Collaborative Research: EAGER: Particle-specific DNA sequencing to directly observe ecological mechanisms of the biological pump

碳被生长在表层海洋中的浮游植物固定在有机物中，当颗粒和有机体下沉时，碳自然地隔离在海洋内部：这一过程被称为“生物泵”。由于其对全球碳循环的公认影响，海洋科学家对生物泵的研究已有数十年之久。然而，我们仍然没有对潜在的过程有足够的了解，以准确地量化和预测碳循环。这种不确定性在很大程度上源于无法将表层海洋中的特定浮游生物与从表层海洋下沉的颗粒类型直接联系起来。为了解决生物泵研究中缺失的这一环节，这项工作将直接观察浮游生物是如何通过嵌入跨学科现场计划的新的、特定于颗粒的观测方法运出表层海洋的，该计划将精细地解析上层海洋浮游生物群体以及由此产生的跨空间和跨时间的碳沉降量。生物在不同类型的下沉颗粒中的遗传特性将通过对单独收集的颗粒的遗传内容进行测序来确定。这一分子方法的新应用将明确地将太平洋五个地点的表面浮游生物与下沉颗粒联系起来。这项工作有可能通过确定地表生态系统和下沉的碳颗粒之间以前未知的联系来改变我们对生物泵的理解。由于这项工作嵌入了一个跨学科的领域计划，包括生物地球化学建模人员和遥感科学家，这些数据将直接输入到生物泵的新模型中，从而提高我们量化和预测海洋碳吸收的能力。该项目将培养1名研究生和至少2名本科生。研究结果将通过博客、视频和参与机构的公共交流渠道传达给非科学公众。准确预测全球碳循环需要了解连接表层浮游生物群落和从表层海洋下沉颗粒碳通量(输出)的具体过程，但目前生物泵研究的方法学范式并不直接观察这些过程。该项目将全面确定谁从表层海洋输出，以及如何利用嵌入采样计划的新的粒子分辨光学和分子技术，该采样计划以高时间和空间分辨率表征出口事件。调查表明，表层水中不同类型的浮游生物是通过不同的出口途径运出表层海洋的，了解这些联系是全球碳循环建模的关键知识。如果成功，这项工作有可能通过直接确定将表层浮游生物与颗粒输出联系起来的机制来改变我们对生物泵的概念理解，而不依赖于批量采样方案和大规模相关分析。在2017年1月至2月从夏威夷到西雅图的邮轮上，将在五个开阔海域地点研究颗粒出口环境。表面浮游生物群落的特征将是卫星观测、连接在自由漂移的连续仿形走钢丝机上的传感器、原位全息相机、显微镜以及对18S和16S rRNA基因片段进行测序的组合。输出的颗粒将同时被各种专门的沉积物捕集器捕获，其特征将通过确定单个颗粒类型的遗传含量与其在表面群落中的来源直接相关。将从凝胶层中分离出单个颗粒，并对16S和18S rRNA基因片段进行扩增和测序。这项工作将首次将分子方法与特定于颗粒的观察相结合，从而能够同时识别哪些有机体被出口，以及负责这些有机体出口的过程。

Carbon is fixed into organic matter by phytoplankton growing in the surface ocean, and is naturally sequestered in the ocean interior when particles and organisms sink: a process called the "biological pump." Because of its recognized influence on the global carbon cycle, ocean scientists have studied the biological pump for decades. However, we still do not have a sufficient understanding of the underlying processes to accurately quantify and predict carbon cycling. Much of this uncertainty stems from an inability to directly link specific plankton in the surface ocean with the types of particles sinking out of the surface ocean. To address this missing link in biological pump research, this work will directly observe how plankton are transported out of the surface ocean using novel, particle-specific observational approaches embedded within an interdisciplinary field program that will finely resolve upper ocean plankton groups and the resulting amount of sinking carbon across space and in time. The genetic identity of organisms within different types of sinking particles will be determined by sequencing the genetic contents of individually collected particles. This new application of a molecular method will definitively link surface plankton with sinking particles at five locations across the Pacific Ocean. This work has the potential to transform our understanding of the biological pump by identifying previously unknown links between surface ecosystems and sinking carbon particles. Because this work is embedded within an interdisciplinary field program, including biogeochemical modelers and remote sensing scientists, these data will feed directly into new models of the biological pump, improving our ability to quantify and predict carbon uptake by the ocean. This project will train 1 graduate student and at least 2 undergraduate researchers. Findings will be communicated to the non-scientific public through blogs, videos, and the public communication channels of participating institutions.Accurate prediction of the global carbon cycle requires an understanding of the specific processes that link surface plankton communities and sinking particulate carbon flux (export) out of the surface ocean, but current methodological paradigms in biological pump research do not directly observe these processes. This project will comprehensively determine who is exported from the surface ocean and how using new, particle-resolving optical and molecular techniques embedded within a sampling scheme that characterizes export events at high time and space resolution. The investigation suggests that different plankton types in the surface waters are transported out of the surface ocean by distinct export pathways, and that an understanding of these connections is critical knowledge for global carbon cycle modeling. If successful, this work has the potential to transform our conceptual understanding of the biological pump by directly identifying mechanisms that link surface plankton with particle export, without relying on bulk sampling schemes and large-scale correlation analysis. Particle export environments will be studied at five open ocean locations during a cruise from Hawaii to Seattle in January-February 2017. The surface plankton communities will be characterized by a combination of satellite observations, sensors attached to a free-drifting, continuously profiling WireWalker, an in situ holographic camera, microscopy, and by sequencing 18S and 16S rRNA gene fragments. Exported particles will simultaneously be captured by various specialized sediment traps and their characteristics will be directly related to their sources in the surface community by identifying the genetic contents of individual particle types. Individual particles will be isolated from gel layers and the 16S and 18S rRNA gene fragments will be amplified and sequenced. This work would, for the first time, combine molecular approaches with particle-specific observations to enable simultaneous identification of both which organisms are exported and the processes responsible for their export.