Quantifying CO2 removal at enhanced weathering sites: a multiproxy approach

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

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

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Abstract

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 sillicate minerals. We propose a new 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 of the oceans.
Original languageEnglish
Pages (from-to)9854-9864
Number of pages11
JournalEnvironmental Science and Technology
Volume57
Issue number26
Early online date21 Jun 2023
DOIs
Publication statusPublished - 4 Jul 2023

Keywords

  • Radiocarbon
  • Carbon dioxide removal
  • Mineralisation
  • Isotopic tracers
  • Monitoring

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