Paleoceanographic modeling of temperature‐salinity profiles from stable isotopic data

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Abstract
Temperature‐salinity (T‐S) profiles in ancient seawater can be estimated from oxygen isotopic compositions of well‐preserved calcitic fossils sampled from known paleodepth gradients. The proposed model uses isotopic compositions of fossils to determine possible combinations of temperature and salinity during deposition (given estimates of average salinity, isotopic composition, and net global hydrologic fractionation for ancient oceans). Increasing density with depth constrains those combinations to narrow ranges. This graphic method superposes curves for density and isotopic composition in T‐S space, to reveal possible ancient T‐S profiles. Application of this method to oxygen isotope data from Ordovician brachiopods deposited on the eastern continental slope of North America demonstrates its usefulness and yields a stable seawater column in which brackish intermediate waters overlie warmer, more saline deep waters.