Seawater was collected from the western Arctic Ocean for measurements of 18O, 226Ra and 228Ra. The fractions of river runoff and sea ice melt-water in water samples were estimated by using δ18O-S-PO* tracer system. The mean residence time of river water in the Canada Basin was calculated based on the relationship between 228Ra/226Ra)A.R. and the fractions of river runoff in the shelf and deep ocean. Our results showed that the river runoff fractions in the Canada Basin were significantly higher than those in the shelf regions, suggesting that the Canada Basin is a major storage region for Arctic river water. 228Ra activity concentrations in the Chukchi shelf and the Beaufort shelf ranged from 0.16 to 1.22 Bq/m3, lower than those reported for shelves in the low and middle latitudes, indicating the effect of sea ice melt-water. A good positive linear relationship was observed between 228Ra/226Ra)A.R. and the fraction of river runoff for shelf waters, while the 228Ra/226Ra)A.R. in the Canada Basin was located below this re-gressive line. The low 228Ra/226Ra)A.R. in the Canada Basin was ascribed to 228Ra decay during shelf wa-ters transporting to the deep ocean. The residence time of 5.0―11.0 a was estimated for the river water in the Canada Basin, which determined the time response of surface freshening in the North Atlantic to the river runoff into the Arctic Ocean. Seawater was collected from the western Arctic Ocean for measurements of 18O, 226Ra and 228Ra. The fractions of river runoff and sea ice melt-water in water samples were estimated by using δ18O-S-PO * tracer system. The mean residence time of river water in the Canada Basin was calculated based on the relationship between 228Ra / 226Ra) AR and the fractions of river runoff in the shelf and deep ocean. Our results showed that the river runoff fractions in the Canada Basin were significantly higher than those in the shelf regions, suggesting that the Canada Basin is a major storage region for Arctic river water. 228Ra activity concentrations in the Chukchi shelf and the Beaufort shelf ranged from 0.16 to 1.22 Bq / m3, lower than those reported for shelves in the low and middle latitudes, indicating the effect of sea ice melt-water. A good positive linear relationship was observed between 228Ra / 226Ra) AR and the fraction of river runoff for shelf waters, while the 228Ra / 226Ra) AR in the Ca The low 228Ra / 226Ra) AR in the Canada Basin was ascribed to 228Ra decay during shelf wa-ters transporting to the deep ocean. The residence time of 5.0-11.0 a was estimated for the river water in the Canada Basin, which determined the time response of surface freshening in the North Atlantic to the river runoff into the Arctic Ocean.