Revisiting the additionality and durability of carbon uptake in large-scale ocean iron fertilization.

Century-scale ocean iron fertilization in the southern sector of the Southern Ocean yields about ∼30 PgC total uptake (∼0.3 PgC year -1 ), with ∼50% retained after 30 years.

• Why it matters: Meeting 1.5° to 2°C warming limits needs rapid emission cuts plus additional CDR of ∼2 to 3 PgC year -1, but durability and additionality of large-scale OIF remain uncertain.
• What they did: Using simulations, the study evaluates sustained OIF in the SSO versus other iron-limited regions, then compares post-termination carbon retention after 30 years and quantifies offset by anomalous outgassing.
• The result: In other regions, fertilization-linked uptake is largely offset by 70 to 100% outgassing, while SSO retention is negligible elsewhere; the SSO is identified as most favorable for durable OIF.

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