Dissolved iron distribution in the western and central subarctic Pacific : HNLC water formation and biogeochemical processes

• Published in: Limnology and Oceanography
• Main Authors: Nishioka, Jun, Obata, Hajime
• Format: Article in Journal/Newspaper
• Language: English
• Published: Association for the Sciences of Limnology and Oceanography / wiley
• Subjects: Subarctic
• Online Access: http://hdl.handle.net/2115/68796; https://doi.org/10.1002/lno.10548

It is well known that phytoplankton growth is broadly limited by iron (Fe) availability in the subarctic Pacific. To investigate which Fe sources control the amplitude of seasonal variation in biogeochemical parameters in the subarctic Pacific, we examined the spatial variation in the west-to-east distribution of dissolved Fe (DFe) across the western and central subarctic Pacific through the Japanese GEOTRACES program. The vertical section profile of the western subarctic Pacific gyre showed high dissolved Fe concentrations from the bottom of the surface mixed layer to as deep as approximately 3000 m, suggesting that Fe-rich intermediate water is transported laterally and distributed across the western subarctic gyre, over 2000 km. The section data also indicate that the influence of the western Fe-rich intermediate water does not reach the Alaskan gyre. Fe* index (= [DFe] (observed) – [PO4] (observed) × RFe:P) distribution clearly indicates that the western Fe-rich intermediate water is well explained by external sedimentary Fe sources and water transport systems from a subpolar marginal sea, the Sea of Okhotsk, and the continental margin. The spatial pattern of Fe to nutrient stoichiometry supplied 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.