New Insights on Benthic Mg/Ca Paleothermometry in the Western South Atlantic

Abstract. Close relationship exists between the Mg/Ca ratio in foraminiferal shells and the calcification temperature. Even when most paleoceanographic studies focused on near-surface property reconstructions leaving the deep ocean less explored, during the last years, new Mg/Ca-Temperature calibrations were established for the benthic genera Uvigerina and Cibicidoides. Among the main conclusions, it has been established that secondary factors exist affecting the Mg incorporation into the benthic shells, particularly at low temperatures. In order to establish a potential relationship between the Mg/Ca ratios of the aforementioned genera for the western South Atlantic and tropical Atlantic, 38 core-Top samples are analyzed here. Our results confirm the existence of other parameters than just temperature affecting Cibicidoides and Uvigerina Mg/Ca, suggesting that the effect of all these other parameters together produces a variable offset between both genera that can be linearly approached. We develop an algorithm that allows transforming the Mg/Ca data measured on one of these two genera into the other. This not only would allow performing a continuous Mg/Ca record independent of which benthic genera is available for study but also potentially leads to new and more accurate Mg/Ca-Temperature calibrations allowing to get more, high-resolution bottom water temperature reconstructions.