Collaborative Research: A porewater perspective on benthic sources of neodymium to the North Atlantic

记录深海环流的变化对于理解过去的气候变化非常重要。在深海沉积物中记录的钕（Nd）同位素已被用来重建过去的海洋环流。然而，最近的几项研究表明，一些Nd从下面的沉积物中释放到海水中，这将使使用Nd同位素精确跟踪海洋深水的能力复杂化。该项目将调查西北大西洋海底沉积物和近底水中的Nd。研究区域是北大西洋深水形成的位置。更广泛的影响包括指导支持，允许两名早期职业科学家担任实地项目的联合首席科学家。此外，来自STEM专业学生比例不足的机构的高中生，以及来自少数族裔服务机构的本科生，也得到了支持。Nd同位素作为古环流代用物的解释框架依赖于由水团混合驱动的深海信号，而海底Nd源对海洋的影响很小。它还要求在沉积物中准确记录Nd同位素，并随时间独立地知道端元组成。最近的研究对这一框架提出了挑战，表明来自海洋沉积物的底栖生物通量可能对深水同位素组成起主要控制作用。然而，直接底栖生物通量测量的全球覆盖范围有限（仅来自主要在北太平洋的10个已公布地点），妨碍了对海洋Nd循环的全面了解。该项目将（一）量化Nd从沉积物流向底水的通量，（二）研究这些通量如何影响北大西洋深水的同位素组成，（三）研究成岩反应在确定孔隙水稀土元素地球化学中的作用，以及（四）确定海洋档案中记录的同位素信号。该项目的现场部分将占据拉布拉多海的两个深度样带，它将包括从短岩心中收集沉积物和孔隙水，相应的过滤底水和深海颗粒，以便全面描述该系统。研究地点将允许调查区域地质和水深在设置Nd到海水的底栖通量方面的作用。总之，该项目将是迄今为止对底栖Nd通量的控制、底栖Nd通量对北大西洋深水Nd同位素组成的影响、促进Nd释放的沉积环境条件以及这些过程对自生Nd同位素记录的影响进行最彻底的研究之一。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Documenting deep ocean circulation changes is important to understanding past climate variability. Neodymium (Nd) isotopes, recorded in deep ocean sediments, have been used to reconstruct past ocean circulation. However, several recent studies suggest that some Nd is released into seawater from the underlying sediment, which would complicate the ability to use Nd isotopes to accurately track deep water in the ocean. This project will investigate Nd in seafloor sediments and near bottom water in the Northwest Atlantic. The study region is a location where North Atlantic Deep Water is formed. Broader impacts include mentoring support to allow two early-career scientists to serve as co-chief scientists for the field program. There is also support for high school students from an institution with a high percentage of students that are underrepresented in STEM, and undergraduates from a minority-serving institution.The interpretive framework of Nd isotopes as a paleo circulation proxy relies on deep ocean signals being driven by mixing between water masses with little influence from benthic sources of Nd to the ocean. It also requires that Nd isotopes are recorded accurately in sediments and endmember composition is independently known through time. Recent studies have challenged this framework, suggesting that benthic fluxes from ocean sediments may exert a primary control on deep water isotopic composition. However, the limited global coverage of direct benthic flux measurements (from only 10 published locations primarily in the North Pacific) prevents a complete understanding of the marine Nd cycle. This project will (i) quantify the fluxes of Nd to bottom water from sediments, (ii) examine how those fluxes affect the isotopic composition of North Atlantic Deep Water, (iii) investigate the role of diagenetic reactions in setting pore water rare earth element geochemistry, and (iv) determine what isotopic signals are recorded in marine archives. The field component of this project will occupy sites along two depth transects in the Labrador Sea, and it will involve collecting sediment and pore water from short cores, corresponding filtered bottom water, and deep-sea particles, in order to fully describe the system. The study location will allow for investigation of the role that regional geology and water depth play in setting the benthic flux of Nd to seawater. Altogether, this project will be one of the most thorough investigations to date of the controls on benthic Nd flux, the impact of benthic fluxes on the Nd isotopic composition of North Atlantic Deep Water, the sedimentary environmental conditions that facilitate Nd release, and the impact of these processes on authigenic Nd isotope records.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.