Dataset: Dissolved concentrations of nickel and copper from bottle samples collected on Leg 2 (Hilo, HI to Papeete, French Polynesia) of the US GEOTRACES Pacific Meridional Transect (PMT) cruise (GP15, RR1815) on R/V Roger Revelle from October to November 2018

Samples were obtained from the GEOTRACES GP15 cruise aboard the R/V Roger Revelle (RR1814 from September 18 to October 21 of 2018, and RR1815 from October 24 to November 23 of 2018). The Revelle was equipped with the GEOTRACES CTD/rosette (Model 32G, Sea-Bird Electronics). This rosette contained 24 Teflon-coated 12-liter (L) GO-FLO bottles for trace metal clean sampling (Model 10812 T, General Oceanics) with sensors for dissolved oxygen, conductivity, chlorophyll fluorescence, pressure, beam transmittance, and temperature. These samples were preserved by filtering them through 0.2-micrometer (µm) Acropak-200 Supor capsule filter (Pall Corporation) and storing them in acid-washed 1 L Low-Density Polyethylene (Nalgene; LDPE) bottles. Samples (1L) were acidified to pH = 1.8 with 1 mL concentrated distilled HCl and added with 1 mL 30% H2O2 (Optimaᵀᴹ grade; Fisher; CAS#: 7722-84-1), and left for over 1 month.

Metal concentration analyses were identical to those used in Hawco et al. (2020). For each sample, 15 milliliters (mL) seawater was transferred to a acid-washed 15 mL polypropylene Falcon tube (VWR; Catalog #89049-172), then 50 microliters (µL) of an isotope spike (containing ⁵⁷Fe, ⁶²Ni, ⁶⁵Cu, ⁶⁷Zn, ²⁰⁷Pb, and ¹¹⁰Cd) was added to the 15 mL tube and thoroughly mixed with the sample. The samples would then sit overnight before they were preconcentrated by a SC-DX seaFAST system (Elemental Scientific; M-SFS2-MG-52). The seaFAST system helped to preconcentrate the seawater samples and remove the salt matrix. About 10 mL of seawater was injected through the Nobias PA-1 column of seaFAST and 0.5 mL eluent (1M HNO₃ containing 1 ppb In) was used to elute trace metals for concentration measurement. The trace metal concentrations were then measured by a Thermo Element 2ᵀᴹ Inductively Coupled Plasma - Mass Spectrometer. Concentrations of copper (Cu) and nickel (Ni) were derived by using an isotope dilution method.