Uranium stable isotope fractionation in the Black Sea: Modern calibration of the 238U/235U paleo-redox proxy

The isotopic compositions of redox-sensitive metals, including uranium (U), in marine sediments have recently emerged as powerful diagnostic tracers of the redox state of the ancient ocean–atmosphere system. Reliable interpretation of sedimentary isotopic information requires a thorough understanding of the environmental controls on isotopic fractionation in modern anoxic environments before being applied to the paleo-record. In this study, the...