Radioactive 129I has travelled the equivalent of a third of the way round the globe, since being released from nuclear fuel reprocessing plants in the UK and France. The iodine’s 15,000 km journey begins in the nuclear plants at Sellafield and La Hague and continues via the Arctic Ocean and then southward via the Grand Banks towards Bermuda, where it is found at very low concentrations about 20 years later. This tracer has been used to provide the most complete up-to-date, high-accuracy mapping of the oceanic currents that transport CO2 and other greenhouse gases from the atmosphere to the abyssal depths of the deep North Atlantic Ocean. These results are being presented at the Goldschmidt geochemistry conference in Paris.