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

国际地学研究计划的目标是了解海洋中痕量化学元素及其同位素的分布。该项目将在2018年美国在太平洋进行的地理追踪探险中测量稳定的钡同位素。钡是一种微量元素，其分布与GEOTRACES计划的所有三个主题有关，因为钡可用于：研究海洋内的化学循环；追踪海洋边界上的元素交换；以及推断过去的环境条件。这里收集的数据将是此类数据中的第一个，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计划的一部分进行，将通过提供丰富的解释框架来最大化对钡同位素数据的投资回报。该项目试图了解内部循环和边界过程之间的相互作用如何决定太平洋盆地尺度的钡浓度和同位素分布。尽管具有营养物样的溶解剖面，但海洋钡循环与主要藻类营养物质有着根本不同的边界条件：钡循环不是由有机质的生产驱动的，而是由其再矿化驱动的。海洋“黄昏地带”下沉的有机物的呼吸作用释放二氧化碳，矿化营养物质，促进微米级重晶石晶体的沉淀。由于重晶石是海水中颗粒态Ba2+的主要载体，海洋中Ba2+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。这里收集的数据将被用来检验各种前所未有的海洋学条件下的假设：微粒物质的形成、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；假定的软金属硫化物在最低含氧区的形成；以及深海神秘悬浮粒子的来源。这项建议将通过培训本科生研究人员以及通过与区域保护组织合作向区域科学教育工作者举办研讨会和客座讲座来促进教育。

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.