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、永久分层的亚热带环流生物群落的扩大，尤其是在南半球。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。由于其庞大的规模，少营养环流对全球碳和硫（如二甲硫；DMS）循环以及全球气候都很重要。然而，影响少营养环流中DMS通量的生态和生理过程仍然复杂且未解决。该项目将调查生物源硫化合物的原位水平，并评估从少营养环流到本格拉上升流生产水域的南大西洋区域样带的藻类群落结构和生理状态。由于南大西洋的风成铁通量低，该地区被认为是铁和大量营养物质共同限制的。但对该地区的原位生理状况和藻类群落结构进行直接调查的研究很少，特别是对铁和常量营养素的共限研究较少。研究人员将进行几个诊断性的营养富集实验，以评估藻类类特异性的生物地球化学反应。他们将利用最先进的、远洋的、高速的、细胞分选的流式细胞仪来确定藻类类生物硫化合物的特定浓度，并从原位种群和诊断性营养富集实验中估计C/Chl比率。了解藻类特定类别的DMSP:Chl比率对于提高确定DMS到大气通量的预测模型的准确性非常重要。此外，研究人员将利用铁胁迫的分子生化指标（黄伏还毒素）评估原位藻类种群的生理状态。基于荧光的方法将用于估计藻类类特定的光合作用效率，初级生产和光合作用与辐照参数的瞬时测量。这些测量对于估算初级产量的遥感算法和确定和预测海洋生物地球化学对气候变暖的更广泛影响的气候建模人员至关重要。南大西洋浮游植物群落结构和生理特征尚不清楚，但对全球生物地球化学模型具有重要意义。这项研究将提供定量的实证结果，建模者可以利用在这一重要地区建立鲁棒的，机械精确的数值模型。此外，确定Benguela上升流区铁生理状态和藻类群落组成将为了解这一高产区提供重要的信息。该项目还将在几个层面上做出重大的教育贡献，包括研究生和本科生、博士后助理的计划研究参与，以及社区外展和教育活动。

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.