Influence of changing deep ocean circulation on the Phanerozoic oxygen isotopic record

Abstract

Isotopic segregation in seawater caused by changing ocean circulation may in part explain the enigmatic oxygen isotopic record of Phanerozoic marine carbonates. Paleoceanographic evidence suggests that circulation of warm saline deep waters has occurred during at least two periods of warm global climate; those saline deep waters should have preferentially stored 18O in the deep oceans. Corresponding depletion of 18O in surface waters would have resulted in lower δ 18O of marine carbonates deposited on continental shelves. Modeling of paleoceanographic isotopic data suggests that this “storage” effect is similar in magnitude (but opposite in sign) to that of modern enrichment of 18O in the oceans by glacial storage. Modeling of carbonate compositions through time that takes into account such storage effects (as predicted by changing global climate) suggests that large changes in the mean oceanic isotopic composition, but neither extreme temperatures nor sudden changes in mean ocean compositions, are needed to explain the isotopic record.