About 5% of each FAME fraction from each sample were measured in duplicate on a Thermo Trace GC coupled via a combustion interface (1000 °C) to a Thermo Finnigan MAT 252 isotope ratio mass spectrometer. Results are reported in ‰ relative to VPDB. During measurement, standard mixtures containing 12 externally-calibrated alkanes was measured every 6 runs to monitor average absolute deviations from known δ¹³C values. Accuracy was consistently ≤0.2‰. Reproducibility for the duplicate measurements of each compound ranged from <0.1‰ to 0.7‰. The δ¹³C values of n-FAMEs were subsequently corrected for the derivative methyl carbon to derive n-FA δ¹³C values including error propagation.