Defining uncertainty and error in planktic foraminiferal oxygen isotope measurements

Abstract

Foraminifera are the backbone of paleoceanography. Planktic foraminifera are one of the leading tools for reconstructing water column structure. However, there are unconstrained variables when dealing with uncertainty in the reproducibility of oxygen isotope measurements. This study presents the first results from a simple model of foraminiferal calcification (Foraminiferal Isotope Reproducibility Model; FIRM), designed to estimate uncertainty in oxygen isotope measurements. FIRM uses parameters including location, depth habitat, season, number of individuals included in measurement, diagenesis, misidentification, size variation, and vital effects, to produce synthetic isotope data in a manner reflecting natural processes. Reproducibility is then tested using Monte Carlo simulations. Importantly, this is not an attempt to fully model the entire complicated process of foraminiferal calcification; instead we are trying to include only enough parameters to estimate the uncertainty in foraminiferal δ18O records. Two well-constrained empirical datasets are simulated successfully, demonstrating the validity of our model. The results from a series of experiments with the model show that reproducibility is largely controlled by the number of individuals in each measurement, but also strongly a function of local oceanography, if the number of individuals is held constant. Parameters like diagenesis or misidentification have an impact on both the precision and the accuracy of the data. FIRM is a tool to estimate isotopic uncertainty values and to explore the impact of myriad factors on the fidelity of paleoceanographic records, particularly for the Holocene.