Decoupled carbonate chemistry controls on the incorporation of boron into Orbulina universa

• Main Authors: Howes, Ella L, Kaczmarek, Karina, Raitzsch, Markus, Mewes, A, Bijma, N, Horn, I, Misra, Sambuddha, Gattuso, Jean-Pierre, Bijma, Jelle
• Format: Dataset
• Language: English
• Published: PANGAEA 2017
• Subjects: Alkalinity; total; standard deviation; Aragonite saturation state; Bicarbonate ion; Bottles or small containers/Aquaria (<20 L); Calcite saturation state; Calculated using seacarb; Calculated using seacarb after Nisumaa et al. (2010); Carbon; inorganic; dissolved; Carbonate ion; Carbonate system computation flag; Carbon dioxide; Chromista; Coast and continental shelf; EXP; Experiment; Foraminifera; Fugacity of carbon dioxide (water) at sea surface temperature (wet air); Heterotrophic prokaryotes; Laboratory experiment; Mediterranean Sea; OA-ICC; Ocean Acidification International Coordination Centre; Other studied parameter or process; Partial pressure of carbon dioxide (water) at sea surface temperature (wet air); Pelagos; pH; Potentiometric; Potentiometric titration; Registration number of species; Salinity; Single species; Species; Temperate; Temperature; water; Type; Uniform resource locator/link to reference; Villefranche-2012; δ11B; Ocean acidification; Planktonic foraminifera
• Online Access: https://doi.pangaea.de/10.1594/PANGAEA.868943; https://doi.org/10.1594/PANGAEA.868943

In order to fully constrain paleo-carbonate systems, proxies for two out of seven parameters, plus temperature and salinity are required. The boron isotopic composition (delta 11B) of planktonic foraminifera shells is a powerful tool to reconstruct changes in past surface ocean pH. As [B(OH)]4- is substituted into the biogenic calcite lattice in place of [CO3]2-, it has been suggested that B/Ca ratios in biogenic calcite are a possible proxy for [CO3]2-. However, differentiating between the effects of pH and [CO3]2- is problematic, as they co-vary closely in natural systems, and so the major control on boron incorporation remains unclear. To deconvolve the effects of pH and [CO3]2- on the B/Ca ratio and to test whether d11B remains constant at constant pH, but under changing [CO3]2- (pH 8.05 with 238, 285 and 532 µmol/kg [CO3]2-) and vice versa, we decoupled pH and [CO3]2- (276 +/- 19.5 µmol/kg [CO3]2- with pH 7.7, 7.9 and 8.05) and grew the planktonic foraminifer Orbulina universa in these manipulated culture media. Measurements of the isotope composition of boron and the B/Ca ratio were performed simultaneously using a femtosecond laser ablation system coupled to an MC ICP-MS. Results show that delta11B is controlled by pH and does not respond to changes in [CO3]2-. On the other hand, the B/Ca ratio is driven by [HCO3]- independently of pH. This suggests that B/Ca ratios in foraminiferal calcite may be used as a second, independent, proxy for paleo-carbonate system reconstructions.