Dataset: Mass-dependent barium isotope and dissolved barium concentration results from barite–fluid laboratory equilibration experiments

Laboratory barite–fluid equilibration experiments were conducted in the NIRVANA Labs at the Woods Hole Oceanographic Institution using trace metal clean procedures. Labware was cleaned with hydrochloric acid and nitric acid, ultra-pure reagents were used, and critical solution handling was carried out in laminar flow workbenches. Experiments used synthetic barite and artificial seawater as a marine analogue system. The barite seed material was 99.998 weight percent pure barium sulfate (Puratronic, Alfa Aesar, Lot 24177) with a nominal grain diameter of 3 micrometers. A 25 liter stock of artificial seawater with salinity 35 ± 0.5 was prepared following Smith and Chanley (1975) and adjusted to approximately pH 8.1 with concentrated potassium hydroxide. The artificial seawater stock contained a background dissolved barium concentration of 26 ± 0.8 nanomoles per liter from the reagent salts. All reactions were carried out at ambient temperature of 20 ± 2 degrees Celsius.

Mass-dependent isotope experiments were conducted in duplicate in 1 liter acid-washed high-density polyethylene reactors at three initial leverage values. All barium in these experiments possessed natural abundances, and no additional dissolved barium was added. Reactors were initiated under barite-undersaturated conditions corresponding to Ωbarite ≈ 0.1, with initial dissolved barium concentration of 26 ± 0.8 nanomoles per liter. Reactors were agitated continuously on an orbital shaker table. Prior to sampling, reactors were removed from the shaker table for 10 minutes to allow settling of the solid phase. Fluid aliquots of 2 milliliters were collected periodically and immediately filtered through acid-cleaned 0.22 micrometer polyethersulfone membrane disc filters. After collection, filtrates were acidified to 0.024 molar hydrochloric acid, at pH less than or equal to 2, and stored for several weeks before analysis. Experiments were incubated under constant agitation for up to 429 hours, and one duplicate from each leverage set was terminated at an intermediate time to allow analysis of the solid phase.

Recovered barite samples were dissolved by alkaline conversion to barium carbonate using a modification of the method of Breit et al. (1985). Briefly, recovered solid-phase material was reacted in perfluoroalkoxy alkane vials with 1 molar sodium carbonate solution, followed by sonication, heating at 80 degrees Celsius, repeated decantation, rinsing with 18.2 megaohm-centimeter water, and final dissolution in 2 molar hydrochloric acid.

Mass-dependent barium isotope analyses followed Bates et al. (2017). Dissolved samples were equilibrated with a 135Ba–136Ba double spike, pre-concentrated from 5 milliliters of seawater matrix by barium–calcium carbonate co-precipitation, dissolved in hydrochloric acid, and purified by passing samples twice through AG 50W-X8 cation-exchange resin before analysis by multi-collector inductively coupled plasma mass spectrometry.