Reconstructing Devonian Paleotemperature Using the Stable Oxygen Isotope Composition of Bulk Carbonate Rocks

Past climates present an opportunity to observe how temperature interacts with other Earth systems. To make these connections, a well-resolved paleotemperature record during past periods of global change is needed. Oxygen isotope paleothermometry records changes in seawater 18O/16O and temperature for the carbonate-water system. The scarcity of well-preserved fossil material typically used for oxygen isotope paleothermometry during the Devonian leads to a deficiency in the temporal and spatial coverage of a paleotemperature record. Contrary to the assumption that bulk carbonate rocks do not preserve the original temperature signal due to diagenetic alteration, recent evidence suggests that bulk carbonates do record temperature trends. Here I show that bulk carbonate data from the Devonian likely preserve primary paleotemperature signals. I find strong agreement between my bulk record and a previously compiled fossil record. Due to its abundance in the geologic record, carbonate rocks provide ample data to possibly generate a continuous paleotemperature record throughout the Phanerozoic and into the Precambrian that can be compared to other Earth records, such as global biodiversity trends. Using our bulk carbonate-derived temperature record, we found that in general cooler temperatures corresponded with biologic radiation while extreme warm temperatures or rapid shifts in temperature corresponded with the loss of biodiversity or even mass extinction events. These conclusions of how temperature relates to the biosphere are invaluable in helping climate scientists project future impacts from anthropogenically-driven climate change