Dataset: Barium isotope tracer experiment 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.  

For the isotope-tracer experiments, most dissolved barium in solution was supplied as dissolved 135Ba, whereas solid-phase barium in the seed barite possessed natural abundances. Dissolved 135Ba was derived from 135BaCO3 powder that was dissolved in hydrochloric acid and reconstituted in ultra-high purity water before addition to experiments. Experiments were carried out in duplicate in 1 liter acid-washed high-density polyethylene reactors at three initial leverage values. The amount of 135Ba spike added was adjusted based on temperature, salinity, and preexisting dissolved barium in the artificial seawater to achieve an initial barite saturation state of Ωbarite = 1.3. Reactors were agitated continuously on a New Brunswick Scientific Innova 2100 orbital shaker table. Reactors were removed from the shaker table 10 minutes before sampling to allow settling of the solid phase. Fluid aliquots of 2 milliliters were collected through time and immediately filtered through acid-cleaned 0.22 micrometer polyethersulfone membrane disc filters. A control reactor without seed barite was run under the same conditions to assess adsorption of barium to reactor walls.

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.

For isotope ratio analysis, filtered samples were diluted with 2 percent nitric acid and indium was added as an internal standard to a final concentration of 1 nanogram per milliliter. Samples were diluted and measured at salinity 1.75 to minimize non-spectral matrix effects. Filtered samples were analyzed for 137Ba:135Ba at the Woods Hole Oceanographic Institution Plasma Facility.