U.S. GEOTRACES Pacific Meridional Transect: Tracing Basin-scale Nutrient Cycling and Carbon Export with Dissolved and Particulate Barium-isotopic Distributions

国际GEOTRACES项目的目标是了解海洋中微量化学元素及其同位素的分布。该项目将在2018年美国GEOTRACES太平洋探险队中测量钡的稳定同位素。钡是一种微量元素，其分布与GEOTRACES项目的所有三个主题相关，因为钡可以用于：研究海洋中的化学循环；海洋边界微量元素交换；并推断过去的环境条件。在这里收集到的数据将是钡同位素的第一个同类数据，并将阐明这种元素的地球化学循环。此外，将这项工作作为GEOTRACES项目的一部分，通过提供丰富的解释框架，将最大限度地提高钡同位素数据的投资回报。该项目旨在了解内部循环和边界过程之间的相互作用如何设置太平洋盆地尺度的钡浓度和同位素分布。尽管具有类似营养物的溶解剖面，但海洋钡循环与主要藻类营养物具有根本不同的边界条件：钡循环不是由有机物的产生驱动，而是由其再矿化驱动。海洋“边缘地带”下沉的有机物的呼吸作用释放二氧化碳，使营养物质矿化，并促进微米级重晶石晶体的沉淀。由于重晶石是海水中颗粒钡的主要载体，因此海洋中钡的丰度和同位素组成与生物碳泵“暗端”的全球碳和营养循环有关。在这里收集的数据将用于测试一系列前所未有的海洋学条件下的假设：颗粒物质的形成、输出和再生以及与海底过程的联系；边界源对区域和全球微量元素和同位素收支的重要性在低氧带假定的软金属硫化物的形成；以及深海中神秘悬浮粒子的起源。该提案将通过培训本科生研究人员，并通过与一个区域保护组织合作，为区域科学教育者举办研讨会和客座讲座，为教育做出贡献。

The goal of the international GEOTRACES program is to understand the distributions of trace chemical elements and their isotopes in the oceans. This project would measure stable isotopes of barium on a 2018 U.S. GEOTRACES expedition in the Pacific Ocean. Barium is a trace element whose distribution is relevant to all three themes of the GEOTRACES program, as barium can be used to: study chemical cycling within the oceans; trace exchanges of elements at ocean boundaries; and infer past environmental conditions. The data collected here will be the first of their kind for barium isotopes and will illuminate the geochemical cycle of this element. Moreover, conducting this work as part of the GEOTRACES program will maximize the return on investment in the barium isotope data by providing a rich interpretative framework.This project seeks to understand how the interplay between internal cycling and boundary processes sets basin-scale barium concentration and isotopic distributions in the Pacific Ocean. Despite possessing a nutrient-like dissolved profile, marine barium cycling has a fundamentally different boundary condition to the major algal nutrients: barium cycling is not driven by production of organic matter but rather by its remineralization. Respiration of sinking organic matter in the ocean's 'twilight zone' releases carbon dioxide, mineralizes nutrients, and promotes precipitation of micron-size crystals of barite. Since barite is the major vector of particulate barium in seawater, the abundance and isotopic composition of barium in the oceans is tied to global carbon and nutrient cycling at the 'dark end' of the biological carbon pump. The data collected here will be used to test hypotheses across an unprecedented range of oceanographic conditions regarding: the formation, export, and regeneration of particulate material and the connection to seafloor processes; the importance of boundary sources to regional and global trace element and isotope budgets; the formation of putative soft-metal sulfides in oxygen-minimum zones; and the origin of enigmatic suspended particles in the deep open ocean. This proposal will contribute to education by training undergraduate research fellows and through presentation of seminars and guest lectures to regional science educators through collaboration with a regional conservation organization.