Collaborative Research: Shelfbreak frontal dynamics: mechanisms of upwelling, net community production, and ecological implications

中大西洋湾的大陆架断裂支撑着一个多产和多样化的生态系统。目前的范例表明，这种生产力是由大陆架断裂前沿的几种上升流机制驱动的。这种上升流提供的营养物质刺激了浮游植物的初级生产，这反过来又促进了更高营养水平的生产。虽然在某些情况下观察到浮游植物生物量的局部增强，但奇怪的是，从卫星和船上取样的时间平均测量中都没有这种特征。为什么浮游植物生物量不会因为上升流而平均增加？一种假设是，浮游动物的放牧阻止了生物量在季节性和较长时间尺度上的积累，将过剩的产量转移到更高的营养水平，从而促进了生态系统的整体生产力。然而，另一种可能性是，由于水中测量的分辨率相对较低，而且锋面增强可能发生在卫星可观测的深度以下，这些高度间歇性过程的净影响在长期观测手段中没有得到充分体现。部署在新英格兰南部的海洋观测倡议先锋阵列为检验这些假设提供了一个独特的机会。系泊仪器和自主水下航行器的结合将以前所未有的空间和时间分辨率促进对锋面系统的观测。这将提供一个理想的四维（时空）环境，在这个环境中进行详细的锋面动力学和浮游生物群落研究，需要检查控制该锋面系统中浮游植物种群的机制。该项目还将：(1)通过研究生和本科生参与研究来促进教学、培训和学习；(2)通过公共论坛、印刷媒体和实地工作的视频纪录片等手段提供广泛的信息传播；(3)通过提供基于科学的沿海生态系统管理所需的知识，为改善社会福祉和提高经济竞争力做出贡献。特别强调通过商业渔业研究基金会与渔业建立联系。研究人员将进行三次巡航，以获得先锋阵列内部的物理、化学和生物特性。营养分布将与水文分析一起分析，以探测锋面上升流的特征和相关的营养供应。研究人员预计，营养供应的增加将导致浮游植物组合的变化，这些变化将通过传统的流式细胞仪、成像流式细胞仪（imaging FlowCytobot， IFCB）、光学成像（Video Plankton Recorder， VPR）、传统的显微镜方法和色素分析来量化。浮游动物将分别用IFCB和VPR来测量从微型到中型浮游动物的大小类别，并进行微观分析。对上升流的生物反应将通过测量初级生产力、浮游动物放牧率和净群落产量来评估。这些观察结果将在一个物理-生物耦合模型的背景下进行综合，以检验可能解释先前观察结果的两个假设：(1)食草动物介导的控制和(2)欠采样。后播模拟也将用于诊断各种上升流机制的相对重要性。这项工作的智力价值源于我们的跨学科方法，先进的观察技术，以及在最先进的耦合模型背景下的综合分析。该项目将解决关于重要生态系统的水动力学和生产力的长期问题，从而提高对复杂大陆架制度中物理-生物相互作用的理解。鉴于锋面系统在全球沿海海洋中的重要性，预计所获得的知识将在所研究的特定区域之外具有广泛的适用性。

The continental shelf break of the Middle Atlantic Bight supports a productive and diverse ecosystem. Current paradigms suggest that this productivity is driven by several upwelling mechanisms at the shelf break front. This upwelling supplies nutrients that stimulate primary production by phytoplankton, which in turn leads to enhanced production at higher trophic levels. Although local enhancement of phytoplankton biomass has been observed in some circumstances, such a feature is curiously absent from time-averaged measurements, both from satellites and shipboard sampling. Why would there not be a mean enhancement in phytoplankton biomass as a result of the upwelling? One hypothesis is that grazing by zooplankton prevents accumulation of biomass on seasonal and longer time scales, transferring the excess production to higher trophic levels and thereby contributing to the overall productivity of the ecosystem. However, another possibility is that the net impact of these highly intermittent processes is not adequately represented in long-term means of the observations, because of the relatively low resolution of the in-water measurements and the fact that the frontal enhancement can take place below the depth observable by satellite. The deployment of the Ocean Observatories Initiative (OOI) Pioneer Array south of New England has provided a unique opportunity to test these hypotheses. The combination of moored instrumentation and autonomous underwater vehicles will facilitate observations of the frontal system with unprecedented spatial and temporal resolution. This will provide an ideal four-dimensional (space-time) context in which to conduct a detailed study of frontal dynamics and plankton communities needed to examine mechanisms controlling phytoplankton populations in this frontal system. This project will also: (1) promote teaching, training and learning via participation of graduate and undergraduate students in the research , (2) provide a broad dissemination of information by means of outreach in public fora, printed media, and a video documentary of the field work, and (3) contribute to improving societal well-being and increased economic competitiveness by providing the knowledge needed for science-based stewardship of coastal ecosystems, with particular emphasis on connecting with the fishing industry through the Commercial Fisheries Research Foundation.The investigators will conduct a set of three cruises to obtain cross-shelf sections of physical, chemical, and biological properties within the Pioneer Array. Nutrient distributions will be assayed together with hydrography to detect the signature of frontal upwelling and associated nutrient supply. The investigators expect that enhanced nutrient supply will lead to changes in the phytoplankton assemblage, which will be quantified with conventional flow cytometry, imaging flow cytometry (Imaging FlowCytobot, IFCB), optical imaging (Video Plankton Recorder, VPR), traditional microscopic methods, and pigment analysis. Zooplankton will be measured in size classes ranging from micro- to mesozooplankton with the IFCB and VPR, respectively, and also with microscopic analysis. Biological responses to upwelling will be assessed by measuring rates of primary productivity, zooplankton grazing, and net community production. These observations will be synthesized in the context of a coupled physical-biological model to test the two hypotheses that can potentially explain prior observations: (1) grazer-mediated control and (2) undersampling. Hindcast simulations will also be used to diagnose the relative importance of the various mechanisms of upwelling. The intellectual merit of this effort stems from our interdisciplinary approach, advanced observational techniques, and integrated analysis in the context of a state-of-the-art coupled model. The project will address longstanding questions regarding hydrodynamics and productivity of an important ecosystem, leading to improved understanding of physical-biological interactions in a complex continental shelf regime. Given the importance of frontal systems in the global coastal ocean, it is expected that knowledge gained will have broad applicability beyond the specific region being studied.