Climate model: a century of Southern Ocean iron fertilization adds ~30 PgC uptake, below past 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.orgScience 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.