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Cited by 63CO2 Sequestration and Geologic InteractionsMarine and coastal ecosystemsClimate Change and Geoengineering

The additionality problem of ocean alkalinity enhancement

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Bach, Lennart Thomas·2024·Biogeosciences
DOI 10.5194/bg-21-261-2024

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Abstract

Abstract. Ocean alkalinity enhancement (OAE) is an emerging approach for atmospheric carbon dioxide removal (CDR). The net climatic benefit of OAE depends on how much it can increase CO2 sequestration relative to a baseline state without OAE. This so-called “additionality” can be calculated as follows: Additionality=COAE-ΔCbaseline. So far, feasibility studies on OAE have mainly focussed on enhancing alkalinity in the oceans to stimulate CO2 sequestration (COAE); however, the primary focus has not been on how such anthropogenic alkalinity would modify the natural alkalinity cycle and associated baseline CO2 sequestration (ΔCbaseline). Here, I present incubation experiments in which materials considered for OAE (sodium hydroxide, steel slag, and olivine) are exposed to beach sand to investigate the influence of anthropogenic alkalinity on natural alkalinity sources and sinks. The experiments show that anthropogenic alkalinity can strongly reduce the generation of natural alkalinity, thereby reducing additionality. This is because the anthropogenic alkalinity increases the calcium carbonate saturation state, which reduces the dissolution of calcium carbonate from sand, a natural alkalinity source. I argue that this “additionality problem” of OAE is potentially widespread and applies to many marine systems where OAE implementation is considered – far beyond the beach scenario investigated in this study. However, the problem can potentially be mitigated by dilute dosing of anthropogenic alkalinity into the ocean environment and the avoidance of OAE in natural alkalinity cycling hotspots, such as in marine sediments. Understanding a potential slowdown of the natural alkalinity cycle through the introduction of an anthropogenic alkalinity cycle will be crucial for the assessment of OAE.

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  • In extreme experimental scenarios, alkalinity addition can suppress sediment CaCO3 dissolution such that the OAE scenario results in lower net alkalinity addition than natural sediments alone.

    “In extreme, experimental scenarios, alkalinity addition can suppress sediment CaCO3 dissolution such that the OAE scenario results in lower net alkalinity addition than natural sediments alone. 52”

    From A framework for understanding efficiency losses of Ocean Alkalinity Enhancement (2026) · cites this paper as [52]

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Cited by

Sorted by citations

Authors
Bach, L. T.
Affiliations
University of Tasmania (AU)
Corresponding author
Bach, Lennart Thomas
ORCID
Bach, Lennart Thomas
Venue
Biogeosciences
Publisher
Copernicus GmbH
Published
2024-01-16
Volume
21
Issue
1
Pages
261-277
ISSN
  • 1726-4170 (ISSN-L)
  • 1726-4189
DOI
10.5194/bg-21-261-2024
OpenAlex
W4390933587
Cited by
63
References
5
Citations by year
2026: 22 · 2025: 33 · 2024: 6 · 2023: 2
FWCI
6.62
Type
journal article
Language
en
Open access
Licence
Locations
  • Biogeosciences (publishedVersion, cc-by)
  • DOAJ (DOAJ: Directory of Open Access Journals) (submittedVersion, cc-by-sa)
  • Informationszentrum Lebenswissenschaften (ZB MED) (submittedVersion, cc-by)
Funders
Australian Research Council (FT200100846)
Topics
  • Physical Sciences › Environmental Science › Environmental Engineering › CO2 Sequestration and Geologic Interactions
  • Physical Sciences › Earth and Planetary Sciences › Oceanography › Marine and coastal ecosystems
  • Physical Sciences › Environmental Science › Global and Planetary Change › Climate Change and Geoengineering
Keywords
ocean alkalinity enhancement, additionality, carbon dioxide removal, calcium carbonate dissolution, beach sand, sodium hydroxide, steel slag, olivine, calcium carbonate saturation, marine sediment, CO2 sequestration

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