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

碳被生长在海洋表面的浮游植物固定在有机物中，当颗粒和有机体下沉时，碳被自然地隔离在海洋内部：这个过程被称为“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进行了数十年的研究。然而，我们仍然没有足够的了解潜在的过程，以准确量化和预测碳循环。这种不确定性很大程度上源于无法将海洋表层的特定浮游生物与海洋表层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从海洋表面运输出来的，使用跨学科领域项目中嵌入的新颖、特定粒子的观测方法，该项目将精细地解决上层海洋浮游生物群体和由此产生的跨空间和时间的下沉碳量。不同类型沉降颗粒内生物的遗传特性将通过对单个收集颗粒的遗传内容进行测序来确定。这种分子方法的新应用将明确地将太平洋五个地点的表层浮游生物与下沉颗粒联系起来。这项工作有可能通过识别地表生态系统和下沉碳颗粒之间以前未知的联系来改变我们对生物泵的理解。因为这项工作是一个跨学科的领域项目，包括生物地球化学建模师和遥感科学家，这些数据将直接输入生物泵的新模型，提高我们量化和预测海洋碳吸收的能力。本项目将培养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沟通渠道传达给非科学公众。准确预测全球碳循环需要了解将表层浮游生物群落与海洋表层下沉颗粒碳通量（输出）联系起来的具体过程，但目前生物泵研究的方法范式并没有直接观察这些过程。该项目将全面确定谁从海洋表面出口，以及如何使用嵌入在采样方案中的新型粒子分辨光学和分子技术，以高时间和空间分辨率表征出口事件。研究表明，地表水中不同类型的浮游生物通过不同的出口途径被运输出表层海洋，了解这些联系对全球碳循环建模至关重要。如果成功，这项工作有可能通过直接识别将表面浮游生物与颗粒出口联系起来的机制来改变我们对生物泵的概念理解，而不依赖于大量采样方案和大规模相关分析。在2017年1 - 2月从夏威夷到西雅图的巡航期间，将在五个开放的海洋地点研究粒子出口环境。海面浮游生物群落的特征将由卫星观测、附着在自由漂流的传感器、连续分析的WireWalker、原位全息相机、显微镜和18S和16S rRNA基因片段测序相结合来描述。输出的颗粒将同时被各种专门的沉积物捕集器捕获，它们的特征将通过识别单个颗粒类型的遗传含量与它们在地表群落中的来源直接相关。单个颗粒将从凝胶层中分离出来，16S和18S rRNA基因片段将被扩增和测序。这项工作将首次将分子方法与特定粒子观察相结合，从而能够同时确定哪些生物被出口以及导致它们出口的过程。

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.