Bottom turbidity, boundary layer dynamics, and associated transport of suspended particulate materials off the Fukushima coast

Abstract

Long-term monitoring and intensive field experiments for the bottom layer off the Fukushima coast were performed from October 2012 to November 2014 to understand the bottom processes, which are closely related to the spatial distribution and temporal variations of radiocesium in sea sediment. In this section, focusing on autumn 2012, we examine the bottom processes for a 32-m depth site (Sta. B) off Iwaki, Fukushima. Observational results showed that the bottom shear stresses from waves generally dominated over those from currents in this depth region, and the bottom turbidity increased in high wave conditions. Stepwise and significant southward cumulative transports of bottom turbidity were observed when high waves with long periods (LPW) coming from an E–ENE direction were superimposed on the southward current flow that has a periodicity of 5 days; both phenomena are influenced by successive passages of low pressure systems and the associated spatial distribution of atmospheric pressure. The combination of waves and currents caused by meteorological disturbance is a key process in the transport of suspended particulate material off the Fukushima coast.