Seasonal and interannual variation in Santa Barbara Basin water temperatures observed in sediment trap foraminiferal Mg/Ca

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.