Ca and Mg fractionation in C3 and C4 grasses and their implications for reconstructing paleodiets and serving as biosignatures

Abstract

Recent studies have shown isotopic variability in the enamel of mammalian primary consumer species like bison (Bison bison). Since enamel records the isotopic composition of the host animal’s diet, intra-trophic level variability carries paleoenvironmental information that could be used to reconstruct paleotemperatures and trophic levels. The cause of this variability remains a topic of debate in the stable isotope community. Preliminary research shows Ca and Mg isotopes inversely covary following nutrient uptake in the roots of grasses, which pass along the same isotopic relationship to bison through diet. This result is surprising given Ca and Mg’s similar chemistry as divalent cations and suggests an unknown fractionation mechanism preferentially selects either heavy or light isotopes of Ca and Mg. However, intra-trophic level variability requires dietary differences between bison populations. One difference is the abundance of C3 and C4 grasses in their grazing lands, often a reflection of temperature. This study explores variability in the primary consumer trophic level (bison) by analyzing the Ca and Mg isotopic differences between C3 and C4 grasses. We hypothesize that observed intra-trophic level variability in bison enamel reflects fractionation in bison during metabolism. In addition, advances in mass spectroscopy open celestial bodies in the Solar System to new forms of analysis with the potential to identify life. In fulfillment of the Planets and Life certificate, this thesis explores if measurements of δ26Mg and δ13C in the lithographic record could serve as biosignatures. We hypothesize that δ26Mg excursions used in conjunction with δ13C excursions can serve as biosignatures and are detectable by current and planned Mars rovers.