Atmospheric deposition of trace metals to the western North Pacific Ocean observed at coastal station in Japan

To understand the atmospheric input of trace metals to surface seawaters, the total deposition samples were collected simultaneously from three coastal stations in Japan. The trace metal concentrations (Al, Sc, Ti, Mn, Fe, Co, Ni, Cu, Zn, Cd, Pb, and Th) were then determined for particulate and dissolved fractions using a high-resolution ICP-MS. The observed total Fe flux (average, 194 μg/m2/day) at the northern station (Kushiro, KU), which is close to HNLC region of western North Pacific, was within the lower limit of the previous estimation for coastal area of Japan based upon a model. Except for Sc and Fe, all the elements showed an increasing tendency toward dissolution with decreasing the pH from 5.7 to 3.4. At the southern station (Cape Hedo, HE), the tendency toward dissolution of Ti, Mn, Zn, Cd, Pb and Th was twice higher than that at the other two stations. A higher dissolved fraction of these metals was observed with higher enrichment factors at the HE station, which implies an anthropogenic effect on the dissolution of trace metals. In order to elucidate the relationship between anthropogenic sources and this dissolution tendency of Al and Fe, we calculated the Sc-normalized enrichment factors (ScEF). The relationship between the ScEF and the dissolution tendency indicated a higher dissolution tendency of Al or Fe in the sample having a higher ScEF. These results indicated that in addition to low pH condition the variation of the source control the tendency toward dissolution of metals in the deposition samples.