text: Jean-Claude Duplessy, a former student of the Ecole Normale Supérieure (Ulm), a physics graduate, is a geochemist. His work has contributed to a better understanding of how the ocean has functioned over the recent history of the Earth. He is a recognized pioneer in rebuilding ocean dynamics through the use of carbon isotopes and foraminiferous shell oxygen in marine sediments. He was one of the first to see the importance of a high quality chronology for a reliable interpretation of measurements related to climate variations in the Earth's past.