The specific features of pollution spread in the northwest Pacific Ocean

We present two calculations of pollutant dispersal in the Pacific Ocean: (1) during possible ship-wrecks in the process of spent nuclear fuel transportation from Petropavlovsk-Kamchatsky and (2) pollutant spread from the Japanese coast after the Fukushima-1 nuclear disaster on March 11, 2011. The circulation was calculated using a σ model of ocean hydrothermodynamics developed at the Institute of Numerical Mathematics (INM), Russian Academy of Sciences (RAS); it is adapted to cover the Pacific Ocean basin from the equator to the Bering Strait with a high (1/8)° spatial resolution and it is capable of reproducing the mesoscale ocean variations. The pollutant dispersal in the case of possible shipwrecks was estimated for currents characteristic for a statistically average year with atmospheric forcing in accordance with the so-called normal CORE year data. The pollution spread from the Fukushima-1 nuclear power plant (NPP) was estimated by calculating the circulation with the real atmospheric forcing in accordance with the NCEP analysis data obtained from the Hydrometeorological Centre of Russia. It is noteworthy that a simplified assimilation of the observed sea surface temperature (SST) was performed. In both cases the currents were calculated simultaneously with the transport calculation of the pollutant as a passive admixture, which corresponds to a real-time calculation of pollutant transport. A map analysis of pollution dispersal shows that the horizontal transport is substantially more intense in the upper ocean layers than in deep ones. Therefore, like in the North branch of Kuroshio, pollutants can be delivered to the deep layers not through deep-water horizontal transport, but rather as a result of vertical downwelling from the already contaminated upper layers. However, the complex three-dimensional structure of the horizontal and vertical transport may lead to reverse situations. A calculation of pollution transport from the Fukushima-1 NPP showed that radioactive pollution would propagate eastward and not present the danger for Russian territory. Moreover, even for an exaggerated scenario of pollution emission, the background pollution level will be exceeded only in a narrow region within 50 km of the Japanese coast.