Ocean Alkalinity enhancement

Oceans & marine

Ringed plovers (Charadrius hiaticular) arriving from the Arctic on Tromlingen, Raet National Park

The oceans are the largest carbon sink for atmospheric carbon, and have taken up over 30% of anthropogenic emissions. Carbon uptake mainly occurs directly through ocean-atmosphere interaction or through weathering processes. Due to this uptake of carbon the oceans turn more acidic overtime, and since the start of the industrial revolution oceans have become 30% more acidic. This has all sorts of effects, as it for example impacts marine biochemistry, and prevents certain organisms from successfully growing.

Ocean Alkalinity Enhancement (OAE) seeks to counter the acidification of the oceans and enhance their Ph by introducing alkalinity (Renforth and Henderson 2017). This would serve to restore the oceans to a previous state, and it could also increase the future carbon uptake potential of the ocean. Although most attention has been paid to enhanced weathering on land (NASEM 2022), OAE is increasingly being considered as one of the main potential ocean based CDR methods. There are different potential OAE techniques, with GESAMP (2019) listing the following: Adding lime directly to the ocean, Adding carbonate minerals to the ocean, Accelerated weathering of limestone, Electrochemical enhancement of carbonate and silicate mineral weathering, Brine thermal decomposition of desalination reject brine, Open ocean dissolution of olivine, Coastal spreading of olivine, and Enhanced weathering of mine waste.

Technological Readiness Level (TRL)

Low 1

There are research projects on OAE as a CDR method (see RETAKE: retake.cdrmare.de/), as well as some proposals for small scale experiments (see the olivine weathering experiment at the port of Rotterdam: Pokharel et al, 2023), and private companies that look at the commercial development of OAE (see: Planetary Technologies, planetarytech.com/). Many open questions still remain, for instance around issues like the durability of carbon sequestration of OAE (Hartmann et al, 2023), the stability of the added alkalinity (Moras et al., 2022), the measure’s broader environmental sustainability (Foteinis et al, 2022), and potential measurement and verification techniques (GESAMP, 2019; NASEM, 2022). All proposed materials have their potential benefits and drawbacks (Bach et al, 2019). There is also no clarity about the best possible distribution methods, with ships (Burt et al, 2021; Caserini et al., 2021) and aircraft (Gentile et al, 2022) being considered. NASEM (2022) note that although some basic physical processes around the 'seawater-Co2 system and alkalinity thermodynamics are well understood', current research is largely based on modeling studies, and there is large uncertainty about the actual effect and impacts of OAE for CDR purposes. GESAMP (2019) equally concludes that ‘'[i]nsufficient research and testing has been done on these topics to allow informed decision-making on large-scale deployment.' The IPCC AR6 wg3 Synthesis Report (2023, p. 52) also notes that it considered OAE to be of relatively lower maturity as opposed to other CDR measures. The State of Carbon Dioxide Removal report also ascribes it a very low technological readiness level (Smith et al, 2023).

Technological Readiness Level (TRL)

A technology with a TRL of 1-3: TRL 1 – Basic; TRL 2 – Concept formulated; TRL 3 – Experimental proof of concept

Scalability

Medium 2

OAE is being considered in both coastal areas and open seas, and although much depends on the durability of the achieved carbon capture and the potential unintended side effects, NASEM (2022) therefore attributes the measure a medium to high potential for scalability.' GESAMP (2019) states that logistical and practical considerations make it likely that OAE will potentially find its first applications on a local and coastal scale.

Scalability

Physically somewhat scalable; linear efficiency

Timeliness for near-future effects

Medium 2

As many open questions remain about the feasibility and most promising OAE method, research programs as the one lined out in NASEM (2022) are needed to be able to evaluate the potential timeliness of this measure.

Timeliness for near-future effects

Implemented in time to make some difference, although questionable

Northern + Arctic potential

High 3

OAE could be deployed regionally, and would then have most pronounced alkalinity effects there (Jin and Cao, 2023). Burt et al (2021) find that such applications could potentially have an ever greater global effect than a global distribution scheme. This statement is confirmed by Wang et al (2022), as they specifically tested OAE application in the Bering Sea in their model and found it to have surprisingly high efficacy.

Northern + Arctic potential

Very detectable impacts in the Arctic, above the global average; technology ideally/preferably located here

Global potential

High 3

Model studies show OAE could have significant but variant global potential (Taylor et al., 2016; Fakhraee et al., 2022), with Feng et al. (2017) for instance finding that large- scale application could draw down as much as 800Gt CO2 from the atmosphere by 2100. NASEM (2022) estimates the potential global carbon sequestration of OAE to be over 1 Gt CO2/yr. The IPCC AR6 wg3 (2022) report and The State of Carbon Dioxide Removal report (Smith et al, 2023) both provide a very broad carbon capture potential estimate of 1 to 100 GtCO2 per year. However, to all this it has to be added that to make a significant impact, large amounts of material would have to be used (DOSI, 2022).

Global potential

Major impacts detected

Cost - benefit

Medium 2

Costs of OAE would be highly dependent on chosen material, strategies, goals etc,. Köhler et al (2010) for example estimate a cost of €70 to 150 per tonne of captured carbon with olivine. NASEM (2022) roughly estimates up to 150 dollars per tonne of captured CO2. The State of Carbon Dioxide Removal report and the IPCC AR6 wg3 give a figure of 40 to 260 $/tCO2 (Smith et al, 2023).

Cost - benefit

Significant investment costs needed, but still much cheaper than the avoided damage costs (e.g., 30%).

Environmental risks

Medium 2

NASEM’s (2022) attributes a medium level of potential environmental risks to this measure. Ferderer et al (2022) find limited effects of OAE on phytoplankton in comparison to the measure’s CDR potential, but urge more research is needed. They furthermore remark that the benefits and drawbacks of OSE will be complex and plural, and that these will have to be weighed against the detrimental effects of ocean acidification. It is however generally accepted that significantly more research needs to be done to provide more clarity on this matter (GESAMP, 2019). Apart from detrimental environmental effects in the ocean, there could also be significant effects on land as a result of the mining of the materials needed (Smith et al, 2023).

Environmental risks

More widespread and possibly regional impacts that extend beyond the immediate solution deployment location

Community impacts

Unknown 0

Both ocean acidification and OAE will have significant effects on coastal communities (Doney et al., 2020; Foteinis, 2022). Effects of OAE could have side benefits, as Pokharel et al (2023) for example suggests might be the case in relation to toxicity in the port of Rotterdam.

Ease of reversibility

Easy 3

The effect of OAE would overtime naturally subside.

Ease of reversibility

Easily reversible naturally

Risk of termination shock

Medium 2

Gesamp (2019) writes that ‘the duration of deployment of enhanced ocean alkalinity would need to be continuous if sustained carbon dioxide removal and/or ocean acidification mitigation are required.’ Jin and Cao (2023) equally find that a sudden termination of OAE would cause a rapid warming, although this warming would only be up to the expected level had it not been deployed in the first place, and not comparable to the effects of suddenly stopping SAI. They also find that such a termination would have a very substantial effect on ocean acidification, which would very rapidly start to decrease if no new alkalinity were added.

Risk of termination shock

Medium or relatively significant termination shock or damage

Legality/governance

Medium 2

Like ocean fertilization, OAE could be included to fall to a certain extent under the London Protocol, although additions would have to be made for this (DOSI, 2022).

Legality/governance

Fits within existing structures to a certain degree, but some policy changes are needed to deploy at scale

Scientific/media attention

Medium 2

There has been substantial interest in marine and land-based enhanced weathering as a CDR measure (NASEM, 2022). Some research projects and private companies are already exploring OAE, but many issues still remain open and research would have to be expanded significantly (GESAMP, 2019; NASEM, 2022).

Recently, a protest in the UK against Planetary Technologies plan to add magnesium hydroxide to wastewater gained media attention (www.theguardian.com/uk-news/2023/apr/17/protesters-urge-caution-over-st-ives-climate-trial-amid-chemical-plans-for-bay-planetary-technologies).

Scientific/media attention

Some attention within the scientific community, including published research and funding programmes; some media attention; some commercial interest

References

Bach, L. T., Gill, S. J., Rickaby, R. E., Gore, S., & Renforth, P. (2019). CO2 removal with enhanced weathering and ocean alkalinity enhancement: potential risks and co-benefits for marine pelagic ecosystems. Frontiers in Climate, 1, 7. https://doi.org/10.3389/fclim.2019.00007

Burt, D. J., Fröb, F., & Ilyina, T. (2021). The sensitivity of the marine carbonate system to regional ocean alkalinity enhancement. Frontiers in Climate, 3, 624075. https://doi.org/10.3389/fclim.2021.624075

Caserini, S., Pagano, D., Campo, F., Abbà, A., De Marco, S., Righi, D., ... & Grosso, M. (2021). Potential of maritime transport for ocean liming and atmospheric CO2 removal. Frontiers in Climate, 22. https://doi.org/10.3389/fclim.2021.575900

Doney, S. C., Busch, D. S., Cooley, S. R., & Kroeker, K. J. (2020). The impacts of ocean acidification on marine ecosystems and reliant human communities. Annual Review of Environment and Resources, 45, 83-112. https://doi.org/10.1146/annurev-environ-012320-083019

DOSI (2022). “Ocean Alkalinity Enhancement.” Deep Ocean Stewardship Initiative Policy Brief. https://www.dosi-project.org/wpcontent/uploads/Alkalinity-Enhancement-Policy-Brief.pdf

Fakhraee, M., Li, Z., Planavsky, N., & Reinhard, C. (2022). Environmental impacts and carbon capture potential of ocean alkalinity enhancement. https://doi.org/10.21203/rs.3.rs-1475007/v1

Ferderer, A., Chase, Z., Kennedy, F., Schulz, K. G., & Bach, L. T. (2022). Assessing the influence of ocean alkalinity enhancement on a coastal phytoplankton community. Biogeosciences, 19(23), 5375-5399. https://doi.org/10.5194/bg-19-5375-2022

Foteinis, S., Andresen, J., Campo, F., Caserini, S., & Renforth, P. (2022). Life cycle assessment of ocean liming for carbon dioxide removal from the atmosphere. Journal of Cleaner Production, 370, 133309. https://doi.org/10.1016/j.jclepro.2022.133309

Gentile, E., Tarantola, F., Lockley, A., Vivian, C., & Caserini, S. (2022). Use of aircraft in ocean alkalinity enhancement. Science of the Total Environment, 822, 153484. https://doi.org/10.1016/j.scitotenv.2022.153484

Hartmann, J., Suitner, N., Lim, C., Schneider, J., Marín-Samper, L., Arístegui, J., Renforth, P., Taucher, J., and Riebesell, U. (2023) Stability of alkalinity in ocean alkalinity enhancement (OAE) approaches – consequences for durability of CO2 storage, Biogeosciences, 20, 781–802, https://doi.org/10.5194/bg-20-781-2023

Jin, X.Y. & Cao, L. (2023). Comparison of the carbon cycle and climate response to artificial ocean alkalinization and solar radiation modification. Advances in Climate Change Research. https://doi.org/10.1016/j.accre.2023.03.002

Köhler, P., Hartmann, J., & Wolf-Gladrow, D. A. (2010). Geoengineering potential of artificially enhanced silicate weathering of olivine. Proceedings of the National Academy of Sciences, 107(47), 20228-20233. https://doi.org/10.1073/pnas.1000545107

Moras, C. A., Bach, L. T., Cyronak, T., Joannes-Boyau, R., & Schulz, K. G. (2022). Ocean alkalinity enhancement–avoiding runaway CaCO 3 precipitation during quick and hydrated lime dissolution. Biogeosciences, 19(15), 3537-3557. https://doi.org/10.5194/bg-19-3537-2022

National Academies of Sciences, Engineering, and Medicine. 2022. A Research Strategy for Ocean-based Carbon Dioxide Removal and Sequestration. Washington, DC: The National Academies Press. https://doi.org/10.17226/26278.

Pokharel, R., Wu, G., King, H. E., Kraal, P., Reichart, G. J., & Griffioen, J. (2023). Two Birds With One Stone: Artificially Enhanced Olivine Weathering for Sediment Management and CO2 Sequestration in the Port of Rotterdam (No. EGU23-10281). Copernicus Meetings. Available at: https://ui.adsabs.harvard.edu/abs/2023EGUGA..2510281P/abstract

Renforth, P., & Henderson, G. (2017). Assessing ocean alkalinity for carbon sequestration. Reviews of Geophysics, 55(3), 636-674. https://doi.org/10.1002/2016RG000533

Taylor, L. L., Quirk, J., Thorley, R. M., Kharecha, P. A., Hansen, J., Ridgwell, A., ... & Beerling, D. J. (2016). Enhanced weathering strategies for stabilizing climate and averting ocean acidification. Nature Climate Change, 6(4), 402-406. https://doi.org/10.1038/nclimate2882

Wang, H., Pilcher, D. J., Kearney, K. A., Cross, J. N., Shugart, O. M., Eisaman, M. D., & Carter, B. R. (2023). Simulated impact of ocean alkalinity enhancement on atmospheric CO2 removal in the Bering Sea. Earth's Future, 11(1), e2022EF002816. https://doi.org/10.1029/2022EF002816

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