Where to deploy oceanic geoengineering

Oceanic regions known as High-Nutrient-and-Low-Chlorophyll, or HNLC, are at the cornerstone of an ongoing debate regarding the deployment of oceanic geoengineering to mitigate climate change. HNLC regions are unique because they have excess macronutrients like nitrate and phosphate, yet lack key micronutrients like iron and without iron, green plankton cannot perform photosynthesis and capture carbon. Ocean iron fertilization, or OIF, is a scheme that artificially increases iron concentrations through addition from a vessel, enhancing CO2 uptake and burial through sinking, with the goal of removing CO2 from the atmosphere. A big problem is that we don't know where HNLC clusters actually are, and this is key for the success of OIF. Global maps of iron concentration would reveal HNLC clusters, but dissolved iron is incredibly challenging to measure. We simply don't have the technology to directly map oceanic iron, but there is another way through reverse engineering. I used a data-driven approach to balance the expected interaction of nutrients (phosphate, nitrate, and silicate) and productivity (chlorophyll, phytoplankton, POC, PIC, and NPP) expected under iron limitation. This revealed that the strongest HNLC clusters are small, remote, and located within the Southern Ocean. OIF has already been done 12 times since 1993, with half of them in the southern polar region, with the most promising result (EIFEX experiment) located closest to one of my identified clusters. My method also identifies other oceanic regimes, completing a quartet (HNLC, HNHC, LNHC, and LNLC). Low-Nutrient-and-Low-Chlorophyll, or LNLC regions, are much larger than HNLCs and optimal to deploy atmospheric cloud seeding to reflect sunlight and enhance albedo, cooling the oceanic surface. In summary, my idea detects the precise location where oceanic geoengineering can be deployed for optimal results.




Trigger (intervention)




Feedback Dynamics


Timescale and scaleability





Matias Bofarull Oddo

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