Iron supply from the marginal seas and its influence on biological production in the North Pacific Ocean

Jun Nishioka, Hokkaido University, Institute of Low Temperature Science, Sapporo, Japan, Hajime Obata, The University of Tokyo, Atmosphere and Ocean Research Institute, Kashiwa, Japan, Toru Hirawake, Hokkaido University, Faculty of Fisheries Sciences, Hakodate, Japan and Ichiro Yasuda, the University of Tokyo, Atmosphere and Ocean Research Institute, Kashiwa, Japan
Although the subarctic North Pacific is high nutrient low chlorophyll region, where phytoplankton growth is limited by iron (Fe) availability, the area has high bio-pCO2drawdown. The overall picture of the processes for supplying Fe and macro-nutrients, however, are not fully understood yet. In this study, we compiled comprehensive observed data in the North Pacific in these 20 years, including the marginal seas and its island chains, and construct a dissolved Fe (DFe) dataset with nutrients and hydrographic parameters. The dataset can withstand the analysis of the distribution of the chemical parameter on isopycnal surface. Firstly, we constructed 3D DFe diagram of the North Pacific including subpolar marginal seas by using the dataset. The isopycnal analysis indicates that the DFe rich water propagate from the Okhotsk Sea Intermediate Water (OSIW) to the wide area of Upper-NPIW (26.6-27.0 sigma theta) in the western North Pacific, especially from 155E to the west. The spatial pattern of Fe to nutrient stoichiometrysupplied from the intermediate water to the surface, in comparison with reported Fe and nutrient demand in surface phytoplankton, quantitatively explains the differences in surface macronutrient consumption between the western and eastern gyre as well as the formation of the high nutrient and low chlorophyll region in the whole subarctic Pacific. These results highlighted an importance of marginal seas and intermediate water formation for circulating micro- and macro-nutrients and controlling bio-pCO2drawdown in the subarctic Pacific.