Seawater samples were collected in the GEOTRACES GA02 Cruise Leg 3 from Punta Arenas (Chile) to Las Palmas (Spain), March-April 2011. 5-10 L of seawater were collected depending on the sample depth and stored in a cubitainer for each sample. The samples were filtered using 0.2 μm Sartobran cartridges and acidified using ultrapure Seastar hydrochloric acid (HCl) to pH ~ 2 shortly after sampling.

We preconcentrated rare earth elements from seawater using C18 cartridges (Waters Corp., Sep-Pak classic C18 cartridge 360 mg 55-105 μm) loaded with complexing agent 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 method by Jeandel et al. (1998), Lacan and Jeandel (2004), Pahnke et al. (2012). Specifically, C18 cartridges were first cleaned in a 0.5N HCl bath overnight, then 10 mL of 6N HCl were introduced through the cartridge, and then they were flushed with > 500 mL of Milli-Q water. Cartridges were in a neutral environment (MilliQ® water) after cleaning. For each 5 L sample, 300 μL of complexing agent HDEHP/H2MEHP was loaded on a clean cartridge. Seawater samples were adjusted to pH ~ 3.5 by adding Optima® ammonium hydroxide. The seawater samples were pumped through the cartridges at 20mL/min by a peristaltic pump. Afterward, the cartridges were eluted with 10 mL of 0.01N HCl to remove barium. After barium elution, the cartridges were eluted with 35 mL of 6N hydrochloric acid at 10 mL/min by the peristaltic pump to collect the REEs. The REEs were dried and further purified by Eichrom RE-spec column chemistry. Nd fractions were extracted from REEs by LN-spec column chemistry.

The Nd isotopic ratios were measured on MC-ICP-MS (a ThermoScientific Neptune-Plus®) at Lamont-Doherty Earth Observatory of Columbia University. Nd fractions from column chemistry were dried by evaporation and dissolved in 600-800 μL of 3% nitric acid (HNO3). The international Nd standard JNdi-1 was analyzed between every sample and the average of the standards is reported relative to the recommended value of 143Nd/144Nd = 0.512115 (Tanaka, 2000). For different concentrations of JNdi-1, the measured 143Nd/144Nd isotopic ratios were 0.512079 ± 0.000014 (2σ, n = 126) for 20ppb solutions, 0.512079 ± 0.000013 (2σ, n = 190) for 15 ppb solutions, and 0.512058 ± 0.000022 (2σ, n = 37) for 10ppb solutions. Nd isotopic ratios were normalized to 146Nd/144Nd = 0.7219 for mass fractionation.

We are awaiting the results of Nd isotopic ratios at the crossover station (~40°S and ~42°W) from University of Cambridge.