Fig. 6.

Cartoon highlighting the various pathways that can lead to δ⁵⁶Fe fractionation. (A) Stage I, depth of 300 m. (B) Stage I, euphotic zone. (C) Stages II and III, euphotic zone. For simplicity, no differentiation between inorganic Fe and Fe complexation to natural organic ligands was made; rather, we treated inorganic Fe and organically complexed Fe as one group. Water column measurements from both the 2008 and the 2012 voyages indicate that the majority (>90%) of DFe was complexed to high-affinity Fe-binding ligands (FeL) (3).