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颗粒和水团的运输过程的强大示踪剂。大西洋沉积物中231Pa230Th同位素对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该示踪剂沉积物记录有助于解开大西洋子午线翻转环流(AMOC)历史的最好例子。令人惊讶的是，最近的研究结果显示，目前表层沉积物中的通风与231Pa230特征之间存在差异，这可能是由于颗粒组成对两种同位素在沉积物中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，我建议研究北大西洋深水形成早期阶段及其在热带大西洋的分布期间Th和Pa的清除行为，方法是分析2010年在热带和北大西洋执行的两次RV Meteor(M81/1)号游轮(2010年2月/3月，西班牙加那利斯港的GEOTRACES邮轮A11号)和北大西洋西部的RV Pelagia探险64PE319/321号(GEOTRACES邮轮A02号，苏格兰斯克拉布斯特-巴西福塔莱萨，2010年4月至7月)期间收集的一组全面的溶解和颗粒样本。这些巡航是GEOTRACES的官方探险，专门专注于使用超痕量金属清洁采样设施。大量其他痕量元素及其同位素(TEI)的高分辨率分布将为理解控制痕量金属清除过程的可能影响以及研究可能的校正程序以改进231Pa230th AMOC通风代理提供最佳可获得的背景。

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.