The First OAE Credits: An Independent MRV Review

Carbon to Sea’s MRV Blog Series: This is the second installment in Carbon to Sea’s monitoring, reporting, and verification (MRV) blog series. I’m Anna Madlener, Senior Manager for MRV at Carbon to Sea. In our first post, we introduced the distinction between closed- and open-system carbon dioxide removal (CDR) and what that means for MRV of ocean alkalinity enhancement (OAE).

In this post, we analyze the first OAE credits, provide recommendations for continuously improving the MRV process, and identify key scientific opportunities for the OAE research community. Our analysis is followed by a detailed Q&A, which we synthesized based on independently collected questions.

Table of Contents

Overview

In Halifax, Canada, the ocean alkalinity enhancement (OAE) startup Planetary is partnering with researchers at Dalhousie University to test OAE from coastal outfalls, with the aim of demonstrating its efficacy and safety as a carbon dioxide removal (CDR) solution. On June 16, 2025, Planetary received the first OAE carbon credits, issued by the registry Isometric. Shortly after, the buyer coalition Frontier announced a $31M offtake agreement with Planetary, a five-year contract to purchase additional credits subject to ongoing government permitting and continuous demonstration of carbon removal. These developments illustrate growing private sector interest in OAE while underscoring the need for transparency and independent evaluation of OAE crediting.

To increase public understanding and provide independent evaluation of this first credit issuance, Carbon to Sea sought questions from the OAE community in early July 2025 and invited input from the crediting parties (see Methodology). This document presents relevant findings and points to opportunities for collective improvement for monitoring, reporting, and verification (MRV), followed by a detailed account of synthesized questions and answers.

Carbon to Sea is a non-profit climate science funder and does not participate in crediting, verification, or endorsement of carbon credits. Instead, we aim to ensure OAE develops transparently and responsibly while enabling ongoing evaluation of its efficacy and environmental safety. We do this by asking critical questions, aligning science, policy, and practice, while directing resources toward unresolved uncertainties. This can include supporting private sector engagement, particularly where they create unique opportunities for scientific learning and evaluation. For example, Carbon to Sea supported research at Planetary’s Halifax site through scientific and technical grants in 2023, as well as through a Joint Learning Opportunity in 2024, and is currently accepting applications for a Joint Learning Opportunity in 2026.

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Initial Findings and Recommendations for Improvement

The first operational MRV prototype for mineral OAE from a coastal outfall marks an important step forward, only possible through early projects and significant scientific research advancements. Isometric’s registry protocol was followed and the verification process was completed as intended. As such, the outcome represents meaningful progress toward rigorous, transparent, and responsible carbon accounting that protects the environment and builds public trust.

Nonetheless, open questions for the private sector, scientific research, and the field at large remain. While this significant milestone demonstrates how OAE quantification from coastal outfalls can function in practice, it also enables insights into areas for MRV improvement. Carbon to Sea, building on input from an open consultation period, has identified several actionable recommendations for suppliers, registries, and the scientific community  to reduce uncertainties, close knowledge gaps, and improve data accessibility:

1. Develop methods for robust operational in-water evidence of feedstock dissolution
2. Clarify model validation methods and progress
3. Ensure consistent and transparent reporting of uncertainty
4. Update requirements for environmental monitoring at increasing scale  
5. Improve data accessibility and sharing practices

Carbon to Sea remains committed to supporting scientific research that advances understanding of OAE efficacy and environmental safety. We believe that continued evolution in these areas will strengthen transparency, scientific rigor, and comparability across the field.

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Develop methods for robust operational in-water evidence of feedstock dissolution

Why this matters for MRV: Mineral OAE projects raise ocean surface alkalinity through the application of alkaline materials, or “feedstock.” The feedstock dissolves in seawater where it has a theoretical potential to raise alkalinity by an amount that is dependent on the feedstock’s chemical composition as well as the chemistry of the seawater to which it is added, furthermore referred to as its alkalinity enhancement potential. The rate and completeness of this dissolution and its alkalinity enhancement potential have an impact on CDR efficacy, and therefore suppliers need to provide operational evidence of this step. 

What was done so far: For Planetary’s credits, dissolution rates and alkalinity enhancement potentials in Halifax Harbor were derived from laboratory tests, supplemented by in-situ alkalinity and other proxy measurements (e.g., partial pressure of CO₂ (pCO₂), total suspended solids (TSS)). These measurements showed measurable alkalinity and TSS signals in line with expected dissolution rates. Following this early feedback, a new section highlighting qualitative insights in this regard has been included in a new report of Planetary’s October credit issuance (p.21). Additional results from academic measurements across the harbor have been presented in a variety of fora and showed evident alkalinity increases as a result of addition, but are not required and reported as part of the credit verification.  

What can be done in the future: Across the field, advancing scalable measurement approaches will be key to demonstrating in-situ alkalinity increases, alongside standardizing how feedstock kinetics are characterized and reported. These developments will help ensure that laboratory and field data can be more reliably compared and integrated into models.

Isometric’s OAE protocol would benefit from a clearer explanation of the role of required measurements, distinguishing between providing operational evidence of alkalinity increases versus model validation, as this could then also be directly integrated into reporting guidelines for these measurements. Additionally, the protocol could begin to specify a minimum temporal and spatial coverage of measurements required to capture signals of an alkalinity increase, with careful thought of when and where such signals are likely to be visible.

For project suppliers such as Planetary, future quantification reports could include a concise summary that clearly links lab-based feedstock characterization, field evidence of alkalinity change, and the assumptions embedded in the dissolution model used for crediting. Presenting these connections up front would strengthen understanding in how modeled and measured data together support quantifying removals.

See questions 5, 6, and 7 for more background on how we arrived at this recommendation.

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Clarify model validation methods and progress

Why this matters for MRV: Modeling is an important step in quantification, encompassing all measurements and inputs into a holistic estimate of carbon removal. Model validation is required to demonstrate how well all models represent the real world and changes resulting from OAE. Tracer studies and model–observation comparisons are currently the most straightforward approaches to achieve this. Importantly, model validation occurs in stages and is often separated into physical, biogeochemical, and intervention validation. Not all aspects of all models can be validated before an OAE addition and rather must build on results from early projects.

What was done so far: Planetary’s quantification relies on four models: a simplified dissolution model, a regional ocean model, a global ocean model, and a simplified diffusivity model (see question 8). Each model underwent validation consistent with Isometric’s requirements. The regional model was developed and validated by Dalhousie University through tracer studies and comparison against long-term physical and biogeochemical datasets, with results and code shared with verifiers before crediting and now published. The global model used a pre-validated academic framework and was additionally checked to confirm that its biogeochemistry matched observed data in the project region. The dissolution and diffusivity models were validated analytically against outputs from the regional and global  models.

What can be done in the future: Developing shared standards for model validation would help clarify what constitutes sufficient validation, how it should be demonstrated, and increase general understanding of how well models capture OAE dynamics under real-world conditions. In the interim, validation documents should be easier to locate and interpret, helping non-academic readers identify where models stand and how they are used in quantification. Expanding such sharing and clarifying expectations for documenting and publishing validation across all model assets would improve transparency. 

Following validation against baseline data, additional model–observation comparisons using in-trial results will show how well models represent key features of OAE additions, such as feedstock dispersion and alkalinity production. While time-intensive, this work will strengthen confidence in model performance and should be gradually incorporated into future crediting rounds when detectable signals match spatial scales of the models. Planetary has already indicated they are working on such comparisons together with Dalhousie University, and Isometric outlines recommendations with respect to this iterative process in their protocol.

See question 8 for more background on how we arrived at this recommendation.

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Ensure consistent and transparent reporting of uncertainty 

Why this matters for MRV: Because OAE occurs over time and space in the ocean, quantifying its impact requires both measurements and models. Inherently, both approaches carry uncertainty as they aim to represent the real world in a simplified way. As such, delivery of OAE credits is always associated with uncertainties that must be quantified and transparently accounted for. 

What was done so far: In its first crediting round in June, Planetary’s reported uncertainty comprised a set of feedstock, model, and emissions uncertainties, amounting to a discount of 14.35%, which was deducted from the net CDR estimate. Model uncertainty was represented by assessing interannual variability and selected parametric effects, in line with Isometric’s guidance to focus on the largest expected uncertainty source.

In the October round, interannual variability in the regional model was removed because the model could now incorporate observed atmospheric boundary and input conditions for the crediting period. In addition to the other remaining uncertainty sources, Planetary applied a 5% deduction to reflect unquantified systemic uncertainties in the regional model, such as resolution limits and sediment interactions, that were identified in the published validation paper. This 5% is a precautionary discount rather than a statistically-derived quantification. 

What can be done in the future: For research and the private sector, developing a shared framework for uncertainty reporting would help ensure consistent, comparable, and transparent quantification across projects. Such a framework should clarify which uncertainties are reported, which remain unquantified, and how confidence levels are expressed.  

To support this, a staged approach could balance scientific rigor and practicality: smaller pilots could apply general, conservative approaches to unquantified uncertainties, while larger projects progressively include fuller analyses. Interim measures such as buffer pools could help manage unquantified uncertainties, allowing retrieval as new in-trial data or research becomes available.

Planetary and Isometric can strengthen trust and transparency by harmonizing how uncertainties are structured, disclosing which ones remain unquantified, and adding statistical confidence bounds of the reported uncertainty values. Clearer documentation and guidance from Isometric on expectations to integrate systemic uncertainty assumptions in future crediting rounds would improve consistency.

See question 9 for more background on how we arrived at this recommendation.

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Update requirements for environmental monitoring at increasing scales

Why this matters for MRV: Environmental monitoring plans are designed to capture effects on marine life as a result of an OAE activity and must reflect the unique characteristics of a site, including the material selected and the dosing mechanism used. Consequently, it is important that monitoring needs are site- and case-specific—in particular with respect to feedstock and dissolution rates—and continuously updated to reflect new scientific evidence.

What was done so far: In the Isometric protocol, environmental safety requirements include feedstock characterization prior to discharge, monitoring water quality parameters, such as pH, total suspended solids (TSS), turbidity, and dissolved oxygen, and establishing thresholds that would necessitate adaptive management. To this end, Planetary developed a first-of-its-kind stop trigger framework that reflects local regulation and background conditions. Projects using a mineral feedstock must also monitor the seafloor for undissolved feedstock. Planetary currently samples for total metals on a monthly basis, and cooperates with researchers at Dalhousie University studying benthic community changes and environmental DNA. In addition to these requirements, Planetary voluntarily monitors chlorophyll-a, a proxy for phytoplankton biomass, near the outfall.

What can be done in the future: For the research community, an important next step is to develop environmental monitoring that is relevant and yields results fast enough for decision-making in the field. This includes exploring which ecological baselines (e.g., chlorophyll-a) can inform adaptive management and feedback loops. Carbon to Sea recommends reviewing and adopting the Environmental Impact Monitoring Framework, recently published for public comment, which can serve as guidelines for projects, registries, and others alike and allows distinction between different project stages.

For future protocol revisions, Isometric could consider adding the monitoring of plankton indicators as requirements, while carefully defining when and how such requirements are applied. This will become increasingly relevant as projects move toward continuous or higher-frequency dosing, where potential cumulative or delayed changes may need to be assessed.

Planetary could provide increased insights into how academic environmental monitoring efforts, such as those by Dalhousie University, inform its experimental design and stop trigger framework.

Additional environmental safety tools are currently under development via Hourglass Climate’s Framework for Ecotoxicological Modeling of mCDR and Ocean Visions’ marine CDR Environmental Impact Assessment Framework.

See questions 11, 12, and 13 for more background on how we arrived at this recommendation.

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Improve data accessibility and sharing practices

Why this matters for MRV: To close knowledge gaps of OAE’s efficacy and safety, it is imperative that relevant data from private sector learning opportunities becomes accessible. Researchers, policymakers, and the public need to understand not only the crediting outcomes but also the assumptions, measurements, and models that underpin them. This allows independent validation of claims, accelerates learning, and helps align the private sector and scientific community around shared evidence.

What was done so far: The Isometric protocol defines three data categories: crediting, ecological, and “scientifically relevant” data. Most crediting data are included in project reports that Isometric links to on their registry page as data sources for removal calculations. However, the current PDF format makes it difficult to navigate to specific numbers, key figures, or time series. Planetary also shares select “scientifically relevant” information, such as imagery or time series from sensor data, and provides underlying datasets upon request. In addition, Planetary collaborates with Dalhousie University, whose long-term monitoring and academic publications provide independent insights, though these are reported separately from verification timelines. Together, these efforts signal progress but also reveal the need for more structured, accessible, and verifiable data-sharing practices.

What can be done in the future: Shared definitions of “scientifically relevant” data, such as voluntarily collected measurements or additional model outputs, would improve consistency and comparability across OAE projects. Establishing when and how such data are shared will be key as crediting expands. Strengthening data infrastructure for independent access would also build transparency and trust. Carbon to Sea is currently exploring how to support timely and interoperable data sharing across the OAE community, building on our OAE Field Data Protocol. 

Isometric could improve accessibility of reported data sources by providing direct access, or explicit reference, to specific report sections containing key figures and sensor data time series on a supplier’s registry page. This would facilitate broader understanding of origins of key data points.

Guidance on which data must be shared only with registries and verifiers versus those accessible to researchers and the public would enhance traceability and scientific value.

For project suppliers such as Planetary, clarifying expected contributions from academic partnerships, who generate valuable insights but often have differing data sharing timelines considering peer-review needs, would strengthen transparency and demonstrate how external science contributes to protocol compliance and field-wide learning.

See questions 7, 8, and 10 for more background on how we arrived at this recommendation.

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Closing Remarks

The question solicitation process and resulting Q&A, shared below, was designed to surface questions early during private-sector engagement, at a stage where projects are balancing technology demonstration and limited resources with ongoing scientific research. Many, but not all, of the areas for consideration identified above are difficult to resolve in small-scale pilots and reflect broader scientific challenges of monitoring and verifying OAE processes at low dosing levels. It is important that rigor increases as projects continue to evolve and progress, with more specific monitoring requirements, better-documented uncertainty deductions and model validation, and more comprehensive environmental safety assessments as the science evolves alongside projects.

The Carbon to Sea Initiative will continue to support research that actively enhances our understanding of OAE efficacy and safety. We will explore specific opportunities emerging from this Q&A process in the coming months and look forward to analyzing future credits as new evidence and reports emerge.

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Acknowledgements

We would like to thank all those who submitted questions or shared feedback with Carbon to Sea. Furthermore, we appreciate the honest, timely, and generous answers from employees at Planetary, Isometric, Submarine Scientific, and 350Solutions as we conducted this independent review of the first OAE credits. 

Special thanks to:

• Max Holloway, Will Burt, Robert Izett, and Steve Rackley from Planetary
• Jing He and Sophie Gill from Isometric
• Veronica Tamsitt from Submarine Scientific
• Lily Schacht and Tim Hansen from 350 Solutions

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Summary of Resources 

Isometric Protocol and Explainers: Isometric OAE protocol; Air-Sea CO₂ Uptake Module v1.0 (used for the first credit issuance); Rock and Mineral Feedstock Characterization Module; Isometric OAE credits explainer; Protocol Public Consultation Feedback; Isometric’s VVB Policy; Isometric Explainer Webinar

June 2025 Crediting Data and Reports: Planetary Nova Scotia Mineral OAE Project registry page; Registry credits page; Project Design Document; Quantification Report; Operations & Monitoring Report; Crediting Datapoints; Planetary Emissions Statement; Validation report; Verification report

October 2025 Crediting Data and Reports: Registry credits page; Project Design Document (Sep 2025 update); Quantification Report; Operations & Monitoring Report; Global Model Validation Report; Crediting Datapoints; Verification Report

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Methodology

Through a public feedback form, Carbon to Sea received written submissions between June 28 and July 10, 2025, and held several conversations with academic experts from the OAE community. Together with background questions from Carbon to Sea, a set of questions was shared with the four crediting parties—Planetary (project developer), Isometric (credit registry and issuer), 350Solutions (verifier), and Submarine (model subject matter expert verifier)—for input. This input, along with all publicly available information on the registry page, was synthesized into cohesive questions and answers and edited for clarity in the section below.

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Questions & Answers

Crediting Process

1. How was the OAE protocol developed?

The Isometric Ocean Alkalinity Enhancement from Coastal Outfalls Protocol was developed in accordance with the Isometric Standard, which outlines accounting and governance rules for all carbon removal pathways credited by Isometric. To date, Isometric has published 14 protocols across six carbon removal areas (e.g., marine, biosphere, Direct Air Capture, and others). All standards, protocols, and modules used across protocols undergo a public consultation process. Isometric’s crediting approach has been approved by the Integrity Council for the Voluntary Carbon Market (ICVCM) and the International Carbon Reduction and Offset Alliance (ICROA). 

The OAE protocol was developed by Isometric’s in-house Science Team through collaboration with ocean scientists from their Science Network. Quantification methods in the protocol were also informed by Isometric’s research partnership with [C]Worthy, a non-profit organization focused on building modeling tools for ocean-based carbon dioxide removal (oCDR). 

Before publication, the OAE protocol was shared for feedback with external participants through a workshop at the 2024 AGU Ocean Sciences Meeting (with over 50 attendees across academia, NGOs, government, and the private sector) and a public consultation period in spring 2024. The current protocol was published on May 31, 2024, and is planned to be reviewed and updated through Isometric’s biannual public consultation process in 2026.

To date, Isometric is the only registry crediting OAE products in the voluntary carbon market via this protocol. They also developed four other protocols for marine and riverine carbon removal pathways. 

Further information on this question can be found in: OAE protocol | Public Consultation Feedback

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2. How does the crediting process work?

Broadly, credits are certified and issued in three steps. 

1. Project Design Document: First the project developer creates a Project Design Document (PDD) that lays out their plans to implement the protocol. 
2. Validation: An independent validation and verification body (VVB) reviews the PDD and supporting documentation to confirm that it is inclusive of all requirements laid out in the protocol. Validation can occur before activities start, or while they are already ongoing. As long as no operational and scientific changes are made at a project site, it is validated for five years once this step is completed.
3. Verification: At self-determined time intervals, the project developer submits a greenhouse gas statement with supporting documentation to the registry and the VVB for verification of claimed carbon removals. In this step, operations, monitoring, and quantification reports are verified via data review, cross-checks and site visits, ensuring that actual project activities are in line with the validated PDD (see question 3). If deemed sufficient, the claimed removal is issued as credits on the registry.  

Planetary submitted a Project Design Document (PDD) describing how it would follow the requirements of the protocol that was published on March 25, 2025. Validation was conducted by 350Solutions, an accredited VVB, with additional review by a subcontracted scientist, and included a site visit on September 23, 2024. A validation report was also published on March 25, 2025. 

In April 2025, Planetary submitted documentation for the reporting period February 2024 – March 2025, accounting for any modeled CO₂ uptake during this period. Verification by 350Solutions and credit issuance by Isometric was concluded in June 2025. 

Further information on this question can be found in: Isometric’s VVB Policy | Validation report | Verification report | Project PDD | Planetary registry page

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3. How does validation and verification work?

In Isometric’s case, the Validation and Verification Body (VVB) is selected by the registry, not the project developer. In this case, 350Solutions served as VVB. Potential VVBs complete conflict-of-interest checks and must regularly demonstrate valid accreditation, such as via ISO standards or regulation (see “Accreditation” in Isometric’s VVB Policy). They are paid a flat fee by Isometric, tied to a buyer’s order rather than the final verified credits, designed to avoid an incentive to over-credit project activities. 

The CDR supplier (Planetary) submitted documentation outlining net removals and supporting evidence, including dosing records, lab results, monitoring data, model inputs and outputs, and a life cycle analysis. The VVB reviewed this documentation to check whether requirements of the protocol were met and whether calculations based on the data produced the claimed removals.

According to the VVB, verification included:

• Cross-checking raw data such as lab results, dosing records, monitoring measurements, and Life Cycle Assessment (LCA) data.
• Reviewing and re-performing calculations.
• Assessing monitoring measurements and model inputs/outputs, with a modeling scientist subcontracted to provide subject matter expertise. Importantly, “verified” in this context does not mean direct observation of CO₂ removal. It refers to model-based quantification and supporting evidence being reviewed and deemed in line with the protocol, as outlined further in the Quantification section below. 
• A site visit to observe alkalinity dosing at the outfall and data collection practices. On-land measurements (weights of feedstock, dosing rates, water composition before/after dosing, energy and fuel use) and in-water measurements (monitoring moorings) were inspected where practical, though among hundreds of samples, not every sampling activity could be observed directly.
• Reviewing a risk assessment of potential reversals, with a 2%-buffer pool deducted according to the Isometric Standard’s buffer categorization for “low-risk reversal” pathways such as OAE. Carbon to Sea notes that this buffer pool refers to storage uncertainties, not to uncertainties of removal. Because it is difficult to prove reversal does not occur, recovering this buffer pool is unlikely.

The VVB provides a findings list covering clarifications, evidence requests, or non-compliance instances if they occurred. These must be addressed before crediting. The Verification Report summarizes the process, compliance status, and the final credited removals. Reports are published on the registry.

Further information on this question can be found in: Verification report

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Quantification

4. How was CO₂ removal quantified?

Quantifying CDR requires comparing the effect of an intervention against its counterfactual scenario. Because OAE takes place across a range of space- and time-scales, best practice guidance for quantifying the resulting CDR includes a combined reliance on in-water measurements and modeling to estimate CDR efficiency over time. Theoretically, one mole of added alkalinity can remove approximately 0.8 moles of CO₂. This assumes full feedstock dissolution and an alkalinity increase, no secondary effects like CaCO₃ precipitation (Moras et al, 2024 and Cambpell et al, 2022), and full equilibration of the alkalized water with the atmosphere (He and Tyka, 2023). These factors are known as efficiency drivers. Uncertainties are associated with the underlying efficiency as well as with the methods chosen to quantify net removal.

To quantify the total net impact of the project, Planetary calculated the total estimated gross removals over a period of time based on exact feedstock added. To do this, they derived a carbon removal potential of their feedstock, based on its expected dissolution and ability to enhance alkalinity (see question 5), and simulated this addition in a combination of models that are validated against baseline measurements. They then subtracted the CO₂ emitted as a result of project activities as well as an uncertainty estimate from the gross CDR modeled to have occurred during the chosen reporting period. This was compared to a counterfactual modeled scenario without an OAE addition.

The table below summarizes the type of CDR, numbers, and methods that Planetary reported for their first crediting instance. Key underlying approaches are further discussed in the subsequent questions. 

Type of CDR	Description	Resulting modeled CDR	Method of Quantification	Further Q&A Discussion	Documentation
Full theoretical CDR potential	Theoretical gross CDR based on carbon removal potential of 1103.2 tonnes of added alkaline feedstock (mix of MgO and MgCO3) assuming full equilibration	1300 t	Mean CDR potential using ocean properties from a 6-month regional model simulation, and accounting for the mass of added feedstock; feedstock characterization via laboratory studies to derive CDR potential, sampling at the dosing location, and some proxy measurements in the water to confirm expected conditions.	Question 5	Quantification Report, p. 5, additional  conversation with Planetary
Gross reported CDR	CDR modeled to have occurred during reporting period (i.e., crediting occurs “ex-post”)	881.8 t	Combination of three different models, each validated statistically and/or against subsets of measurements, to simulate feedstock dissolution, alkalinity addition based on dosing timeseries, and upscaling into global uptake.	Question 7	Quantification Report, p. 6
Net CDR	CDR remaining after project emissions are subtracted	730.4 t	Cradle-to-grave life cycle analysis (LCA) modeling of sourcing, transport, operations, and end-of-life (151.3 tCO2 for full amount of feedstock dosed). Data were collected from suppliers, freight and warehousing records, expense reports, and on-site metering.		Quantification Report, p. 10, Emissions Statement
Creditable CDR	CDR remaining after joint uncertainties of modeled CDR, feedstock dosed, its alkalinity potential, and emissions calculations are deducted	625.6 t	Ensemble runs and sensitivity analyses of a simplified model to derive general model uncertainties. Monte Carlo simulations of the emissions inventory to estimate uncertainties in LCA discount. Together, model and emission uncertainties resulted in a 14.35% discount.	Question 8	Quantification Report, p. 8-10
Credited CDR	Isometric issued 625.6 tonnes as credits, of which 12.513 tonnes are allocated to a buffer pool	625.6 t	The buffer pool represents 2% of the total credit amount, based on Isometric’s rules for low-risk reversal pathways.		Isometric OAE credits explainer Isometric Credit Page

Additional data on the above is reported in the document entitled “TC24 Impact, Uncertainty, and Emissions Factors.xlsx” and shown on the registry page, but this document is not available to the public and was not reviewed for this assessment.

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5. How is the mineral feedstock assessed?

Background

Mineral OAE projects raise ocean surface alkalinity through the application of alkaline “feedstock.” Characterizing the feedstock encompasses three key aspects:

1. Expected CDR potential (resulting from a feedstock’s ability to increase alkalinity in water, also referred to as equivalent hydroxide or EQOH)
2. Dissolution kinetics (how fast and under which conditions a feedstock dissolves in the water)
3. Environmental safety (such as via ecotoxicity tests and screening for impurities such as trace metals; see question 12 for further information)

Generally, laboratory analyses can characterize EQOH content and how fast feedstocks dissolve in laboratory environments, while models can further simulate dissolution and mixing with the receiving waters. Feedstock dissolution kinetics refers to the physics of minerals dissolving in the water, and is an active area of research within OAE. These kinetics are unique to each site and project, and are sensitive to conditions such as water temperature, salinity, currents, and mixing as well as feedstock composition. The dissolution kinetics, along with in-water mixing and transport, influence if and how long heightened alkalinity can be detected in the water, whether particles accumulate on the seafloor, and how quickly the alkalized water equilibrates with the atmosphere to remove CO₂ (Schulz et al, 2023). Feedstock that remains in mineral form cannot release its alkalinity for neutralizing acid in the water and therefore enable CO₂ drawdown. 

While dissolution on short timescales can vary, scientific understanding is that eventually the feedstock will dissolve (Moras et al, 2024 and Cambpell et al, 2022), unless buried in the seafloor, and can lead to atmospheric CO₂ drawdown as long as the resulting decarbonized water comes in contact with the atmosphere (He and Tyka, 2023 and Zhou and Tyka et al., 2025). Generally, OAE efficiency modeling suggests that in most places around the world, the full CDR potential is reached within 10-15 years, taking into account varying dissolution, subduction and air-sea equilibration rates (Zhou and Tyka et al., 2025). 

For crediting with Isometric, each project must submit a feedstock characterization assessment according to the Rock and Mineral Feedstock Characterization Module.

Expected CDR potential

To understand the expected CDR potential through the increase of alkalinity after feedstock addition, Planetary followed the protocol to calculate the EQOH content (PDD, p. 85-88). This analysis yielded that, on average, 1 tonne of feedstock results in 494.36 kgOH (kg of hydroxide), with a 4.33% uncertainty associated with it (Quantification Report, p. 6). This value represents the feedstock’s CDR potential, and is prescribed to the model as a fixed term to quantify CDR based on total feedstock added (Quantification Report, p. 9). In-situ EQOH measurements—still an active research area—could eventually serve as a key operational check of a feedstock’s realized CDR potential, and providing direct or proxy measurements to do so is currently not a specific requirement by the protocol.

Feedstock dissolution

Planetary’s reporting and monitoring requirements are based on the use of a fast-dissolving feedstock (full dissolution within 1 day) based on laboratory tests (PDD, p. 91). Differences in lab dissolution rate measurements, for example between Planetary’s in-house measurements and those conducted elsewhere, are explained as being due to different experimental methods and conditions (solution pH, temperature, etc.; PDD, p. 91). Using these analyses, they have developed a one-dimensional (1-D) dissolution model that provides necessary inputs regarding particle size and alkalinity addition to the regional model (see question 8).

To test whether delays in feedstock dissolution would affect the total cumulative potential CO₂ uptake after 10 years, Planetary reported running a sensitivity analysis via the 1-D dissolution model using a slower dissolving brucite feedstock. Because outcomes were reportedly negligible, no further uncertainty discount was taken for delayed feedstock dissolution as this would not affect the overall creditable tons after 10 years based on the CDR potential of the total dosed, faster dissolving feedstock (Quantification Report, p. 8). Importantly, undissolved feedstock that accumulates on the seafloor and is buried permanently cannot contribute to CDR in the future (for more information, see question 13).

Future considerations

It is an active area of scientific research to further understand feedstock dissolution kinetics, to improve model capability, and to develop adequate monitoring standards subsequently, such that they can be referenced and relied upon by private sector groups like Planetary.

Results from feedstock characterization using Isometric’s module must be made available for verification. Isometric further notes that sharing characterization insights will be vital in improving model-based capabilities to assess dissolution. Some feedstock characterization data is not available publicly, such as detailed account of feedstock origin (Planetary notes it can be shared upon request, PDD, p. 74-76) or EQOH data (results shared in reports, and underlying data points visible, yet not accessible on the registry page). 

Further information on this question can be found in: Feedstock Characterization Module | Crediting Data | PDD | Quantification Report

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6. How was the measurement plan developed?

Background

Generally, measurement plans for OAE projects are developed to address two main goals: to monitor environmental safety of the receiving waters (see question 11 for more detail) and to support the quantification of CDR. Via the protocol, Isometric requires a number of parameters to be observed across the outfall, “mixing zone,” and larger open areas.

Importantly, the protocol does not prescribe exact sampling methods, frequencies, or locations as these will vary depending on the project and site. Projects are required to describe and justify a tailored monitoring plan that also includes relevant monitoring for environmental risks for their specific project and location. It is the VVB’s responsibility to determine whether the proposed plan can fulfill scientific requirements.

Baseline data

Before any CDR activity begins, it is vital to establish baselines of the background physical and carbonate state of a site. This is both important for model validation and to distinguish any measurement signals of a CDR activity from a site’s regular variability. A variety of baseline data were available for Planetary’s site in Halifax Harbour through decades-long water quality monitoring programmes from as early as the 1980s as well as through weekly boat surveys of central Bedford Basin by the Department of Fisheries and Oceans Canada (1992-present) and Dalhousie University (2008-present).

In addition, Dalhousie University initiated OAE-specific monthly baseline surveys of the harbor and wider basin in the spring of 2022, prior to Planetary’s alkalinity additions (full list of parameters in PDD pp. 54-55).

Measurement activities

In Planetary’s case, two rhodamine dye tracer experiments led by Dalhousie University were used to estimate dilution and dispersion of material from the outfall. Planetary notes they did not apply the traditional regulatory concept of “mixing zone” as no regulatory mixing zone has been previously established at this site. Furthermore, the site has a unique waterfall-style outfall that creates a complex plume, which is not well represented by standard plume modeling software. Thus, the dye tracer experiments provide a more accurate conceptual model of the plume mixing to define “in-plume” and “out-of-plume” categories to comply with required monitoring locations (PDD, p. 51). Based on ongoing analysis at Dalhousie University, the plume is estimated to extend 50-100 m away from the outfall (Operations & Monitoring Report, p. 17). All required measurements were taken in the  cooling water outfall pipe up- and downstream of alkalinity addition (PDD, p. 51, see figure below). Boat-based sampling was conducted for all required and other voluntary parameters in and out of the plume, which was considered satisfactory to the requirement in the protocol to monitor “at the edge of the mixing zone” (PDD, p. 51, see figure below). Additional voluntary measurements were taken on a mooring approximately 5 m from the outfall. Carbon to Sea’s understanding is that the spatial extent of the plume and the resulting monitoring plan may be adapted as the research analysis further refines plume behavior. 

Notably, other independent research activities by Dalhousie University collected data that is not required by Isometric and was therefore not reported as part of this verification process. However, it is relevant to state that to the best of Carbon to Sea’s knowledge, this data is used to continuously learn about Planetary’s process and OAE in general, and to continuously refine Dalhousie’s ROMS model.

Questions below further discuss various ways in which such measurements were used in Planetary’s operations. 

Further information on this question can be found in: OAE Protocol Monitoring Requirements | PDD | Operations & Monitoring Report

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7. Are measurements used to demonstrate alkalinity enhancement?

Background

Measurements taken directly in the water are an essential part of each project, providing insight into water conditions that are indicative of efficiency drivers and environmental safety. Measurements are also used to confirm that computational models adequately represent real-world processes (see question 8). A critical question that came up during this feedback solicitation process was how measurements were used for quantification. Commonly misconceived, the list of measurements required under the protocol are not used to directly quantify CO₂ removal and do not serve as requirements for model validation. Instead, in-pipe measurements quantify alkalinity dosing rates that are used as input to the models. In-water measurements provide information to show that water quality thresholds are respected (see question 11) and that alkalinity was added—supporting evidence of feedstock dissolution before model-based quantification. Lastly, while the list of required measurements from Isometric may eventually be used for validating a model’s representation of OAE additions, they are not the same measurements required to validate the baseline physical and biogeochemical skills of models.

Direct and indirect evidence of dissolution

Planetary acknowledged that this distinction was not always explicit in documentation. They did in some instances use total alkalinity (TA), total suspended solids (TSS), and pCO₂ data to qualitatively demonstrate successful alkalinity addition, feedstock dissolution, and OAE-induced pCO₂ reduction in the immediate vicinity of the project (Operations & Monitoring Report, p. 7 and pp. 12-17). Furthermore, Planetary monitored the seafloor for undissolved feedstock accumulation, which would indicate an efficiency loss if buried permanently (see also question 13 for further context). Indirectly, all these measurements serve quantification via operational evidence of feedstock addition and dissolution. Going forward, in-trial measurements will be used for further model validation, but these comparisons were not yet concluded at the time of this crediting round (see also question 8).

Secondary precipitation

Once alkalinity increase occurs, it is important to confirm that this increase can be maintained. Systematic lab and mesocosm studies show that stable minerals in the water can fall out of solution—thereby reducing seawater alkalinity—when strong and prolonged pH spikes are induced. To manage the risk of secondary precipitation, Planetary used pH measurements at the end of the outfall pipe ensuring levels below a pH < 9 threshold (PDD, p. 48), consistent with protocol requirements. Current research suggests that parameters such as pH and aragonite saturation provide reasonable indicators for precipitation risk (Suitner et al, 2024). However, broader studies are needed to test the reliability of these thresholds and operationally confirm the absence of secondary precipitation through regular in-situ monitoring, for example using optical sensors. This would validate the general application of these thresholds going forward.

Future considerations

Roughly 60% of the reported gross CDR during the reporting period—not of the total CDR expected—was modeled to have occurred in the near-field domain (Quantification Report, p. 9, Table 4.3). Further monitoring in this region, confirming dissolution and no secondary precipitation, could be an opportunity for improvement and are already alluded to in Planetary’s reports (Operations & Monitoring Report, p. 17). While this may prove difficult in small pilots due to the background noise and detectability limits of alkalinity, it may be possible in more continuous dosing scenarios such as the one Planetary is gearing up for. Academic data from collaborations with Dalhousie University has been presented in various public events, clearly demonstrating the successful in-water increase of alkalinity, but not all of this data is available in peer-reviewed literature yet and not required as part of the verification process. It will be important to continuously update protocol requirements according to these findings. 

In its subsequent crediting round in October 2025, Planetary included this feedback and added a new “Evidence of Dissolution” section in the Operations and Monitoring report that qualitatively highlights how in-situ measurements of TA, TSS, and turbidity data supported feedstock dissolution assumptions. They further intend to refine this section in upcoming crediting documents. Desirably, further OAE research at large eventually enables quantitatively linking these measurements to their role in the quantification chain. 

Further information on this question can be found in: OAE Protocol Monitoring Requirements | PDD | Registry Dosing Date Examples | Operations & Monitoring Report | Quantification report

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8. Which models were used and were they validated?

Background

When models are built, they rely on fundamental physical and chemical equations to simulate an environment and use data to constrain a simulation at its domain boundaries, such as via atmospheric, hydrological, or biogeochemical forcings. Because the ocean is a complex system, each new setup of a model requires careful calibration and validation, in particular new regional models. This can be done in multiple ways, and is intended to ensure that the model reliably represents reality. Common scientific methods for validation include comparing models to tracer experiments, such as using a non-harmful rhodamine dye, and comparing models against real-world observations. When outputs don’t align, a model is typically adjusted via parameterizations of certain processes to better match measurements. Model validation is essential for MRV as they are the final tool for calculating removal, and it is important to distinguish between validating underlying models’ capabilities to represent the real world—for example by comparing it to long-term baseline data—versus its ability to accurately model an alkalinity addition and additional CO₂ uptake by comparing against in-trial measurements (Fennel et al, 2023).

According to Isometric’s Air-Sea CO₂ Uptake Module (v1.0, Section 4.1), models must demonstrate a high fidelity representation of the physical flow field as well as the carbonate system to ensure accurate representation of CO₂ uptake through air-sea gas exchange. According to the module, models qualify as “previously validated” if they have a track record in science or industry, demonstrated via peer-reviewed journals. New models without a track record must be validated via established scientific methods, but are not required to be validated against in-trial measurement data upfront. 

The term model validation is not always clearly defined and here it is important to differentiate between the VVB’s “validation” process of cross-checking all requirements, data, and model code—versus the underlying model being statistically “validated” against real-world data to adequately represent the real world. Below, we refer to the latter process whenever we say “model validation,” and to the former when we refer to the “VVB validation.” The VVB and subcontracted scientist reviewed and approved all models for compliance with the protocol and scientific accuracy. 

Note: Since initial VVB validation and verification began based on Planetary’s PDD, Isometric has held a public consultation period and published a new version of the Air-Sea CO₂ Uptake Module, which will now require that previously validated models be revalidated if used in a new region or with major configuration changes.

Planetary’s modeling approach

Planetary’s quantification relied on four models, reviewed by Isometric, the VVB and the subcontracted, independent scientist. 

• A simplified, one-dimensional dissolution model to represent release, dissolution, and sinking of feedstock particles, used as input to ROMS. 
• A regional ROMS model of Halifax Harbor, built by Dalhousie University, to quantify regional CO₂ uptake.
• A global ECCO/MITgcm model, an open source model, to simulate the fate of alkalinity and CO₂ beyond the coastal zone.
• A one-dimensional diffusivity model, used to expand uncertainty and sensitivity analyses of the regional and global model.

The Air-Sea CO₂ Uptake Module and Appendix 2 of the OAE Protocol only lay out requirements for model validation for the regional and global model. The dissolution and diffusivity model were additional tools used by Planetary; these types of models are not explicitly described in Isometric’s OAE Protocol.

1-D dissolution model 

Planetary used a one-dimensional (1-D) dissolution model to represent how feedstock particles dissolve and sink in the water column, independent of its exact location. This model is sometimes referred to in documents as a 1-D alkalinity release model (PDD, p. 14, p. 17) or a 1-D sinking and dissolution model (PDD, p. 91). It generates depth-dependent alkalinity release profiles that can be used to force the regional ROMS model of Halifax Harbor with the dosed alkalinity content by simplifying the full particle size distribution into a 2-phase proxy, with a dissolved and particulate fraction, the latter having a prescribed dissolution and sinking rate. This model provides the particle input information used in the model setup of ROMS as outlined by Isometric’s Appendix 2, Table A2-3 (particle size distribution, dissolution rate (modeled), particle shape, particle density). It is validated by demonstrating that it reproduces analytical results of how much alkalinity is released within the water column (PDD, pp. 17-19,  pp. 91-92). 

ROMS model

Initial validation of the Halifax ROMS model, developed by Dr. Katja Fennel’s group at Dalhousie University, was carried out by comparing model results against long-term time series from the Scotian Shelf and Halifax Harbor, including temperature, salinity, oxygen, DIC, and total alkalinity. These data come from work led by researchers at Dalhousie University and are presented in Wang et al, 2025 (published in April 2025, preprint available since October 2024, providing validation for physical circulation) and Laurent et al. (in review, preprint published July 22, 2025, providing validation for biogeochemistry).

While Laurent et al. was not initially publicly available at the time of the first credit issuance in June, all model validation data was made available to verifiers prior to certification. 

ECCO model

The physical representation of the ECCO model representing global uptake was considered as pre-validated via three academic publications (Zhang et al, 2018; He and Tyka, 2023; Carroll et al, 2020) as indicated also in the PDD (p. 63). Planetary undertook an additional validation of biogeochemical properties to demonstrate the model’s ability to reproduce spatial and seasonal variability of the carbonate system in the region of modeled air-sea gas exchange.

A separate document was provided sharing these comparisons of modeled baseline DIC, total alkalinity, and pCO₂ against gridded data products (i.e., not individual datapoints) via CMEMS Surface ocean carbon fields, SOM-FFN, and OceanSODA-ETHZ datasets. The document was submitted for initial project verification and, following feedback received through this Q&A process, was made available as part of the next crediting round in October 2025.

Importantly, this measurement data used for ECCO model validation is different from Isometric’s requirement for monitoring of parameters (see question 6 and 7). This is because validating a global model requires wider spatial and temporal coverage of observations and relies on publicly available academic data products.

1-D diffusivity model 

This model represents a single water column and tracks how added alkalinity affects the carbonate system and air-sea gas exchange in this column. Each column is matched to local wind fields and a seasonally varying mixed-layer depth for the region and is calibrated against ROMS and ECCO outputs. Alkalinity addition is represented through an alkalinity release field generated from the 1-D dissolution model. The primary role of this diffusivity model is exploratory: it runs sets of sensitivity cases (e.g., mixed-layer depth, vertical diffusivity, dissolution rate) to see how assumptions shift modeled uptake—at a fraction of the computational cost of full physics–biogeochemical models. Outputs from ROMS and ECCO are used alongside this model to inform the uncertainty analysis.

The diffusivity model does not determine credited CO₂ removal. Instead, it supports the near-field (ROMS) and far-field (ECCO) modeling by expanding parameter space and clarifying which factors most influence the model-based CO₂ removal estimates (PDD, p. 14-15, p. 70; Quantification Report, p. 8). Additional details on model code and validation of the diffusivity model were provided during project validation, but not publicly available as this model falls outside of concrete protocol requirements. Academic work outlining further details on this model is ongoing but not yet publicly available (PDD, p. 71, citing Yee, R., Musgrave, R., and Rackley, S., 2023).

Future considerations

Importantly, the measurement data used in the model validations to date is different from Isometric’s required monitoring of parameters (see question 6 and 7). In upcoming crediting rounds, Planetary has indicated that they will provide continued model-observations comparisons against the in-trial measurement data, including data collected by Dalhousie University (PDD, p. 74). It should be noted that this is a critical task towards field-wide assessment of a model’s capacity to represent alkalinity additions and additional CO₂ uptake, but not an Isometric requirement to perform at this stage. Rather, it is considered a desirable and iterative improvement for the OAE community at large, as indicated in the Appendix 2 of Isometric’s protocol. Carbon to Sea recommends clarifying when and how such validations will be required going forward and how they may be reflected via uncertainty considerations in the interim.

Furthermore, because the dissolution model is not used directly to quantify air-sea CO₂ uptake, it is Carbon to Sea’s understanding that its underlying model code, configuration, and validation does not fall under Isometric’s requirement to be publicly shared, although Planetary has indicated to make this model available upon request by interested researchers. Carbon to Sea recommends clarifying expectations in the protocol in this regard.

Further information on this question can be found in: Model Validation requirements Air-Sea CO₂ Uptake Module (v 1.0, used for this crediting)  | Quantification report | PDD | Laurent et al ROMS model publication | Global model validation report

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9. How was the uncertainty discount calculated?

Background

Because OAE occurs over time and space, quantifying its impact requires measurements and models. Inherently, both carry uncertainty as they aim to represent the real world in a simplified way. Uncertainty can arise from varying sources, and categorizing them in a consistent taxonomy is an ongoing focus for oceanographic modelers and MRV experts:

• Validation data uncertainty: uncertainty arising from the quality and extent of observational data used to validate the model.
• Boundary and input condition uncertainty: uncertainty related to the data used to force models, such as atmospheric boundary conditions or alkalinity dosing inputs.
• Parametric uncertainty: uncertainty introduced by parameterizations used to represent complex processes within the model.
• Systemic uncertainties: uncertainty reflecting how accurately and extensively the model’s underlying equations represent real-world processes and resolve the right spatial scales.

The Isometric Air-Sea CO₂ Uptake Module (v1.0, used for these credits) requires disclosing known limitations of each model used for quantification, and assessing the magnitude of the largest expected source of model uncertainty by using an ensemble of simulations that provide an estimate of its spread. Furthermore, the module requires applying conservative treatment for unquantified uncertainties as well as a plan to reduce these over time.

Model uncertainties

Planetary’s initial June 2025 uncertainty discount comprises boundary condition and parametric uncertainties in the model:

• Planetary identified the largest uncertainty source to be interannual variability, which is a boundary condition uncertainty arising from atmospheric forcing conditions, because wind and waves are a primary driver for air-sea gas exchange. Depending on actual observed weather, real CO₂ uptake can be lower or higher than modeled one. Planetary calculated the uncertainty in removal associated to interannual variability by constructing an ensemble of model runs that included years with and without extreme weather (e.g. hurricanes) to capture a wider range of environmental conditions, so the resulting discount is designed to avoid overstating CO₂ removal. Interannual variability yielded an uncertainty in the near-field model (ROMS) of 7.27% and in the far-field model (ECCO) of 19.26%. When these two independent estimates are combined, the overall variability is 8.9%. The combined uncertainty is calculated using a standard “root-sum-of-squares” method, which is a common way to combine independent sources of uncertainty without double-counting them, designed to avoid overstating the potential CO₂ removal (see Quantification Report, pp. 7-9). 
• Planetary quantified additional parametric uncertainty by varying mixed-layer depth, diffusivity, and feedstock dissolution rates. Their impact on the air-sea gas flux representation, driving air-sea CO₂ uptake, was quantified through 10 additional runs using the 1-D diffusivity model. Only some of those uncertainties were considered independent of interannual variability, and resulted in an additional joint parametric uncertainty of 6.51% in the air-sea CO₂ flux parameterization (Quantification Report, p. 8). In the subsequent October crediting round, Planetary increased this uncertainty to 7.4%, reflecting the full ensemble of sensitivity runs, not just those independent of interannual variability (TC25.1 Quantification Report, p. 10). 
• Additional input condition uncertainties are included for mass of feedstock dosed (0.25%) and its alkalinity enhancement potential (4.33%, see also question 5).

After each uncertainty is carried—or “propagated”—through the model, the gross CDR calculation yields a 11.85% uncertainty.The uncertainty quantification and propagation are described in the Quantification Report (p. 6 onward), and the full suite of ROMS and ECCO sensitivity studies are on pp. 16-17 of the PDD.

Overall uncertainty

In addition to uncertainty in the model representation of CDR, uncertainties in project emissions are added, yielding an overall uncertainty of 14.35% that is deducted from net CDR (Quantification Report, p. 10; see also question 4):

• Gross CDR calculation (11.85%):
  • Uncertainty in mass of feedstock dosed (0.25%)
  • Uncertainty in the feedstock CDR potential (4.33%)
  • Interannual variability (8.90%)
  • Uncertainty in the air-sea CO₂ flux parameterization (6.51%)
• LCA – Project emissions (5.27%):
  • Alkalinity production and transportation emissions 
  • Operational energy use emissions
  • Project establishment emissions
  • End-of-life emissions

Future considerations

Uncertainties will be recalculated for each reporting period. In the subsequent October crediting round, Planetary has eliminated interannual variability in the ROMS model as the largest uncertainty by running a simulation with actual observed boundary conditions for the crediting period. While the largest uncertainty now stems from parameterizations made, Planetary also included a new 5% uncertainty for systemic uncertainties in the ROMS model. This is described as “small but non-negligible resolution effects and residual uncertainty regarding sediment interactions” that were identified in the academic validation (TC25.1 Quantification Report, p. 9). 

Quantifying every uncertainty is computationally demanding and could potentially double-count correlated effects, since individual uncertainties are not necessarily strictly additive (Fennel et al, 2022 and Fennel, 2025). Systemic uncertainties, additionally, cannot always be resolved by a single project and remain an active area of research. It is important to continuously incorporate new research findings into such quantifications while adequately disclosing knowledge gaps such as Planetary did via the newly added 5% systemic uncertainty. Lastly, it would be beneficial to also report confidence estimates around uncertainty quantification.

Further information on this question can be found in: Quantification Report | Air-Sea CO₂ Uptake Module (v 1.0, used for this crediting) 

Note: Since issuance of both June and October credits, Isometric has held a public consultation period and published a new version 1.1 of the Air-Sea CO₂ Uptake Module, which introduces a new uncertainty taxonomy.

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10. Is model and measurement data accessible?

The project supplier must report all data of their full process to the verifier, including process-relevant data such as feedstock dosing or model configuration and code for full reproducibility. The majority of this data is shared in cleaned formats on Isometric’s project registry page through document links and Excel tables. For the initial crediting event in June, only ECCO model data was publicly available. Since then, the model code location for the ROMS model has become public alongside the Laurent et al preprint publication, which is now also indicated in an updated version of Planetary’s PDD (p. 69).

Beyond that, via the Isometric protocol, suppliers are encouraged but not required to share additional data that is “relevant for scientific research,” which remains undefined by Isometric. To Carbon to Sea’s knowledge, Planetary’s monitoring and model data beyond what is shared in PDFs is available upon request. 

Additionally, Planetary partners with Dalhousie University whose results are made available through peer-reviewed publications. Dalhousie researchers collect oceanographic data through the Ocean Alk-Align project as well as Carbon to Sea’s 2024 Joint Learning Opportunity, some of which is used by Planetary for scientific understanding but not required to be submitted via verification.

Further information on this question can be found in: Crediting Data

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Environmental Safety

11. How does Planetary approach environmental monitoring?

Environmental monitoring plans must be designed to assess ecosystem health as a result of an OAE activity and must reflect the unique characteristics of a site, including the material selected and the dosing mechanism used.

Baseline data

It is vital to establish a representative baseline prior to alkalinity additions to assess the background state, identify relevant species, and adapt monitoring plans to address case- and site-specific criteria adequately. As detailed in question 6, baseline monitoring for Planetary’s Halifax site captured the background physical and carbonate conditions of the harbor through long-term government and academic datasets since the 1980s. These monitoring programs include metal concentrations, chlorophyll-a (a proxy for phytoplankton biomass), and, since 2022, environmental DNA (eDNA), which serves as a proxy for biodiversity by counting species’ abundance (Rees et al, 2014).

Monitoring scope

Based on this background knowledge, Planetary developed a feedstock-specific environmental monitoring plan that tracks the contents and composition of the effluent stream and nearby waters using key parameters at the outfall and a mooring roughly 5 m from it (PDD, p. 42). According to Planetary, current monitoring suggests alkalinity signals dilute to below detection within 1–2 km of the outfall, so risks are expected to be concentrated in this area. Observed parameters for environmental monitoring include metals, total suspended solids (TSS), pH, and total alkalinity, analyzed by third-party laboratories and compared to environmental quality standards (PDD, pp. 44-45). Additionally, chlorophyll-a data is collected near the outfall.

Furthermore, academic collaborators at Dalhousie University are observing eDNA and benthic communities (see question 13) throughout Bedford Basin to further investigate ecosystem health—however, these academically-led monitoring campaigns are not a requirement in the protocol and therefore not reported as part of the verification process.

Thresholds and stop triggers

In the PDD, Planetary outlines assessment of risk and mitigations of natural resources on pages 21 onward. A “stop trigger” framework is in place to halt dosing if set thresholds are exceeded (PDD, pp. 44-45). For example, these can include sustained elevated pH levels, oxygen decreases, or elevated total metals concentrations (Operations & Monitoring Report, pp. 25-26). Thresholds are set by Planetary following guidelines from the Canadian Council of Ministers of the Environment (CCME) and limitations established from historical data records from the area (PDD, p. 21 and Operations & Monitoring Report, p. 14), as required by the protocol. Notably, the protocol does not prescribe ecological stop trigger values “due to the difficulty of establishing ecological baselines and attributing ecological changes.” It could be clarified that establishing site- and case-specific baselines are important to inform ecological thresholds and should be a desirable near-term goal, acknowledging more research may be needed here to develop more generally applicable frameworks.

Future considerations

Assessing ecosystem health will need to evolve when dosing becomes continuous in order to capture potential cumulative or delayed effects. Understanding the likelihood and risk of these potential effects is an ongoing area of research and requires careful observation of sites where dosing is slowly increased. To date, dosing at Planetary’s site has been intermittent, yet as they intend to move toward continuous multi-month dosing, systematic studies of potential long-term and delayed effects should take place. Similarly to ecological thresholds, the Isometric protocol does not yet prescribe cumulative or long-term studies.

According to the protocol, all ecological data must be made available to the public. To date, this data is available in the forms of plots in the public reports on the registry, and Planetary is preparing to make further forms of data available following the Carbon to Sea Data Management Protocol, including contributing it to future fit-for-purpose repositories  (see question 10).

Further information on this question can be found in: OAE Protocol | PDD | Operations & Monitoring Report

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12. Were ecotoxicity tests incorporated in the project?

Background

Ecotoxicity testing evaluates how organisms respond to exposure to a substance, measuring concentrations at which no harmful effect, some effects, or large effects are seen (Schmitt-Jansen et al, 2008). For OAE, ecotoxicity matters since adding alkaline materials to the ocean could negatively affect marine life. The increase in alkalinity modifies pH and other aspects of the carbonate system, which can directly affect biological processes. Furthermore, natural minerals may contain impurities such as heavy metals (Bach et al., 2019).

A common challenge of ecotoxicity studies is their imperfect replication of natural conditions. On one hand, they aim to indicate impacts for full feedstock dissolution, but this cannot always be achieved in laboratory setups due to the absence of contributing natural factors such as currents and mixing. As a result, when feedstocks do not resolve fully, their lethality can be underestimated. Vice versa, it can be overestimated because in nature, the feedstock would not stay concentrated in such a controlled environment and rather dilute away from the source of addition (Vighi and Villa, 2013).

Laboratory tests

Planetary acknowledged further information was required indicating whether full dissolution was taken into account in their tests, and added clarifying context to their October Operations Report when discussing ecotoxicity results (p. 6). They explain that toxicity tests did not involve artificially dissolving the feedstock in the test vessels to ensure full feedstock dissolution, as this may not be representative of natural conditions. Where necessary, test solutions underwent common methods to prepare water solutions that better reflect potential concentrations before adding test species. These methods include mimicking OAE by preparing elutriates or letting the feedstock leach into the water for up to 24 hours prior to conducting the ecotoxicology tests. According to Planetary, this approach—as opposed to artificially dissolving the feedstock with vigorous mixing or using artificial solvents to dissolve it—was selected because it more closely mimics exposure in the natural environment, where dissolution is not limited by solubility because the feedstock dilutes more rapidly across larger volumes of receiving water. 

Future considerations

Isometric’s protocol does not specifically require ecotoxicity studies, and ecotoxicity testing designed to inform OAE field studies is still an emerging field, hence best practices have not yet been established. It is an active area of research and will be important to further integrate findings into private sector activities.

Further information on this question can be found in: October Operations & Monitoring Report

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13. Is the seafloor monitored for undissolved alkalinity accumulation?

Background

Accumulation of undissolved feedstock on the seafloor is problematic as it can reduce the CDR potential if buried permanently or lead to precipitation in the worst case. It can also lead to changes of natural alkalinity fluxes or biological activity on the seafloor, reducing the additionality of any occurred CDR. 

Monitoring scope

Planetary reported that seafloor samples for total metals concentration are collected at least monthly both by the outfall and at other stations throughout the basin, as required by the protocol. The topmost layer of these mud samples are analyzed for a complete suite of metals. Planetary outlined that if they begin to see metals concentrations increase over time, particularly those associated with the feedstock, that would be a strong indication of seafloor accumulation. Seabed imagery was also collected before, during and after dosing at the outfall. To Planetary reports, no such accumulation occurred during operations of the first reporting period (Operations & Monitoring Report, p. 14, full section describing outfall monitoring p. 12-18). 

Additionally, an academic-led effort is underway to understand whether Planetary’s activities led to changes in seafloor biology or sediment chemistry. Dr. Chris Algar, leading this research, is also looking at benthic alkalinity fluxes, to assess whether Planetary’s work could be increasing or decreasing natural seafloor fluxes. Carbon to Sea recently spotlighted Dr. Algar’s work in more detail, which was funded via our 2024 Joint Learning Opportunity. 

Future considerations

For future crediting efforts, Planetary could provide increased insights into how academic environmental monitoring efforts, such as those by Dalhousie University, inform its experimental design and stop trigger framework.

Further information on this question can be found in: Operations & Monitoring Report

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Other

14. Can additional feedback be provided? 

Isometric has recently updated its Standard to require a public review process for future Project Design Documents of all CDR pathways. While this change will not apply retroactively to the Nova Scotia project, feedback on Planetary’s work can still be submitted directly to the registry at project-feedback@isometric.com.

Additionally, questions, comments, and feedback about this question solicitation process can be sent to feedback@carbontosea.org.

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Out of Scope

The following questions were submitted but considered outside the scope of this Q&A, which was focused narrowly on the first OAE credit issuance. They are documented here for transparency:

1. How do companies plan to scale?
   Rationale: Scaling pathways are project- and business-specific, not part of credit issuance protocols.
   
2. How will open-ocean MRV work?
   Rationale: This Q&A was specific to coastal outfall projects; open-ocean approaches raise distinct MRV challenges that require separate treatment. Ongoing research such as Dr. Adam Subhas’ LOC-NESS project is currently researching methods that could eventually be translated into open ocean MRV practices.
   
3. What does the funding landscape look like?
   Rationale: Financing and funding dynamics are outside the technical scope of MRV and credit verification.

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References

Bach, Lennart T., Steven J. Gill, Rosalind E. M. Rickaby, Samantha Gore, and Philip Renforth. 2019. “CO₂ Removal with Enhanced Weathering and Ocean Alkalinity Enhancement: Potential Risks and Co-benefits for Marine Pelagic Ecosystems.” Frontiers in Climate, article 00007. doi:10.3389/fclim.2019.00007.

Campbell, James S., Spiridon Foteinis, Vivienne Furey, Oliver Hawrot, Daniel Pike, Simon Aeschlimann, Cynthia N. Maesano, Pierluigi L. Reginato, David R. Goodwin, Loren L. Looger, Edward S. Boyden, and Philip Renforth. 2022. “Geochemical Negative Emissions Technologies: Part I. Review.” Frontiers in Climate 4: 879133. doi:10.3389/fclim.2022.879133.

Carroll, Dustin, Dimitris Menemenlis, Jess F. Adkins, Kevin W. Bowman, Helene Brix, Stéphanie Dutkiewicz, et al. 2020. “The ECCO-Darwin Data-Assimilative Global Ocean Biogeochemistry Model: Estimates of Seasonal to Multidecadal Surface Ocean pCO₂ and Air–Sea CO₂ Flux.” Journal of Advances in Modeling Earth Systems 12: e2019MS001888. doi:10.1029/2019MS001888.

Fennel, Katja, J. P. Mattern, Scott C. Doney, et al. 2022. “Ocean Biogeochemical Modelling.” Nature Reviews Methods Primers 2 (76). doi:10.1038/s43586-022-00154-2.

Fennel, Katja, Long, Matt C., Algar, Chris, Carter, Brendan, Keller, David, Laurent, Arnaud, Mattern, Jean Paul., Musgrave, Ruth, Oschlies, Andreas, Ostiguy, Josiane, Palter, Jaime B., and Whitt, Daniel B. 2023: “Modelling considerations for research on ocean alkalinity enhancement (OAE).” Guide to Best Practices in Ocean Alkalinity Enhancement Research. https://doi.org/10.5194/sp-2-oae2023-9-2023.

Fennel, Katja. 2025. “The Verification Challenge of Marine Carbon Dioxide Removal.” Annual Review of Marine Science. doi:10.1146/annurev-marine-032123-025717. 

He, Jing, and Michael D. Tyka. 2023. “Limits and CO₂ Equilibration of Near-Coast Alkalinity Enhancement.” Biogeosciences 20: 27–43. doi:10.5194/bg-20-27-2023.

Laurent, Arnaud, Bin Wang, Dariia Atamanchuk, Subhadeep Rakshit, Kumiko Azetsu-Scott, Chris Algar, and Katja Fennel. 2025. “A High-Resolution Nested Model to Study the Effects of Alkalinity Additions in Halifax Harbour, a Mid-Latitude Coastal Fjord.” EGUsphere (preprint). doi:10.5194/egusphere-2025-3361. 

Moras, Christina A., Tyler Cyronak, Lennart T. Bach, Richard Joannes-Boyau, and Kai G. Schulz. 2024. “Effects of Grain Size and Seawater Salinity on Magnesium Hydroxide Dissolution and Secondary Calcium Carbonate Precipitation Kinetics: Implications for Ocean Alkalinity Enhancement.” Biogeosciences 21: 3463–3475. doi:10.5194/bg-21-3463-2024.

Rees, Helen C., Beth C. Maddison, Daniel J. Middleditch, James R. M. Patmore, and Kevin C. Gough. 2014. “The Detection of Aquatic Animal Species Using Environmental DNA: A Review of eDNA as a Survey Tool in Ecology.” Journal of Applied Ecology 51: 1450–1459. doi:10.1111/1365-2664.12306.

Schmitt-Jansen, Mechthild, Uwe Veit, Gert Dudel, and Rolf Altenburger. 2008. “An Ecological Perspective in Aquatic Ecotoxicology: Approaches and Challenges.” Basic and Applied Ecology 9 (4): 337–345. doi:10.1016/j.baae.2007.08.008. 

Schulz, Kai G., Lennart T. Bach, and Andrew G. Dickson. 2023. “Seawater Carbonate Chemistry Considerations for Ocean Alkalinity Enhancement Research: Theory, Measurements, and Calculations.” In Guide to Best Practices in Ocean Alkalinity Enhancement Research, edited by Andreas Oschlies, Anna Stevenson, Lennart T. Bach, Katja Fennel, Rosalind E. M. Rickaby, Terre Satterfield, Robert Webb, and Jean-Pierre Gattuso. Copernicus Publications, State Planet 2 (2). doi:10.5194/sp-2-oae2023-2-2023.

Suitner, Nicolas, Gaël Faucher, Cai Lim, Juliane Schneider, Christina A. Moras, Ulf Riebesell, and Jens Hartmann. 2024. “Ocean Alkalinity Enhancement Approaches and the Predictability of Runaway Precipitation Processes: Results of an Experimental Study to Determine Critical Alkalinity Ranges for Safe and Sustainable Application Scenarios.” Biogeosciences 21: 4587–4604. doi:10.5194/bg-21-4587-2024.

Vighi, Marco, and Sara Villa. 2013. “Ecotoxicology: The Challenges for the 21st Century.” Toxics 1: 18–35. doi:10.3390/toxics1010018.

Wang, Bin, Arnaud Laurent, Qiantong Pei, Jinyu Sheng, Dariia Atamanchuk, and Katja Fennel. 2025. “Maximizing the Detectability of Ocean Alkalinity Enhancement (OAE) while Minimizing Its Exposure Risks: Insights from a Numerical Study.” Earth’s Future 13: e2024EF005463. doi:10.1029/2024EF005463.

Zhou, Mengnan, Michael D. Tyka, David T. Ho, et al. 2025. “Mapping the Global Variation in the Efficiency of Ocean Alkalinity Enhancement for Carbon Dioxide Removal.” Nature Climate Change 15: 59–65. doi:10.1038/s41558-024-02179-9.

Zhang, Hong, Dimitris Menemenlis, and Ian Fenty. 2018. ECCO LLC270 Ocean-Ice State Estimate. Massachusetts Institute of Technology, ECCO Consortium. doi:1721.1/119821. 

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