Natural waters usually demonstrate the disturbance of radioactive equilibrium between parent U-238 and and daughter U-234 (usually, U-234/U-238 approximate to 0.8-3 in activities). The ratio of U-234/U-238 > 10 found in groundwaters can be explained by climatic variations, and it is result of U-234 accumulation in permafrost rocks during cold periods and its more rapid loss compared to U-238 during thawing. We tested this hypothesis for data on uranium isotope composition in water, and also chemo- and biogenic formations of the World Ocean. Most significant enrichment in U-234 is discovered in the northern and internal seas during climatic warmings, which is consistent with an inferred influence of the permafrost formation and degradation on the anomalous increase of U-234/U-238 in groundwaters. Sampling of the Barents Sea shows that the uranium-234 enrichment in oceanic water increases with increase (a) of isolation from oceanic circulation system, (b) of the relative length of the coastal line, (c) and the contribution of continental waters to the chemical balance of the basin.