Steiner, Zvi; Mutzberg, André; Achterberg, Eric Pieter: Macro nutrient concentrations measured in the South Pacific along SONNE cruise SO289 [dataset bundled publication]. PANGAEA, https://doi.pangaea.de/10.1594/PANGAEA.995895 (dataset in review)

The concentrations of nitrate, nitrite, soluble reactive phosphorous (SRP) and silicic acid were measured in 2634 water samples collected from 23 February to 3 April 2022 during RV Sonne cruise SO289 from Chile to New Caledonia. The seawater samples were collected in 15 mL polypropylene sample vials from two different CTDs, a regular stainless steel CTD (ss-CTD) and a trace metal clean titanium CTD (Ti-CTD). In addition, surface water samples were collected along the cruise using a trace metal clean tow-fish. Containers and caps were rinsed three times with the sample water before the actual sampling. Samples were placed in the fridge immediately after collection (4 °C in dark) in case they could not be immediately analysed. Analysis of macro nutrients was undertaken on board by segmented flow injection analysis using a QUAATRO39 (Seal Analytical) auto-analyser including a XY2-autosampler unit. The system set-up included 4 channels for nitrate + nitrite (TON), silicate, nitrite, and phosphate. The analytical methods followed during the cruise correspond to those described by QuAAtro Applications: Method No. Q-068-05 Rev. 11 for TON, Q-066-05 Rev. 5 for Silicate, Q-070-05 Rev. 6 for Nitrite and Q-064-05 Rev. 8 for Phosphate. Limits of detection were: nitrate (0.020 µmol kg−1), nitrite (0.008 µmol kg−1), SRP (0.011 µmol kg−1) and silicic acid (0.096 µmol kg−1). Surface water samples and Ti-CTD samples with TON concentration <100 nM were analysed for TON and SRP using a modified detector set up with 1000 mm flow cells, which provided significantly lower detection limits. These samples were filtered and stored at −20 °C prior to analyses on board with the modified QUAATRO39 (Seal Analytical) auto-analyser. Limits of detection of the nano-nutrient system were: TON (0.005 µmol kg−1) and SRP (0.001 µmol kg−1). Certified Reference Material for Nutrients in Seawater (RMNS) was used for every run in order to I) guarantee repeatability and reproducibility between analytical runs and to II) validate the data set in terms of compatibility within the scientific community. Nutrient analyses were validated with KANSO CRM, Lot-No. CC, CL for macro molar Nutrients and CK for nano molar nutrient concentrations.