*2.4. Analysis of Carbonate Chemistry and Inorganic Nutrients*

Seawater was collected from the CTD/Ro system for the determination of dissolved inorganic carbon (CT) and total alkalinity (AT) into borosilicate glass bottles (250 mL) with ground glass stoppers. The samples (*n* = 190) were preserved with 0.05 mL of saturated solution of mercuric chloride (HgCl2) and stored refrigerated and dark until post-cruise analysis. Samples (*n* = 93) for the determination of nutrients and ammonia were collected directly after the samples had been taken for the AT and CT. For nutrient analysis, 20 mL of water was collected in polyethylene scintillation vials, preserved with 0.2 mL chloroform, and kept refrigerated (4 ◦C) until analysis occurred within a few weeks after sample collection. For ammonium analysis, waters were collected in the same type of vials and kept frozen (−20 ◦C) without preservatives until analysis.

AT and CT were measured at the IMR's CO2 Laboratory following standard procedures [48,62,65]. The remaining carbonate system parameters (pH in total scale pHT, partial CO2 pressure pCO2, aragonite saturation ΩAr and calcite saturation ΩCa) were calculated from AT and CT with the program CO2SYS [66] using the thermodynamic constants from Mehrbach et al. (1973) [67] and KSO4 from Dickson (1990) [68], and refitted by Dickson and Millero (1987) [69] on the total scale. The concentrations of silicate and phosphate were set to zero during the calculations, and the errors introduced by this simplification were negligible compared to uncertainties from other sources.

Inorganic nutrient analyses were carried out at IMR's Chemical Laboratory using an Alpkem Flow Solution IV autoanalyzer (RFA methodology) for the colorimetric determination of inorganic nutrients: nitrite (NO2 −), nitrate (NO3 −) [70,71], phosphate (PO4 <sup>3</sup>−) [72] and silicate (SiO4 4) [72]. Nitrate concentrations were calculated by subtracting the nitrite from combined nitrate + nitrite concentration. Ammonium (NH4 +) was measured fluorometrically using an excitation/emission filter combination with an Alpkem Flow Solution IV autoanalyzer [73,74].
