Abstract On geological timescales, oceanic [Mg21] and [Ca21] vary with changing rates of weathering,seafloor spreading and dolomite formation. Accurate reconstruction of the ratio between [Mg21] and[Ca21] in seawater (Mg/Casw), may potentially be reconstructed using foraminiferal Mg/Ca ratios. Since bothtemperature and seawater Mg/Ca impact foraminiferal Mg/Ca, successful reconstruction of Mg/Caswrequires quantification of both these parameters independently on foraminiferal Mg/Ca, as well as theircombined effect on Mg-incorporation. Here we present the combined and isolated impacts of temperatureand Mg/Casw on Mg incorporation in two model species, the benthic hyaline (i.e., perforate) foraminiferElphidium crispum and porcelaneous (i.e., miliolid) foraminifer Quinqueloculina sp. using controlled growthexperiments. Specimens of these two species were kept at four different temperatures (ranging from 10 to278C) and three Mg/Casw’s (3.4, 6.4 and 8.5 mol/mol), resulting in 12 experimental conditions. Newly growncalcite was analyzed for a number of elements (Na, Mg and Sr) by laser ablation-ICP-MS. Results show thatalthough the Mg/Ca varied by more than an order of magnitude between species, the sensitivity of Mgincorporation with respect to temperature appeared not to be influenced by Mg/Casw. By extension, theseresults may also help improving accuracy in the reconstruction of past Mg/Casw based on foraminifera withcontrasting Mg/Ca.
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