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

研究人员假设，大的热带河流羽状流与低N：P比例提供了一个理想的生态位的固氮生物组合（DDAs）。他们认为，这些生物在表层海洋中固定N2的能力是亚马逊河羽流中大量C出口的原因。他们之前在亚马逊河羽流中的观察帮助揭示了由内共生固氮蓝藻Richelia及其硅藻宿主（例如Hemiaulus）组成的水华是新生产和碳出口的重要来源。以前的工作主要集中在DDAs对来自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品的命运在很大程度上未被研究。现在已知，DDAs是亚马逊河羽流中大量CO2下降的原因，200米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。这使得研究人员假设，这种更大的出口是由于聚集和下沉的DDAs本身或放牧的DDAs的浮游动物。在这项研究中，研究人员将进行一系列的现场，卫星和模拟研究，旨在了解生态和跟踪的命运固定的DDAs和其他浮游植物生活在羽。通过检查C和硅酸盐（Si）出口从近海表层沃茨，通过上层海洋食物网，中层，并下降到深海海底，他们将量化的影响，亚马逊河的生物过程，控制碳封存和这些区域过程的影响，对C，N和Si的预算。这项研究将超越以往的研究，因为它们将量化1）在浮游植物物种演替的背景下DDAs的分布，营养需求和活动，2）CO2下降对浮游植物混合的敏感性，3）放牧和聚集过程有助于下沉通量，4）该通量的组成，以及5）到达海底的这种物质的比例。这一努力真正代表了碳封存和泵效率的衡量标准。生态建模将被用来把观测结果从实地研究和卫星到更大的大西洋盆地的背景下，热带气候变率在年际和更长的时间scale.Intellectual优点：PI已经确定了一个潜在的显着的，但知之甚少，生态系统控制，气候敏感的碳封存途径，似乎违反了一个低效的公海生物泵的预期。由于初级生产燃料的异地来源的N，如N2固定可以驱动一个净的，生物介导的转移C从大气到海洋，C封存的DDAs在亚马逊河羽是一个区域性的重要过程。由于在其他热带河流系统中也发现了DDA，它们可能代表了一种全球性的重要生物泵机制，但以前却被忽视了。更广泛的影响：亚马逊河比其他任何河流都更能吸引公众的想象力。这项研究旨在利用这种备受瞩目的地球科学，以促进科学素养的所有公民。该项目将支持研究生和博士后教育，本科生通过培训巡航，并通过COSEE-West，中大西洋COSEE和COSEEOS计划对K-12教师和本科生进行海洋科学教育。这项研究的结果将通过同行评审的出版物，公共数据库和ANACONDAS网站提供给其他科学家，以及通过SFSU RTC海湾地区发现博物馆计划向公众提供。

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.