We have generated a Santa Barbara Basin sediment trap Mg/Ca record to evaluate culture-based calibration equations for the temperate/subpolar planktonic foraminiferal species Globigerina bulloides and Neogloboquadrina pachyderma (dextral). G. bulloides and N. pachyderma Mg/Ca are significantly correlated with seasonal variations in temperature of the near-surface and subthermocline depths, respectively. The average deviation between Mg-based and δ18O -based temperature estimates is ¿0.6¿C for G. bulloides and ¿0.8¿C for N. pachyderma. Differences between Mg-derived temperatures and instrumental temperatures may be due to cleaning methods, environmental factors such as seasonal variations in foraminiferal depth habitats, or possible secondary effects on Mg/Ca. Core-top Mg/Ca of both G. bulloides and N. pachyderma is in excellent agreement with average values from the sediment trap, lending strong support for the interpretation of downcore Mg/Ca from these species as annual average near-surface and thermoclinal temperatures.