Description: Determination of dissolved trace metals concentration: dFe and dMn concentrations were estimated from the initially sampled seawater. To this end, 100 mL of seawater were filtered through HCl-cleaned polycarbonate filters (0.2 μm pore size) using a TMC Nalgene filtration system and the filtrate was collected into PE bottle and stored triple bagged at 2 ̊C until analysis. Concentrations of the dFe and dMn were determined on a SeaFast system (Elemental Scientific, Omaha, NE, USA) coupled to an inductively coupled plasma mass spectrometer (ICP-MS, Element2, Thermo Fisher Scientific, resolution of R = 2000). During the pre-concentration step, an iminodiacetate (IDA) chelation column (part number CF-N-0200, Elemental Scientific) was used. The pre-filtered seawater samples were acidified to pH=1.7 with a double distilled nitric acid (HNO~3~) and were UV-treated using a 450 W photochemical UV power supply (ACE GLASS Inc., Vineland N. J., USA) to minimize adsorption of TMs onto the bottle walls and to reduce the formation of Mn and Fe hydroxides during storage. During each UV digestion step, two blanks were taken. The ICP-MS was optimized daily to achieve oxide forming rates below 0.3%. Each seawater sample was analyzed via standard addition to minimize any matrix effects, which might influence the quality of the analysis. To assess the accuracy and precision of the method, a NASS-7 (National Research Council of Canada) reference standard was analyzed in a 1:10 dilution (corresponding to environmentally representative concentrations) at the beginning, in the middle and at the end of each run (two batch runs; n = 18). The measured values were in the limits of the certified NASS-7 reference material, with a concentration of 351 ± 26 ng L^-1^ for dFe and 750 ± 60 ng L^-1^ for dMn (mean ± strandard deviation). The detection limits for Mn and Fe were 8.1 pM and 81.8 pM, respectively. Determination of the chlorophyll a fluorescence: For the 18 additional stations, chlorophyll a fluorescence measurements were collected using a Fast Repetition Rate Fluorometer (FRRf) coupled to a FastAct Laboratory system (FastOcean PTX), both from Chelsea Technologies Group. Samples were first dark acclimated for 1h before the meeasurement was perfomed.