Advection and mixing of deep water masses in the tropical and western North Atlantic Ocean from thorium and protactinium isotopes

天然放射性核素是识别和量化海洋中粒子和水团运输过程的有力示踪剂。231Pa/230Th同位素对在大西洋沉积物中的分布已被广泛用于追踪过去的深水通风。西北大西洋深水形成区被认为是最好的例子，这种示踪剂的沉积物记录可以帮助揭示大西洋经向翻转环流（AMOC）的历史。令人惊讶的是，最近的研究结果显示，地表沉积物中的现代通风与231Pa/230Th特征之间存在差异，这可能是由于颗粒组成对沉积物中两种同位素的差异去除产生了意想不到的巨大影响。因此，西北大西洋现在是231Pa/230Th作为古环流示踪剂适用性的测试案例。在这里，我建议研究Th和Pa在北大西洋深水形成的早期阶段及其在热带大西洋分布期间的清除行为，通过分析2010年由RV Meteor （M81/1）执行的两次巡航（2010年2月/3月，加那利-西班牙港，特立尼达和多巴哥）和RV Pelagia探险64PE319/321 (GEOTRACES Cruise A02，Scrabster，苏格兰- Fortaleza，巴西，2010年4月- 7月)在热带和北大西洋西部。这些巡航是GEOTRACES的官方考察，专注于使用超痕量金属清洁取样设施。大量其他微量元素及其同位素（TEIs）的高分辨率分布将为了解控制微量金属清除过程的可能影响因素提供最佳背景，并研究改善231Pa/230Th AMOC通气代理的可能校正程序。

Natural radionuclides are powerful tracers to identify and quantify transport processes of particles and of water masses in the ocean. The distribution of the isotope pair 231Pa/230Th in Atlantic sediments has been widely used to trace past deep water ventilation. The formation area of deep water in the NW Atlantic has been considered the best example where the sediment record of this tracer can help unravel the history of Atlantic Meridional Overturning Circulation (AMOC). It came as a surprise that recent findings showed a discrepancy between present day ventilation and the 231Pa/230Th signature in surface sediments, which may be due to an unexpectedly large influence of particle composition on the differential removal of the two isotopes to the sediments. The NW Atlantic thus is now a test case for the applicability of 231Pa/230Th as paleocirculation tracer. Here I propose to study the scavenging behaviour of Th and Pa during the early stages of the formation of North Atlantic Deep Water and during its distribution in the tropical Atlantic by analyzing a comprehensive set of dissolved and particulate samples collected in 2010 along the sections of two cruises executed with RV Meteor (M81/1) (GEOTRACES Cruise A11, Canaries – Port of Spain, Trinidad and Tobago in February/March 2010) and during RV Pelagia expedition 64PE319/321 (GEOTRACES Cruise A02, Scrabster, Scotland – Fortaleza, Brasil, April - July 2010) in the tropical and western North Atlantic. These cruises were official GEOTRACES expeditions uniquely focused on the use of ultra trace metal clean sampling facilities. The high-resolution distribution of a large suite of other trace elements and their isotopes (TEIs) will provide the best achievable background to understand the possible influences controlling the scavenging process of trace metals and to investigate possible correction procedures to improve the 231Pa/230Th AMOC ventilation proxy.