Turning up the carbon dial

Can we lock away more carbon in soils and sediments to combat climate change?

The classic paradigm for carbon burial in soils and sediments assumes that to bury and store more carbon, and hence lock more carbon away from the atmosphere, we need to make more carbon in the form of primary productivity. This paradigm assumes that of the total carbon produced, a fixed proportion is eventually buried and stored. Hence if we make more, we bury more.

But what if we could increase the proportion of the total carbon that’s buried and stored?

We wouldn’t necessarily need to make more to bury more. Instead we could make the same amount, or even make less, but turn up the preservation efficiency.

This could allow us to bury and store more carbon in soils to combat climate change and improve their fertility for food production and security. More carbon in soils also supports myriad other soil ecosystem functions, like water holding capacity that helps prevent flooding.

We could also bury and store more carbon in near-shore marine sediments – so-called blue carbon. This could also help combat the climate emergency.

So how do we increase the proportion of total carbon that’s buried and stored? – how do we turn up the preservation efficiency?

We need to understand how carbon is buried and stored. And one of the main ways involves soil and sediment minerals. These bind with carbon and protect it from decomposition. They can also change carbon from easily decomposable to less easily decomposable forms. Together these binding and transforming processes are responsible for most of the carbon burial and storage in soils and sediments. But we don’t yet fully understand how these processes work, for example:

Research Question 1: What controls whether carbon is bound and transformed with minerals?

Research Question 2: Will these controls change as soils and sediments get warmer?

Research Question 3: How long does the mineral-carbon stay buried – decades, centuries, millennia?

Research Question 4: And crucially, can we manipulate these processes to turn up the proportion of the total carbon that’s buried and stored?

 

What will I do?

In this project you’ll investigate the factors that control the formation, stability and longevity of mineral-carbon. You’ll use natural and experimental minerals and carbon sources, from soil and sediment environments. You’ll determine why some types of mineral-carbon are more stable than others and how long they last in the environment. Then you’ll use these insights to recommend actions that can promote the formation of stable mineral-carbon in soils and sediments.

Can we produce a road map for how to turn up preservation efficiency and which soils and sediments are best to focus our efforts?

This is what decision makers and land managers need to know. This way we can capitalise on the natural ability of soils and sediments to lock carbon away from the atmosphere.

Where will I do this?

You’ll join a vibrant research group at the University of Leeds (called the Cohen Geochemistry Group). We have world-leading expertise in carbon cycling, soil and sediment biogeochemistry. We use both experimental and analytical approaches to measure and characterise organic carbon.

You’ll develop new ways to extract carbon from mineral-carbon complexes. Then you can analyse it and determine how it formed, how stable it is, and how long it will last in the environment. Your supervisory team recently developed an exciting new concept called the Mineral Carbon Pump, and you’ll build on this. This concept describes how minerals pump carbon from easily decomposable to less easily decomposable forms. And you’ll figure out how to supercharge this pump to bury and store more carbon.

You’ll receive specialist scientific training in state-of-the-art experimental and analytical techniques and modelling approaches. Then there’s training in a wide variety of key transferable skills within the YES DTN, from computer programming and modelling, to media skills and public outreach. There’s also plenty of opportunities to present your research at national and international conferences. For example at Goldschmidt, which is the premier international geochemistry conference. At events like these you’ll meet like-minded people and expand your network. This will help you to continue your research in academia or in other career paths in industrial and commercial practice.

 

Is there more information about the structure of this project? 

Your supervisory team envisage this project going something like this:

Typically, you’ll spend the first few months of your PhD getting to know the background literature, and discussing ideas with your supervisory team. You’ll need to get up to speed on the global carbon cycle, and particularly the processes responsible for carbon burial in soils and sediments. There’s lots of classic papers your supervisory team can recommend, like this one. We’ll help you to read and understand these.

Then you’ll need to drill down into the specific ways in which soil and sediment minerals can bind and transform carbon. This helps to protect carbon from decomposition and hence promote carbon burial (there’s a recent review article here).

Then with your supervisory team we’ll help you identify the knowledge gaps in the literature and devise ways to investigate these.

Is there more information about the sorts of experiments I might do?

If we consider Research Question 1 above ‘What controls whether carbon is bound and transformed with minerals?’. You’ll learn that we know some types of minerals, like iron and manganese minerals, are good for carbon binding and transformation. But we don’t know about other, often more common minerals, like clays. Clays make up the majority of the minerals in soils and sediments but we still don’t know whether they can transform carbon into less easily decomposable forms.

So to investigate this you could set up laboratory experiments. For example, you could mix clays with various carbon sources (like plant debris, marine algae) and then incubate these under various soil and sediment conditions (like different pH). Then you could extract the carbon and analyse it to see if its been transformed, and what sort of carbon its turned into.

If you varied the temperature of your experiments, then this would help you to address Research Question 2 as well ‘Will these controls change as soils and sediments get warmer?’

Then you could subject your carbon to various tests to see how long it might survive in the environment – and thus how long it could lock carbon away from the atmosphere. For example, you could try to destroy it with chemicals, or with heat, or even try to feed it to microbes to see if they can break it down. This would help you for Research Question 3 ‘How long does the mineral-carbon stay buried – decades, centuries, millennia?’

What impact might my project have?

Once you’ve figured out what minerals and what types of carbon are best for mineral-carbon burial, and what conditions are best for promoting carbon binding and transformation, then you can apply this new knowledge to Research Question 4. You might be able to see a way in which different types of soils (like forest, agricultural or urban soils) and areas of the near-shore (like muddy marine sediments) could be encouraged to store more carbon. You can publish your results via the scientific literature and popular media, and make use of your new networks to engage with soil and sediment stakeholders to share your findings.

Perhaps we should amend soils with certain types of minerals to promote mineral-carbon formation? What do you think?!

 

Here’s the details for the links in the text above: (if you can’t access any please email Caroline Peacock for copies):

soil ecosystem functions: https://www.nature.com/scitable/knowledge/library/soil-carbon-storage-84223790/ Ontl and Schulte, 2012. Soil Carbon Storage. Nature Education Knowledge 3(10): 35.

blue carbon: https://www.thebluecarboninitiative.org/

soil and sediment minerals: https://www.youtube.com/watch?v=TUHmBkPtkPU&t=92s Building long term carbon stocks in soils

Cohen Geochemistry Group: https://environment.leeds.ac.uk/earth-surface-science-institute/doc/cohen-research-group

Mineral Carbon Pump: https://www.nature.com/articles/s43017-023-00396-y Xiao et al., 2023 Introducing the mineral carbon pump. Nature Reviews Earth & Environment, 4: 135-136.

Goldschmidt: https://conf.goldschmidt.info/goldschmidt/2026/meetingapp.cgi

classic papers like this one: https://pubs.acs.org/doi/10.1021/cr050347q Burdige, 2007. Preservation of organic matter in marine sediments:  controls, mechanisms, and an imbalance in sediment organic carbon budgets? Chemical Reviews, 107(2): 467-485.

recent review article here: https://www.sciencedirect.com/science/article/pii/S2772985024000012?via%3Dihub Xu and Tsang, 2024. Mineral-mediated stability of organic carbon in soil and relevant interaction mechanisms. Eco-Environment and Health, 3(1): 59-56.

carbon binding and transformation: https://www.nature.com/articles/s41586-023-06325-9 Moore et al., 2023. Long-term organic carbon preservation enhanced by iron and manganese. Nature, 621, 312-317.