Nutrient controls on climate and life

In this project you will investigate how the availability of iron and manganese in the oceans controls the global carbon and oxygen cycles, and hence the evolution of Earth’s climate and surface conditions over past, present and future timescales.

Project background:

The availability of macronutrients (like phosphorus and nitrogen) and micronutrients (like iron and manganese) has played a fundamental role in regulating climate and surface conditions over Earth’s history, and will play a critical role in sustaining life on our planet into the future.

How do nutrients work to control climate and life? Traditionally nutrients are understood to affect climate and surface temperature through their impact on primary productivity. Nutrients are weathered from the continents and transported to the oceans by rivers, where they fuel photosynthetic primary productivity, which draws down carbon dioxide. When primary producers die most of their sequestered carbon is decomposed and returned to the atmosphere, but a small amount sinks to the sediments and is buried for hundreds of thousands to millions of years. This locks away carbon from the atmosphere and so helps regulate climate and surface temperatures, and it also frees up oxygen that would otherwise be used during decomposition and so helps regulate oxygen levels in the ocean and atmosphere.

Why is this understanding incomplete? New work shows there is a more intricate interplay between nutrient availability and the carbon and oxygen cycles that control climate and life. For example, it has been suggested that the rise of oxygen to breathable levels during the Great Oxidation Event some 2.4 billion years ago was driven by feedbacks between the phosphorus and oxygen cycles (Alcott et al., 2019), while the subsequent regulation of oxygen and carbon dioxide levels within habitable bounds has been modulated by iron and manganese (Moore et al., 2023). Similar key roles in past environmental change are proposed for other nutrients, yet how human perturbations to global nutrient cycling will impact future habitability is largely unknown.

What’s so special about iron and manganese? Iron and manganese in particular may play a dual role in controlling climate and life, because not only are they capable of fuelling photosynthetic primary productivity and thus regulating carbon burial, but they also form iron and manganese minerals in marine sediments that are able to enhance carbon burial independently of primary productivity (Zhao et al., 2023). Moreover, these minerals play an important role in controlling the concentration of other micronutrients in the oceans like nickel and cobalt, upon which primary productivity depends. As such, the availability of iron and manganese, and how this impacts the availability of other key nutrients, may play a critical dual role in controlling the carbon and oxygen cycles, and ultimately the evolution of climate and life on Earth.

 

What will you do?

You will use an exciting combination of experimental, analytical and numerical techniques, depending on your background and interests, to explore the dual role of iron and manganese in controlling the global carbon and oxygen cycles, and hence the evolution of Earth’s climate and surface conditions over past, present and future timescales.

You will build upon recent ground-breaking work by your supervisory team to investigate the interplay between iron and manganese availability, other nutrient cycles like phosphorus, and the carbon and oxygen cycles that control climate and life.

Here’s an example of what you might want to do: You could conduct experiments to investigate how iron and manganese minerals interact with carbon and enhance its preservation and burial, and then analyse your experimental products using advanced microscopy and spectroscopy tools at the world-leading Diamond Light Source synchrotron (Curti et al., 2021).

Image: PhD student in the Cohen Geochemistry Group laboratories preparing an iron mineral, that will later be mixed with carbon to make samples for analysis on one of the microscopy beamlines at Diamond Light Source synchrotron. On the right you can see the structures of two of the most important iron and manganese minerals in marine sediments, a) iron mineral ‘ferrihydrite’, and b) manganese mineral ‘birnessite’.

Image: Diamond Light Source synchrotron in Oxfordshire UK, with two of the beamline scientists helping to set up nanoscale analyses of experimental samples.

Here’s another example: You could help develop a biogeochemical model to investigate how mineral-carbon preservation and burial might have affected the carbon and oxygen cycles in the past, and how Earth’s climate and oxygenation might have responded (Zhao et al., 2023).

Image: Schematic diagram of a global biogeochemical model of the oceanic carbon cycle, developed by your supervisory team (Zhao et al., 2023). Carbon in the oceanic reservoirs (the boxes with a blue background) exists as dissolved inorganic carbon (DIC) or organic carbon (OC), and carbon is exchanged between DIC and OC by various different biogeochemical processes. DIC can then be buried into the sediments as carbonate, while OC can be buried in either a mineral-protected (Prot.) or unprotected (Unpr.) form.

And here’s another example:  You could even combine experiments, analysis and modelling to look at how the availability of iron and manganese have affected the carbon cycle in the past and into the future, and the knock-on effects on climate and life (Moore et al. 2023).

Image: Media coverage of the paper Moore et al. (2023) where Oliver Moore working with your supervisory team show that a chemical reaction between carbon and iron minerals helps preserve and bury carbon in marine sediments, and may have helped create the stable climate and surface conditions necessary for animal life to evolve.

How will I get started with my project? Typically, you will spend the first few months of your PhD getting to know the background and literature, and discussing ideas for investigation with your supervisory team. Then whatever it is that you are interested to do, you will be fully guided and supported by your supervisory team and more widely within the Cohen Geochemistry Group.

What training will I get? You will receive specialist scientific training in state-of-the-art biogeochemical experimental and analytical techniques and biogeochemical modelling approaches, many of which have been developed by your supervisory team at Leeds. In addition, you will be trained in a wide variety of key transferable skills within the PANORAMA DTP, from computer programming and modelling, to media skills and public outreach. You will also be encouraged and supported to present your research at national and international scientific conferences, for example at the international Goldschmidt Conference, which is the premier geochemistry conference.

 

HOW CAN I FIND OUT MORE? If you want to know more about this project, then please email Caroline and we can chat!

 

Here are the papers cited above. These are examples of the sorts of things that you might want to do – these papers were done by PhD and Postdoctoral students working with your supervisory team!

Alcott et al., 2019. Stepwise Earth oxygenation is an inherent property of global biogeochemical cycling. Science 366, 1333-1337. DOI: 10.1126/science.aax6459

Curti et al., 2021. Carboxyl-richness controls organic carbon preservation during coprecipitation with iron (oxyhydr)oxides in the natural environment. Communications Earth & Environment 2, article no. 229. https://doi.org/10.1038/s43247-021-00301-9

Moore et al., 2023. Long-term organic carbon preservation enhanced by iron and manganese. Nature 621, 312-317. https://doi.org/10.1038/s41586-023-06325-9

Zhao et al., 2023. Oxygenation of the Earth aided by mineral organic carbon preservation. Nature Geoscience 16, 262-267. https://doi.org/10.1038/s41561-023-01133-2