度的垂直分布剖面.在伊平屋海岭,甲烷及222Rn的数据表明海底热液活动不强,总210Pb和210Po放射性均低于它们各自母体的放射性,210Pb和210Po在海水中的平均停留时间分别为20和2~5a,而在以“黑色烟雾”为特征的海底热液活动强烈的南奄西海丘,在”烟雾”中的总210Pb含量(0.167×10-3~2.50×10-3Bq/kg)相对其母体226Ra贫乏,而总210Po含量(1.83×10-3~2.83×10-3Bq/kg)则相对其母体210Pb过剩.该处海水中的210Po的放射性高于东海陆架区及冲绳海槽其他海区,并且显示了210Po过剩.210Pb/226Ra以及210Po/210Pb放射性比值的范围分别为0.1~0.4和1.1~7.8.在热液扩散带中210Pb被优先从海水中清除.控制南奄西海丘海水中210Pb浓度的可能机制涉及到210Pb通过扩散作用的横向输送.在热液扩散带中高210Po/210Pb放射性比值表明210Pb的耗尽及210Po从海底热液喷出口的加入.Abstract: Vertical profiles for the uranium-series radioisotopes 210Pb and 210Po were obtained at the two hydro thermal ventsites,the Iheya Ridge and the Minami-Ensei Knoll,in the Mid-Okinawa Trough in 1993 and 1994,respectively.At the Ihey a Ridge,where the hydrothermal activity is not active as reflected by the CH4 and 222Rn data,both the total 210Pb and 210Po activities show deficient relative to their parents,and the mean residence time of 210Pb and 210Po is about 20 and 2~5 a,respectively.At the Minami-Ensei Knoll,which is characterized byblack smokers,the total 210Pb activity(0.167×10-3~2.50×10-3Bq/kg) around the plumes is deficient relative to 226Ra but the total 210Po activity(1.83×10-3~2.83×10-3Bq/kg) is in excess relative to 210Pb.The 210Po activities are higher than those in the East China Sea and the Okinawa Trough,and excess 210Po has beenfound.The 210Pb/226Ra and210Po/210Pb activity ratios are 0.1~0.4 and 1.1~7.8,respectively.210Pb is preferentially scavenged in the hydrothermal plumes.The possible mechanisms governing the concentration of 210Pb in the Minami-Ensei Knoll involve a lateral transport of 210Pb viadiffusion.The high 210Po/210Pb activity ratios in the hydrother mal plumes suggest a depletion of 210Pb and addition of 210Po in the hydrothermal vent area.
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Key words:
- Okinawa Trough /
- hydrothermal vent /
- 210Pb /
- 210Po
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