This document covers technologies designed to produce ocean alkalinity enhancement (OAE) from:
- Mining and distribution of natural rock-based alkaline minerals, including olivine and other silicate rocks as well as limestone and other carbonate minerals, either in open ocean (ocean liming) or coastal environments (coastal enhanced weathering) (Meysman & Montserrat, 2017; Renforth & Henderson, 2017; Lenton et al., 2018; Köhler et al., 2013; Köhler et al., 2010).
- Production of hydroxide minerals, including lime/slaked lime (Kheshgi, 1995) from thermal calcination and magnesium hydroxide from synthetic weathering of olivine (Scott et al., 2021) and distribution in the open ocean.
- Accelerated weathering of limestone (AWL) in ex-situ reactors to sequester non-fossil, point source CO2 emissions. Note that AWL requires a concentrated source of CO2 in seawater because carbonate minerals are oversaturated in seawater at ambient CO2 concentrations.
- Production and addition of hydrated carbonate minerals to seawater for increased alkalinity (Renforth et al., 2022)
In contrast to recent reports (Gagern et al., 2019; EFI, 2020; Rackley, 2020), we consider these four mineral-based pathways of OAE together because of the common upstream and downstream considerations necessary to accelerate the development and testing of OAE pathways.
We consider all electrochemical-based technologies for mCDR, including alkalinity enhancement, in a separate road map due to their separate set of upstream and downstream considerations for electrochemical processes.
We also do not consider enhanced rock weathering in terrestrial ecosystems here despite its similarities with coastal enhanced weathering and its potential for gigaton-scale CDR (Beerling et al., 2020). Enhanced rock weathering in agricultural fields presents its own set of obstacles and development needs, many of which are distinct from those of the marine pathways considered in these road maps.
[post_title] => Overview [post_excerpt] => [post_status] => publish [comment_status] => closed [ping_status] => closed [post_password] => [post_name] => overview [to_ping] => [pinged] => [post_modified] => 2024-09-18 22:30:54 [post_modified_gmt] => 2024-09-18 22:30:54 [post_content_filtered] => [post_parent] => 1944 [guid] => https://oceanvisions.org/roadmaps/ocean-alkalinity-enhancement/state-of-technology-ocean-alkalinity-enhancement/overview/ [menu_order] => 0 [post_type] => page [post_mime_type] => [comment_count] => 0 [filter] => raw )Addition of carbonate minerals to stabilize seawater carbonate chemistry has already been occurring in aquaculture facilities for ~10 years (Bruno & Boyd, 2011), largely as a response to the hatchery failures ~2010 in the US Pacific Northwest and British Columbia from ocean acidification (Washington State Blue Ribbon Panel on Ocean Acidification, 2012). The Chalk-Ex experiment released crushed calcium carbonate in a ~1.5 km2 patch in the Gulf of Maine in the early 2000s. However, this experiment's primary objective was to quantify particles' effects on upper ocean layer optical properties, not to achieve CDR. There are now a number of ongoing field trials, with more planned in the future. OAE's TRL is currently around a 6 (TRL, RMI The Applied Innovation Roadmap for CDR). See the mCDR Field Trial Database for information on current field trials.
[post_title] => Technology Readiness [post_excerpt] => [post_status] => publish [comment_status] => closed [ping_status] => closed [post_password] => [post_name] => technology-readiness [to_ping] => [pinged] => [post_modified] => 2024-04-23 20:49:47 [post_modified_gmt] => 2024-04-23 20:49:47 [post_content_filtered] => [post_parent] => 1944 [guid] => https://oceanvisions.org/roadmaps/ocean-alkalinity-enhancement/state-of-technology-ocean-alkalinity-enhancement/technology-readiness/ [menu_order] => 1 [post_type] => page [post_mime_type] => [comment_count] => 0 [filter] => raw )- Carbon Capture
Methods of OAE that rely on depositing minerals into the ocean to promote additional CO2 uptake depend on how quickly the minerals dissolve relative to how quickly they sink (Fakhraee et al., 2023). Due to the vast quantities of alkaline rocks, and the capacity of the ocean to accommodate similarly vast quantities of bicarbonate ions, OAE has the theoretical potential to capture tens of gigatons of carbon dioxide annually{{1}}. However, given current technological readiness, this remains theoretical. Recent consensus reports cite the following as possible carbon dioxide removal potential from ocean alkalinity enhancement:
- >0.1 – 1.0 Gt CO2/year (NASEM 2022)
- 1 – 15+ Gt CO2/ year (NOAA 2023)
Technical, economic, social, political, and governance factors may also decrease this theoretical CDR potential, although the degree to which they limit the CDR remains to be determined. The most current cost estimates range from $25-160/ton CO2 (NOAA 2023).
- Sequestration Permanence
OAE will result in additional CO2 from the atmosphere being sequestered in the ocean as bicarbonate ions, which cannot exchange with the atmosphere (Renforth & Henderson, 2017). Currently, OAE is thought to have sequestration duration >20,000 years (NOAA 2023).
- Accelerated Weathering of Limestone: Avoided Emissions and Hybrid Methods
When AWL is used to sequester carbon dioxide resulting from the combustion of fossil fuels, it represents avoided emissions, not removal of atmospheric carbon dioxide (negative emissions) (Rau & Caldeira, 1999; Rau, 2011). However, there exist a number of hybrid possibilities to integrate AWL with various non-fossil sources of concentrated carbon dioxide to permanently sequester the carbon dioxide as bicarbonate ions in the ocean. These hybrid approaches include:
- AWL coupled with direct air capture – captured CO2 from a direct air capture (DAC) facility can be concentrated and reacted with limestone in the presence of seawater to trap the captured CO2 as bicarbonate ions.
- The bicarbonate-rich effluent of DAC + AWL can also serve as a substrate to support algal growth (Rau, 2014); however newly-produced algal carbon must be sequestered from return to the atmosphere to generate negative emissions over relevant permanence timescales (> 100 years).
- AWL coupled with bioenergy – CO2 generated from the combustion of biomass (either terrestrial or marine-based) to generate energy can be concentrated and reacted with limestone in the presence of seawater to trap the CO2 as bicarbonate ions. This process is analogous to bioenergy with carbon capture and storage (BECCS) (Hughes, 2012), except that the carbon is stored as bicarbonate ions in the ocean as opposed to being sequestered in geologic reservoirs.
We further consider AWL in these hybrid configurations that generate the removal of atmospheric carbon dioxide and sequestration as bicarbonate in the ocean.
- AWL coupled with direct air capture – captured CO2 from a direct air capture (DAC) facility can be concentrated and reacted with limestone in the presence of seawater to trap the captured CO2 as bicarbonate ions.
- OAE would likely provide localized reductions in ocean acidification, with expected benefit(s) to marine ecosystems (Gattuso et al., 2018; Feng (冯玉铭) et al., 2016).
- In certain areas, calcium or silica additions could act as fertilizers to support plankton populations (Adhiya & Chisholm, 2001).
- OAE may pose ecotoxicological risks from the release of elevated concentrations of trace metals from some minerals during mineral dissolution (Burns & Corbett, 2020).
- The toxicity will depend on the source rock, the concentration of source rock applied, and the seawater chemistry (which determines bioavailability). These trace metal additions could also pose risks to human health if accumulation occurs through food webs (Bach et al., 2019).
- Silicate rocks are likely to have higher metal concentrations than carbonate rocks, and thus may pose a greater ecotoxicological risk (Bach et al., 2019)
- In-situ applications of alkaline materials (e.g. coastal enhanced weathering, ocean liming) may pose greater ecotoxicological risks than ex-situ applications (e.g. reactors for accelerated weathering of limestone) because of the ability to capture and treat the effluent from ex-situ reactors before release into the ocean. However, options exist to mitigate these effects e.g., through rapid dilution in the wake of vessels (Caserini et al., 2021)
- The potential for changes in water column particle concentrations, turbidity, and optical properties from dispersing fine particulates
- The potential for changes in seafloor deposition of particles and their effects on smothering or burial, food webs interactions, light availability and more
- Large-scale mining of silicate or carbonate rocks may pose environmental risks, similar to those typically associated with existing mines including ground vibrations from blasting, noise pollution, decreased air and soil quality, etc.
- Ecological and geochemical impacts of discharging high alkalinity/high pH waters, including precipitation (inorganic mineral formation) of carbonates. However, options to mitigate these effects exist e.g., through rapid dilution in ship's wakes (Caserini et al., 2021).
- OAE may have the potential to shift phytoplankton community composition from carbonate-shell producing plankton (coccolithophores) to silica-shell producing plankton (diatoms) or vice-versa depending on the form of alkalinity addition.
- Potential for bioaccumulation and biomagnification in the food chain (NASEM 2022).
- Dedicated ships/vessels to distribute minerals could cause environmental impacts such as additional noise pollution (Kaplan & Solomon, 2016), the potential transfer of nonindigenous species (Muirhead et al., 2015), and the addition of pollutants from shipping emissions (Dalsøren et al., 2013).
- Risks associated with the expansion of mining activities for OAE
- Demographic changes include, but are not limited to, shifts in gender balance, increase in non-resident workforces, appropriation of land from local communities, social inequality, and impacts on Indigenous communities (NASEM 2022)
- Negative health impacts include cancer, respiratory diseases, injuries, and prolonged exposure to chemical agents (Candeias et al., 2011)
- Environmental implications include impacts to soil and air quality, impacts to ground and surface waters, and erosion.
- Creation of job opportunities from the OAE supply chain
- Amelioration of ocean acidification could increase food security and preserve cultural values (Nawaz et al., 2023)
- 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}}), 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}} (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}}.
- 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)
High-resolution data-assimilative models are needed to support real-world testing of OAE. These modeling tools must:
- Account for complex interactions in the immediate vicinity of the alkalinity release and downstream impacts
- Provide four-dimensional (space and time) estimates of biogeochemistry in zone of influence both in the presence and absence of OAE. The difference between these two simulations can be used to inform CDR estimates that account for background variability in the ocean.
- CDR estimates from OAE must include estimates of the “opportunity cost” of OAE - how did OAE shift phytoplankton community composition, production, and export?
To support the design of proof-of-concept field trials, these models should also:
- Provide estimates of the size and scale of biogeochemical modification to the ecosystem from OAE, allowing for informed placement of sensors to monitor the field trials
- Be capable of simulating passive tracers (e.g. SF6) to inform whether and how these passive tracers may be useful in field trials (e.g., estimating rates of atmospheric CO2 uptake)
- Inform a prioritized set of predictions to be tested during field trials
Field trials for the various OAE technologies are urgently needed to test both carbon sequestration potential and environmental impacts (both positive and negative). While there are a number of OAE field trials underway in the US and abroad, more efforts are necessary. The following activities and products are still needed:
[post_title] => Accelerate Design and Permitting of Controlled Field Trials [post_excerpt] => [post_status] => publish [comment_status] => closed [ping_status] => closed [post_password] => [post_name] => accelerate-design-and-permitting-of-controlled-field-trials [to_ping] => [pinged] => [post_modified] => 2024-04-18 19:14:58 [post_modified_gmt] => 2024-04-18 19:14:58 [post_content_filtered] => [post_parent] => 1946 [guid] => https://oceanvisions.org/roadmaps/ocean-alkalinity-enhancement/first-order-priorities-ocean-alkalinity-enhancement/accelerate-design-and-permitting-of-controlled-field-trials/ [menu_order] => 1 [post_type] => page [post_mime_type] => [comment_count] => 0 [filter] => raw )A new suite of durable, seagoing technologies are needed to support OAE RD&D. Technology development needs include:
[post_title] => Develop New In-Water Tools for Autonomous CDR Operations [post_excerpt] => [post_status] => publish [comment_status] => closed [ping_status] => closed [post_password] => [post_name] => develop-new-in-water-tools-for-autonomous-cdr-operations [to_ping] => [pinged] => [post_modified] => 2023-08-02 14:45:11 [post_modified_gmt] => 2023-08-02 14:45:11 [post_content_filtered] => [post_parent] => 1946 [guid] => https://oceanvisions.org/roadmaps/ocean-alkalinity-enhancement/first-order-priorities-ocean-alkalinity-enhancement/develop-new-in-water-tools-for-autonomous-cdr-operations/ [menu_order] => 2 [post_type] => page [post_mime_type] => [comment_count] => 0 [filter] => raw )Standardized methodologies from third parties to verify the uptake of atmospheric CO2 resulting from ocean alkalinity enhancement will ultimately need to be developed to enable trading of carbon removal credits. See efforts by [C] Worthy, ARPA-E SEA-CO2 grantees, and Carbon to Sea grantees. Key first steps to support the development of these tools include:
- Convening experts to review advances from modeling tools (Develop New Modeling Tools to Support Design and Evaluation) and controlled field trials (Accelerate Design and Permitting of Controlled Field Trials) to identify satisfied and outstanding data needs necessary to quantify additional CO2 uptake as a direct result of OAE. As advances in OAE RD&D are made, the satisfied and outstanding data needs will need to be updated.
- Apply existing (Koornneed & Nieuwlaar, 2009; Hartmann et al., 2013) or develop when necessary, life cycle analysis tools to calculate stored carbon after accounting for emissions from required materials, energy, transportation/dispersal, etc.
- Include aspects of sustained monitoring to verify CDR permanence over long time scales as CDR is scaled.
Research, development, and demonstration of OAE may be accelerated and strengthened by creating partnerships with key industries/sectors, including:
- Transoceanic shipping – cargo vessels often travel at less than full capacity, provide onboard power, and move from port to port providing frequent opportunities to acquire new alkaline material and offload byproducts from alkalinization processes. Developing partnerships with the shipping industry to help the industry fulfill its commitments to decarbonize shipping could be a stepping stone to accelerate ocean-based net negative emissions (e.g. Poseidon Principles).
- Industries generating alkaline byproducts for feedstock into OAE processes (steel, aluminum, cement, lime, and nickel production; coal and biomass combustion) (Renforth, 2019).
- 7 billion tons of alkaline byproducts generated annually from manufacturing and combustion could decrease costs and potentially facilitate transitions to larger-scale OAE (Renforth, 2019).
- Finfish and shellfish aquaculture, as well as coral reefs, where the added alkalinity could be used to optimize chemical conditions, including providing relief from ocean acidification (Gattuso et al., 2018).
- Offshore renewable energy production, including wind and others, both as power sources and as integrated CDR platforms.
- Coastal industries, including desalination and wastewater treatment facilities, which already have infrastructure for pumping/processing seawater or wastewater for alkalinity addition.
- Marine research laboratories that already pump seawater and have expertise, technical equipment and infrastructure to support research and development.
Developing and strengthening relationships with partner industries may also help promote greater public support, as well as potentially offer faster routes to obtaining the necessary permitting.
[post_title] => Accelerate RD&D Through New Partnerships [post_excerpt] => [post_status] => publish [comment_status] => closed [ping_status] => closed [post_password] => [post_name] => accelerate-rdd-through-new-partnerships [to_ping] => [pinged] => [post_modified] => 2024-04-25 00:56:02 [post_modified_gmt] => 2024-04-25 00:56:02 [post_content_filtered] => [post_parent] => 1946 [guid] => https://oceanvisions.org/roadmaps/ocean-alkalinity-enhancement/first-order-priorities-ocean-alkalinity-enhancement/accelerate-rdd-through-new-partnerships/ [menu_order] => 4 [post_type] => page [post_mime_type] => [comment_count] => 0 [filter] => raw )First-Order Priorities to build public support for ocean-based CDR pathways are found in the Public Support road map Additionally, there are some specific opportunities to cultivate public engagement in and support around OAE including:
- Developing targeted public outreach/advocacy campaigns to inform about OAE and its potentials with regards to ameliorating ocean acidification
- Responding to the narrative of OAE as less “nature-based” than, for instance, coastal blue carbon restoration with the concept that OAE represents an acceleration of “natural” chemical weathering.
Ocean Alkalinity Enhancement
Adding alkalinity to seawater to capture CO2