Isotopic data refers to information about the different forms of atoms, called isotopes, found in a sample or substance. It helps scientists understand the composition, origin, or processes related to that material. Full definition
The team presents new isotopic data showing that a burst of oxygen production by photosynthetic cyanobacteria temporarily increased oxygen concentrations in Earth's atmosphere. (sciencedaily.com)
From what I can tell you really can not use isotopic data to determine this accurately at all. (judithcurry.com)
Evidence from isotopic data on Early Holocene bison and other large herbivores in northern Europe. (senckenberg.de)