Dataset: Iron, manganese and nutrient data from four cruises in the eastern tropical North Pacific, 2012 to 2018

Samples were collected and analyzed as described in Bolster et al. Briefly, samples were collected from a trace-metal clean rosette, sampled under filtered nitrogen pressure through acid-washed 0.2 μm polyethersulfone filters into acid-washed low-density polyethylene bottles. Iron(II) was measured using luminol chemiluminescence, using diethylenetriaminepentaacetic acid as a masking ligand to correct for interferents (Bolster et al., 2018). Total dissolved metal samples were acidified with Optima grade hydrochloric acid (final concentration 20 mM) and stored at room temperature for several months. Dissolved iron and manganese were determined using inductively coupled plasma mass spectrometry with an offline preconcentration system. 

Additional hydrographic and nutrient data is provided for some samples. Temperature, salinity, and oxygen were measured using a CTD, and measurements of phosphate, nitrate, and nitrite were performed using a nutrient auto-analyzer onboard, as described in Selden et al.

Trace metal samples were collected in 5 L Teflon-coated external spring “Niskin-type” bottles (Ocean Test Equipment) mounted on a powder-coated trace metal clean rosette (Sea-Bird Electronics). Samples were preconcentrated using a seaFAST system (ESI), and quantified using isotope dilution for iron and standard additions for manganese. Analyses were performed on an inductively coupled mass spectrometer in medium resolution mode (Thermo Element 2), using indium as an internal standard. Trace metal quantification was performed using Microsoft Excel 2016.

Temperature, salinity, and oxygen were determined from a Sea-Bird SBE 11plus CTD and a model 43 dissolved oxygen sensor, attached to a sampling rosette for dissolved nutrient concentrations. Nutrients were measured using an Astoria‐Pacific nutrient autoanalyzer.

A number of samples have no measured values for total dissolved iron and manganese, either because sample collection was not logistically possible, or because some of the samples were lost in transit.