Global Core Top Calibration of delta O-18 in Planktic Foraminifera to Sea Surface Temperature

Abstract

The oxygen isotopic composition of planktic foraminiferal calcite (𝛿18Oc) is one of the mostprevalent proxies used in the paleoceanographic community. The relationship between𝛿18Oc,temperature, and seawater oxygen isotopic composition (𝛿18Ow) is firmly rooted in thermodynamics, andexperimental constraints are commonly used for sea surface temperature (SST) reconstructions. However,in marine sedimentary applications, additional sources of uncertainty emerge, and these uncertaintyconstraints have not as of yet been included in global calibration models. Here, we compile a global dataset of over 2,600 marine sediment core top samples for five planktic species:Globigerinoides ruber,Trilobatus sacculifer,Globigerina bulloides,Neogloboquadrina incompta, andNeogloboquadrinapachyderma. We developed a suite of Bayesian regression models to calibrate the relationship between𝛿18Ocand SST. Spanning SSTs from 0.0 to 29.5◦C, our annual model with species pooled together has amean standard error of approximately 0.54‰. Accounting for seasonality and species-specific differencesimproves model validation, reducing the mean standard error to 0.47‰. Example applications spanningthe Late Quaternary show good agreement with independent alkenone-based estimates. Our pooledcalibration model may also be used for reconstruction in the deeper geological past, using modern plankticforaminifera as an analog for non-extant species. Our core top-based models provide a robust assessmentof uncertainty in the𝛿18Ocpaleothermometer that can be used in statistical assessments of interproxy andmodel-proxy comparisons. The suite of models is publicly available as the Open Source software librarybayfox, for Python, R, and MATLAB/Octave.