Isotopically anomalous metabolic oxygen in marine vertebrates as physiology and atmospheric proxy

Pack et al. (2013) showed that the triple oxygen isotope composition of bioapatite along with a mass balance model of land-living mammals can be used as proxy for the 17O anomaly of ambient air O2 and hence pCO2 in combination with the global primary productivity (GPP). Here, we present an analytic protocol for high-precision triple oxygen isotope analyses along with new data of tooth enamel of a set of marine vertebrates, including sharks, dolphins, and whales. The goal is to demonstrate whether traces of anomalous inhaled oxygen are also found in these species, whether differences are observed between sharks and marine mammals, and if the triple oxygen isotopes hence could provide information about marine vertebrate physiology, e.g., metabolic rate or drinking behavior.

Marine mammal data show a clear signature of isotopically anomalous metabolic oxygen in their bioapatite. This is related to a low flux ratio of isotopically normal drinking and food water to anomalous metabolic oxygen. Traces of anomalous metabolic oxygen are also observed in shark bioapatite. Sharks and mammals have overlapping 18O/16O ratios, but distinct 17O signatures. Our new data suggest that triple oxygen isotopes are a valuable new tracer to assess the physiology of extant and extinct marine vertebrates and may provide a new proxy for past atmospheric CO2 mixing ratios and global primary biosphere production (Feng et al. 2022).

Feng et al. (2022) Geochimica et Cosmochimica Acta 328, 85-102.

Pack et al. (2013) Geochimica et Cosmochimica Acta 102, 306-317.