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

有机物质的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，只有一小部分由地表水中的生物产生的有机物质进入了深海。其余的可能被细菌或更大的生物分解或消耗（呼吸）；每个过程的作用仍然存在疑问。在最近太平洋研究结果的指导下，研究人员将利用氨基酸中碳和氮的稳定同位素来确定北大西洋春季水华中新鲜藻类物质、浮游动物粪便和细菌的输入。有了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，这样他们就可以用来帮助预测全球碳运输的模式。这项工作将是一个大型海洋野外项目（NASA EXPORTS）的一部分。在这个项目中收集的大量数据将有助于发展和解释同位素模型。为了广泛分享调查结果，调查人员将制作并发行几集《海洋之声》（Voice of the Sea），这是一档地方电视节目，将在夏威夷和太平洋岛屿播出。剧集将在网上发布，并通过社交媒体向南佛罗里达社区宣传。该项目将支持迈阿密大学（University of Miami）的一名博士生和一名本科生，该大学为25%的西班牙裔人口提供服务，以及夏威夷大学（University of Hawaii）的一名博士生和一名本科生，夏威夷大学是一所指定的少数族裔服务机构。拟议的工作将使用独立于孵化技术或代谢率测量的经验方法，评估粪便中包装有机物、颗粒分解、微生物改造和浮游动物饮食利用对不同海洋省份颗粒通量垂直模式的相对重要性。根据他们在太平洋相对低通量环境中的现有工作，研究人员开发了两种新兴模型：(1)混合模型，使用氨基酸的化合物特异性同位素分析（AA-CSIA）来估计植物碎屑、粪便颗粒和微生物降解颗粒的组成，从而可以检测这些物质的垂直变化机制和大小分布；(2)进入深海的碳通量与中远洋食物网对小颗粒、降解颗粒的依赖之间存在反比关系。在这个项目中，研究人员将对这两个模型进行测试，方法是将相同的方法应用于最近NASA EXPORTS在北大西洋春季开花的高生产率、高通量状态下的实地研究。在亚北极太平洋进行的第一次EXPORTS实地研究提供了开发模型所依据的一些材料。研究人员新开发的同位素指标的应用和改进将有助于开发一个全球通用的同位素框架，用于评估颗粒有机物的降解历史及其与中远洋膳食资源的关系，包括通常不被视为后生动物膳食资源的微生物降解的小颗粒。这项工作利用了现有的综合实地项目，特别侧重于建立一个将海洋表面特性与有机碳垂直通量联系起来的预测框架。拟议的工作直接解决了EXPORTS科学问题2：是什么控制着光照良好的海洋表面下有机物垂直转移的效率？这项工作的结果还将为碳通量组成和远洋食物网资源的全球模型提供观测比较。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值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.