Thorium isotope samples were collected from the ship’s Niskin bottle rosette, and in some cases, surface water (from roughly 15 m depth) was also collected using a Teflon diaphragm pump (Cole Palmer) operated from the ship’s deck. Water was filtered at 0.45 μm using Acropak filter cartridges and acidified to 0.024 M HCl (~pH 1.5) at sea.
Surface samples for both trace elements and thorium isotopes were taken every 12 hours between July 25 and August 3, roughly at sunrise and sunset (Hawaii Standard Time). This timing was motivated to observe the maximum possible change in dissolved elemental concentrations since it coincides with the highest contrast in surface water biomass (maximum at sunset, minimum at sunrise). Depth profile samples for trace elements were collected on July 30 at 10:00 AM, except for the sample from 180 m, which was collected on August 2 at 4:00 PM, due to a misfiring of the original 180 m Vanes deployment. Thorium depth profile samples were collected on July 31 at 2:00 AM (station 43 of KM1513). 
On KM1427 (December 2014), thorium isotope samples were collected as on KM1513. 

The elements Sc, Mn, Fe, Co, Ni, Cu, Zn, Cd, and Pb from the Lagrangian sampling (KM1513) were analyzed at Texas A&M University using an offline SeaFAST-pico preconcentration system (ESI, Omaha, NE) and a Thermo Finnigan Element XR high‐resolution inductively-coupled mass spectrometer (HR-ICP-MS) housed at the R. Ken Williams Radiogenic Isotope Facility. Notably, samples were not UV oxidized, and thus cobalt concentrations must be considered to be operationally defined ICP-labile cobalt (lCo). Accuracy was assessed by analyzing aliquots of the SAFe D1 seawater consensus standard. Precision is reported as error bars for each analysis and was assessed using the standard deviation of duplicate or triplicate analyses of all samples. 

Note trace metal data that did not meet the principal of oceanographic consistency were marked in parentheses in the worksheet. These data could not be determined specifically to have been contaminated but we treat them with caution and they were not considered in the publication.

Thorium isotopes (232Th and 230Th) were analyzed at MIT by Fe co-precipitation from 4 L samples, acid digestion, anion exchange chromatography, and a Nu Plasma II ICP-MS. Accuracy was assessed by analysis of the SWS2010-1 standard (Anderson et al., 2012) (Table 2) as well as an in-house thorium isotope standard (MITh-1). Reported uncertainty for thorium isotopes represents the uncertainty in isotope ratios measured on the ICP-MS.

Select samples were also analyzed for dissolved aluminum (dAl) concentrations. These samples were sub-sampled from the water filtered from the ATE sampler, filtered directly into 125 mL acid washed PMP bottles and acidified to 0.006 M HCl and microwaved for 58 seconds/125mL of sample. These samples were then acidified to 0.012 M HCl (~pH 2) and stored for shipboard analysis on a later cruise (R/V Revelle cruise RR1815 in November 2018) for dAl using flow injection analyses. Replicate standards were used to assess precision and accuracy of this method, and reported errors are the relative standard deviation of standard analyses.