Bedrock ground to powder by Greenland’s glaciers can bind significant amounts of carbon dioxide in acidic soils and also has great potential when used as a fertiliser for organically grown plants
Two experiments with rock pulverised to silt by Greenlandic glaciers have shown that it helps acidic soils to bind significant amounts of carbon dioxide, while also giving organic farmers a highly effective fertiliser.
Known as glacial rock flour, the fine grey powder can sequester so much carbon dioxide through a technique known as enhanced weathering that the Danish scientists who carried out the experiments believe it can be “an important part” of mitigating climate change.
In one of the experiments, glacial rock flour consisting of silicate was applied to acidic agricultural soil. The results showed that one ton of glacial rock flour can absorb 14.6kg of carbon dioxide over a period of three years, or a total of 728 kg of carbon dioxide per hectare. If this were applied to all suitable land in Denmark, more than 27 million tons of carbon dioxide would be removed from the atmosphere — or slightly less than the 29 million tons of carbon pollution the country emitted in 2021.
“It’s a simple and scalable solution that could be used both in Denmark and around the world,” said Christiana Dietzen, a soil scientist at the University of Copenhagen and lead author of the paper about the carbon sequestration-experiment, which appeared in the International Journal of Greenhouse Gas Control.
One advantage of glacial rock flour is that it does not have to be ground. Other materials that could be used for enhanced weathering, such as basalt, must be ground in an energy-intensive process first. In addition, glacial rock flour is found in virtually unlimited quantities in Greenland, with more being produced each year than could be gathered for export, according to Ms Dietzen.
She notes, however, that the emissions created by gathering and transporting glacial rock flour could exceed the amount of carbon it can remove from the atmosphere.
More potatoes and maize thanks to glacial rock flour
The second experiment, this one lasting a year, showed for the first time that glacial rock flour is also a potent fertiliser for organic plants. In the experiment, plants treated with organic fertiliser did not produce greater yields — presumably because the soil they were grown in was nutrient-rich anyway — but plants grown on the part of the field treated with glacial rock flour did: maize yields were 24% higher, and potato plants produced 19% more yields. However, because the study only ran for one year, the team is unable to say what effect glacial rock flower has on yields over time.
“The soil conditions at this site were suitable for capturing carbon dioxide, and the glacial rock flour also provided a co-benefit of somewhat increased soil fertility. On the other hand, we have done some experiments in Ghana, where we saw a really impressive increase in crop yields of 35% on average that have persisted so far for four growing seasons,” said Ms Dietzen, who also contributed to the second study, which appeared in Nutrient Cycling in Agroecosystems.
The effect of enhanced weathering on carbon-dioxide sequestration is not immediately apparent, according to the study. After the three-year experiment, the researchers found that only 8% of the maximum potential carbon-dioxide uptake of the glacial rock flour was achieved.
The implication here is that though this process is effective, it is not a quick solution, but could take decades to realise its full potential,” Ms Dietzen said. However, if it is implemented now enhanced weathering can contribute to achieving global goals of achieving net-zero by 2050.
The researchers have just received funding to start a new research centre aimed at continuing to investigate the use of glacial rock flour. Several three-year trials are also to be held in Denmark, Ghana and Australia. “Hopefully within this time frame the first commercial applications of glacial rock flour will also have begun on Danish agricultural fields so that the process of capturing carbon dioxide can begin.”
Julia Hager, PolarJournal
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