Trace/minor element:calcium ratios in cultured benthic foraminifera. Part I: Inter-species and inter-individual variability

Trace/minor element signatures (D_Cd, D_Ba, D_Mg, and D_Sr) were measured in the tests (shells) of benthic foraminifera cultured in a trace-metal-concentration-controlled system. The culture system was constructed of inert materials and designed to limit microhabitat effects. This system ensured that variation observed in cultured foraminiferal element:calcium (TE/Ca) signatures was due to biologically mediated (vital) effects only. Two species, Bulimina aculeata and Rosalina vilardeboana, reproduced prolifically during two 4-to-8-month culture periods. In every case (i.e., for both species and each element), the inter-individual variability was larger than the analytical precision. Mean (±1 standard deviation) D_E signatures for B. aculeata were: D_Cd: 1.5 ± 0.4, D_Ba × 10: 2.1 ± 0.7, D_Mg × 1000: 0.62 ± 0.15, and D_Sr × 10: 1.5 ± 0.1. Cultured B. aculeata D_Mg, calibrated from culture and core-top (live) field specimens, predicted temperatures within ±2.0 °C. The observed inter-individual variability from culture specimens was as large or larger than comparable results from core-top investigations. R. vilardeboana D_Cd signatures were significantly lower, while D_Ba, D_Mg, and D_Sr signatures were significantly higher than B. aculeata values. Since our culture system minimizes microhabitat variability, the variation in measured TE/Ca ratios suggests that biological processes are a significant factor in inter-individual and inter-species variability. Comparison of cultured and field-collected foraminiferal D_Ba signatures supports previous findings that pore-water chemistry is a major environmental influence on foraminiferal test chemistry.