Collaborative Research: Isotopic Indicators for Mechanisms of Organic Matter Degradation in the Northeast Pacific (EXPORTS)

生物泵在很大程度上负责将有机碳从表面垂直输送到海洋内部。然而，只有一小部分在地表水中产生的有机物质被隔离在深海中。其余的被细菌和更大的有机体消耗或呼吸。这项拟议工作的首要目标是表征细菌与大型有机体对有机物质随深度降解的相对影响。在亚热带太平洋最新结果的指导下，研究人员将使用不同氨基酸中氮的稳定同位素的测量(氨基酸的化合物特定同位素分析，称为AA-CSIA)，以及不同形式氨基酸的丰度的测量，以及这些分析得出的其他参数，以确定不同的降解过程如何影响大小颗粒的分配和通量。通过提高AA-CSIA技术的解释能力，研究人员建议确定：1)微生物和浮游动物消费对亚北极东北太平洋生物碳泵效率的相对重要性，以及2)经过微生物改变的小颗粒有多少为水中浮游动物的新陈代谢提供燃料。这项工作利用了现有的综合实地计划(NASA出口)，该计划专门侧重于建立一个预测框架，将表层海洋属性与有机碳的垂直通量联系起来。作为出口计划的一部分，将在生物泵的所有方面收集大量数据，这将有助于开发和解释研究人员的氨基酸同位素工具。结果将通过制作和发行几集海洋之声广泛传播，这是一档地方电视节目，将在夏威夷和许多太平洋岛屿播出。剧集还将发布在网上，并通过社交媒体向南佛罗里达州社区宣传。该项目将支持迈阿密大学的一名博士生和一名本科生，该大学为25%的拉美裔人口服务，以及一名硕士学生和一名本科生在夏威夷大学，这是一所指定的少数族裔服务机构。拟议的工作引入了一个新的地球化学框架，以区分海洋有机质中微生物和浮游动物的变化。这种方法以来自亚热带太平洋的样品为试点，直接询问未经修正的下沉物质，使用氨基酸化合物特定同位素分析(AA-CSIA)来确定微生物和浮游动物降解路径的累进和累积影响。拟议的工作(1)将扩展这一解释框架，以明确定义末端成员的特征，如粪便颗粒，并将这一改进的方法应用于亚北极东北太平洋的一个研究地点，以(2)通过对比生产力和通量衰减的垂直长度尺度来确定海洋位置的退化机制的垂直进展，以及(3)确定在不同的碳通量条件下，微生物降解的生物量是否对于为水中后生动物提供燃料至关重要。拟议的工作将与美国国家航空航天局出口项目合作，在海洋站Papa时间序列站点进行。与该计划的合作为完善AA-CSIA解释提供了一个独特的机会，同时还提供了密集的数据收集，定义了生产率、粒度分布和通量以及众多生物参数。在比较亚热带和亚北极太平洋地区时，拟议的工作将测试生产力和浮游生物群落结构的差异如何影响从表层到中层深处微生物和浮游动物对植物碎屑的垂直消耗和变化模式。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

The biological pump is largely responsible for the vertical transport of organic carbon from the surface to the ocean interior. However, only a small fraction of organic material produced in surface waters is sequestered in the deep ocean. The rest is consumed, or respired, by bacteria and larger organisms. The overarching goal of the proposed work is to characterize the relative influences of bacteria versus larger organisms on the degradation of organic material with depth. Guided by recent results from the subtropical Pacific, the investigators will use measurements of stable isotopes of nitrogen in different amino acids (compound-specific isotopic analysis of amino acids, known as AA-CSIA), along with measurements of the abundances of different forms of amino acids, and other parameters derived from these analyses to identify how the partitioning and flux of large and small particles are affected by different degradation processes. By improving the interpretive power of the AA-CSIA technique the investigators propose to determine: 1) the relative importance of microbial and zooplankton consumption on the efficiency of the biological carbon pump in the subarctic northeast Pacific, and 2) how much microbially-altered small particles fuel the metabolisms of mid-water zooplankton. This work capitalizes on an existing, comprehensive field program (NASA EXPORTS) specifically focused on building a predictive framework relating surface ocean properties to the vertical flux of organic carbon. The tremendous amount of data to be collected on all aspects of the biological pump as part of the EXPORTS program will aid the development and interpretation of the investigators' amino acid isotopic tool. Results will be broadly communicated via production and distribution of several episodes of Voice of the Sea, a local television program that will air in Hawaii and across many Pacific islands. Episodes also will be posted online and publicized through social media to the south Florida community. This project will support a Ph.D. student and an undergraduate student at University of Miami, which serves a 25% Hispanic population, and an M.S. student and an undergraduate student at University of Hawaii, which is a designated minority-serving institution.The proposed work introduces a new geochemical framework to distinguish microbial versus zooplankton alteration of marine organic matter. Piloted on samples from the subtropical Pacific, this approach interrogates unamended sinking material directly, using amino acid compound-specific isotopic analysis (AA-CSIA) to determine the progressive, cumulative impact of microbial and zooplankton degradative pathways. The proposed work (1) will extend this interpretive framework to explicitly define end-member signatures such as fecal pellets and will apply this refined method to a study site in the subarctic northeast Pacific to (2) determine the vertical progression of degradative mechanisms in an oceanographic location with contrasting productivity and vertical length scales of flux attenuation and (3) determine whether microbially- degraded biomass is important for fueling midwater metazoans under contrasting carbon flux conditions. The proposed work will be conducted in collaboration with the NASA EXPORTS program at the Ocean Station Papa time-series site. Teaming with this program presents a unique opportunity to refine AA-CSIA interpretation in parallel with intensive data collection defining productivity, particle size distribution and flux, and numerous biological parameters. In comparing subtropical and subarctic Pacific locations, the proposed work will test how differences in productivity and plankton community structure influence vertical patterns of consumption and alteration of phytodetritus by microbes and zooplankton, from surface to mesopelagic depths.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.