Samuel Epstein (December 9, 1919 – September 17, 2001) was a Canadian-American geochemist who developed methods for reconstructing geologic temperature records using stable isotope geochemistry. He was elected to the United States National Academy of Sciences in 1977, and a fellow of the Royal Society of Canada in 1997.
In 1947, Epstein moved to the United States to begin a research fellowship with Harold Urey's group at the University of Chicago. While at Chicago, Epstein, along with Ralph Buchsbaum, Heinz A. Lowenstam, C. R. McKinney and others developed the carbonate-water isotopic temperature scale, allowing ancient ocean temperatures to be determined from precise measurements of 18O/16O in geological samples of calcium carbonate. This method is still the most widely used geochemical climate proxy for locations and times not sampled in ice core records. Epstein joined the faculty of the California Institute of Technology in 1952, and continued to explore the new field of stable isotope geochemistry. He and his students used mass spectrometry to study natural variations in the isotopic abundances of hydrogen, carbon, oxygen and silicon, with applications to archeology, biochemistry, climatology, and geology.
Epstein remained at Caltech as a Professor and Professor Emeritus until shortly before his death on September 17, 2001.