• Field trials are beginning to get underway (See mCDR Field Trial Database) however characterization of benefits, risks, and scaling considerations remains a gap. An increase in controlled field trials across diverse ecosystems to determine marine chemistry and biology impacts and feedbacks are needed. (Develop New Modeling Tools to Support Design and Evaluation, Accelerate Design and Permitting of Controlled Field Trials).
• It is challenging to verify additional CO₂ uptake from the atmosphere as a result of OAE given the ocean’s dynamic CO₂ flux “background state”. New methodologies are needed to observe additional sequestration from the atmosphere into the ocean (Develop New Modeling Tools to Support Design and Evaluation, Develop New In-Water Tools for Autonomous CDR Operations).
• Laboratory experiments are needed across a range of seawater chemistries expected as a result of equilibrated OAE scenarios (e.g. high total alkalinity and high dissolved inorganic carbon^[1]Comments from Dr. Ros Rickaby, ‘Workshop on Ocean-based CDR Opportunities and Challenges, Part 2: Technological and Natural Approaches to Ocean Alkalinity Enhancement and CO₂ Removal’ on 27th January 2021 ), along with various alkaline materials and their associated major (e.g. magnesium, calcium) and minor (e.g. nickel, cadmium) elemental concentrations to characterize environmental impacts (Accelerate Design and Permitting of Controlled Field Trials).
  • Look to the ocean acidification community’s effort to develop standardized protocols for guidance (Gattuso et al., 2015)  as the OAE community builds out standardized protocols and treatments levels for consistency and intercomparability
  • Existing database(s) of ecotoxicological tests need to be reviewed (EPA, Environmental Protection Agency) for possible OAE source materials (e.g. Ca(OH)₂) and co-occurring metals (e.g. Ni, Cd) to identify known ecotoxicological effect and lethality thresholds and current gaps in our understanding.
• Global, local, and regional predictions of physical, chemical, and biological outcomes and feedbacks of OAE from high-resolution models are needed (Develop New Modeling Tools to Support Design and Evaluation)
• Laboratory experiments are needed on silicate and carbonate mineral kinetics and dissolution catalysts (Subhas et al., 2017) to better understand mineral dissolution rates in marine environments and means to accelerate them (Accelerate Design and Permitting of Controlled Field Trials).
  • The coastal enhanced weathering facility jointly administered by Universiteit Antwerpen, the University of Gent, and VLIZ provides mesocosm and monitoring equipment to conduct mineral dissolution experiments in tank conditions closely approximating real-world beach and shallow water settings. 
• Life cycle assessments are necessary to calculate net CDR benefits, taking into account all emissions associated with supply chains (Develop CDR Monitoring and Verification Protocols). 
• There may be good value in summarizing best practices, lessons learned, and pitfalls from lime treatment of acid rain-affected lakes and watersheds to accelerate OAE development and testing^[5]Comments from Dr. Tim Kruger, ‘Workshop on Ocean-based CDR Opportunities and Challenges, Part 2: Technological and Natural Approaches to Ocean Alkalinity Enhancement and CO₂ Removal’. A Research Strategy for Ocean Carbon Dioxide Removal and Sequestration, U.S. National Academy of Sciences.  27th January 2021. Accessible at: https://www.nationalacademies.org/event/01-27-2021/a-research-strategy-for-ocean-carbon-dioxide-removal-and-sequestration-workshop-series-part-2 (Taylor et al., 2021; Naturresursavdelningen, 2010)
• To systematically assess several of the knowledge gaps listed (whether and how OAE can be a safe, scalable, and permanent CDR method), Additional Ventures created the non-profit initiative Carbon to Sea. Carbon to Sea has funded several research and technology projects which aim to close knowledge gaps and push technology innovation forward.

• Current observational technologies (sensors, ROVs, AUVs, etc.) and modeling tools are not widespread and easily available to fully support field trials with the desired spatial and temporal frequency of monitoring and sampling needed (Develop New In-Water Tools for Autonomous CDR Operations).
• New technologies are needed to reduce the cost and environmental impacts of mining, grinding, and distribution of alkaline rocks with minimum environmental impact (Beerling et al., 2020).
• Assessment of the potential to re-purpose existing supply chains for coal and cement to provide an easier ramp up to meet the production and distribution scales required (Accelerate RD&D Through New Partnerships). 
• Assessment of the potential to scale the cement and lime industries to meet the expected needs of calcination (Renforth et al., 2013; Renforth & Henderson, 2017)(Accelerate RD&D Through New Partnerships).
• Identification of sources of renewable energy at sufficient scale to power OAE (Develop New In-Water Tools for Autonomous CDR Operations) 
• For in-situ application with hydroxide minerals, methods to handle the heat generated from adding hydroxides to the ocean because this is an exothermic (heat-releasing) reaction (Develop New In-Water Tools for Autonomous CDR Operations).
• For point source OAE, cost-effective and safe methods need to be developed that optimize the distribution, dispersal and dilution of any strong chemical bases to avoid impacts of excessively alkaline (pH>9) waters on marine ecosystems. Dilution may require pumping large amounts of seawater, which need to be optimized for energy and cost (Develop New In-Water Tools for Autonomous CDR Operations). However, it may be possible to use existing large-volume discharges such as power station cooling water discharges that can be as high as 90 cubic meters per second for a 1600 MWe nuclear power station. In addition, another option would be to utilize the rapid dilution available in ships’ wakes (Caserini et al., 2021).

Many of the opportunities and challenges around building public awareness and support for mCDR are not specific to OAE, but there are several hurdles specific to OAE: 

• OAE faces challenges in terms of public perception of potential environmental risks that are not necessarily faced by what are considered more “nature-based” approaches (e.g., coastal blue carbon restoration) (Bertram & Merk, 2020) (Growing and Maintaining Public Support).
  • There is a great deal of hesitancy and resistance around any mCDR pathway that relies on adding materials to the ocean. 
  • Earlier ocean iron fertilization experiments (Schiermeier, 2009) could offer opportunities to adopt best practices and avoid mistakes made when building public support for OAE. 
• Negative perceptions exist about the large-scale mining that would likely be needed to generate sufficient rock supplies to support global-scale OAE (Growing and Maintaining Public Support).
• Clear communication strategies need to be developed to respond to the “geoengineering” narrative of OAE (Growing and Maintaining Public Support). 
• The public discussion around OAE (and mCDR generally) is growing and has been featured in popular news sources (Wired, MIT Technology Review).
• Funding has increased markedly in the past years, including funding from the US government.

Advancing the development and testing of OAE will require governance structures that both enable the permitting of legitimate testing and development and ensure that the public interests are protected.  

• There is currently no clear international regime that governs research and development in OAE. The closest regimes would be the London Convention and the London Protocol, but currently they are not built to govern OAE scientific field trials in marine waters^[1]Note that the London Convention and London Protocol cover all waters up to the baselines used to measure the territorial sea and the EEZ. In addition, London Protocol Parties have to either apply the Protocol to marine internal waters (i.e., behind the baselines e.g., estuaries) or they have to adopt other effective permitting and regulatory measures for marine internal waters. .
• Small-scale OAE field trials by “invited Parties and other Governments” with prior environmental impact assessments may be allowed under the United Nations Convention on Biological Diversity (CBD)  Section X/33(8)(w). The CBD, however, is not legally binding  and not all countries are party to the CBD (for example, the United States)