Southern Ocean Experiment (SOFeX): Primary/Bacterial Production and Taxon-Specific Growth and Photosynthetic Responses

这是一个名为南大洋铁实验(SOFEX)的项目的一部分，目的是在南极绕极洋流内的一小块区域播撒铁，通过测量添加铁的惰性示踪剂(SF6)的分布来跟踪这片水域，并评估对这种添加的化学和生物反应。最近的观察表明，铁在南大洋所有区域的有机物质的生产和出口中起着控制作用。此外，由于南大洋拥有世界上最大的无机常量营养素池，它最有可能通过充当二氧化碳的汇来影响大气中二氧化碳的浓度--为了预测铁供应的自然变化对碳分配的影响，我们必须了解铁浓缩时发生的复杂生物相互作用。这项调查将测量富铁水域内外的初级生产力，以量化铁对现场浮游植物在几天的时间尺度上的直接反应。将测量三种尺寸分级的生产率：5克、5但20克和20~tm。三种粒度组分的定量分类组成将通过高效液相色谱(HPLC)直接测定。出于两个原因，还将测量相同组分的光合作用与辐照度(P与E)的响应。首先，P-E反应是铁限制的一个敏感指标。其次，这些数据将被用来研究铁/辐射相互作用，因为已经假设，适应低光的浮游植物比适应高光的浮游植物需要更多的铁(这在南大洋特别重要)。还将使用色素标记技术直接测量浮游植物的分类群特定生长率。最后，该项目将使用一种新的快速重复率(FRR)荧光技术，该技术将近乎实时地提供P与E的响应，使研究人员能够评估量子效率和总体光合作用沿浓缩斑块的梯度的空间(水平和垂直)响应。解决硅藻相对于其他类群的反应对于准确模拟浮游植物对不同铁供应的反应至关重要，因为硅藻水华在向深海输出碳的过程中发挥着关键作用。

This is part of a project - the Southern Ocean Iron Experiment (SOFeX) - to seed a small area within the Antarctic Circumpolar Current with iron, to follow this patch of water by measuring the distribution of an inert tracer (SF6) added with the iron, and to assess the chemical and biological responses to this addition. Recent observations have indicated that iron plays a controlling role in the production and export of organic matter in all regions of the Southern Ocean. Furthermore, because the Southern Ocean contains the largest pool of inorganic macronutrients of the world ocean, it has the greatest potential to influence the concentration of atmospheric carbon dioxide by acting as a sink for C02- In order to predict the impact of natural variations in iron supply on carbon partitioning, it is imperative that we understand the complex biological interactions that occur upon iron enrichment. This investigation will measure primary productivity within and outside the iron-enriched patch of water to quantify the direct response of iron to the in situ phytoplankton assemblage on time scales of days. Productivity of three size fractions will be measured: 5gm, 5 but 20 gm, and 20 ~tm. The quantitative taxonomic composition of the three size fractions will be directly determined by high performance liquid chromatography (HPLC). The photosynthesis versus irradiance (P vs E) responses of the same fractions also will be measured for two reasons. First, the P vs E response is a sensitive measure of iron limitation. Secondly, the data will be used to investigate iron/irradiance interactions because it has been hypothesized that phytoplankton adapted to low light require more iron than do those adapted to higher iffadiances (a condition especially important in the Southern Ocean). The taxon-specific growth rates of phytoplankton will also be measured directly using a pigment-labeling technique. Finally, the project will use a new Fast Repetition Rate (FRR) fluorescence technique that will provide P vs E responses in near real-time, allowing the investigators to assess the spatial (both horizontal and vertical) responses of quantum efficiency and bulk photosynthesis along gradients across the enriched patch. Resolving the responses of diatoms relative to other taxa is critical for accurate modeling of the phytoplankton response to varying iron supply because diatom blooms play a pivotal role in the export of carbon to the deep sea.