The deep nitrogen cycle – nitrogen storage in the subduction system

This project is available from the academic year 2022/23 onwards.

Theme: Solid Earth Dynamics

Primary Supervisor:

John Brodholt

Earth Sciences, UCL

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Secondary Supervisor:

Andrew Thomson

Earth Sciences, UCL

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Project Description:

Nitrogen forms an integral part of the main building blocks of life, including DNA, RNA, and proteins. N2 is the dominant gas in Earth’s atmosphere, and nitrogen is likely stored in all of Earth’s geological reservoirs, including the crust, the mantle, and the core. After the subduction of organic matter stored on the ocean-floor nitrogen has normally been assumed to behave like the noble gases during mantle processes, an unreactive and incompatible gas phase. However, empirical data suggest that nitrogen may exist in many forms throughout mantle conditions. Since Earth is a dynamic planet, with active plate tectonics, the relative efficiency of nitrogen in-gassing (subduction) and outgassing (volcanoes) will control surface and mantle nitrogen reservoirs on geological timescales, therefore influencing the ability of our planet to develop and sustain a stable life-supporting atmosphere. Understanding the speciation, compatibility and behaviour of nitrogen through the subduction cycle is of critical importance to understanding the evolution of planet Earth as we know it today.

This Ph.D. project will provide the opportunity to explore the transport and storage of nitrogen in mantle phases throughout the entire subduction system, from ocean-floor to the upper/lower mantle boundary region. The Ph.D. would be completed in the high-pressure labs at UCL, using a combination of experimental techniques in collaboration with St Andrews University. Throughout the project there will be opportunities for the student to visit analytical labs and large national facilities (e.g. synchrotron and neutron sources) in the UK, Europe, USA and Japan depending on project requirements.

Policy Impact of Research:

Nitrogen is hugely important to life. Studying volatile storage and degassing into and from the mantle will help us understand the origins and maintenance of life on planet Earth throughout its history.

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