Distribution and Chemical Reactivity of Dissolved Iron in Surface Waters of Northwestern Pacific Marginal Seas

Spatial variation and chemical reactivity (based on differential ion exchange method) of dissolved iron in surface seawater from northwestern Pacific marginal seas, including the South China Sea (SCS), Western Philippine Sea (WPS), East China Sea (ECS), and Taiwan Strait (TWS), were determined. Total dissolved Fe concentration ranged from 0.2 nM in the oligotrophic SCS waters to 1-3 nM in offshore marginal sea (Taiwan Strait and northern SCS) and shelf (ECS) waters, and 10-50 nM in coastal waters off China and Taiwan. The cation exchangeable (Chelex-100 retained) fractions accounted for the majority of dissolved Fe in offshore water, and the dissolved inert (unexchangeable) Fe fractions made up 50-90% of dissolved Fe in coastal waters. The anion exchangeable (AGMP 1 retained, organic) Fe fractions were the smallest among the fractions determined, and only eminent in coastal waters, especially near river mouths. This study suggests that Fe was more active and formed strong Fe complexes, and removed quickly offshore. The distributions of Fe including all its different reactivity fractions revealed that Fe behavior is source dependent.