Ocean Alkalinity
Enhancement
TTS v1.0 - Annex K
Ocean Alkalinity Enhancement increases the ocean's natural capacity to absorb atmospheric CO₂ by adding alkaline minerals - lime, crushed olivine - or by electrochemically generating alkalinity directly in seawater. The added alkalinity shifts inorganic carbonate chemistry, drawing down dissolved CO₂ as stable bicarbonate ion, which in turn draws additional CO₂ from the atmosphere into the surface ocean to re-establish equilibrium - leveraging the largest active carbon reservoir on Earth's surface.
Submit OAE Project View TTS v1.0 Annex K →How this pathway works
Seawater carbonate chemistry naturally buffers atmospheric CO₂ concentrations - the ocean already holds roughly fifty times more carbon than the atmosphere, primarily as dissolved bicarbonate ion. Ocean Alkalinity Enhancement (OAE) accelerates this natural buffering by deliberately adding alkalinity to seawater, shifting the carbonate equilibrium so that more atmospheric CO₂ dissolves and converts to stable bicarbonate, effectively increasing the ocean's CO₂ storage capacity without a corresponding increase in seawater acidity (pCO₂).
Under the Teravent Technology-Based Carbon Standard (TTS v1.0) Annex K, OAE projects earn Teravent Technology Credits of the Removal type (TTC-R) for verified net tonnes of atmospheric CO₂ drawn into stable ocean bicarbonate storage, net of full lifecycle project emissions. Because seawater re-equilibration with the atmosphere occurs over months to a few years following alkalinity addition - rather than instantaneously - and because open-ocean monitoring carries inherent measurement challenges relative to enclosed or terrestrial systems, this pathway defaults to Class II durability, with a pathway to Class III for projects that demonstrate exceptionally robust monitoring and modelling confidence.
Three methodology variants are approved under Annex K, spanning mineral alkalinity addition, electrochemical alkalinity generation, and managed coastal weathering. Each carries distinct measurement approaches and ecological safeguard requirements given the marine environment.
TTS v1.0 - Annex K
This pathway is governed exclusively by the Teravent Technology-Based Carbon Standard (TTS v1.0). No external registry, standard, or methodology is referenced or incorporated. All requirements - additionality, quantification, durability, safeguards, and credit issuance - are defined within TTS v1.0 and Annex K specifically.
Three approved methodology variants
TTS v1.0 Annex K approves three discrete methodology types for the Ocean Alkalinity Enhancement pathway, differentiated by alkalinity source and delivery mechanism. All three require ocean carbon uptake modelling validated against a dedicated distributed monitoring, reporting, and verification (dMRV) sensor network.
Quicklime (calcium oxide) or finely crushed olivine is dispersed into seawater, either from dedicated dosing vessels operating along defined transects or from coastal outfall points, where the material dissolves and reacts to raise local seawater alkalinity. Quicklime dissolves rapidly, providing near-immediate alkalinity increase; crushed olivine dissolves more slowly, offering a lower-cost feedstock at the expense of a longer, less certain dissolution timeline requiring more conservative crediting assumptions.
- Alkaline material mass dosed per dispersal event, metered at ±5% accuracy
- dMRV sensor network measuring seawater pH, total alkalinity, and pCO₂ across the plume footprint and reference control sites
- Ocean carbon uptake model validated against dMRV data at each verification, quantifying net atmospheric CO₂ drawdown
- Trace metal impurity assay of the alkaline feedstock (particularly nickel and chromium for olivine sources), verified against DNSH thresholds
- Marine ecosystem monitoring at dispersal sites - phytoplankton community composition, local pH excursion extent
Seawater is electrolysed to split it into an alkaline (hydroxide-rich) stream and an acidic stream. The alkaline stream is returned to the ocean, directly raising local alkalinity without requiring mined mineral feedstock, while the acidic byproduct stream is either neutralised, used industrially, or reacted with silicate minerals to permanently sequester the acid - avoiding simple ocean acidification at the discharge point. This methodology avoids feedstock mining and transport emissions at the cost of higher electricity intensity relative to mineral addition.
- Alkaline stream output flow rate and hydroxide concentration, metered at ±3% accuracy
- Acid byproduct stream fate documented and verified - neutralisation, industrial use, or silicate mineral reaction, never direct ocean discharge
- dMRV sensor network measuring seawater pH, alkalinity, and pCO₂ near the discharge point and reference control sites
- Electrolysis cell energy consumption per tonne alkalinity generated, logged for lifecycle deduction
- Ocean carbon uptake model validated against dMRV data at each verification
Rather than dispersing alkaline material from vessels into open water, this methodology spreads crushed reactive silicate minerals - typically olivine - directly on beaches or shallow coastal zones, where continuous wave action accelerates dissolution and mixing into the surrounding seawater. This approach lowers logistics costs relative to vessel-based dispersal but concentrates dissolution and any associated ecological effects within a defined, more easily monitored coastal footprint.
- Mineral mass applied per coastal site, metered at ±5% accuracy
- Fixed coastal dMRV sensor array measuring pH, alkalinity, and pCO₂, paired with offshore reference sites for comparison
- Coastal sediment and beach ecosystem monitoring for trace metal accumulation and benthic community impacts
- Ocean carbon uptake model validated against dMRV data at each verification, accounting for site-specific wave energy and dissolution kinetics
- Recreational and fisheries use consultation documented for publicly accessible coastal sites
Which emission sources must be counted
TTS v1.0 Module 3 requires a full lifecycle GHG emissions inventory within the project boundary, deducted from the modelled net atmospheric CO₂ uptake to arrive at the Net TTC figure.
Measurement, reporting
& verification
Teravent's Science Advisory Board assesses each pathway against four MRV dimensions. Ocean Alkalinity Enhancement carries the most significant open-ocean measurement challenge of any Teravent pathway, driving comparatively lower permanence and quantification confidence relative to terrestrial or industrial pathways, offset by very high additionality clarity given the pathway's early commercial stage.
Alkaline material dosing is metered at the vessel, outfall, or coastal application site to ±5% accuracy (±3% for electrolysis output). The defining MRV challenge for this pathway is confirming the resulting atmospheric CO₂ uptake, since the ocean's air-sea equilibration process operates over months to years and across a diffuse, moving water mass rather than a fixed containment boundary. Teravent requires a distributed monitoring, reporting, and verification (dMRV) sensor network - moored buoys, autonomous underwater gliders, or satellite-linked sensors - measuring seawater pH, total alkalinity, and pCO₂ across the affected plume and paired reference control sites, feeding a validated ocean carbon uptake model reviewed by an independent oceanographic expert at each verification.
Demonstrating additionality
TTS v1.0 Module 2 requires all projects to pass a three-test additionality framework, with a Technology Readiness Level (TRL) screen applied ahead of the common practice test. Ocean Alkalinity Enhancement remains an early-stage marine CDR approach globally, so virtually all current projects qualify for the streamlined TRL-based screen.
Leakage types & deductions
TTS v1.0 Module 3 defines three leakage types applicable across all engineered pathways. Ocean Alkalinity Enhancement carries distinctive marine leakage considerations related to feedstock sourcing and localised ecosystem effects.
Buffer pool & reversal risk
Once atmospheric CO₂ has re-equilibrated into stable ocean bicarbonate, reversal risk is exceptionally low - bicarbonate ion has a residence time in the ocean of tens of thousands of years. The principal source of uncertainty driving buffer pool rates is measurement confidence in confirming how much atmospheric uptake actually occurred, not durability of the storage mechanism itself once confirmed.
| Methodology | Durability Class | Buffer Pool Rate | Primary Uncertainty Drivers |
|---|---|---|---|
| OAE-M01 Mineral Addition | Class II (default) | 10–25% | Dissolution timeline uncertainty (olivine); dMRV plume tracking accuracy |
| OAE-M02 Electrochemical | Class II (default) | 10–20% | Early-stage technology; acid stream fate verification |
| OAE-M03 Coastal Weathering | Class II (default) | 10–22% | Wave-energy-dependent dissolution rate variability |
Key registration criteria
Projects must meet all of the following minimum requirements to qualify for registration under TTS Annex K. Additional methodology-specific requirements are detailed in the Annex K methodology tables for each OAE-M code.
Sustainable Development
Goal alignment
All Teravent registered Ocean Alkalinity Enhancement projects must complete an SDG impact assessment at registration and at each verification period. Three SDGs are systematically tracked for this pathway, reflecting its dual climate and marine ecosystem dimensions. Projects may apply for co-benefit quality labels where independently verified indicators are met.
Deployment scope: Coastal regions with access to shipping infrastructure, mineral feedstock sourcing, or suitable coastal application sites - currently most active in the North Atlantic, Northern Europe, and select Pacific coastal regions with established marine research infrastructure.
Ready to register your
OAE project?
Submit a Project Concept Note under TTS v1.0 Annex K to begin your registration. Select the OAE-M code matching your alkalinity source, deploy a dMRV sensor network, validate your ocean carbon uptake model, and appoint an accredited VVB to review your PDD and marine environmental impact assessment.