The phrase "various isotopes" refers to different forms of the same element. Isotopes have the same number of protons but different numbers of neutrons in their atomic nuclei. Full definition
Greg Holland, a postdoctoral researcher in isotope geochemistry at the University of Manchester in England, and his colleagues measured the amounts of various isotopes of noble gases in the Bravo Dome gas field in New Mexico, where magmatic gases — primarily carbon dioxide — that allow the mantle to be sampled are buried hundreds of meters below. (scientificamerican.com)
Via various isotope analyses and flow models, Jasechko (2017) estimated that between 42 - 85 % of all groundwater stored in the upper 1 kilometer of the earth's crust is water that had infiltrated the ground more than 11,000 years ago, during last Ice Age. (landscapesandcycles.net)
With data on various isotopes and aridity and CO2 concentrations now complete, the mirroring of the climate change in the horse size is quite exact. (earthtimes.org)