Dissolved Al in the Southern Ocean

Sampling and Analytical Methodology:

Samples were taken using 24 internally Teflon-coated PVC 12 litre GO-FLO Samplers (General Oceanics Inc.) mounted on an all-titanium frame (De Baar et al., 2008). This frame was connected to a 17.7 mm diameter Kevlar hydrowire with seven independent internal signal/conductor cables (Cousin Trestec S.A.) and controlled from onboard. Each GO-FLO sampler had a special ultraclean all-teflon PTFE valve (Cole Parmer; PN A-06392-31) installed. Samples for trace metal analysis were collected from the GO-FLO bottles in a class 100 clean room environment. The water was filtered over a 0.2 μm filter cartridge (Sartrobran-300, Sartorius) under pressure (1.5 atm) of (in-line prefiltered) nitrogen gas exerted via a special connector instead of the regular air bleeding valve at the top of each GO-FLO sampler. Sub-samples for Al were taken in cleaned LDPE sample bottles (125 mL) from each GO-FLO bottle. All sample bottles were rinsed five times with the sample seawater.
The analyses of dissolved Al were performed on shipboard after the method developed by Resing and Measures (1994) with improvements by Brown and Bruland (2008). This method is a flow injection analysis, based on the fluorescence from the reaction between lumogallion and Al. Samples were stored in a refrigerator (4°C) and analysed usually within 24 h after sampling but always within 36 h. Samples were acidified at least 1 h before analysis with 12 M ultraclean HCl (Baseline® Hydrochloric Acid, Seastar Chemicals Inc.) to a pH of 1.8. In the flow injection system the samples were buffered inline to a pH of 5.5 ± 0.1 with ultraclean 2 M ammonium acetate buffer. This buffer was produced after Aguilar-Islas et al. (2006) by diluting a saturated solution of ammonium acetate crystals to a 2 M solution with MQ (Millipore Milli-Q deionised water R > 18.2 MΩ cm-1). The pH was subsequently adjusted to be between 8.8 and 8.9 with ultraclean ammonium hydroxide. The latter was produced by bubbling 0.2 µm filtered high purity ammonia gas through MQ water.
The buffered sample was pre-concentrated during 200 s on a Toyopearl AF-Chelate 650M (TosoHaas, Germany) column. Hereafter the column was rinsed for 60 s with MQ water to remove interfering salts. The Al was subsequently eluted from the column with 0.16 M HCl (Suprapure, Merck) during 250 s. The eluate of Al in HCl entered the reaction stream which consisted of a lumogallion (Pfaltz & Bauer) solution in 4 M ammonium acetate buffer. The 4 M buffer was produced similar to the 2 M buffer (see above), but with the pH adjusted to be between 6.4 and 6.5 and the lumogallion was a 4.8 mM solution in MQ. The mixing of the HCl and the buffer results in a reaction pH between 5.3 and 5.4 at which an Al-Lumogallion chelate complex is formed which can be detected by its fluorescence. The complex was mixed in a 10 m reaction coil placed in a water bath of 50 °C. Hereafter a 5% Brij-35 (Merck) solution in MQ was added to increase the sensitivity (Resing and Measures, 1994) and mixed in a 3 m length mixing coil. Afterwards the emission of the fluorescent complex was detected on a FIA-lab PMT-FL detector with a 510 until 580 nm emission filter and a 480 until 490 nm excitation filter. Concentrations of Al were calculated in nanomol•L-1 (nM) from the peak heights.
The system was calibrated using standard additions from a 5000 nM Al stock solution (Fluka) to filtered acidified seawater of low (<0.5 nM) Al concentration that was collected in the Antarctic Ocean. A six-point calibration line (0, 1, 2, 4, 6 and 8 nM Al standard additions) and blank determination were made every day. The 3 lowest points (0, 1 and 2 nM Al standard additions) of the calibration line were measured in triplicate and the 3 highest points (4, 6 and 8 nM Al standard additions) in duplicate in order to add more weight to the lower part of the calibration line. The blank was determined by plotting the signals of increasing pre-concentration times (30, 60, 120, 180 and 240 seconds) of the filtered acidified seawater of low (<0.5 nM) Al concentration also used for the calibration. A line was fitted through these data points and the intercept of the line taken as the blank, which was usually below 0.2 nM Al. The latter value of 0.2 nM was also the maximum allowed blank before starting a series of analyses. The limit of detection, defined as three times the standard deviation of the lowest concentration observed, was 0.07 nM. The flow injection system was cleaned every day by rinsing with a 0.5 M HCl solution.

Data Processing:
A standard was measured in triplicate every day. This standard was a sub-sample of a 25 L volume of filtered seawater that was taken at the beginning of the cruise in the South East Atlantic Ocean. The relative standard deviation of the replicate analysis seawater sample that was analysed 36 times on different days in triplicate was 3.16%. The relative standard deviation on single days was on average 1.5%. The average concentration of Al of this standard was 3.56 nM and the deviation from this average for a given measuring day was used as a correction factor. To verify whether this correction was decreasing the inter-daily variability in the dataset, every day a sample which was collected and measured the previous measuring day, was analysed once again. The deviation between the concentrations measured on the different days decreased from 4.8% to 3.5%, indicating the data correction is beneficial. As an independent comparison, the certification samples collected on the American SAFe cruise (Johnson et al., 2007) were analysed in triplicate for Al. The resulting concentrations of Al for both SAFe Surface (S) and SAFe deep (D2) from 1000 m, agreed very nicely the community consensus value on the absolute concentrations of Mn in the SAFe samples. The dataset was scanned for obvious outliers and these have been quality flagged with the number 4. Some samples gave anomalous nutrient results for the intended depth and were assumed to have been closed at the wrong depth and quality flagged with the number 8. All other values are assumed to be correct and flagged with the number 0.

采样与分析方法：
样品采用24个内部涂有Teflon的PVC 12升GO-FLO采样器（通用海洋学公司）采集，这些采样器安装在全钛制框架上（De Baar等，2008年）。该框架通过直径为17.7毫米的Kevlar水线与七条独立的内部信号/导线电缆（Cousin Trestec S.A.）相连，并由船载设备控制。每个GO-FLO采样器都安装了一个特殊的超洁净全Teflon PTFE阀门（Cole Parmer；PN A-06392-31）。用于痕量金属分析的样品在100级洁净室环境中从GO-FLO瓶中收集。水样通过0.2微米过滤芯（Sartorius的Sartobran-300）在1.5大气压的氮气（在线预过滤）压力下过滤。铝的子样品从每个GO-FLO瓶中取出，置于清洁的LDPE样品瓶（125毫升）中。所有样品瓶均用样品海水冲洗五次。
溶解铝的分析是在船上进行的，采用Resing和Measures（1994）开发的方法，并由Brown和Bruland（2008）进行了改进。该方法是一种流动注射分析，基于鲁米加林与铝的反应产生的荧光。样品储存在冰箱中（4°C），通常在采样后24小时内分析，但必须在36小时内完成。在分析前至少1小时用12 M超洁净HCl（Baseline®盐酸，Seastar化学公司）将样品酸化至pH 1.8。在流动注射系统中，样品通过超洁净2 M乙酸铵缓冲液在线缓冲至pH 5.5 ± 0.1。该缓冲液是通过将乙酸铵晶体饱和溶液稀释至2 M溶液（Millipore Milli-Q去离子水R > 18.2 MΩ cm-1）制备的。随后，用超洁净的氨水将pH调整至8.8至8.9之间。后者是通过将0.2 µm过滤的高纯度氨气通过MQ水冒泡产生的。
在Toyopearl AF-Chelate 650M（TosoHaas，德国）柱上对缓冲样品进行200秒的预浓缩。之后，用MQ水冲洗60秒以去除干扰盐。随后，在250秒内用0.16 M HCl（Suprapure，Merck）从柱中洗脱铝。HCl中的铝进入由4 M乙酸铵缓冲液中的鲁米加林溶液组成的反应流。4 M缓冲液的制备方式与2 M缓冲液类似（见上文），但pH调整至6.4至6.5之间，鲁米加林为MQ中的4.8 mM溶液。HCl和缓冲液的混合导致反应pH介于5.3至5.4之间，此时形成Al-Lumogallion螯合物复合物，可通过其荧光检测。该复合物在50°C水浴中的10米反应线圈中混合。之后，向其中加入5% Brij-35（Merck）溶液在MQ中以提高灵敏度（Resing和Measures，1994），并在3米长的混合线圈中混合。之后，在510至580 nm发射滤光片和480至490 nm激发滤光片的FIA-lab PMT-FL检测器上检测荧光复合物的发射。铝的浓度从峰高计算得出，单位为纳米摩尔·升-1（nM）。
系统使用从5000 nM铝储备溶液（Fluka）到过滤酸化低浓度（<0.5 nM）海水标准溶液的标准添加进行校准，该溶液是在南大洋收集的。每天进行六点校准线（0、1、2、4、6和8 nM铝标准添加）和空白测定。校准线的三个最低点（0、1和2 nM铝标准添加）重复测量三次，三个最高点（4、6和8 nM铝标准添加）重复测量两次，以增加校准线下部部分的权重。空白是通过绘制低浓度（<0.5 nM）酸化海水过滤后预浓缩时间增加（30、60、120、180和240秒）的信号来确定的。这些数据点的线性拟合的截距被用作空白，通常低于0.2 nM铝。该0.2 nM的值也是开始一系列分析前允许的最大空白值。检测限定义为观测到的最低浓度标准偏差的三倍，为0.07 nM。每天用0.5 M HCl溶液冲洗流动注射系统进行清洁。
数据处理：
每天对标准样品进行三次测量。该标准样品是从南大西洋东部海域巡航开始时取的25升过滤海水的子样品。在36天内对重复分析的海水样品进行三次重复分析，相对标准偏差为3.16%。单日的相对标准偏差平均为1.5%。该标准样品的平均铝浓度为3.56 nM，特定测量日的测量值与平均值的偏差用作校正因子。为了验证这种校正是否减少了数据集的日间变化，每天对前一天收集和测量的样品再次进行分析。不同天测量的浓度之间的偏差从4.8%降至3.5%，表明数据校正是有益的。作为独立的比较，对在美国SAFe巡航（Johnson等，2007）上收集的认证样品进行铝的三次重复分析。SAFe表面（S）和SAFe深部（D2）从1000米测得的铝浓度与社区对SAFe样品中Mn绝对浓度的共识值非常吻合。数据集被扫描以查找明显的异常值，这些异常值已用数字4进行质量标记。一些样品给出了异常的营养结果，对于预期的深度，假定这些样品在错误的深度关闭，并用数字8进行质量标记。所有其他值均假定是正确的，并用数字0进行标记。