Collaborative Research: Nitrogen fixation, nutrient supply and biological production in the Gulf of Mexico

该项目将研究物理、化学和生物因素在向墨西哥湾温带海岸和近海水域供应氮这一基本营养物质方面的相互作用。墨西哥湾是一个经济重要但研究不足的边缘海，拥有主要的商业和休闲渔业以及大量的化石燃料矿藏。重氮营养(固氮)蓝藻定期在墨西哥湾近海和沿海水域繁殖，有限的数据表明，它们为远洋食物网贡献了大量的氮和碳。这些重氮菌也可能在向其他生物供应氮的过程中发挥关键作用，包括鱼毒赤潮甲藻。尽管它很重要，但目前人们对促进墨西哥湾氮固定的因素或不同物理和生物过程在创造有利于限制水体中氮的条件方面的相对重要性知之甚少。墨西哥湾受到河流输入和平流过程的强烈影响，为研究营养动态、生产力的物理强迫、陆地-海洋联系以及土地利用和气候变化对海洋生态系统的潜在影响提供了一个极好的模式系统。墨西哥湾相对较小的盆地为量化和研究与广泛的其他沿海和海洋系统相关的物理、化学和生物过程之间的相互作用提供了机会。土地利用和气候变化可能影响墨西哥湾的循环和水文地理，以及河流输入的大小和性质，所有这些都对墨西哥湾的生物地球化学产生不确定的影响。这项研究将为这些进程提供及时的见解，并将为评估和预测未来土地利用和气候变化对系统的影响提供一个了解基线。这个项目将对我们理解调节氮气固定的因素及其在支持温带水域生物群中的作用做出重要贡献。这项工作包括以下具体目标：1.确定墨西哥湾的主要重固氮菌群，并表征它们在不同地区和水团中的分布和活动。量化平流过程、中尺度特征和河流输入对墨西哥湾营养限制和氮素固定的影响，并评估受这些过程影响的不同区域的氮素固定的控制和不同区域的重氮菌组合的时空生态位分异程度。使用卫星数据和物理模型在空间上扩大我们的测量范围，并评估墨西哥湾固定氮气的区域意义。研究人员还将使用物理/生物耦合模型来探索物理强迫的可变性，以及可能的土地利用和气候变化情景在改变墨西哥湾的营养动态和固定氮气方面的潜在影响。研究人员和他们的机构对本科生和研究生教育有着坚定的承诺。该项目包括对研究生、技术员和本科生的支持。除了同行评议的论文和网站外，还将利用针对K-12教师的研讨会，以及让高中教师参与研究的计划，在当地社区广泛传播该项目的成果。调查人员致力于增加海洋科学界的多样性，并在其机构积极开展招聘和培训工作。

This project will study the interplay of physical, chemical, and biological factors in supplying nitrogen, an essential nutrient, to temperate coastal and offshore waters of the Gulf of Mexico. The Gulf is an economically important but understudied marginal sea with major commercial and recreational fisheries as well as extensive fossil fuel deposits. Diazotrophic (N2-fixing)) cyanobacteria bloom regularly in offshore and coastal waters of the Gulf and the limited data suggest that they contribute significant quantities of both nitrogen and carbon to the pelagic food web. These diazotrophs may play also a critical role in supplying N to other organisms, including the ichthyotoxic red tide dinoflagellate Karenia brevis. Despite its importance, little is currently known of the factors that promote N2-fixation in the Gulf or the relative significance of different physical and biological processes in creating conditions that favor N limitation in the water column. The Gulf of Mexico is strongly influenced by both riverine inputs and advective processes, providing an excellent model system for studying nutrient dynamics, physical forcing of productivity, terrestrial-oceanic linkages, and the potential impact of land use and climate change on marine ecosystems.The relatively small basin of the Gulf of Mexico provides an opportunity to quantify and study interactions among physical, chemical, and biological processes relevant to a broad range of other coastal and oceanic systems. Land-use and climate change are likely to affect the circulation and hydrography of the Gulf, as well as the magnitude and nature of riverine inputs, all with uncertain impacts on the biogeochemistry of the Gulf of Mexico. This research will provide timely insights into these processes and will generate a baseline of understanding for evaluating and predicting the impact of future land use and climate changes in the system. This project will make an important contribution to our understanding of the factors that regulate N2-fixation and its role in supporting the biota in temperate waters. The following specific goals are included in the work:1. Identify the major diazotroph groups in the Gulf of Mexico and characterize their distribution and activity in different regions and water masses.2. Quantify the impact of advective processes, mesoscale features, and riverine inputs on nutrient limitation and N2-fixation in the Gulf, and evaluate the controls on N2-fixation and the degree of spatial and temporal niche differentiation among diazotroph assemblages in different regions affected by these processes.3. Use satellite data and physical models to scale up our measurements spatially and to evaluate the regional significance of N2-fixation in the Gulf of Mexico. The researchers will also use a coupled physical/biological model to explore variability in the physical forcing and the potential impact of likely land use and climate change scenarios in altering nutrient dynamics and N2-fixation in the Gulf of Mexico.The investigators and their institutions have a strong commitment to undergraduate and graduate education. This project includes support for graduate students, a technician, and undergraduates. In addition to peer-reviewed papers and websites, workshops aimed at K-12 teachers, and a program involving high school teachers in research will be used to disseminate the results of this project broadly in the local community. The investigators are committed to increasing the diversity of the ocean science community and are active in recruiting and training efforts at their institutions.