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Quantifying CO2 Removal at Enhanced Weathering Sites: a Multiproxy Approach

Knapp, William J.; Stevenson, Emily I.; Renforth, Phil; Ascough, Philippa L.; Knight, Alasdair C.G.; Bridgestock, Luke; Bickle, Michael J.; Lin, Yongjie; Riley, Alex L.; Mayes, William M.; Tipper, Edward T.


William J. Knapp

Emily I. Stevenson

Phil Renforth

Philippa L. Ascough

Alasdair C.G. Knight

Luke Bridgestock

Michael J. Bickle

Yongjie Lin

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Dr Alex Riley
Lecturer in Environmental Science

Edward T. Tipper


Enhanced weathering is a carbon dioxide (CO2) mitigation strategy that promises large scale atmospheric CO2 removal. The main challenge associated with enhanced weathering is monitoring, reporting, and verifying (MRV) the amount of carbon removed as a result of enhanced weathering reactions. Here, we study a CO2 mineralization site in Consett, Co. Durham, UK, where steel slags have been weathered in a landscaped deposit for over 40 years. We provide new radiocarbon, δ13C, 87Sr/86Sr, and major element data in waters, calcite precipitates, and soils to quantify the rate of carbon removal. We demonstrate that measuring the radiocarbon activity of CaCO3 deposited in waters draining the slag deposit provides a robust constraint on the carbon source being sequestered (80% from the atmosphere, 2σ = 8%) and use downstream alkalinity measurements to determine the proportion of carbon exported to the ocean. The main phases dissolving in the slag are hydroxide minerals (e.g., portlandite) with minor contributions (<3%) from silicate minerals. We propose a novel method for quantifying carbon removal rates at enhanced weathering sites, which is a function of the radiocarbon-apportioned sources of carbon being sequestered, and the proportion of carbon being exported from the catchment to the oceans.


Knapp, W. J., Stevenson, E. I., Renforth, P., Ascough, P. L., Knight, A. C., Bridgestock, L., …Tipper, E. T. (2023). Quantifying CO2 Removal at Enhanced Weathering Sites: a Multiproxy Approach. Environmental Science and Technology, 57(26), 9854-9864.

Journal Article Type Article
Acceptance Date Jun 1, 2023
Online Publication Date Jun 21, 2023
Publication Date Jul 4, 2023
Deposit Date Jun 21, 2023
Publicly Available Date Jun 26, 2023
Journal Environmental science & technology
Print ISSN 0013-936X
Electronic ISSN 1520-5851
Publisher American Chemical Society
Peer Reviewed Peer Reviewed
Volume 57
Issue 26
Pages 9854-9864
Keywords Radiocarbon; Carbon dioxide removal; Mineralisation; Isotopic tracers; Monitoring
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