Constraining calcification habitat using oxygen isotope measurements in tropical planktonic foraminiferal tests from surface sediments

Geochemical signals from planktonic foraminiferal tests provide a wide array of tools to investigate past hydrographic changes, but these techniques are limited by our understanding of the habitat at which these organisms form their shell. Quantitative constraints on the variability of the calcification habitat of these organisms can thus lead to better interpretations of these signals and more quantitative constraints on indirect properties related to these signals. We compiled oxygen isotope data from the Tropics to investigate global trends in the apparent calcification depth (ACD) of commonly used planktonic foraminifera. Using Globigerinoides ruber albus, Trilobatus sacculifer, Globorotalia tumida, Neogloboquadrina dutertrei and Pulleniatina obliquiloculata, we find that our ACD estimates for the global tropics largely match regional ACD estimates from other studies. G. ruber and T. sacculifer seem to calcify in the surface mixed layer with a mean ACD and 95% confidence interval of 17 [0,86] m and 48 [0,128] m, respectively, and G. tumida, N. dutertrei, and P. obliquiloculata seem to calcify below the mixed layer with a mean ACD of 210 [123,385] m, 114 [42,173] m, and 94 [0,169] m, respectively. The global data set enables the determination of calcification depths across locations with a wide range of thermocline depths. We find that G. tumida exhibits a calcification depth that is more spatially invariant, while N. dutertrei and P. obliquiloculata seem to calcify deeper in the water column in regions where the thermocline is deeper, as has been previously suggested.