Ocean Science & Climate — Carbon Removal

Volcanoes and Dust Prove Phytoplankton Can Pull Carbon From the Air

We have no shortage of unproven climate schemes, but “feed the ocean and tiny plankton will eat CO₂” is one of the few ideas backed by millions of years of real data. Nature runs the experiment every day, and satellites have been watching.

• Most of the open ocean is a desert: plankton have sunlight and nutrients but run out of one key ingredient, usually iron.
• Add iron and plankton multiply, pulling carbon dioxide out of the atmosphere; remove the iron and the bloom fades within weeks.
• The mechanism has been verified by volcanic eruptions, desert dust clouds, whale activity, and a nine-month bloom sparked by the 2019–20 Dust Australian wildfires.

The chemistry is almost elegantly simple. Phytoplankton are the ocean’s plants, and like any plant they need minerals to grow. In vast stretches of open water, sunlight is plentiful but iron — locked away in deep water or scarce in the surface layer — holds them back. Give them a trace of iron and they multiply rapidly, each cell converting dissolved CO₂ into living tissue. When they die, a fraction of that carbon sinks into the deep ocean, effectively parking it for centuries.

What makes this compelling is not theory but observation. Nature adds iron to iron-starved water constantly, and we have been measuring the result for decades. In 2008, Alaska’s Kasatochi volcano blanketed the Gulf of Alaska with ash and one of the largest plankton blooms ever recorded followed within days. Iceland’s 2010 Eyjafjallajökull eruption and Hawaii’s 2018 Kīlauea event produced the same pattern across thousands of kilometres of Pacific.

Dust is the planet’s most reliable delivery service. Every year, millions of tons of iron-rich soil blow from the Sahara across the Atlantic and from the Gobi across the Pacific. When floating ocean robots happened to be sitting in the North Pacific during a Gobi dust cloud in 2001, they recorded the living carbon in the water nearly doubling within two weeks. A 2024 study of a decade of robot data found that dust-borne nutrients currently sustain about a third of all plant growth across the Southern Ocean each year — rising to two-thirds during the dustier last ice age. Even Australia’s 2019–20 wildfires sent ash drifting south, igniting a satellite-visible bloom that kept recycling itself for nine months.

The takeaway for climate science is rare in the geoengineering world: the causal chain is real and well-documented, so engineered iron fertilisation is not starting from zero. The open questions are scale, measurement and ecological side effects — but the basic mechanism, that feeding the ocean can pull carbon from the air, is one of the best-understood relationships in marine science.