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

本项目是南大洋铁实验（SOFeX）的一个组成部分。SOFeX是一项在南极环极洋流内的一小块区域播种铁的努力，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的产生和输出中起着控制作用。此外，由于南大洋拥有世界海洋中最大的无机常量营养素库，因此它作为二氧化碳的汇，对大气二氧化碳浓度的影响潜力最大。为了预测铁供应的自然变化对碳分配的影响，我们必须了解铁富集时发生的复杂生物相互作用。该组件将测量富铁水体外的初级生产力，以量化铁对原位浮游植物组合的直接反应，以天为时间尺度。将测量三种尺寸分数的生产率：5um， 5但20 um和20 um。三种大小馏分的定量分类学组成将由高效液相色谱法直接测定。由于两个原因，还将测量相同馏分的光合作用与辐照度（P vs. E）响应。首先，P / E响应是铁限制的敏感指标。其次，这些数据将用于研究铁与辐照度的相互作用，因为据推测，适应弱光的浮游植物比适应高辐照度的浮游植物需要更多的铁（这在南大洋特别重要）。将测量斑块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（由于刺激浮游植物光合作用和DOC产生而添加有机底物的结果，或通过增加对铁添加产生的浮游植物生物量增加的放牧）。利用色素标记技术直接测量浮游植物的分类特异性生长速率。解决硅藻相对于其他分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，因为硅藻华在向深海输出碳方面起着关键作用。SOFeX项目的结果将提供对南大洋生物地球化学和生态对铁富集的反应的见解，并对这一鲜为人知但至关重要的海洋区域的功能产生新的理解。

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.