Rare earth elements and neodymium isotopes in the South Pacific: impact of hydrothermal activity, particle fluxes, and ocean circulation

了解影响海洋中痕量元素及其同位素(TEI)的生物地球化学过程及其对TEI分布和预算的影响，对于全面了解TEI作为微量营养素和示踪剂的作用至关重要。钕(ND)同位素和稀土元素(REE)是非常有用的海洋示踪剂，已被广泛应用于提高我们对现代和过去海洋过程和变化的理解。稀土元素的颗粒反应性和ND同位素携带的源信息使其对于阐明海洋中溶解的TEI来源和修改、颗粒的清除和水团的横向运输特别有用。在这里提出的研究中，我将检验以下假设：热液颗粒导致强烈的稀土元素清除，以及特有的稀土和钕同位素特征，从而能够追踪南太平洋热液羽流的命运，并有可能将其上升到南大洋表面。此外，我还将检验贫营养的副热带南太平洋环流中极低的颗粒通量是否导致横向平流对该地区溶解稀土分布的主导控制。该项目将通过新西兰的投入和/或与新西兰边缘和Kermadec热液系统的接触，进一步评估对新形成的南大洋水团的原始溶解的ND同位素特征进行修改的可能性。因此，这项研究将深入了解东太平洋海隆南部高度活跃的热液系统以及浅层和浅海热液系统对太平洋溶解稀土元素和钕同位素的影响，以及迄今基本上未被研究的克马德克弧热液系统。预期结果将对全球海洋稀土元素预算、稀土和钕同位素作为示踪剂的使用以及所研究的过程对其他溶解的稀土元素的影响产生深远的影响。

Knowledge of the biogeochemical processes affecting trace elements and their isotopes (TEIs) in the ocean and their impact on TEI distributions and budgets is essential for a comprehensive understanding of the roles of TEIs as micronutrients and tracers. Neodymium (Nd) isotopes and rare earth elements (REEs) are highly useful marine tracers and have been widely applied to improve our understanding of both modern and past processes and changes in the ocean. The particle reactivity of REEs and the source information carried by Nd isotopes make them particularly useful for elucidating dissolved TEI sources and modifications in the ocean, scavenging by particles, and lateral transport by water masses. In the study proposed here, I will test the hypotheses that hydrothermal particles lead to intense REE scavenging and characteristic REE and Nd isotope signatures that allow tracing the fate of hydrothermal plumes in the South Pacific and potentially their upwelling to the surface of the Southern Ocean. Moreover, I will test whether the extremely low particle fluxes in the oligotrophic subtropical South Pacific gyre lead to a dominant control of lateral advection on the distribution of dissolved REEs in this area. The project will further assess the potential modification of the original dissolved Nd isotope signatures of newly formed Southern Ocean water masses through input from New Zealand and/or contact with the New Zealand margin and the Kermadec hydrothermal system. The study will therefore provide insight into the impact of the highly active hydrothermal system of the southern East Pacific Rise, as well as the shallow and with respect to TEIs so far largely unstudied hydrothermal system of the Kermadec Arc on dissolved REEs and Nd isotopes in the Pacific. The expected results will have far-reaching implications for the global REE budget in the ocean, the use of REEs and Nd isotopes as tracers, as well as for the impact of the studied processes on other dissolved TEIs.