Collaborative Research: Impact of the Amazon River Plume on Nitrogen Availability and Planktonic Food Web Dynamics in the Western Tropical North Atlantic

这是一个在热带北大西洋西部水域的实地研究的重点项目，该水域在河流高峰期受到亚马逊河羽流的影响。亚马逊羽流地区在一个动态系统中支持不同的浮游生物群落，该系统由河流本身的运输提供的营养物质以及通过物理混合和上升流从近海水域携带的营养物质驱动。这在一系列空间和时间尺度上的物理、化学和生物过程之间产生了强烈的相互作用。该实地计划将把环境特性的直接测量与浮游植物营养供应和营养限制的重点实验研究以及浮游植物氮向浮游动物食物网的转移联系起来。亚马逊羽流在旺季表现出不同群落的紧密并列，使其成为评估养分可获得性、养分供应和栖息地寿命如何相互作用以推动近海生态系统动态和功能的理想地点。该项目将包括德国的合作者，并将无缝地整合教育和研究工作。调查人员及其机构坚定地致力于本科生和研究生教育，并通过积极的招聘和培训努力增加海洋科学界的多样性。该团队在让本科生和研究生参与他们的实地和实验室研究方面有着很好的记录。计划中的两次研究巡航将为学生和技术人员提供与跨学科和国际研究团队互动的机会。该项目的最终目标是了解促进亚马逊羽流周围不同固氮生物群落(重氮营养生物)和其他浮游植物群落的过程和相互作用，并探索这些富含固氮微生物的群落对浮游动物生物量和产量的影响。研究小组包括在营养和稳定同位素生物地球化学、遥感以及利用自然产生的镭同位素表征水团来源和历史方面具有专长的科学家。这种方法的结合将提供一个独特的机会来解决与浮游生物群落结构、初级生产以及与远洋生态系统次级生产的联系有关的基本问题。该项目将解决以下主要问题：a.什么机制促进生物可利用磷的优先输送，以及由此产生的与亚马逊羽流北部高峰期相关的强烈的氮素限制？B.是什么因素导致亚马逊羽流内部和周围的固氮菌之间存在明显的生态位分离，以及与亚马逊河羽流和近海上升流过程相关的水文和生物地球化学控制如何影响不同的重氮菌群落？C.不同类型的重氮菌固定的氮是如何促进二次生产的，以及重氮菌氮在食物链中的移动效率如何？

This is a focused program of field research in waters of the Western Tropical North Atlantic influenced by the Amazon River Plume during the high river flow season. The Amazon Plume region supports diverse plankton communities in a dynamic system driven by nutrients supplied by transport from the river proper as well as nutrients entrained from offshore waters by physical mixing and upwelling. This creates strong interactions among physical, chemical, and biological processes across a range of spatial and temporal scales. The field program will link direct measurements of environmental properties with focused experimental studies of nutrient supply and nutrient limitation of phytoplankton, as well as the transfer of phytoplankton nitrogen to the zooplankton food web. The Amazon Plume exhibits a close juxtaposition of distinct communities during the high-flow season, making it an ideal site for evaluating how nutrient availability, nutrient supply, and habitat longevity interact to drive offshore ecosystem dynamics and function. This project will include German collaborators and will seamlessly integrate education and research efforts. The investigators and their institutions have a strong commitment to undergraduate and graduate education and to increasing the diversity of the ocean science community through active recruiting and training efforts. The team has a strong track record of involving both undergraduate and graduate students in their field and lab research. The two research cruises planned will provide opportunities for students and technicians to interact with an interdisciplinary and international research team. The ultimate objectives of this project are to understand the processes and interactions that promote distinct communities of nitrogen-fixing organisms (diazotrophs) and other phytoplankton around the Amazon Plume and to explore the impacts of these diazotroph-rich communities on zooplankton biomass and production. The research team includes scientists with expertise in nutrient and stable isotope biogeochemistry, remote sensing as well as specialists in characterizing water mass origin and history using naturally occurring radium isotopes. This combination of approaches will provide a unique opportunity to address fundamental questions related to plankton community structure, primary production, and links to secondary production in pelagic ecosystems. The project will address the following key questions focused on fundamental issues in plankton ecology resulting from previous research in this region:A. What mechanisms promote the preferential delivery of bioavailable phosphorus and the resulting strong nitrogen limitation associated with the northern reaches of the Amazon Plume during the high flow season? B. What factors lead to the clear niche separation between diazotrophs within and around the Amazon Plume and how are the distinct diazotroph communities influenced by hydrographic and biogeochemical controls associated with the Amazon River Plume and offshore upwelling processes? C. How does the nitrogen fixed by the different types of diazotrophs contribute to secondary production, and how efficiently does diazotroph nitrogen move through the food web?