Dr. Paul Aharon is the former Ray. E. Loper Endowed Chair in Geology since 2001, and Professor Emeritus since 2016. His expertise lay in the acquisition of light stable isotopes (Carbon, Hydrogen, Nitrogen, Oxygen and Sulfur) by Isotope Ratio Mass Spectrometry (IRMS), Secondary Ion Mass Spectrometry (SIMS) and heavy radioactive isotopes (Uranium-Thorium Series) by Multiple-Collector Inductive Plasma Mass Spectrometry (MC-ICPMS). Applications include isotopes as tracers of source, reconstruction of regional and global water, ice and carbon cycles during the Quaternary, chronology of layered geological materials such as corals, giant clams and speleothems and marine-based gas hydrates. Present investigations are focused on speleothems in the Southeast US and on the island of Niue in the tropical Pacific that serve as time capsules of past hydroclimate variability and El-Niño-Southern Oscillation (ENSO) frequency and intensity changes.