Isotopic ratios refer to the measurements of the proportions of different versions of an element in a sample. It compares the amounts of different isotopes - atoms with different numbers of neutrons - in a substance. Full definition
Atmospheric scientists call this shift the Suess effect, and the change in isotopic ratios of carbon due to fossil - fuel use is easy to see over the last century. (theatlantic.com)
The study of the rubidium / strontium isotopic ratios in a set of meteorite samples shows the general approach to (myintimcity.com)
In collaboration with the Institute for Arctic and Alpine Research (INSTAAR) of the University of Colorado, ESRL / GMD now routinely monitors carbon isotopic ratios of CO2 and CH4. (esrl.noaa.gov)