Previously he was an Assistant Professor at the University of South Carolina. He received a BA in chemistry from Carleton College, followed by graduate studies in the MIT/WHOI Joint Program and a postdoc at Caltech. John studies the biogeochemical cycling of trace metals and their stable isotope ratios in the oceans. His research has included the first high-spatial resolution sections of trace metal isotopes in the ocean, as well as laboratory experiments and numerical modeling to interpret this natural data.