Zinc (Zn) is an essential micronutrient for bacteria and phytoplankton in the ocean. Nevertheless, biogeochemical cycles of Zn have not been fully revealed yet in the ocean since determination of Zn in seawater is very difficult because of contamination problems (Fitzwater et al., 1982). Laboratory studies examining the influence of Zn on phytoplankton growth showed that coastal species could be zinc-limited (Bruland et al., 1983) and that Zn was important for silicate uptake by diatoms (Rueter and Morel, 1981). It is also suggested that the Zn incorporated into the diatom frustules records the Zn speciation in the seawater at the time of growth and the resulting Zn:Si ratio of the diatom opal can be used for paleo interpretations of Zn speciation in the ocean (Elwood and Hunter, 1999). In this study, using recent clean technique, We have established a precise determination method of picomolar level of Zn in seawater. Using this method, vertical distributions of Zn and the relationship between Zn and silicate in the northwestern Pacific, Sea of Okhotsk and Sea of Japan (East Sea) were investigated.
