Does ocean alkalinity enhancement actually work? A key physics problem may sink it.
Ocean alkalinity enhancement (OAE) involves spreading crushed minerals like olivine into the ocean to increase seawater's ability to absorb CO₂. The idea is that the particles dissolve in the sunlit surface layer, locking away carbon. But a 2024 modeling study found a critical flaw: in real, dynamic ocean conditions, particles can sink out of the mixed layer up to ten times faster than the old textbook 'Stokes settling' speed predicted [7]. That means the minerals may drop into deep water before they fully dissolve, drastically reducing—or even eliminating—the intended carbon removal. The study showed this was true across a range of particle sizes, so simply grinding the minerals finer may not fix it [7].
This finding overturns a core assumption that has underpinned many OAE proposals. Earlier work assumed particles would linger in the surface layer long enough to react. The new results suggest that ocean turbulence and density layers can create 'fluid instabilities' that flush particles downward much faster [7]. If this holds in field trials, OAE's real-world effectiveness could be far lower than models have projected.
Which blue carbon methods are proven—and which are still just speculation?
The scientific consensus, as of a 2023 review, is clear: coastal wetlands—mangroves, seagrasses, and tidal marshes—are the only ocean-based carbon sinks with solid evidence of climate mitigation benefit [3]. These ecosystems have been studied for decades, with a 2022 bibliometric analysis showing research on their carbon-sink capacity has grown 20% per year since the 1990s [2]. Protecting and restoring them is considered a 'known' pathway: we can measure the carbon they store, and human actions to stop their loss or replant them do increase storage [3].
In contrast, the same 2023 review categorizes macroalgae (seaweed) farming, tidal flats, and marine sediments as 'emerging' pathways—meaning we have insufficient information to guarantee their climate benefit is real and additional [3]. For example, while seaweed grows fast and absorbs CO₂, it's unclear how much of that carbon is permanently sequestered versus quickly released back into the water. The review also labels calcifying organisms (like corals and shellfish) and marine fauna as 'non-actionable'—the science is clear that there is no net mitigation benefit, or the uncertainty is too high to justify action [3].
A 2025 modeling study adds another layer: even for well-known methods like bioenergy with carbon capture and storage (BECCS), land constraints severely limit potential. In land-constrained scenarios, BECCS deployment fell from a median of 1.8 to just 0.3 gigatons of CO₂ per year—a drop of over 80% [1]. This underscores that even proven methods face hard physical limits.
Can we trust the measurements—and who decides what's safe?
A major uncertainty across all ocean carbon removal methods is monitoring, reporting, and verification (MRV). A 2026 review emphasizes that effective implementation of ocean alkalinity enhancement and macroalgae-based strategies 'necessitates rigorous MRV frameworks to ensure their quantifiable efficacy and environmental integrity' [5]. In plain terms: without reliable ways to measure how much carbon is actually stored and for how long, it's impossible to know if a project is working or just creating false credits.
Beyond measurement, there is a governance vacuum. A 2022 article notes that ocean CDR research 'presents the risk of uncertain impacts to human and environmental welfare, yet there are no domestic regulations aimed at ensuring the safety and efficacy of this research' [4]. The authors propose a 15-point code of conduct for responsible research, covering principles like fairness, equity, and transparency [4]. This lack of regulation is especially concerning because the history of ocean carbon sequestration has followed cycles of 'hype, controversy and disappointment,' as a 2024 study found—and the current hype is driven more by new coalitions and narratives than by a reduction in scientific uncertainty [6].
Social and justice issues add another layer of uncertainty. A 2024 structured literature review warns that bringing blue carbon to market 'presents risks to local people and communities with livelihood and other connections to these environments' [8]. The review identifies four themes needing attention: social acceptability, engagement and benefit-sharing, data deficits, and institutional governance reform [8]. In short, even if the science were settled, the social and political dimensions remain deeply uncertain.
About These Sources
This answer is built on 8 peer-reviewed studies — published from 2022 to 2026, 5 from 2024 or later, 7 in Q1 journals, collectively cited 199 times — selected as the most relevant from 9 studies that passed quality screening, drawn from 49 papers retrieved from a database of over 500 million.
Sources used in this answer
Deep uncertainty in carbon dioxide removal portfolios
A 2025 modeling study found deep uncertainty in CDR portfolios: ocean alkalinisation could become dominant in high-removal scenarios, but BECCS deployment fell from 1.8 to 0.3 GtCO₂/yr under land constraints, and DACCS had the widest outcome range (interquartile 4–8.7 GtCO₂/yr).
The Evolution of Blue Carbon Science
A 2022 bibliometric analysis of 1,729 blue carbon papers found research grew 20% per year, with mangroves receiving ~38% of attention, and the term 'blue carbon' became a hot topic between 2017–2020.
Blue carbon pathways for climate mitigation: Known, emerging and unlikely
A 2023 review reaffirms coastal wetlands as proven climate mitigation sinks, categorizes macroalgae and marine sediments as 'emerging' with insufficient evidence for additional benefit, and labels calcifying organisms and marine fauna as 'non-actionable'.
A Code of Conduct Is Imperative for Ocean Carbon Dioxide Removal Research
A 2022 article argues that ocean CDR research lacks domestic regulations to ensure safety and efficacy, proposing a 15-point code of conduct covering responsible research, fairness, and equity.
Ocean Carbon Dioxide Removal and Storage
A 2026 review states the ocean absorbs 2.6–3.0 PgC/yr (~30% of anthropogenic CO₂), and emphasizes that ocean alkalinity enhancement and macroalgae-based strategies require rigorous MRV frameworks to ensure quantifiable efficacy and environmental integrity.
The rise, fall and rebirth of ocean carbon sequestration as a climate 'solution'
A 2024 study using scientometrics and interviews found ocean CDR has followed cycles of hype, controversy, and disappointment; the current hype is driven by new sociotechnical coalitions, not by reduced scientific uncertainty.
Assessing the effective settling of mineral particles in the ocean with application to ocean-based carbon-dioxide removal
A 2024 modeling study found that in dynamic, stratified ocean conditions, mineral particles can settle up to 10× faster than Stokes settling due to fluid instabilities, meaning negligible dissolution occurs before particles leave the mixed layer—regardless of particle size.
Blue carbon as just transition? A structured literature review
A 2024 structured literature review on blue carbon's social dimensions identifies four themes: conceptual issues, governance issues, emergent lessons, and future research needs including social acceptability, justice, data deficits, and institutional reform.