NOAA/WDS Paleoclimatology - Central and Southern Atlantic Ocean benthic foraminiferal Mg/Ca, DCO2-3 and BWT Data from core top samples

Existing benthic foraminiferal Mg/Ca-temperature calibrations are surrounded by substantial uncertainties mainly due to low temperature sensitivity of Mg/Ca in most benthic foraminifers and the effect of carbonate ion concentration on benthic foraminiferal Mg/Ca. Here we present Mg/Ca analysis of Rose Bengal stained and exceptionally well-preserved tests of the infaunal benthic foraminifer Globobulimina spp. from 39 eastern equatorial Atlantic core top samples. Mg/Ca in Globobulimina spp. varies between 2.5 mmol/mol and 9.1 mmol/mol corresponding to bottom water temperatures (BWT) between 1.8? and 19.1? and ??CO?_(3 pore water)^(2-) between 33.7±4 and -34.3±4 µmol/kg in sediment depths between 1 and 10 cm. Mg/Ca and BWT are linearly correlated with a best fit of Mg/Ca[mmol/mol]=(0.36±0.02)*BWT[°C]+2.22±0.19 (r2=0.92, p: 11*10-20, and n=39). Using total alkalinity and pH data of pore water samples from 64 Atlantic multi-corer sites, we obtained ??CO?_(3 pore water)^(2-)data from the depth habitat range of Globobulimina spp. (= 1 cm = 10 cm below sediment surface). We show that ??CO?_(3 pore water)^(2-) is significantly lower than and linearly co-varies with the ??CO?_3^(2-) of the overlying bottom water: ??CO?_(3 pore water)^(2-)=(0.67±0.05)*??CO?_(3 bottom water)^(2-)-(39.84±1.98); r2=0.75, p: 6*10-20, n=64. We found a Mg/Ca sensitivity of 0.009±0.0044 mmol/mol per µmol/kg ??CO?_(3 pore water)^(2-) and Mg/Ca temperature sensitivity of 0.32 ±0.06 mmol/mol/°C after a correction for the ??CO?_(3 pore water)^(2-) effect. This study provides a robust Mg/Ca-temperature calibration, highlights that ??CO?_(3 pore water)^(2-) is spatially and most likely temporally variable, and contradicts the notion that infaunal foraminiferal Mg/Ca is relatively immune from ??CO?_(3 )^(2-) changes in the overlying bottom water. Furthermore, comparison of down core Mg/Ca data of Cibicides pachyderma and Globobulimina spp. demonstrates that the high temperature sensitivity of Mg/Ca in Globobulimina spp. presents a more robust paleothermometer to reconstruct past changes in the thermal state of the deep ocean.