Excess ~(222)Rn profiles in the bottom layer of the Japan Sea and their implication for bottom water dynamics

摘要

Vertical profiles of excess radon-222 (~(222)Rn; half life: 3.82 days) in bottom seawaters between 8 and 780 m above the seafloor were measured in the Japan Sea, a semi-closed deep marginal sea in the northwest Pacific Ocean. All of the profiles observed at three locations (two profiles in the Japan Basin and one in the Yamato Basin) show curious zigzag patterns with ~(222)Rn maxima and minima, in contrast to a generally known steady-state profile of ~(222)Rn exponentially decreasing with the distance above the bottom. The observed ~(222)Rn profiles demonstrate the existence of horizontal supplies of ~(222)Rn-enriched waters in the bottom layer of the Japan Sea with timescales as short as the half-life of ~(222)Rn, probably in relation with the interaction between bottom currents and topographic features.