Characterising the efficiency of Enhanced Weathering as an atmospheric CO2 removal strategy using isotopic tracers

Dr Christopher Pearce, Prof Rachael James, Dr Juerg Matter, Grace Andrews (Project Vesta), Stephen Romaniello (Project Vesta)
Rationale: 

The implementation of new approaches for reducing atmospheric CO2 levels is urgently required if we are to achieve the Paris Agreement target of limiting the post-industrialization increase in global temperature to 1.5°C. Enhanced Weathering (EW) is a geoengineering strategy that facilitates CO2 removal by accelerating the rate of silicate rock or mineral weathering via application to agricultural or coastal environments [1,2]. Although EW has been tested in laboratories and in small field trials, its effectiveness at sequestering significant quantities of CO2 over human timescales has yet to be determined.

This project will apply a combination of chemical and isotopic techniques to constrain the rate and nature of rock/mineral weathering, as well as the fate of the weathering products, in a series of EW field trials being conducted in terrestrial and marine environments in the UK, USA, Malaysia and Caribbean. The results will inform how the extent and stability of atmospheric CO2 removal varies with climatic conditions, silicate mineralogy, and local soil/seawater chemistry, and will assess different mechanisms for quantifying and monitoring these changes - an essential requirement for the long-term implementation of this CO2 removal strategy. The outcomes of this project will also contribute to the development of an IPCC Tier 1 EW Greenhouse Gas Removal methodology.

 

Methodology: 

The mineral dissolution and precipitation mechanisms that underpin the EW CO2 removal process will be investigated using an array of state-of-the-art isotopic techniques. For example; Radiogenic 87Sr/86Sr measurements will be used to quantify the extent of silicate vs. carbonate mineral weathering; Stable d7/6Li, d26/24Mg and d88/86Sr will help trace the formation of secondary minerals in soil environments (e.g. [3]); and d30/28Si and d56/54Fe may improve our understanding of olivine dissolution and elemental uptake in coastal environments. These approaches will be used in conjunction with other physical and chemical measurements (e.g. water flux/exchange, alkalinity, pH and metal abundances) to quantify the rate of weathering and atmospheric CO2 drawdown, and to establish an optimal EW monitoring strategy.

Samples will be derived from active terrestrial EW trials being conducted in the UK, Illinois USA, and Sabah Malaysia through the Leverhulme Centre for Climate Change Mitigation (www.lc3m.org) and UKRI-funded Greenhouse Gas Removal Demonstrator project, as well as from coastal EW trials being conducted by Project Vesta in the USA and Caribbean (www.projectvesta.org). There will be opportunities to visit and conduct fieldwork at these locations. Field samples will be complemented by a series of laboratory-based experiments that characterise weathering mechanisms and their associated isotopic and chemical responses under a range of well-constrained conditions.

 

Location: 
NOC, Southampton
Training: 

The INSPIRE DTP programme provides comprehensive personal and professional development training alongside extensive opportunities for students to expand their multi-disciplinary outlook through interactions with a wide network of academic, research and industrial/policy partners. The student will be registered at the University of Southampton and hosted at the National Oceanography Centre. Specific training will include:

  1. Collection of water, soil/sediment and biomass samples from active EW field trials, and conducting associated in-situ physical and chemical measurements (e.g. pH and alkalinity).
  2. Determination of trace element concentrations and isotopic ratios by inductively coupled plasma mass spectrometry (ICP-MS), thermal ionization mass spectrometry (TIMS) and multi-collector (MC) ICP-MS.
  3. Laboratory-based experiments for quantifying the rate of silicate rock/mineral dissolution and the associated precipitation of secondary minerals, and their effect on the chemical and isotopic composition of the surrounding fluid.
  4. Use of geochemical models such as PHREEQC and CO2SYS to constrain changes in aqueous geochemistry and mineral saturation states, and coupling with physical parameters such as discharge/flow rates to establish atmospheric CO2 drawdown.

In addition to exchanges associated with the INSPIRE DTP, the student will also have opportunities to work closely with national and international collaborators involved in all of the active EW trials and programmes.

 

Eligibility & Funding Details: 

Please see https://inspire-dtp.ac.uk/how-apply for details.

Background Reading: 

[1] Beerling D.J., Kantzas E., Lomas, M.R., Wade, P., Eufrasio, R.M., Renforth, P., Sarkar, B., Andrews, M.G., James, R.H., Pearce, C.R., Mercure, J.F., Pollitt, H., Holden, P.B., Edwards, N.R., Khanna, M., Koh, L., Quegan, S., Pidgeon, N.F., Janssens, I.A., Hansen, J. and Banwart, S.A. (2020). Potential for large-scale CO2 removal via enhanced rock weathering with croplands. Nature v583, p242-248.

[2] Hartmann, J. West, A.J., Renforth, P., Köhler, P., De La Rocha, C.L., Wolf-Gladrow, D.A., Dürr, H.H. and Scheffran, J. (2013). Enhanced chemical weathering as a geoengineering strategy to reduce atmospheric carbon dioxide, supply nutrients, and mitigate ocean acidification. Reviews of Geophysics, v51, p113-149.

[3] Pogge von Strandmann, P.A.E., Renforth, P., West, A.J., Murphy, M.J., Luu, T.H. and Henderson, G.M. (2021). The lithium and magnesium isotope signature of olivine dissolution in soil experiments. Chemical Geology, v560, 120008.

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