Vertical profiles of dissolved selenium in the North Pacific

Abstract

Vertical distribution of selenite, selenate, and organic selenium compound in the North Pacific was determined. The general feature of vertical profiles of total dissolved selenium is as follows; The concentration increases with depth from 0.5–1.0 nM in the surface layer to 1.3–1.4 nM at the depth of approximately 1 km, while it is almost constant or slightly increases with depth in the deeper layers. Selenite displays a nutrient-type vertical profile. The content of selenate is variable, but its mean concentration in waters below 2 km depth is higher than that in the upper 1 km layer. The vertical profiles of organic selenium compound in the upper 1 km layer are similar to those of nutrients with some exceptional high values. In the bottom layer, the concentration of organic selenium compound increases with depth. The regeneration ratios of selenite or organic selenium compound to nutrients were evaluated to clarify the relation between selenium and biological activities. Selenium species, especially selenite in sea water, seem to be controlled by biological activities.