Climate model: a century of Southern Ocean iron fertilization adds ~30 PgC uptake, below past estimates
Earth System Model simulations show sustained iron fertilization removes 0.3 PgC per year in the southern Southern Ocean, while global rates are 2–7 times lower than idealized estimates.
A study in Science Advances used an Earth System Model to assess how much carbon large-scale ocean iron fertilization could remove and how long it would stay out of the atmosphere. The simulations ran under emissions-driven scenarios. The authors note that pathways limiting warming to 1.5–2 °C require emission cuts plus additional carbon dioxide removal of about 2–3 PgC per year science.org
Science Advancesscience.orgOpen source ↗.
Uptake by region
According to the simulations, sustained fertilization over a century in the southern sector of the Southern Ocean gives a moderate contribution of about 30 PgC, or 0.3 PgC per year. In other iron-limited regions, the additional uptake is largely offset, by 70–100%, by non-fertilized regions. Global carbon removal rates come out 2–7 times lower than earlier idealized estimates.
Durability and limits
When fertilization stops after 30 years, the ocean retains 50% of the additional carbon in the southern sector of the Southern Ocean, while retention in other regions is negligible. The authors name several constraints: local and remote nutrient depletion, re-entrainment of previously sequestered carbon, incomplete macronutrient drawdown and reduced phytoplankton carbon-to-phosphorus ratios. Incomplete macronutrient drawdown accounts for the largest difference from earlier studies. It reflects controls by light, top-down controls and the rate of macronutrient resupply.
The authors say that further assessment requires applying the standardized design across modeling institutions and analyzing top-down and bottom-up controls on nutrient drawdown.
