Mg/Ca-temperature calibration for the benthic foraminifera Melonis barleeanum and Melonis pompilioides

An important tool for deep-sea temperature reconstruction is Mg/Ca paleothermometry applied to benthic foraminifera. Foraminifera of the genus Melonis appear to be promising candidates for temperature reconstructions due to their wide geographical and bathymetric distribution, and their infaunal habitat, which was suggested to reduce secondary effects from carbonate ion saturation (Δ[CO₃²⁻]). Here, we make substantial advances to previous calibration efforts and present new multi-lab Mg/Ca data for Melonis barleeanum and Melonis pompilioides from more than one hundred core top samples spanning in situ bottom temperatures from −1 to 16 °C, coupled with morphometric analyses of the foraminifer tests. Both species and their morphotypes seem to have a similar response of Mg/Ca to growth temperature. Compilation of new and previously published data reveals a linear dependence of temperature on Mg/Ca, with a best fit of Mg/Ca (mmol/mol) = 0.113 ± 0.005 ∗ BWT (°C) + 0.792 ± 0.036 (r² = 0.81; n = 120; 1σ SD). Salinity, bottom water Δ[CO₃²⁻], and varying morphotypes have no apparent effect on the Mg/Ca-temperature relationship, but pore water Δ[CO₃²⁻] might have had an influence on some of the samples from the tropical Atlantic.