Samples were collected using GO-FLO Teflon Trace Metal Bottles, filtered to 0.2 μm or 0.45 μm (depending on filter type), acidified to pH ≈ 2 with hydrochloric acid, and stored for several years prior to processing. Aliquots containing five milliliters of seawater were cleanly subsampled from each sample, weighed, and an appropriate quantity of 136Ba–135Ba double spike added. Following spike–sample equilibration, barium was co-precipitated with calcium carbonate via dropwise addition of sodium carbonate. The resultant precipitate was dissolved in hydrochloric acid and twice passed through cation-exchange columns to purify Ba from matrix elements.
Samples were aspirated, desolvated, and analyzed using a 100 μL/min nebulizer, Aridus II desolvation system, and ThermoFisher Neptune multi-collector ICP-MS, respectively. All instrumentation was sitated at the WHOI Plasma Facility. Barium-isotopic compositions were calculated from simultaneous monitoring of ion beams corresponding to m/z 131 (Xe, xenon), 135 (Ba), 136 (Xe; Ba; Ce, cerium), 137 (Ba), 138 (Ba; La, lanthanum; Ce), 139 (La) and 140 (Ce).
Problem Report:
Sample from 1,000 m (Event #42; St. 12b) has an asymmetric uncertainty due to possible evaporative losses; positive uncertainty is +1.4 nmol/kg, whereas negative uncertainty is −6.3 nmol/kg (both are one standard deviation).
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