Rare earth elements in the East Sea (Japan Sea): Distributions, behaviors, and applications

Abstract

The distributions of rare earth elements (REEs) were measured at 14 stations from 0 to 3365 m (n = 176) in the entire East Sea for the first time. The East Sea has its own deep-convection system, which operates on a time scale that is approximately one tenth that of the global ocean; it is also a downwind region of Asian dust. The vertical distributions of REE concentrations increased with depth, similar to those in the North Atlantic Ocean. However, the concentrations of REEs were 1.3–2.7 fold higher than those in the North Atlantic Ocean, associated with relatively larger atmospheric depositions of dust from the Asian continent. In this environmental condition, the removal of Ce relative to the other REEs was about an order of magnitude more efficient than that in the North Pacific Ocean. As such, in the deep layer below 750 m, large increases of heavy-REEs (HREEs) relative to light-REEs (LREEs), opposite to the re-mineralization trend, were observed suggesting that LREEs were preferentially re-scavenged by sinking particles. In addition, the boundary scavenging of REEs was also observed for all REEs in the bottom layer of the East Sea. On the other hand, the warm surface waters of REEs, Tsushima Warm Water (TWW) showed large fractionations, relative to the other water masses. This REE pattern traced the deep physical mixing proportions of TWW up to 750 m (∼10%). Thus, the unique distribution patterns of REEs in this sea illustrate the geochemical scavenging characteristics of REEs, which are concealed in the major oceans, as well as water mass mixing patterns in the upper ocean.