The concentration of 129I was measured in water samples from three depth profiles collected in the central Arctic Ocean during 1996. The results indicate >7¿108 atoms/liter in the cold, low salinity, 100-m-deep surface layer, and 0.06¿108 atoms/liter at a depth below 3 km. The total inventory of 129I in the region is estimated at about 2.7¿1027 atoms, representing 34% of the total discharge from Sellafield and La Hague until 1996. Marine input accounts for a major part (>90%) of the 129I inventory in the central Arctic Ocean while input from fresh water (ice melting and rivers), bomb tests and nuclear dumping contribute by about 3%. The inventory suggests a maximum marine transport time of 11 years for 129I from La Hague-Sellafield to the central Arctic. The 129I concentration at a depth below 3 km is about one order of magnitude higher than the estimated pre-anthropogenic global marine value, reflecting contribution from anthropogenic sources. ¿ 1999 American Geophysical Union