The concentrations of nitrate, nitrite, soluble reactive phosphorous (SRP) and silicic acid were measured in 119 water samples collected from 23 February to 3 April 2022 using an underway trace metal clean tow-fish during RV Sonne cruise SO289 from Chile to New Caledonia. 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), and silicic acid (0.096 µmol kg−1). TON (nitrate + nitrite) and SRP were re-analysed 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).

Zero values in the data columns mean below detection limit (