Triple oxygen isotopes in biogenic and sedimentary carbonates

The O-17 anomaly (Delta O-17) of natural waters has been shown to be sensitive to evaporation in a way analogous to deuterium excess, with evaporated bodies of water (e.g., leaf waters, lake waters, animal body waters) tending to have lower Delta O-17 than primary meteoric waters. In animal body water, Delta O-17 relates to the intake of evaporated waters, evaporative effluxes of water, and the Delta O-17 value of atmospheric O-2, which itself carries signatures of global carbon cycling and photochemical reactions in the stratosphere. Carbonates have the potential to record the triple oxygen isotope compositions of parent waters, allowing reconstruction of past water compositions, but such investigations have awaited development of methods for high-precision measurement of Delta O-17 of carbonate. We describe optimized methods based on a sequential acid digestion/reduction/fluorination approach that yield Delta O-17 data with the high precision (similar to 0.010 parts per thousand, 1 sigma) needed to resolve subtle environmental signals. We report the first high-precision Delta O-17 dataset for terrestrial carbonates, focusing on vertebrate biogenic carbonates and soil carbonates, but also including marine invertebrates and high-temperature carbonates. We determine apparent three-isotope fractionation factors between the O-2 analyte derived from carbonate and the parent waters of the carbonate. These in combination with appropriate temperature estimates (from clumped isotope thermometry, or known or estimated body temperatures) are used to calculate the delta O-18 and Delta O-17 of parent waters. The clearest pattern to emerge is the strong O-17-depletion in avian, dinosaurian, and mammalian body water (from analyses of eggshell and tooth enamel) relative to meteoric waters, following expected influences of evaporated water (e.g., leaf water) and atmospheric O-2 on vertebrate body water. Parent waters of the soil carbonates studied here have Delta O-17 values that are similar to or slightly lower than global precipitation. Our results suggest that Delta O-17 will have useful application to paleoenvironmental studies of continental environments where the effects of evaporation are important, and where vertebrate body water may record an isotopic signal of evaporated water sources and atmospheric oxygen. (C) 2014 Elsevier Ltd. All rights reserved.