GSA Annual Meeting in Phoenix, Arizona, USA - 2019

Paper No. 22-4
Presentation Time: 9:00 AM-5:30 PM


FORSTER, Clayton1, BELL, Alex1, BURKE, Joshua1, PERDUE, Nathan1, RIDDLE, Daniel1, SMITH, Russel1, TOLMAN, Alex2 and ZANAZZI, Alessandro1, (1)Earth Science, Utah Valley University, Orem, UT 84058, (2)Department of Earth Science, Utah Valley University, Orem, UT 84058

With the goal of investigating the relationship between the diet and the isotopic composition of human fingernails, we analyzed the bulk carbon (δ13C) and nitrogen (δ15N) stable isotope composition of 199 fingernail clippings from seven students attending the Isotope Geochemistry course at Utah Valley University. We collected the fingernail clippings in January, February, and March 2019. During the same period, the students also kept a detailed record of their daily diet. In terms of controlling factors, the position in the trophic chain of the consumer primarily affects his/her δ15N value. Every level up from the primary producers adds ~4‰. The plants consumed directly by the individual or by the animals he/she eats mainly control his/her δ13C value. C3 plants (e.g., rice and vegetables) discriminate less against 13C than C4 plants (e.g., corn and millet) and therefore have a lower δ13C (~-27‰ vs. ~-13‰). In addition, there is an increase of ~1‰ in the δ13C value for each level in the trophic chain. Additional minor factors that may affect the δ13C and δ15N of human keratin are health, age, sex, metabolic/physiological processes (e.g. urea excretion rate), agricultural practices (e.g., use of synthetic fertilizers vs. manure), climate, and food origins (e.g., corn from the Midwest U.S. vs corn from Mexico). Average (±1 sd) δ13C (vs. PDB) and δ15N (vs. air) of all students are -17.82±0.70‰ and 9.10±0.32‰, respectively. The small isotopic variability in fingernails likely results from globalization in food production and distribution. We also found higher average δ-values in omnivores (δ13C=-17.68±0.57‰; δ15N=9.13±0.33‰; n=179) than in the vegetarian student (δ13C=-19.03±0.49‰; δ15N=8.90±0.12‰; n=20). Higher δ-values in omnivores vs. vegetarians likely reflect the higher position in the trophic chain and the dominant use of corn for livestock feeding. Results from this study can be useful for the geographical allocation of individuals in forensic cases and for investigating the paleodiets of mummies in archeological studies.