Quantification of Trichodesmium spp. vertical and horizontal abundance patterns and nitrogen fixation in the western North Atlantic

Trichodesmium spp 的定量。

• 批准号: 0925284
• 负责人: Dennis McGillicuddy
• 金额: $ 132.11万
• 依托单位: Woods Hole Oceanographic Institution
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2009
• 资助国家: 美国
• 起止时间: 2009-12-01 至 2013-09-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0925284&HistoricalAwards=false
• 关键词: Quantification; Trichodesmium; spp.; vertical; horizontal

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).The diazotroph Trichodesmium spp. constitutes a major pathway of nitrogen flow into marine planktonic ecosystems, but estimates of its impact on global nitrogen budgets vary widely. Sampling is made difficult by the fragility of the organism with the consequence that Trichodesmium spp. are difficult to manipulate in both field and laboratory experiments. Optical methods that sample the organism nondestructively are thus appealing. A recent transatlantic survey using the Video Plankton Recorder (VPR) revealed unexpectedly high abundance of Trichodesmium spp. at depth, suggesting the vertical distribution of the organism within theeuphotic zone may be more uniform than previously thought. Application of a simple bio-optical model of productivity to the observed profile of abundance suggests the depth-integrated nitrogen fixation rate could be three to five times higher than that based on the canonical profile of exponential decrease in abundance with depth. However, the observations described in Davis and McGillicuddy (2006) come from a latitude range where Trichodesmium spp. are not especially abundant. This raises a key question: is there a similar vertical distribution in waters further to the south, where Trichodesmium spp. are an order of magnitude more abundant overall? If so, are the deep populations actively fixing nitrogen? If so, the implications for the global nitrogen budget would be substantial.To answer these questions, the PIs will survey the waters of the southern Sargasso Sea and tropical Atlantic on two cruises. Along-track VPR measurements will be used to document the abundance and distribution of the organism on the scale of meters to thousands of kilometers. Standard hydrographic station work will provide for comparison of VPR-based estimates with microscope counts, as well as some additional in situ optical methods. A combination of nifH gene expression assays and direct determinations of N2-fixation rates will be made to assess whether or not the deep populations are actively fixing nitrogen.These observations will be synthesized in the context of an eddy-resolving numerical model. This will permit investigation of the mechanisms controlling the vertical and horizontal distribution and abundance of Trichodesmium spp. at multiple scales, including the enigmatic association of relative maxima in abundance with anticyclonic eddies. Moreover, integration of these observations into the numerical model will facilitate revised estimates of nitrogen fixation by Trichodesmium spp. in the North Atlantic.The intellectual merit of this project is its interdisciplinary approach (physics and biology), advanced observational techniques (optical imaging, molecular methods) and integrated analysis in the context of state-of-the-art coupled physical-biogeochemical models. This project will provide new insights into the complex oceanographic phenomena regulating nitrogen fixation and its impact on biogeochemical cycling at the scale of an ocean basin.Broader impacts of this project include training of graduate and undergraduate students, and enhancement of an existing web-based outreach program www.whyville.net geared toward promoting science literacy in children ages 8-14.

该奖项是根据2009年美国复苏和再投资法案（公法111-5）资助的。这是氮流入海洋浮游生态系统的一个主要途径，但其对全球氮收支的影响的估计差异很大。由于生物体的脆弱性，取样变得困难，结果是束毛藻属物种（Trichodesmium spp.）在野外和实验室实验中都难以操作。因此，非破坏性地对生物体进行采样的光学方法很有吸引力。最近一项使用视频浮游生物记录仪（VPR）进行的跨大西洋调查显示，束毛藻属物种的丰度出乎意料地高。在深度，这表明有机体在真光层内的垂直分布可能比以前认为的更均匀。一个简单的生物光学模型的生产力的应用程序所观察到的配置文件的丰度表明，深度集成固氮率可能是三至五倍高于基于典型的配置文件的指数下降的丰度与深度。然而，Davis和McGillicuddy（2006）中描述的观测来自于束毛藻属物种（Trichodesmium spp.）并不是特别丰富。这就提出了一个关键问题：在更南边的沃茨是否也有类似的垂直分布，那里有束毛藻属的物种。总体上是一个数量级的更丰富？如果是的话，深层种群是否在积极地固氮？为了回答这些问题，研究人员将在两次航行中调查南马尾藻海和热带大西洋的沃茨。沿轨道VPR测量将用于记录米到数千公里尺度上的生物体的丰度和分布。标准水文站的工作将提供基于VPR的估计与显微镜计数的比较，以及一些额外的现场光学方法。nifH基因表达测定和固氮率的直接测定相结合，将作出评估是否深层人口积极固定nitrogen.These意见将被合成的背景下，涡分辨数值模式。这将允许调查的机制控制的垂直和水平分布和丰富的束毛藻属。在多个尺度上，包括反气旋涡旋的相对最大丰度的神秘关联。此外，将这些观测结果整合到数值模型中，将有助于修订束毛藻固氮的估计值。这一项目的智力价值在于其跨学科方法（物理学和生物学）、先进的观测技术（光学成像、分子方法）以及结合最先进的物理-地球化学耦合模型进行的综合分析。该项目将提供新的见解，以复杂的海洋学现象调节固氮及其对海洋盆地尺度的地球化学循环的影响。该项目的更广泛的影响包括培训研究生和本科生，并加强现有的基于网络的推广计划www.whyville.net，旨在促进8-14岁儿童的科学素养。