The key features of the large-scale circulation of the Arctic Ocean are reviewed based on distributions of hydrographic parameters and natural and anthropogenic trace substances. Salinity and mass balances, as well as a combination of the tracers tritium and δ18O, suggest a mean residence time of the shelf waters in the Siberian seas of about 3 years. Potential pathways of pollutants released to the Siberian shelf seas from the dumpsites or from river runoff are inferred from the distributions of δ18O and salinity. Transit times needed for dissolved contaminants to cross the central Arctic basins (several years to one or two decades in near-surface waters) and mean residence times of contaminants in the intermediate (several decades) and deep waters (several centuries) are estimated from the distribution of transient tracers (tritium and its radioactive decay product, 3He) and "steady-state" tracers (14C and 39Ar).
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