Dataset: Barium isotope tracer experiment results from natural and synthetic barite–fluid laboratory equilibration experiments in artificial and filtered seawater

Laboratory barite–fluid isotope-tracer experiments were conducted in the NIRVANA Labs at the Woods Hole Oceanographic Institution. A four-condition matrix combined two fluid types, artificial seawater and filtered seawater from Vineyard Sound, Massachusetts, with two barite types, synthetic barium sulfate and natural pelagic barite isolated from Equatorial Pacific sediments. Artificial seawater was prepared following Smith & Chanley (1975) and adjusted to approximately pH 8.1 with concentrated potassium hydroxide. Filtered seawater was collected using the flow-through seawater system at the Environmental Systems Laboratory at the Woods Hole Oceanographic Institution (Huguenin, 1975), collected into 1 liter acid-washed high-density polyethylene bottles, and filtered through a 0.4 micrometer acid-washed polyethersulfone membrane in a clean room. Synthetic barite was Alfa Aesar barium sulfate powder, Lot 24177, and natural pelagic barite was isolated from Equatorial Pacific sediments. Known quantities of barite powder were added to each fluid and kept under constant agitation for up to six months. In each experiment, the dissolved pool was amended with a 136Ba-enriched solution such that the initial fluid 138Ba:136Ba ratio was approximately 0.35 ± 0.03 (±2 standard error, n = 4). Barium-136 additions were adjusted to achieve an initial barite saturation state of 1.3, calculated using PHREEQC. Aliquots of 2 milliliters were sampled over 174 days and filtered through a 0.22 micrometer polyethersulfone membrane filter prior to analysis of the fluid 138Ba:136Ba ratio.