Surface and middle layer enrichment of dissolved copper in the western subarctic North Pacific

Abstract

Vertical distributions of dissolved copper were investigated at two stations in the western subarctic and tropical North Pacific to elucidate the factors controlling its concentration. There was a significant correlation (p-value < 0.05) at the subarctic and tropical stations between dissolved copper and silicic acid between 400-3000 m and 300-2000 m depths, respectively, which implies the importance of diatoms in transporting copper. The dissolved copper concentration at depths shallower than 1000 m was 1.3-2.7 times higher at the subarctic station than that at the tropical station, and at depths shallower than 1500 m, it was 0.97-2.60 nM higher at the subarctic station than the average of other reported values of the North Pacific. This can be attributed to several processes. In the surface layer, horizontal advection of the coastal water by the East Kamchatka Current was considered to be a source of copper because a high concentration was observed within low-salinity surface waters. Supply of copper below the surface layer to 1500 m was probably owing to downward transport by the biological pump and horizontal advection. These results suggest that horizontal transport of copper from coastal or shelf area is important for biological production and Cu distribution in this region.