Collaborative Research: Southern Ocean Iron Experiment (SOFeX): Primary/Bacterial Production and Taxon-Specific Growth and Photosynthetic Response

该项目是南大洋铁实验(SOFEX)的一个组成部分。SOFEX是一项在南极绕极洋流内的一小块区域播撒铁的努力，通过测量添加了铁的惰性示踪剂(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过程中发生的复杂的生物相互作用。这一构成部分将测量富铁水路径外的初级生产力，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微米、5但20微米和20微米。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与E的反应是衡量铁限制的敏感指标。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，适应弱光的浮游植物比适应高辐射的浮游植物需要更多的铁(这在南大洋特别重要)。将测量贴片内外的细菌生物量和产量，以评估对铁添加的异养反应。实验将评估细菌的反应是直接的(无机铁限制去除的结果)还是间接的(由于浮游植物光合作用和DOC产生的刺激而添加有机底物的结果，或者通过增加放牧对添加铁所产生的浮游植物生物量的增加的结果)。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。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。SOFEX项目的结果将提供对南大洋生物地球化学和生态对铁浓缩的反应的洞察，并对这一鲜为人知但关键的海洋区域的功能有一个新的理解。

This project is a component of Southern Ocean Iron Experiment (SOFeX). SOFeX is an effort 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 CO2. 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 component will measure primary productivity within an outside the iron-enriched path 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: 5um, 5 but 20 um, and 20 um. 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 irradiances (a condition especially important in the Southern Ocean). The bacterial biomass and production both within and outside the patch will be measured to assess the heterotrophic response to iron addition. Experiments will assess whether the bacterial response is direct (a result of inorganic iron limitation removal) or indirect (a result of organic substrate addition due to the stimulation of phytoplankton photosynthesis and DOC production, or via increased grazing on the increased phytoplankton biomass generated by iron additions). The taxon-specific growth rates of phytoplankton will also be measured directly using a pigment-labeling technique. 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. The results of the SOFeX project will provide insights into the response of the biogeochemistry and ecology of the Southern Ocean to iron enrichment and produce a new understanding of the functioning of this poorly known, but critical oceanic region.