In an article featured in The Anthropocene, science writer Emma Bryce highlights an intriguing approach to reducing the climate impact of fish farms: sprinkling them with iron. Her reporting draws on a Nature Food study showing that by adding iron ore, these farms could capture significant amounts of carbon dioxide—enough, in some cases, to offset much of aquaculture’s current emissions.
“According to a new research model, adding iron to fish farms could capture at least 100 million tonnes of carbon dioxide a year, in aquaculture-intensive countries. This could be enough to offset most of the carbon impact of aquaculture operations, which contribute between 5 and 7% of the global emissions linked to agriculture and livestock farming each year.
Ironically, part of this solution lies in another polluting problem that fish farms create: mounting quantities of hydrogen sulfide. This toxic gas accumulates when microbes in low-oxygen environments, such as ocean sediments, feed on organic matter. Industrial fish farms add to the issue through fish waste and uneaten feed that settle on the enclosure floor.
Even at low levels, hydrogen sulfide can kill fish in large numbers and spread harmful effects across broader marine ecosystems. But as the researchers explain in their new Nature Food study, iron ore naturally reacts with hydrogen sulfide, forming iron sulfide, which then gets sequestered in the sediment. By locking away hydrogen sulfide, fish farms can reduce its toxic effects. Additionally, this reaction boosts water alkalinity, enabling waters to absorb more CO₂ and convert it into stable forms.
‘Higher alkalinity allows the water to absorb more CO₂ from the atmosphere, converting it into bicarbonate and carbonate, which are stable and stored in the water long term,’ says Mojtaba Fakhraee, a postdoctoral associate at Yale University and lead author on the study.
Using these insights, the researchers modeled what would happen if fish farms worldwide were treated with iron ore to address both fish-killing hydrogen sulfide and greenhouse gas emissions. Their simulations accounted for carbon, iron, and sulfur cycling under various conditions across major aquaculture-producing nations.

Central to their findings is that adding iron ore could sequester up to 100 million tons of CO₂ each year in a large aquaculture nation like China alone. Generally, the study suggests that between 2 and 10 tons of carbon per hectare of fish farm could be locked away annually. Taken together with nations such as India and Indonesia, the potential ranges from 25 to 140 million tonnes of carbon sequestered each year.
Depending on the location, this iron-enrichment strategy could offset an average of 50%—and potentially up to 100%—of aquaculture’s carbon output, possibly transforming the industry into a carbon-neutral or even carbon-negative one. The method also promises a low-carbon source of protein; with iron added, fish farming’s carbon footprint per gram of protein drops significantly compared to beef production. Meanwhile, controlling hydrogen sulfide with iron helps keep fish healthier and waters cleaner.
Of course, mining and transporting iron ore incurs costs. According to the study, incorporating these expenses still places the price of carbon removal at about $100–$300 per ton—similar to other carbon-capture techniques and lower than the social cost of carbon.
The authors note that more field research is needed to gauge potential environmental impacts before large-scale adoption. Still, aquaculture’s rapid global growth suggests a unique window of opportunity. By 2030, fish farming is expected to expand by 22%, providing over half of the fish consumed worldwide. Such controlled systems offer a measurable way to reduce emissions and safeguard marine habitats.
Ultimately, says Fakhraee, the findings ‘present a dual solution: reducing the carbon footprint of aquaculture while also benefiting the environment.’”
(Reference: Fakhraee and Planavsky. “Enhanced sulfide burial in low-oxygen aquatic environments could offset the carbon footprint of aquaculture production.” Nature Food, 2024.)
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