Collaborative Research: Isotopic Indicators for Mechanisms of Organic Matter Degradation under High Productivity and High Carbon Flux Conditions (EXPORTS)

有机物质向下沉降将碳从海洋表面输送出去，这是一个被称为生物泵的过程的一部分。然而，在表层水域中，生物产生的有机物质中只有一小部分进入深海。其余的可以被细菌或更大的有机体碎裂或消耗(呼吸)；每个过程的作用仍然存在疑问。在来自太平洋的最新结果的指导下，研究人员将使用氨基酸中碳和氮的稳定同位素来识别北大西洋春季水华时向生物泵输入的新鲜藻类物质、浮游动物粪便和细菌。利用来自不同地点的数据，研究人员将测试和开发他们的同位素模型，以便它们可以用来帮助预测全球碳运输模式。这项工作将是一个大型海洋实地项目(NASA出口)的一部分。在这个项目中收集的大量数据将有助于同位素模型的开发和解释。为了更广泛地分享结果，调查人员将制作和发行几集《海洋之声》，这是一档将在夏威夷和太平洋岛屿播出的地方电视节目。剧集将被发布在网上，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%的拉美裔人口提供服务，以及夏威夷大学的一名博士生和一名本科生，夏威夷大学是一家指定的少数族裔服务机构。拟议的工作将评估在粪便材料中包装有机物、颗粒分解、微生物改造和浮游动物饮食对不同海洋省份颗粒物通量垂直模式的相对重要性，使用独立于孵化技术或代谢率测量的经验方法。研究人员从他们在太平洋相对低通量环境中的现有工作开发出两个新的模式：(1)混合模式，利用特定化合物氨基酸同位素分析(AA-CSIA)估计植物碎屑、粪便颗粒和被微生物降解的颗粒组成，从而能够探测到这些物质的垂直变化机制和尺寸分布；(2)进入深海的碳通量与中海洋食物网对小型降解颗粒的依赖之间的反向关系。在这个项目中，研究人员将通过将相同的方法应用于NASA最近在北大西洋春季水华高生产率、高通量区域进行的出口实地研究来测试这两个模型。在亚北极太平洋进行的第一次出口实地研究提供了开发模型所用的一些材料。研究人员新开发的同位素指标的应用和改进将有助于制定一个全球通用的同位素框架，以评估颗粒状有机物的退化历史及其与中上层食物资源的关系，包括常常不被视为后生动物食物资源的微生物降解的小颗粒。这项工作利用了现有的综合性实地方案，这些方案专门侧重于建立一个将表层海洋性质与有机碳垂直通量联系起来的预测框架。这项拟议的工作直接解决了出口科学问题2：是什么控制了光线充足的表层海洋下有机物垂直转移的效率？这项工作的结果还将提供与全球碳通量组成和远洋食物网络资源模型的观察性比较。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 downward settling of organic material transports carbon out of the ocean surface, as part of a process called the biological pump. However, only a small fraction of organic material produced by organisms in surface waters makes it to the deep ocean. The rest can be fragmented or consumed (respired) by bacteria or larger organisms; the role of each process remains in question. Guided by recent results from the Pacific Ocean, the investigators will use the stable isotopes of carbon and nitrogen in amino acids to identify the input of fresh algal material, zooplankton feces, and bacteria to the biological pump in the North Atlantic spring bloom. With data from contrasting locations, the investigators will test and develop their isotopic models so they can be used to help predict global patterns in carbon transport. The work will be part of a large oceanographic field program (NASA EXPORTS). The tremendous amount of data collected in this program will aid the development and interpretation of the isotopic models. To share results broadly, the investigators will produce and distribute several episodes of Voice of the Sea, a local television program that will air in Hawaii and the Pacific islands. Episodes will be posted online and publicized through social media to the south Florida community. The project will support a Ph.D. student and an undergraduate student at University of Miami, which serves a 25% Hispanic population, and a Ph.D. student and an undergraduate student at University of Hawaii, a designated minority-serving institution.The proposed work will assess the relative importance of packaging organic matter in fecal material, particle disaggregation, microbial reworking, and zooplankton dietary usage on vertical patterns of particle flux across contrasting oceanic provinces, using empirical methods independent of incubation techniques or metabolic rate measurements. From their existing work in relatively low-flux environments of the Pacific Ocean, the investigators have developed two nascent models: (1) a mixing model that uses the compound-specific isotope analysis of amino acids (AA-CSIA) to estimate the phytodetritus, fecal pellet, and microbially degraded composition of particles, such that the vertical alteration mechanisms and size distribution of these materials can be detected; and (2) an inverse relationship between carbon flux into the deep ocean and the reliance of mesopelagic food webs on small, degraded particles. In this project, the investigators will test these two models by applying the same methods to the recent NASA EXPORTS field study in a high productivity, high flux regime, the North Atlantic spring bloom. The first EXPORTS field study in the subarctic Pacific provided some of the materials from which the models were developed. Application and refinement of the investigators’ newly developed isotopic indicators will enable development of a globally generalized isotopic framework for assessing the degradative history of particulate organic matter and its relationship to mesopelagic dietary resources, including small, microbially degraded particles that are often not accounted for as a metazoan dietary resource. This work capitalizes on existing, comprehensive field programs specifically focused on building a predictive framework relating surface ocean properties to the vertical flux of organic carbon. The proposed work directly addresses EXPORTS Science Question 2: What controls the efficiency of vertical transfer of organic matter below the well-lit surface ocean? The results of this work additionally will provide observational comparisons to global models of carbon flux composition and pelagic food web resources.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.