ABSTRACT

Iron (Fe) in seawater is essential for marine phytoplankton. The bioavailability of Fe to phytoplankton largely depends on its chemical form in seawater. Fe(II) is an important component of surface water because photochemical reduction processes are related to the Fe acquisition mechanism of phytoplankton. However, the marine biogeochemical processes of Fe(II) have not been thoroughly investigated. This study applied the luminol chemiluminescence method to directly determine Fe(II) in acidified seawater in the Kuroshio area, subarctic Pacific, and the Bering Sea. We successfully obtained the vertical profile of Fe(II) in the Kuroshio region, where Fe oxidation has been studied; oxidation rates were consistent with previous studies. The prolonged half-life of Fe(II) in the Bering Sea suggests the possible influence of dissolved organic matter from the marginal sea on Fe(II) oxidation. The long half-life of Fe(II) in the high nutrient, low chlorophyll (HNLC) water may be crucial for supplying Fe to phytoplankton.