Sulfur isotopes 11/14/12 Lecture outline: 1)sulfur cycle 2)biological fractionation 3)S isotopes in the geologic record 4)mass-independent S isotope fractionation Authigenic marine barite (BaSO 4 ) separated from deep-sea cores SEM Photo: Adina Paytan Hydrothermal barite separated from black smokers SEM Photo: Kim Cobb