On the Ratio 230Th/231Pa as a Paleoceanographic Indicator

230Th（半衰期为75,200年）和231 Pa（半衰期为32,500年）这对放射性核素是由其各自的U母体（234U和235U）在海水中衰变产生的，它们提供了海洋中粒子通量和生产力的重要信息。与其他古生产力替代指标相比，它们具有一定的优势：1)两种核素具有恒定的初始产比。(2)受沉积后溶蚀和动员作用的影响较小。(3)以230Th/231Pa为比值时，它们对沉积物聚焦或再分布相对不敏感。另一方面，这个230Th/231Pa比率代理仍然是一个需要锐化和改进的新工具。它的局限性和全部潜力仍有待界定和探索。该项目的主要目的是对这一具有重要前景的古海洋学代用物进行深入研究。将从可能影响沉积物中230Th/231 Pa比值的颗粒组成方面研究230Th和231Pa的清除。将采用一种新的方法来评估海水和单个载体相（粘土、蛋白石、Mn02等）之间230Th和231Pa的分布。在解释过去生产力变化的沉积记录时，单个相的比值应该比总沉积物的比值更有效。该研究将在三个海洋区域进行：西太平洋-冲绳海槽，阿拉伯海和加利福尼亚海流下的区域。研究了230Th/231 Pa与古氧化还原条件的关系，并探讨了将此关系作为研究古氧化还原条件的经验方法的可能性。预计这项研究将有助于我们了解海洋中的碳循环及其对气候变化的反应。

9404614 KU The pair of radionuclides 230Th (half-life 75,200 years) and 231 Pa (half-life 32,500 years) produced by the decay of their respective U parents (234U and 235U) in seawater provide important information about the particle flux and productivity in the oceans. They have certain advantages over other proxy indicators of paleoproductivity: 1) The two nuclides have a constant initial production ratio. (2) They are little affected by post-depositional dissolution and mobilization. (3) When used as ratio 230Th/231Pa, they are relatively insensitive to sediment focusing or redistribution. On the other hand, this 230Th/231Pa ratio proxy is still a new tool needing sharpening and refinement. Its limitations and full potential remain to be defined and explored. The primary objective of this project is to conduct an in-depth investigation on this promising and important paleoceanographic proxy. The scavenging of 230Th and 231Pa will be studied in terms of particle composition which may affect the 230Th/231 Pa ratio in a sediment. A new approach will be employed to assess the distributions of 230Th and 231Pa between seawater and individual carrier phases (clay, opal, Mn02, etc.). The ratios in the individual phases should serve as a more effective index than those of a total sediment for deciphering the sedimentary record of productivity changes in the past. The study will be carried out in three oceanic areas: western Pacific-Okinawa Trough, the Arabian Sea, and regions under the California Current. The relationship between 230Th/231 Pa and the oxygen consumption rate in will be examined and the possibility of using the relationship as an empirical way of studying paleo-redox conditions will be explored. It is anticipated that the study will contribute to our understanding of the carbon cycles in the ocean and their response to climate change.