Actinium-227: A Steady State Tracer for the Deep-sea Basin-wide Circulation and Mixing Studies
- 標題
- Actinium-227: A Steady State Tracer for the Deep-sea Basin-wide Circulation and Mixing Studies
- 作者
- Yoshiyuki Nozaki
- 文件屬性
- 國外期刊
- 知識分類
- 基礎研究
- 出版年
- 1993
- 刊名
- Elsevier Oceanography Series
- 點閱數
- 2575
摘要
The presence of excess 227Ac (half-life, 21.8 years) relative to the parent 231Pa in deep ocean waters indicates its usefulness as a novel tracer of basin-wide circulation and mixing studies on the time scales of less than 100 years. For this purpose, 227Ac is probably best utilized by coupling with 228Ra (half-life, 5.75 years), both of which have their significant source in the bottom sediments. Most important is to develop a new method for simultaneous and accurate determination of 227Ac and 228Ra in seawater. This may be achieved by combination of MnO2-fiber extraction and subsequent α-scintillation counting of 220Rn and 219Rn emanated from the fiber. New data on the vertical profiles of 227Ac and 228Th (as an indicator of 228Ra) obtained in the deepest part of the Izu-Ogasawara Trench down to 9,700 m suggest that they are predominantly governed by isopycnal mixing. Within the trench, both nuclides are nearly constant with depth, suggesting that the water is uniformly mixed. This view is consistent with the distributions of other chemical species and radioisotopes whose concentrations are almost identical to those of the deep water at 5000-6000 m depths around this region.