Collaborative Research: Phytoplankton Community Dynamics and Physiological Status in the South Atlantic Subtropical Gyre and Benguela Upwelling Systems

在过去的几年里，复杂的三维气候模型强调了浮游植物功能群在影响海洋生物地球化学方面的重要性。最近的模型预测，气候变暖将导致低生产力、永久分层的副热带涡旋生物群的扩大，特别是在南半球。因此，加强对本省藻类群落结构、生理状况和生物地球化学的认识势在必行。由于其巨大的大小，少营养环流对全球碳和硫(例如，二甲基硫化物；DMS)循环以及全球气候具有重要意义。然而，影响少营养环中DMS通量的生态和生理过程仍然复杂和未解决。该项目将调查生物硫化物的现场水平，并评估从少营养环流到本格拉上升流多产水域的欠采样南大西洋地带性横断面的藻类群落结构和生理状况。由于南大西洋的风成铁通量较低，该地区被认为受到铁和常量营养素的共同限制。但直接研究该地区的就地生理状态和藻类群落结构的研究很少，特别是关于共同限制铁和大量营养素的研究。研究人员将进行几项诊断营养物质富集性实验，以评估藻类特定的生物地球化学反应。他们将利用最先进的远洋、高速、细胞分选的流式细胞仪来确定藻类生物硫化合物的特定浓度，并从现场种群和诊断性营养物质浓缩实验中估计C/Chl比率。了解藻类特定的DMSP：ChL比率对于提高预测模型的准确性以确定DMS向大气的通量是很重要的。此外，研究人员将使用铁胁迫的分子和生化指标(黄曲霉毒素)来评估就地藻类种群的生理状态。将使用一种基于荧光的方法来估计特定藻类的光合作用效率、初级生产力和光合作用与辐射参数的瞬时测量。这些测量对于估计初级生产量的遥感算法和确定和预测海洋对气候变暖更广泛影响的生物地球化学反应的气候模型者至关重要。南大西洋的浮游植物群落结构和生理特征不是很好，但在全球生物地球化学模型方面很重要。这项研究将提供定量的经验结果，建模人员可以利用这些结果来构建这一重要区域稳健的、力学上准确的数值模型。此外，确定本格拉上升流地区的铁生理状态和藻类群落组成，将为了解这一高生产力地区提供重要的见解。该项目还将在几个层面上对教育作出重大贡献，包括计划让研究生和本科生、博士后助理以及社区外联和教育活动参与研究。

In the past few years, sophisticated three-dimensional climate models have emphasized the importance of phytoplankton functional groups in affecting the biogeochemistry of the oceans. Recent models have predicted that climate warming will lead to expansion of the low productivity, permanently stratified subtropical gyre biome, especially in the southern hemisphere. As a result, it is imperative to increase our understanding of algal community structure, physiological status and biogeochemistry in this province. Due to their sheer size, oligotrophic gyres are important to the global carbon and sulfur (e.g. dimethylsulfide; DMS) cycles and as a result to global climate. Ecological and physiological processes that affect DMS fluxes in oligotrophic gyres, however, remain complex and unresolved. This project will investigate the in-situ levels of biogenic sulfur compounds and assess algal community structure and physiological status in a zonal transect of the undersampled South Atlantic Ocean from the oligotrophic gyre to the productive waters of the Benguela upwelling. Due to low aeolian iron fluxes to the South Atlantic Ocean, the region is believed to be co-limited by iron and macronutrients. But there have been very few studies that have directly investigated the in-situ physiological status and algal community structure in this region, especially with respect to co-limiting iron and macronutrients. The investigators will perform several diagnostic nutrient enrichment experiments to assess algal class-specific biogeochemical responses. They will utilize a state-of-the-art, ocean-going, high speed, cell-sorting flow cytometer to determine algal class specific concentrations of biogenic sulfur compounds, and to estimate C/Chl ratios from in-situ populations and from diagnostic nutrient enrichment experiments. Knowledge of algal class-specific DMSP:Chl ratios is important in improving the accuracy of predictive models to determine the DMS flux to the atmosphere. In addition, the investigators will assess the physiological status of in-situ algal populations using molecular and biochemical indicators (flavodoxin) of iron stress. A fluorescence based approach will be used to estimate algal class-specific photosyntheic efficiency, primary production and instantaneous measurements of photosynthesis vs. irradiance parameters. These measurements will be vital to remote sensing algorithms for estimating primary production and to climate modelers for determining and predicting the oceans biogeochemical response to climate warming Broader Impacts. Phytoplankton community structure and physiology in the South Atlantic Ocean is not well characterized but is important with respect to global biogeochemical models. This research will provide quantitative empirical results that modelers can utilize in constructing robust, mechanistically-accurate numerical models of this important region. In addition, determining the iron physiological status and algal community composition of the Benguela upwelling region will provide important insights into this high productivity region. This project will also make significant educational contributions at several levels, including the planned research involvement of graduate and undergraduate students, postdoctoral associates, and community outreach and educational activities.