Dissolved Iron (DFe) Concentrations and Total Iron Concentrations of Profile and Surface Stations in the Southern Ocean

Dissolved iron (DFe) concentrations of 40 profile stations and 7 surface stations were measured directly on board by an automated Flow Injection Analysis (FIA) after a modified method of De Jong et al. 1998. In addition, unfiltered samples from 17 profiles and 7 surface stations were acidified and stored to determine the total Fe concentrations in the NIOZ laboratory after 6-12 months of dissolution (see table 1). Filtered (0.2µm) and acidified (pH 1.8) seawater was concentrated on a column containing aminodiacetid acid (IDA). This material binds only transition metals and not the interfering salts. After washing the column with ultra pure water, the column is eluted with diluted acid. After mixing with luminol, peroxide and ammonium, the oxidation of luminol with peroxide is catalyzed by iron and a blue light is produced and detected with a photon counter. The amount of iron is calculated using a standard calibration line, where a known amount of iron is added to low iron containing seawater. Using this calibration line a number of counts per nM iron is obtained. Samples were analyzed in duplicate sample bottles, each of which was measured in triplicate, and average DFe concentrations and standard deviation are given. Concentrations of DFe measured on the NBP0901 cruise ranged from 30 pM up to 0.7 nM. The standard deviation varied between 0% and 10% (the latter being exceptional), but was generally < 5% in samples with DFe concentrations higher than 0.1nM. Since samples containing less than 0.1nM DFe are near the detection limit of the system; the standard deviation of these measurements was sometimes high (<30%). The average blank was determined at 0.024nM±0.010nM and was defined as a sample loaded for 10 seconds and measured daily. The average limit of detection, 0.009±0.008 was defined as 3*standard deviation of the mean blank and measured daily. To better understand the day to day variation duplicate sample bottles were measured at least 24h later. The differences between these measurements were rather large, in the order of 5-20%, while the largest differences were measured in samples with low DFe concentrations. To correct for this day to day variation a so-called lab standard sample was measured daily. All data will be corrected for the mean average of this value after the cruise and all data presented so far are uncorrected for this day to day variation. The consistency of the FIA system over the course of the day was verified using a drift standard. The drift was observed to be less than 7% and no corrections have been made for this drift. A certified SAFe standard (Johnson et al. 2007) for the long term consistency and absolute accuracy was measured at a regular basis. Preliminary results The profile from station 16 clearly shows high iron input near the PIG (Fig. 5). DFe concentrations are high throughout the entire water column and indicate a constant input of DFe into the polynya. Profile 107, which is in the central Pine Island Polynya, shows much lower values throughout the first 300 meter which can be explained by the high phytoplankton abundance in the surface water. DFe concentrations during a transect from Pine Island Glacier (PIG) (101 S,30W) through the central Pine Island Polynya in north westwards direction clearly show the high DFe concentrations near the PIG and the rapid decrease of the DFe in the polynya, especially in waters shallower than 50m (Fig. 6). Extreme low DFe values in the central polynya correlate with the biological productive area as observed from the fluorometer data and Chl a measurements.本数据集通过改良的De Jong等（1998）方法，采用自动化流动注射分析法（Flow Injection Analysis, FIA）在船上直接测定了40个剖面站与7个表层站的溶解态铁（Dissolved Iron, DFe）浓度。此外，研究人员对17个剖面的未过滤海水样品及7个表层站样品进行酸化后保存，待6-12个月的溶样过程结束后，于荷兰皇家海洋研究所（NIOZ）实验室测定总铁浓度（详见表1）。将经0.2μm滤膜过滤且酸化至pH 1.8的海水通过装填有氨基二乙酸（IDA）的色谱柱进行富集：该填料仅能结合过渡金属，不会吸附共存的干扰性盐类。先用超纯水洗涤色谱柱，再以稀酸洗脱。将洗脱液与鲁米诺、过氧化氢及铵盐混合后，铁会催化过氧化氢氧化鲁米诺，产生蓝光并通过光子计数器检测。铁的含量通过标准校准曲线计算得到：将已知量的铁添加至低铁背景海水中，由此得到每纳摩尔（nM）铁对应的计数信号。所有样品均设置平行瓶，且每个平行瓶进行三次重复测定，最终给出平均DFe浓度与对应的标准偏差。NBP0901航次测得的DFe浓度范围为30皮摩尔（pM）至0.7纳摩尔（nM）。标准偏差波动于0%至10%之间（后者属于极端情况），当DFe浓度高于0.1nM时，标准偏差普遍小于5%。由于DFe浓度低于0.1nM的样品接近系统检测限，此类样品的测量标准偏差有时较高（小于30%）。 本系统的平均空白值为0.024nM±0.010nM，空白定义为上样10秒并每日测定的样品。平均检测限为0.009±0.008nM，其定义为平均空白标准偏差的3倍，且每日进行测定。为更好地探究日间变异，研究人员对平行样品瓶至少间隔24小时后再次测定。两次测定的差异较为显著，可达5%~20%，其中低DFe浓度样品的差异最大。为校正日间变异，每日均测定所谓的实验室标准样品。航次结束后，所有数据将基于该标准样品的平均值进行校正，而目前已展示的所有数据均未针对日间变异进行校正。研究人员采用漂移标准品验证了FIA系统当日的运行稳定性，观测到系统漂移小于7%，因此未针对该漂移进行校正。此外，研究人员定期测定经认证的SAFe标准（Johnson等，2007），以验证系统的长期稳定性与绝对准确度。 初步分析结果 16号站的剖面数据清晰显示，松岛冰川（Pine Island Glacier, PIG）附近存在显著的铁输入（图5）：整个水柱的DFe浓度均较高，表明冰间湖（polynya）持续有DFe输入。位于松岛冰间湖中部的107号站，其前300米水深的DFe浓度均较低，这可归因于表层水体中丰富的浮游植物生物量。从松岛冰川（PIG，101°S，30°W）向西北方向穿过松岛冰间湖中部的断面数据显示，PIG附近的DFe浓度较高，而冰间湖内的DFe浓度快速降低，尤其在水深小于50米的水体中（图6）。冰间湖中部极低的DFe浓度与荧光计数据及叶绿素a（Chlorophyll a, Chl a）测定结果所反映的生物高生产力区域高度相关。