David Emerson, Alexander B Michaud, Stephen D. Archer, Laura E Sofen, Benjamin S Twining

This paper presents a cost model for implementing a deployment scale effort for conducting ocean iron fertilization (OIF) for marine-based carbon dioxide removal (CDR). The model incorporates basic oceanographic parameters critical for estimating the effective export of newly fixed CO2 into biomass that is stimulated by Fe addition to an Fe-limited region of the Southern Ocean. Estimated costs can vary by nearly a 100-fold between best-case and worst-case scenarios with best-case values of $7/net ton C captured versus worst-case $1500/net ton C captured, without accounting for verification costs. Primary oceanographic factors that influence cost are the net primary productivity increases achieved via OIF, the amount of carbon exported into the deep ocean, and the amount of CO2 ventilated back to the atmosphere. The model compares ship-based versus aerial delivery of iron to the ocean, and estimates aerial delivery can be 30 – 40% more cost effective; however, the specific requirements for aerial delivery require additional research and development. The model also estimates costs associated with verification and environmental monitoring of OIF. These costs increase $/net ton C captured by 3 – 4-fold. Best, intermediate, and worst cases for aerial delivery and ship delivery are $23, $83, $1,735, and $25, $94, $4481, respectively, inclusive of verification costs. The primary goal of this model is to demonstrate the variability in cost of OIF as a CDR method, to better understand where additional research is needed to determine the major factors that may make OIF a tractable, nature-based CDR method.