We present the results of in-situ measurements of 134 Cs and 137 Cs released from the Fukushima Nuclear Power Plant (FNPP) collected at surface and different depths in the western North Pacific in June and July 2012. It was found that 15 month after the incident concentrations of radiocesium in the Japan and Okhotsk seas were at background or slightly increased level, while they had increased values in the subarctic front area east of Japan. The highest concentrations of 134 Cs and 137 Cs up to 13.5 ± 0.9 and 22.7 ± 1.5 Bq m −3 have been found to exceed ten times the background levels before the accident. Maximal content of radiocesium was observed within subsurface and intermediate water layers inside the cores of anticyclonic eddies (100 -500 m). Even slightly increased content of radiocesium was found at some eddies at depth of 1000 m. It is expected that convergence and subduction of surface water inside eddies are main mechanisms of downward transport of radionuclides. In situ observations are compared with the results of simulated advection of these radioisotopes by the AVISO altimetric velocity field. Different Lagrangian diagnostics are used to reconstruct the history and origin of synthetic tracers imitating measured seawater samples collected in each of those eddies. The results of observations are consistent with the simulated results. It is shown that the tracers, simulating water samples with increased radioactivity to be measured in the cruise, really visited the areas with presumably high level of contamination. Fast water advection between anticyclonic eddies and convergence of surface water inside eddies make them responsible for spreading, accumulation and downward transport of cesium rich water to the intermediate depth in the frontal zone.
Abstract.Original data of tritium ( 1 H 3 HO, or HTO) studying of both natural, and artificial (technogenic) origin in natural waters on the country territory and in the seas of the World Ocean are presented. Entry sources of cosmogenic and technogenic HTO in hydrosphere of the Earth from atmosphere and its carrying over to various links of hydrological cycle are considered. The basic laws of the spacetemporal HTO distribution in surface water of the northern part of the Eurasian continent, in the seas washing Russia and in separate water areas of the World Ocean, and also in atmospheric precipitation and Antarctica's firn snow are studied. Prevailing influence of a molecular exchange on the HTO content in the top layer of lakes, the seas and oceans and in atmospheric moisture over the ocean is shown. The theory of a multicomponent isotope balance method is developed for studying of dynamic characteristics of water objects. Priority results of tritium use in the industry (on oil deposits, collieries, mines etc.) and in researches under national and international programs (WESTPAK, SOUTHERN OCEAN, "Isotopes in deposits", the Soviet Arctic and Antarctic expeditions) are given. Systems of national and Far East regional monitoring HTO pollution of natural waters are created. Complexes for HTO measuring with record levels of threshold sensitivity (in the late seventies sensitivity of complex POI equaled to 4 × 10 −6 Bq/ml) have been developed.
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