Nutrient and nitrate isotope data from the southern Benguela upwelling system from February to August 2017
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<p>CTD data:<br /> The temperature and conductivity probes are calibrated annually by the manufacturer while the oxygen sensor was calibrated against discrete seawater samples analyzed for dissolved oxygen concentrations by Winkler titration (Carpenter 1965; Grasshoff et al. 1983).</p> <p>Nutrients:<br /> Duplicate samples were measured for nitrate+nitrite on different days, and the standard deviation for duplicates was <0.5 µM, with a lower standard deviation for lower concentration samples<br /> Duplicate samples for phosphate and nitrite were measured in duplicate on different days of analysis, yielding a standard deviation for duplicates of ≤0.1 µM. </p> <p>Nitrate isotopes:<br /> The N and O isotope ratios of nitrate were measured in triplicate in separate batch analyses and standard deviations for both δ15N and δ18O were <0.3‰. Certified nitrate isotope ratio reference materials in nutrient-free seawater were measured in all batch analyses. These included IAEA-NO3-, with δ15N of 4.7 ± 0.2‰ vs. N2 air (Gonfiantini et al. 1995) and and δ18O of 25.6 ± 0.4‰ vs. VSMOW (Böhlke et al. 2003), and USGS-34, with δ15N of -1.8 ± 0.1‰ vs. N2 air and δ18O of -27.9 ± 0.3‰ vs. VSMOW (Böhlke et al. 2003). Nitrate isotstandards in individual runs were diluted in nutrient-free seawater to concentrations similar to those of the samples to account for potential matrix effects on the δ18O measurements (Weigand et al. 2016). Reproducibility was monitored by analysis of an internal seawater nitrate standard from the deep North Atlantic.</p>
<p>CTD（温盐深）数据：<br />温度与电导率探头每年由制造商进行校准，溶解氧传感器则采用经温克勒滴定法（Carpenter 1965; Grasshoff et al. 1983）测定溶解氧浓度的离散海水样品进行校准。</p><p>营养盐：<br />针对硝酸根与亚硝酸根混合样品开展隔日重复测定，平行样的标准偏差小于0.5 µM，且低浓度样品的标准偏差更低。<br />针对磷酸根与亚硝酸根样品开展隔日重复测定，结果显示平行样的标准偏差不超过0.1 µM。</p><p>硝酸根同位素：<br />采用独立批次分析对硝酸根的氮、氧同位素比值进行三次重复测定，δ¹⁵N与δ¹⁸O的标准偏差均小于0.3‰。所有批次分析均同步测定无营养盐海水中的认证硝酸根同位素比值标准物质，涵盖IAEA-NO₃⁻：相对于大气N₂的δ¹⁵N为4.7 ± 0.2‰、相对于VSMOW的δ¹⁸O为25.6 ± 0.4‰（Gonfiantini et al. 1995），以及USGS-34：相对于大气N₂的δ¹⁵N为-1.8 ± 0.1‰、相对于VSMOW的δ¹⁸O为-27.9 ± 0.3‰（Böhlke et al. 2003）。单次分析批次中的硝酸根同位素标准物质均在无营养盐海水中稀释至与样品相近的浓度，以抵消基质效应对δ¹⁸O测定的潜在影响（Weigand et al. 2016）。通过分析取自北大西洋深部的内部海水硝酸根标准物质，对测定重现性进行监控。</p>
