Seawater samples were collected during the GEOTRACES GP16 cruise on R/V Thomas G. Thompson (TN303) along the East Pacific Zonal Transect in 2013. Five liters (L) of seawater were collected and stored in a cubitainer for each sample. The samples were filtered using 0.2-micrometer (μm) Sartobran cartridges and acidified using ultrapure Seastar hydrochloric acid (HCl) to pH ~ 2 shortly after sampling.

For neodymium (Nd) isotope analysis, rare-earth elements (REEs) were preconcentrated from seawater using C18 cartridges (Waters Corp., Sep-Pak classic, 360-milligrams (mg), 55-105 μm) loaded with complexing agent composed of a mixture of 2-ethylhexyl hydrogen phosphate (HDEHP) and 2-ethylhexyl dihydrogen phosphate (H2MEHP), which was first proposed by Shabani et al. (1992). In this study, we followed the methods by Jeandel et al. (1998), Lacan and Jeandel (2001), and Pahnke et al. (2012). Specifically, C18 cartridges were first cleaned in a 0.5 N HCl bath overnight, passed through 10 milliliters (mL) of 6 N HCl and then flushed with >500 mL of Milli-Q water. Cartridges were stored in Milli-Q water after cleaning. 300 μL of complexing agent HDEHP/H2MEHP was loaded on a clean cartridge for a 5 L sample. Seawater samples were adjusted to pH ≈ 3.5 by adding Optima® ammonium hydroxide before being pumped through the cartridges at 20 mL/minute by a peristaltic pump in the ultra-clean chemistry laboratory at LDEO. Cartridges were then eluted with 10 mL of 0.01 N HCl to remove barium. After barium elution, cartridges were eluted with 35 mL of 6 N HCl at 10 mL/minute by a peristaltic pump to collect REEs. REEs were dried and further purified by TRU-spec column chemistry. Nd fractions were extracted from REEs by LN-spec column chemistry and dried. They were redissolved in 0.3 mL of 3% HNO3 for the Nd isotope analysis.

For REE concentration analysis, a multi-element REE spike enriched in 138La, 142Ce, 145Nd, 149Sm, 153Eu, 155Gd, 161Dy, 167Er, 171Yb, and 176Lu (Wu et al., 2020) was added to each sample (~10 mL). The sample-spike mixture was allowed to equilibrate for at least 24 hours and then was purified and pre-concentrated through the seaFast Automated Preconcentration System for Undiluted Seawater (Elemental Scientific Inc. or ESI, Omaha, Nebraska, USA).

915447_v1_gp16_diss_nd_and_rees_ldeo.csv