Collaborative Research: ETBC: Amazon iNfluence on the Atlantic: CarbOn export from Nitrogen fixation by DiAtom Symbioses (ANACONDAS)

合作研究：ETBC：亚马逊对大西洋的影响：DiAtom Symbioses 固氮产生的碳输出 (ANACONDAS)

• 批准号: 0934036
• 负责人: Deborah Steinberg
• 金额: $ 39.96万
• 依托单位: College of William & Mary Virginia Institute of Marine Science
• 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: 2009-10-01 至 2013-09-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0934036&HistoricalAwards=false
• 关键词: Collaborative; Research; ETBC; Amazon; iNfluence

The investigators hypothesize that large tropical river plumes with low N: P ratios provide an ideal niche for diatom-diazotroph assemblages (DDAs). They suggest that the ability of these organisms to fix N2 within the surface ocean is responsible for significant C export in the Amazon River plume. Their previous observations in the Amazon River plume helped reveal that blooms comprised of the endosymbiotic N2-fixing cyanobacterium Richelia and its diatom hosts (e.g. Hemiaulus) were a significant source of new production and carbon export. The previous work focused largely on the sensitivity of DDAs to external forcing from dust and riverine inputs, so the ecology of these organisms and the fate of their new production were largely unstudied. It is now known that DDAs are responsible for a significant amount of CO2 drawdown in the Amazon River plume, and floating sediment traps at 200 m measured 4x higher mass fluxes beneath the plume than outside the plume. This led the researchers to hypothesize that this greater export is due either to aggregation and sinking of DDAs themselves or to grazing of DDAs by zooplankton.In this study the researchers will undertake a suite of field, satellite and modeling studies aimed at understanding the ecology and tracing the fate of C and N fixed by DDAs and other phytoplankton living in the plume. By examining C and silicate (Si) export from offshore surface waters, through the upper oceanic food web, the mesopelagic, and down to the deep sea floor, they will quantify the impact of the Amazon River on biological processes that control C sequestration and the implications of these regional processes on C, N and Si budgets. The study will go beyond previous research because they will quantify 1) the distribution, nutrient demands, and activity of DDAs in the context of phytoplankton species succession, 2) the sensitivity of the CO2 drawdown to the mix of phytoplankton, 3) the grazing and aggregation processes contributing to the sinking flux, 4) the composition of this flux, and 5) the proportion of this material that reaches the seafloor. This effort truly represents a measure of C sequestration and pump efficiency. Ecological modeling will be used to place observational results from field studies and satellites into the context of the larger Atlantic basin with tropical climate variability on interannual and longer time scales.Intellectual Merit: The PIs have identified a potentially significant but poorly understood, ecosystem-controlled, climate-sensitive C sequestration pathway that seems to violate the expectation of an inefficient open-ocean biological pump. Since primary production fueled by allochthonous sources of N such as N2 fixation can drive a net, biologically mediated transfer of C from the atmosphere to the ocean, C sequestration by DDAs in the Amazon River plume is a regionally significant process. Because DDAs have been found in other tropical river systems, they may represent a globally significant, yet previously overlooked biological pump mechanism.Broader Impacts: The Amazon River has captured the public's imagination more than any other river. This study aims to take advantage of such high profile earth science to promote science literacy among all our citizens. This project will support graduate and postdoctoral education, undergraduates through training cruises, and ocean science education of K-12 teachers and undergraduates through the COSEE-West, the Mid Atlantic COSEE and the COSEEOS programs. The results of this research will be made available to other scientists through peer reviewed publications, public databases, and an ANACONDAS website, as well as to the general public through the SFSU RTC-Bay Area Discovery Museum Program.

研究人员推测，氮磷比较低的大型热带河流羽流为硅藻固氮生物组合（DDA）提供了理想的生态位。他们认为，这些生物体在表层海洋中固定 N2 的能力是亚马逊河羽流中大量碳输出的原因。他们之前在亚马逊河羽流中的观察有助于揭示，由内共生固氮蓝细菌 Richelia 及其硅藻宿主（例如 Hemiaulus）组成的水华是新生产和碳输出的重要来源。之前的工作主要集中在 DDA 对灰尘和河流输入的外部强迫的敏感性上，因此这些生物的生态学及其新产物的命运基本上没有被研究。现在已知，DDA 是亚马逊河羽流中大量 CO2 下降的原因，200 m 处的漂浮沉积物捕集器测得羽流下方的质量通量比羽流外部高 4 倍。这使得研究人员推测，这种更大的输出要么是由于 DDA 本身的聚集和下沉，要么是由于浮游动物对 DDA 的放牧。在这项研究中，研究人员将进行一系列实地、卫星和建模研究，旨在了解生态并追踪 DDA 和生活在羽流中的其他浮游植物固定的 C 和 N 的命运。通过检查近海地表水、上层海洋食物网、中层和深海海底的碳和硅酸盐 (Si) 输出，他们将量化亚马逊河对控制碳封存的生物过程的影响，以及这些区域过程对碳、氮和硅预算的影响。这项研究将超越以前的研究，因为它们将量化 1) 在浮游植物物种演替的背景下 DDA 的分布、营养需求和活动，2) 二氧化碳减少对浮游植物混合的敏感性，3) 导致下沉通量的放牧和聚集过程，4) 这种通量的组成，以及 5) 到达海底的这种物质的比例。这项工作真正代表了碳封存和泵效率的衡量标准。生态模型将用于将现场研究和卫星的观测结果置于更大的大西洋盆地背景中，热带气候在年际和更长的时间尺度上发生变化。 学术价值：PI已经确定了一条潜在重要但知之甚少、受生态系统控制、对气候敏感的碳封存途径，该途径似乎违反了对低效开放海洋生物泵的期望。由于由异源氮源（例如固氮）推动的初级生产可以驱动碳从大气到海洋的净生物介导转移，因此亚马逊河羽流中 DDA 的碳封存是一个具有区域意义的过程。由于在其他热带河流系统中也发现了 DDA，因此它们可能代表了一种具有全球意义但之前被忽视的生物泵机制。 更广泛的影响：亚马逊河比任何其他河流都更能激发公众的想象力。这项研究旨在利用如此引人注目的地球科学来提高我们所有公民的科学素养。该项目将通过 COSEE-West、中大西洋 COSEE 和 COSEEOS 项目支持研究生和博士后教育、本科生培训巡航以及 K-12 教师和本科生的海洋科学教育。这项研究的结果将通过同行评审出版物、公共数据库和 ANACONDAS 网站向其他科学家提供，并通过 SFSU RTC-湾区探索博物馆计划向公众提供。