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Cited by 658CO2 Sequestration and Geologic InteractionsClimate Change and GeoengineeringOcean Acidification Effects and Responses

The DOI matches its Crossref record; 218 of the 220 references it cites were found in a registry or an index; none of the 214 sources its claims cite is checked for support yet.

Assessing ocean alkalinity for carbon sequestration

Open access
Renforth, Phil, Henderson, Gideon·2017·Reviews of Geophysics
DOI 10.1002/2016rg000533
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Abstract

Over the coming century humanity may need to find reservoirs to store several trillions of tons of carbon dioxide (CO 2 ) emitted from fossil fuel combustion, which would otherwise cause dangerous climate change if it were left in the atmosphere. Carbon storage in the ocean as bicarbonate ions (by increasing ocean alkalinity) has received very little attention. Yet recent work suggests sufficient capacity to sequester copious quantities of CO 2 . It may be possible to sequester hundreds of billions to trillions of tons of C without surpassing postindustrial average carbonate saturation states in the surface ocean. When globally distributed, the impact of elevated alkalinity is potentially small and may help ameliorate the effects of ocean acidification. However, the local impact around addition sites may be more acute but is specific to the mineral and technology. The alkalinity of the ocean increases naturally because of rock weathering in which >1.5 mol of carbon are removed from the atmosphere for every mole of magnesium or calcium dissolved from silicate minerals (e.g., wollastonite, olivine, and anorthite) and 0.5 mol for carbonate minerals (e.g., calcite and dolomite). These processes are responsible for naturally sequestering 0.5 billion tons of CO 2 per year. Alkalinity is reduced in the ocean through carbonate mineral precipitation, which is almost exclusively formed from biological activity. Most of the previous work on the biological response to changes in carbonate chemistry have focused on acidifying conditions. More research is required to understand carbonate precipitation at elevated alkalinity to constrain the longevity of carbon storage. A range of technologies have been proposed to increase ocean alkalinity (accelerated weathering of limestone, enhanced weathering, electrochemical promoted weathering, and ocean liming), the cost of which may be comparable to alternative carbon sequestration proposals (e.g., $20–100 tCO 2 −1 ). There are still many unanswered technical, environmental, social, and ethical questions, but the scale of the carbon sequestration challenge warrants research to address these.

Overview

AI snapshot

Written from the paper’s full text.

TL;DR

This review assesses increasing ocean alkalinity as a carbon sequestration route, storing CO₂ as bicarbonate and carbonate ions in the ocean. It finds potentially large capacity and costs that may be comparable to conventional mitigation, but major uncertainties remain about environmental impacts, carbonate precipitation feedbacks, and governance.

Key findings

  • The ocean already stores ≈38,000 Gt C, and the paper suggests it may be possible to sequester hundreds of billions to trillions of tonnes of C without surpassing post-industrial average carbonate saturation states in the surface ocean.
  • Adding Ca²⁺ or Mg²⁺ can sequester close to 2 moles of C per mole of cation; at 400 ppmv, S = 35, T = 17°C, η = 0.831, implying 0.83 moles of C stored per mole of H⁺ consumed, or 1.66 per mole of Ca²⁺ or Mg²⁺ added. Carbonate mineral dissolution gives smaller net uptake of 0.4 to 0.7.
  • If used as the sole destination for all anthropogenic CO₂ over 100–500 years, ocean alkalinity would increase from 2.3 mEq kg⁻¹ to ~3 mEq kg⁻¹, with calcite saturation between 5 and 7.5; average calcite saturation is unlikely to surpass pre-industrial levels, but localized impacts around addition sites may be more acute.
  • Proposed technologies include ocean liming, accelerated weathering of limestone, electrochemical splitting, and enhanced weathering; the paper reports costs/energy broadly comparable to alternatives, e.g. 1–10 GJ tCO₂⁻¹ and $50–150 tCO₂⁻¹ in the conclusions, with the abstract citing $20–100 tCO₂⁻¹.

Methods

  • This is a review and synthesis of the inorganic ocean carbon sink, covering alkalinity chemistry, ocean carbon cycle processes, modeling studies, mineral-based technologies, environmental impacts, and regulation.
  • It draws on published literature, box models and spatially resolved models (e.g. 3-box, Paquay and Zeebe, Ilyina et al., Keller et al., Ferrer-González and Ilyina), technoeconomic comparisons, and proposed experimental scenarios in Table 2.
  • No new primary experiments or field data collection are reported; the analysis is narrative and comparative, with quantitative estimates taken from cited studies and model outputs.

Limitations

  • Stated: many technical, environmental, social, and ethical questions remain unanswered; research is needed to understand impacts and feasibility, and local impacts are specific to the mineral and technology used.
  • Stated: carbonate precipitation at elevated alkalinity is poorly constrained, reaction kinetics are poorly constrained, cost estimates are largely speculative, and monitoring may require years to detect alkalinity changes above background seasonal variability.
  • Evident: the review relies heavily on models and desk-top or bench-scale studies; upscaling to billions of tons CO₂ per year is described as a considerable challenge, and model assumptions such as instant complete olivine dissolution or uniform alkalinity addition limit real-world inference.

Model-written summary. Check it against the paper before relying on it.

Integrity signals

Registry

Crossref · 10.1002/2016rg000533

Cites

218 of 218 references verified0 citation errors · 0 not checkable

Statistics

Nothing to recompute.

Verification

Claims the paper makes

0 of 214 cited sources checked · 0 supported · 0 flagged

Show all 137 claims

  • Probably not a substantial claim. 180
  • It may state two separate claims as one. 129
251 of 251

  • The authors state this as an assumption.

    The growth time for Orbulina universa remains relatively constant, so shell mass is directly analogous to calcification rate.

    “Assuming the growth time for the organism remains relatively constant, the shell mass is directly analogous to calcification rate.”

  • The authors state this as an assumption.

    The proportional change in shell mass is representative of the proportional change in growth rate.

    “However, assuming the proportional change is representative of the proportional change in growth rate, the range of values are substantially less than what would be expected from exclusively abiotic controlled kinetics (~138 % rate change over the same increase in Ωcalcite, see below).”

  • The authors state this as an assumption.

    The composition of particulate inorganic carbon is aragonite or Mg-calcite with molecular mass between 97 and 100 g(carbonate) mol-1 and up to 20% MgCO3.

    “Assuming the composition of the PIC is aragonite or Mg-calcite (molecular mass between 97 and 100 g(carbonate) mol -1 , and assuming up to 20% MgCO3), the concentration of carbonate minerals in the open surface ocean may be between 5.6 and 23.4 μg l -1 .”

  • The authors state this as an assumption.

    The lower end member of the abiotic precipitation rate range is used for the projected increase in carbonate production.

    “While biological carbonate precipitation depends on numerous factors, the abiotic precipitation follows a predicable relationship with Ω, and (assuming the lower end member) would increase from 0.01 to 0.4 Gt C y -1 for an increase in Ωcalcite from its current value to 10 (a 20% increase of carbonate production).”

  • The authors state this as an assumption.

    The rate of olivine dissolution is instant and complete in the modeling.

    “A complication in this relates to the rate of olivine dissolution required, which are assumed to be instant and complete in the modeling.”

  • The paper relies on this without support.

    The use of produced Mg(OH)2 to increase ocean alkalinity has not been explored.

    “The use of the produced Mg(OH)2 to increase ocean alkalinity has not been explored.”

  • The authors state this as an assumption.

    There are no efficiency losses in electrolysis, fuel cell generation, and acid neutralization.

    “Assuming no efficiency losses”

  • The paper relies on this without support.

    The limited technoeconomic assessment of these processes largely focuses on deriving overall energy and carbon balances, and there has been little optimization.

    “The limited technoeconomic assessment of these processes largely focus on deriving overall energy and carbon balances, and there has been little optimization.”

  • The paper relies on this without support.

    Some reaction kinetics are poorly constrained (particularly for artificial materials), resulting in considerable uncertainty in the design of the flow sheet.

    “Furthermore, some of the reaction kinetics are poorly constrained (particularly for artificial materials), resulting in considerable uncertainty in the design of the flow sheet.”

  • The authors state this as an assumption.

    Alkalinity addition effects are modeled assuming instantaneous dissolution within the rapidly mixed wake of a ship.

    “This assumes instantaneous dissolution within the rapidly mixed wake of a ship.”

  • The authors state this as an assumption.

    The dilution formula assumes that the density difference between the disposed chemical and seawater is minimal.

    “equation 32 assumes that the density difference between the disposed chemical and seawater is minimal, and thus has greater relevance to the disposal of liquid.”

  • The paper relies on this without support.

    Storage of large volumes of CO2 may be necessary to prevent dangerous climate change.

    “Storage of large volumes of CO2 may be necessary to prevent dangerous climate change.”

  • The paper relies on this without support.

    The ocean currently stores around 38,000 Gt C, equivalent to about 140,000 Gt CO2, in the form of ocean alkalinity.

    “The ocean currently stores around 38,000 Gt C (equivalent to ~140,000 Gt CO2) in this way”

  • The paper relies on this without support.

    Current ocean alkalinity is 2.3 mEq kg-1.

    “current levels of 2.3 mEq kg -1”

  • The paper relies on this without support.

    The particulate organic to inorganic carbon ratio is greater than 1.

    “As the particulate organic to inorganic carbon ratio is >1”

  • The paper relies on this without support.

    The CO2:rock mass ratio for solid carbonate formation is approximately 0.6.

    “larger than the ~0.6 mass ratio for solid carbonate formation”

  • The paper relies on this without support.

    The expected abiological increase in calcite saturation state of 7 is 140%.

    “expected abiological increase of 140 %”
17 of 17

Claims other papers make about this one

Each is checked against this paper’s own text: does it say what the citing paper says it does?

Self-check

Percentages, sums and reported differences re-computed from the paper’s own numbers.

  • Calcium increase is not less than 0.3%

    Minor

    The paper elsewhere gives the current calcium concentration as 10 mmoles kg -1. An increase of 0.9 mmoles kg -1 is 9% of that concentration, not less than 0.3%.

    Reported 0.3 · recomputed 9

  • Reported alkalinity-measurement precision is off by a factor of ten

    Minor

    Relative to the paper's stated seawater alkalinity of 2.5 mEq kg -1, a precision of 0.005 mEq kg -1 is 0.2%, not 0.02%.

    Reported 0.02 · recomputed 0.2

  • Existing cooling-water flow covers about 2%, not 6%, of CO2 output

    Minor

    The stated 20 m 3 s -1 of existing cooling-water flow is about 2.2% of the stated 900 m 3 s -1 required to treat all the plant's CO2, rather than 6%.

    Reported 6 · recomputed 2.222222

3 of 3

Citations

Cites

Flagged first, then by citations

Show all 220 references

2 of the 220 references couldn’t be matched to a known paper.

Research works printed but not linked: 12

  1. Booth C. E., 1984, Acid‐base balance in the sea mussel Mytihrs edulis. 1. Effects of hypoxia and air exposure on the hemolymph acid‐base status, Mar. Biol. Lett., 5, 347
  2. CEFIC, 2011, Guidelines for Measuring and Managing CO2 Emission From Freight Transport Operations, 1
  3. Ciais P., 2014, Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change, 465
  4. DECC, 2015, Digest of UK Energy Statistics’, 1
  5. Drever J. I., 1988, The Geochemistry of Natural Waters
  6. Edenhofer O., 2014, Climate Change 2014: Mitigation of Climate Change, Contribution of Working Group III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change
  7. 10.2307/30060218 · DOI
  8. 10.2307/30066391 · DOI
  9. Roth R., 2015, From Rail to Road and Back Again?: A Century of Transport Competition and Interdependency, Modern Economic and Social History
  10. USGS, 2014, USGS Minerals Yearbook ‐ Cement, 16.1
  11. White A. F., 1995, Chemical weathering rates of silicate minerals, Reviews in mineralogy, Mineral. Soc. Am., 31, 1
  12. Zeebe R. E., 2001, CO2 in Seawater: Equilibrium, Kinetics, Isotopes

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Metadata

Authors
Renforth, P., & Henderson, G.
Affiliations
  • Cardiff University (GB)
  • University of Oxford (GB)
Corresponding author
Renforth, Phil
ORCID
Venue
Reviews of Geophysics
Publisher
American Geophysical Union (AGU)
Published
2017-07-27
Volume
55
Issue
3
Pages
636-674
ISSN
  • 0096-1043 (ISSN-L)
  • 8755-1209
  • 1944-9208
DOI
10.1002/2016rg000533
OpenAlex
W2625135129
Cited by
655
References
220
Citations by year
2026: 123 · 2025: 117 · 2024: 122 · 2023: 127 · 2022: 67 · 2021: 47 · 2020: 18 · 2019: 12 · 2018: 19 · 2017: 3
FWCI
7.96
Type
journal article
Language
en
Open access
Licence
Locations
  • Reviews of Geophysics (publishedVersion, cc-by)
  • ORCA Online Research @Cardiff (Cardiff University) (acceptedVersion)
Funders
  • U.S. Department of Energy
  • Carnegie Institution of Washington
  • University of Oxford
  • Cardiff University
Topics
  • Physical Sciences › Environmental Science › Environmental Engineering › CO2 Sequestration and Geologic Interactions
  • Physical Sciences › Environmental Science › Global and Planetary Change › Climate Change and Geoengineering
  • Physical Sciences › Earth and Planetary Sciences › Oceanography › Ocean Acidification Effects and Responses
Keywords
ocean alkalinity, ocean carbon sequestration, CO2 sequestration, bicarbonate, carbonate saturation state, ocean acidification, enhanced weathering, accelerated weathering, carbonate precipitation, silicate weathering, limestone weathering

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