Photochemical Speciation of Oxygen Isotopes in the Solar Nebula

We have performed time-dependent photochemical calculations of CO selfshielding in the surface region of a turbulent nebula, and demonstrated that substantial mass-independent fractionation in bulk oxygen isotopes in the nebula was possible on timescales of 10 years. CO photodissociation in the presence of abundant H2 yields δvalues for nebular H2O with δO/δO near 1.0, consistent with measurements in CaAl-rich inclusions. This mechanism provides a self-consistent explanation for the oxygen isotope values of nebular water inferred from secondary minerals in unequilibrated chondrites, and places constraints on the far-ultraviolet radiation in the solar nebula environment and the strength of turbulent vertical mixing in the nebula.