Intermediate layer iron transport supporting the biological production in the Oyashio region

Jun Nishioka1)and Takeshi Nakatsuka2)
1)Institute of Low Temperature Science, Hokkaido University
2)Graduate School of Environmental Studies, Nagoya University


Atmospheric dust has been thought to be the most important source of iron supporting annual biological production in the Western Subarctic Pacific (WSP).  Our study clearly indicates that there is another important source of iron for WSP.  We conducted observations in the Sea of Okhotsk and found that iron was re-suspend from the sediments of the north-western continental shelf area.  This source of iron is transported by ventilation processes, which are driven by sea-ice formation in the Sea of Okhotsk, and which distributes the iron to wide area of the intermediate layer in the WSP.  Furthermore, we observed a clear seasonality in dissolved iron concentrations in the surface waters of the Oyashio region.  The surface waters are significantly influenced by high iron concentrations in the intermediate waters through diffusion and winter mixing.  Therefore, in addition to the traditional view of dust input, iron transported into the mesopelagic zone by ventilation of intermediate waters should be considered as an important source of iron for phytoplankton blooms in the Oyashio region.