Simulated carbon cycle response to ocean iron fertilization and artificial ocean alkalinization

[Geoengineering News]

https://www.sciencedirect.com/science/article/pii/S1674283425001370?via%3Dihub

Authors: Xiao-Yu Jin, Long Cao

23 September 2025

https://doi.org/10.1016/j.aosl.2025.100717

Abstract

Ocean iron fertilization (OIF) and artificial ocean alkalinization (AOA) are two proposed ocean-based carbon dioxide removal methods to mitigate the effects of anthropogenic climate change. In this study, the authors use an Earth system model of intermediate complexity to compare the effects of OIF and AOA on the ocean carbon cycle and ocean biogeochemistry under the RCP8.5 high-emission scenario. In these simulations, both OIF and AOA are applied uniformly over the global ocean. OIF simulation is done by eliminating iron limitation of phytoplankton growth over the global ocean. AOA simulation is designed to bring down the level of atmospheric CO2 to that of OIF simulation. The simulations show that compared with the RCP8.5 scenario, by the end of this century, a globally uniform application of OIF increases oceanic CO2 uptake by 120 PgC (21 % increase). Meanwhile, atmospheric CO2 is reduced by 55 ppm (5.6 % decrease) and cumulative land CO2 uptake decreases by 4 PgC. A pronounced increase in oceanic CO2 uptake occurs mainly in HNLC (high-nutrient, low-chlorophyll) regions associated with OIF-induced increases in phytoplankton growth and net primary production. By the end of this century, compared with RCP8.5, OIF increases the global surface ocean pH by 0.03, but decreases the whole ocean pH by 0.02. Meanwhile, OIF induces a 5.6 % decrease in global ocean oxygen content. By design, AOA causes a similar response of atmospheric CO2, but AOA mitigates both surface and deep ocean acidification and has a minor effect on ocean oxygen.

Source: ScienceDirect