Mg/Ca-paleothermometry in the western Mediterranean Sea on planktonic foraminifer species Globigerina bulloides: Constraints and implications

Abstract

We generated a high-resolution SST Mg/Ca record for the surface-dwelling planktonic foraminifera Globigerina bulloides from the core MD99-2346 collected in the Gulf of Lion, and compared it to that obtained using modern analogue techniques applied to fossil foraminiferal assemblages (SST MAT ). The two temperature records display similar patterns during the last 28,000 years but the SST Mg/Ca estimates are several degrees warmer (∼ +4 °C) than SST MAT. The temperature shift between SST Mg/Ca and SST MAT remained relatively constant over time. This seems to exclude a bias on the Mg/Ca record associated with salinity or secondary Mg-rich calcite encrustation on the foraminiferal tests during early diagenesis. Therefore, anomalously high Mg/Ca suggests either: (1) the empirical equation for G. bulloides of Elderfield and Ganssen (2000) is incorrect; or (2) there is a specific Mediterranean genotypes of G. bulloides for which a specific Mg/Ca-temperature calibration is needed.