Glacial rock flour from Greenland can sequester carbon and help farmers in Africa

Environment and sustainability 10. sep 2023 4 min Professor Minik Thorleif Rosing Written by Kristian Sjøgren

The Greenland Ice Sheet grinds bedrock in Greenland into a fine flour that can absorb CO2 directly from the atmosphere and be used as a mineral fertiliser to increase the yield on farmers’ fields. A researcher says that glacial rock flour has enormous untapped potential, but we need to determine how to best exploit this resource.

The Northern Hemisphere has some of the Earth’s best agricultural land because the great ice sheet that covered Europe and North America during the Pleistocene Ice Age ground the underlying rocks into a fine powder containing many minerals that make the soil extraordinarily fertile for growing crops.

The same processes are happening in Greenland today, with the massive Greenland Ice Sheet that covers most of Greenland grinding the underlying bedrock into a powder called glacial rock flour.

Glacial rock flour is present everywhere in Greenland in very large quantities, and now researchers have found that this has great potential as a very effective mineral fertiliser and can sequester significant quantities of carbon, thereby counteracting climate change.

“Our experiments show that glacial rock flour from Greenland can increase agricultural yield by up to 50% and absorb large quantities of CO2. It has great potential, and we must determine how to exploit this in the future,” explains a researcher involved in the research, Minik Rosing, Professor, Globe Institute, University of Copenhagen.

The research, which was carried out with Christiana Dietzen, a researcher at the Globe Institute, and others has been published in the International Journal of Greenhouse Gas Control and Nutrient Cycling in Agroecosystems.

Can bind many tonnes of atmospheric CO2

The researchers investigated the potential of glacial rock flour to sequester atmospheric carbon and to fertilise fields.

Glacial rock flour can bind CO2 from the atmosphere by enhanced weathering.

CO2 dissolved in water forms carbonic acid, which can dissolve rocks, converting the CO2 into bicarbonate and thereby sequestering the atmospheric CO2.

The bicarbonate eventually ends up in the ocean, where it can remain for millennia and help to make the ocean less acidic, which benefits both animals and plants.

Enhanced weathering is accelerated as the surface area of the rock material increases, meaning that the particles become smaller. Glacial rock flour has ultrafine particles with an extremely large surface area of about 20 km2 per tonne.

Glacial rock flour applied to a field can therefore bind considerable CO2 in the soil relatively rapidly. The researchers calculated how much in one of their studies.

“One tonne of glacial rock flour can absorb 250 kg of CO2. Naturally, the question is how much CO2 is emitted by shipping glacial rock flour from Greenland to Denmark or elsewhere. We calculate that transporting glacial rock flour less than 10,000 km has a positive climate effect and that transporting glacial rock flour through the increasingly decarbonised transport infrastructure to apply it to fields will positively counteract climate change,” says Minik Rosing.

The researchers also calculate that applying glacial rock flour to all the agricultural fields in Denmark with identical conditions to those in the study would bind 27 million tonnes of CO2, which is the same amount emitted in Denmark in 1 year.

“However, we are not sure how long this process will take, probably closer to a decade than a couple of years. Nevertheless, glacial rock flour does not require any processing before being applied, and Greenland has almost unimaginable quantities of it,” explains Minik Rosing.

Up to 50% increase in crop yield

In the other study, the researchers investigated the potential of glacial rock flour as a mineral fertiliser on farms in Denmark and Ghana.

The researchers applied glacial rock flour to some fields and potash mineral fertiliser (high in potassium) to other reference fields and compared the yields.

In Denmark, this improved the yield by 15–20% on fields in western Jylland and 30% on a barley field in Fyn the first year and a further 22% the second year.

In Ghana, applying glacial rock flour also achieved higher yields on maize fields, increasing by 30–50% over five harvests in 3 years relative to the reference fields.

Minik Rosing explains that the higher yield in Ghana was achieved because the soil does not have the same concentration of the minerals crops require as the soil in the two test sites in Denmark. Tropical and subtropical regions therefore have the greatest potential for glacial rock flour.

“Remember that glacial rock flour may be an alternative to no fertiliser at all in Ghana, whereas in Denmark glacial rock flour has to compete with highly tuned agriculture in which the soil is constantly monitored and the things needed are added precisely. The greatest potential is therefore outside high-income countries,” he adds.

Making depleted fields fertile

Minik Rosing also sees great potential for using glacial rock flour to restore agricultural land.

In many places around the world, precious rainforest is being cut down to make way for new fields. Near the new fields are often older fields that have been depleted of minerals and are therefore no longer suitable for growing crops.

But spreading glacial rock flour on the depleted fields and re-establishing their potential for growing crops could minimise the felling of trees in the rainforest.

“The challenge is that increasing yield requires much glacial rock flour. In Ghana, we used 10 tonnes per hectare. Although we achieved good yield, we do not know how long the application is effective and whether new glacial rock flour need be applied to the fields every 3, 5 or 10 years,” says Minik Rosing.

High-income countries should pay to ship glacial rock flour to Africa

Although the researchers have shown that glacial rock flour has both climate and agricultural potential, there is still a long way to go before ships with glacial rock flour sail from Greenland to all corners of the globe.

Establishing whether this is financially viable is a prerequisite and Minik Rosing and colleagues are working on this part of the equation in a new research project that will establish where using glacial rock flour will be relevant and what this will cost.

Glacial rock flour fertilises acidic soil extremely well, and this is mainly located in tropical regions.

The application of minerals to the soil is already managed well in high-income countries, and glacial rock flour must be capable of doing something that modern conventional fertilisers cannot.

“But a possible solution is that the countries that need to reduce their CO2 emissions pay to transport glacial rock flour to Africa, which needs to increase agricultural production but cannot afford the same fertiliser methods that are used in high-income countries,” concludes Minik Rosing.

Quantification of CO2 uptake by enhanced weathering of silicate minerals applied to acidic soils” has been published in the International Journal of Greenhouse Gas Control. “Greenlandic glacial rock flour improves crop yield in organic agricultural production” has been published in Nutrient Cycling in Agroecosystems. The Novo Nordisk Foundation supported the project.

Minik Rosing is professor at Geological Museum and Natural History Museum at University of Copenhagen. He was one of the leaders of the Galathea 3 Exp...

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