Abstract. Iron fertilization is explored by tracking dissolved iron (DFe) through its life cycle from injection by external sources (birth) to burial in the sediments (death). We develop new diagnostic equations that count iron and phosphate regenerations with each passage through the biological pump and partition the ocean's DFe concentration according to the number of its past and future regenerations. We apply these diagnostics to a family of data-constrained estimates of the iron cycle with sources σ tot in the range 1.9-41 Gmol yr −1. We find that for states with σ tot >7 Gmol yr tot and have ranges of 0.05-2.2 and 0.01-1.4, respectively. Memory of birth location fades rapidly with each regeneration, and DFe regenerated more than ∼5 times is found in a pattern shaped by Southern Ocean nutrient trapping. We quantify the natural fertilization efficiency at any point r in the ocean as the global export production resulting from the DFe at r, per iron molecule. We show that this efficiency is closely related to the mean 10 number of future regenerations that the iron will experience. At the surface, the natural fertilization efficiency has a global mean in the range 0.7-7 mol P (mmol Fe) −1 across our family of state estimates and is largest in the central tropical Pacific, with the Southern Ocean having comparable importance only for high iron-source scenarios.