Statistical Analysis

The stable carbon isotope values were expressed in δ notation which illustrated the deviations of the isotope ratio of a sample relative to a standard, for instance

where R_sam and R_std are the ¹³C/¹²C of the sample and standard, respectively.

Analysis of variance (ANOVA) was used to determine if means differed significantly between the USA and China. Linear discriminant analysis (LDA) was performed for dimensionality reduction. All of the analysis was performed using R Studio 2022.07.01 (Posit software, PBC, Boston, MA) and R 4.2.1 (The R Foundation for Statistical Computing, Vienna, Austria).