Can Contaminated Waters from the Fukushima Daiichi NPP Penetrate the East China Sea?

Abstract

Mesoscale eddies play a pivotal role in the dispersion and transport of pollutants in the ocean, influencing their horizontal and vertical distribution over vast areas. These rotating structures, ranging from tens to hundreds of kilometers in diameter, effectively trap, transport, and mix water masses, redistributing contaminants away from their sources. This study investigates the southward transport mechanisms of contaminated waters released from the Fukushima Daiichi Nuclear Power Plant (FDNPP), particularly near the Kuroshio Current. Using advanced Lagrangian modeling, we analyze the influence of mesoscale eddies, cross-jet transport, and interactions with adjacent water masses on the movement of pollutants into regions south of the Kuroshio. The findings reveal that the Kuroshio Current captures contaminated waters, forming cyclonic rings that detach and drive pollution southwestward. This process is further enhanced by the dissipation of cyclonic eddies, which facilitate the spread of contaminants toward the eastern periphery of the current. Cross-jet advection, resulting from the weakening of the Kuroshio near Taiwan, also contributes to westward transport. Additionally, the influence of East Asian monsoons introduces a 6-month recurrence cycle, sustaining long-term pollutant flux and promoting stable accumulation in the region. Three key mechanisms are identified for the successful transport of Lagrangian particles from FDNPP to the East China Sea: cross-jet transport in the Kuroshio Extension, leading to cyclonic ring formation, southwestward advection of these rings or their daughter eddies, and specific Kuroshio flow regimes allowing east-to-west pollutant transport.