GSA Annual Meeting in Phoenix, Arizona, USA - 2019

Paper No. 220-11
Presentation Time: 4:20 PM


PASSEY, Benjamin H., Department of Earth & Environmental Sciences, University of Michigan, 1100 North University Avenue, Ann Arbor, MI 48109, HU, Huanting, Shanghai Jiao Tong University, Shanghai, China and WASILJEFF, Joonas A.M., Department of Geosciences and Geography, University of Helsinki, Gustaf Hällströmin katu 2 (Physicum) P.O. Box 64 00014 University of Helsinki, Helsinki, Finland

The vertebrate biomineral triple oxygen isotope pCO2 barometer proposed by Pack et al. (2013) (Geochim. Cosmochim. Acta 102, 306-317) is based on the premise that body water and hence biominerals of land-dwelling vertebrates contains a small fraction of oxygen derived from atmospheric O2 (through respiration), and that the triple oxygen isotope composition of atmospheric O2 is sensitive to atmospheric pCO2 and global gross primary productivity (GPP). A significant challenge with this barometer is dealing with the variable ‘dilution’ of the atmospheric O2 signal relating to differing water-use strategies amongst vertebrates. In other words, water-conserving animals will have a larger relative fraction of O2-derived oxygen than will animals with high water-intake requirements. Here we further elaborate on the ‘environmental physiology isotope concordance’ (EPIC) approach for addressing this biological signal. In short, the EPIC approach makes use of endmember body water triple oxygen isotope models for the most water-conserving (e.g., kangaroo rat, ostrich), and water-promiscuous (e.g., hippopotamus, elephants) physiologies. Each model results in a predicted relationship between biomineral Δ17O and atmospheric O2 Δ17O. For any given assemblage of contemporaneous vertebrates, there should be a concordant atmospheric O2 Δ17O value (or range of values) which, when propagated through the endmember body water models, can predict all of the measured biomineral Δ17O values. No assumptions about the water-balance ecophysiology of extinct animals are required, but greater the range of water-balance physiologies sampled in the contemporaneous assemblage, the more narrowly-constrained will be the estimate of atmospheric O2 Δ17O, and hence pCO2. We summarize published and unpublished vertebrate Δ17O data spanning the past 160 million years and use the EPIC approach to interpret these in terms of atmospheric pCO2. We will also address challenges that must be overcome for full realization of the vertebrate triple oxygen isotope pCO2 method, including addressing variability in past GPP, and minimizing sample size requirements.