Using plant physiological stable oxygen isotope models to counter food fraud

Fraudulent food products, especially regarding false claims of geographic origin, impose economic damages of $30–$40 billion per year. Stable isotope methods, using oxygen isotopes (δ18O) in particular, are the leading forensic tools for identifying these crimes. Plant physiological stable oxygen isotope models simulate how precipitation δ18O values and climatic variables shape the δ18O values of water and organic compounds in plants. These models have the potential to simplify, speed up, and improve conventional stable isotope applications and produce temporally resolved, accurate, and precise region-of-origin assignments for agricultural food products. However, the validation of these models and thus the best choice of model parameters and input variables have limited the application of the models for the origin identification of food. In our study we test model predictions against a unique 11-year European strawberry δ18O reference dataset to evaluate how choices of input variable sources and model parameterization impact the prediction skill of the model. Our results show that modifying leaf-based model parameters specifically for fruit and with product-independent, but growth time specific environmental input data, plant physiological isotope models offer a new and dynamic method that can accurately predict the geographic origin of a plant product and can advance the field of stable isotope analysis to counter food fraud.

ShellChron 0.2.8: A new tool for constructing chronologies in accretionary carbonate archives from stable oxygen isotope profiles

This work presents ShellChron, a new model for generating accurate age-depth models for high-resolution paleoclimate archives, such as corals, mollusk shells and speleothems. Reliable sub-annual age models form the backbone of high-resolution paleoclimate studies. In absence of independent sub-annual growth markers in many of these archives, the most reliable method for determining the age of samples is through age modelling based on stable oxygen isotope or other seasonally controlled proxy records. ShellChron expands on previous solutions to the age model problem by modelling seasonal variability in the proxy record using a combination of growth rate and temperature sinusoids in sliding window approach. This new approach creates smoother, more precise age-depth relationships for multi-annual proxy records with the added benefit of allowing assessment of the uncertainty on the modelled age. The modular script of ShellChron allows the model to be tailored to specific archives, without being limited to δ18Oc proxy records or carbonate archives, with high flexibility in assigning the relationship between the input proxy and the seasonal cycle. The performance of ShellChron in terms of accuracy and computation time is tested on a set of virtual seasonality records and real coral, bivalve and speleothem archives. The result shows that several key improvements in comparison to previous age model routines enhance the accuracy of ShellChron on multi-annual records while limiting its processing time. The current full working version of ShellChron enables the user to model the age of a 10-year long high-resolution (16 samples/yr) carbonate records with monthly accuracy within one hour of computation time on a modern personal computer. The model is freely accessible on the CRAN database and GitHub. Members of the community are invited to contribute by adapting the model code to suit their research topics.