Dataset belonging to "Constraining sulfur incorporation in calcite using controlled growth experiments" Version 8

The sulfur over calcium ratio (S/Ca) in foraminiferal shells was recently proposed as a new and independent proxy for reconstructing marine inorganic carbon chemistry. This new approach assumes that sulfur is incorporated into CaCO3 predominantly in the form of sulfate (SO42-) through lattice substitution for carbonate ions (CO32-), and that S/Ca thus reflects seawater [CO32-]. Although foraminiferal growth experiments validated this approach, field studies showed controversial results suggesting that the potential impact of [CO32-] may be overwritten by one or more parameters. Hence, to better understand the inorganic processes involved, we here investigate S/Ca values in inorganically precipitated CaCO3 (S/Ca(cc)) grown in solutions of CaCl2 - Na2CO3 - Na2SO4 - B(OH)3 - MgCl2. Experimental results indicate the dependence of sulfate partitioning in CaCO3 on the carbon chemistry via changing pH and suggest that faster precipitation rates increase the partition coefficient for sulfur. Based on the positive correlation found between S/Ca(cc) and the concentration of only one aqueous sulfate species, CaSO40, we here suggest a critical evaluation of this potential proxy. As sulfate complexation seems to control sulfate uptake in inorganic calcite, application as a proxy using foraminiferal calcite may be limited to periods for which seawater chemistry is well-constrained. As foraminiferal calcite growth is modulated by inward Ca2+ flow to the site of calcification coupled to outward H+ pumping, sulfate incorporation as CaSO40 ion-pair in the foraminifer’s shell also provides a mechanistic link for the observed relationship between S/Ca(cc) and [CO32-].