- Carbon Capture - The ultimate CDR potential of large-scale macroalgal cultivation and sequestration is as yet difficult to determine. Recent consensus reports cite the following as possible carbon dioxide removal potential from macroalgae cultivation and sequestration:
- 0.1 – 1.0 Gt CO2/year (NASEM 2022: A Research Strategy for Ocean-Based Carbon Dioxide Removal and Sequestration)
- 0.1 – 0.6 Gt CO2/ year (NOAA 2022: Carbon Dioxide Removal Research)
Theoretically, macroalgal cultivation and sequestration could be scaled to between one and greater than ten gigatons of CDR per year{{1}}, but realized CDR may be much lower due to a number of factors, including:
-
- Competition for space with existing ocean stakeholders – commercial shipping, commercial fishing, indigenous rights, marine protected areas, non-seaweed aquaculture, etc.
- Challenges with expanding to offshore environments – engineering of moorings and farm structures, challenges with operations and maintenance in distant environments{{2}},{{3}}- and the likely associated cost increases (at least at first) associated with offshore operations
- Most open ocean environments require nutrient additions to sustain macroalgal yields. If these nutrients come from the deep ocean, they will be accompanied by high CO2 water that can be released and will offset macroalgal carbon sequestration to some degree (which needs to be quantified).{{4}},{{5}}
- If macroalgal farms are located closer to the coastal zone, excess anthropogenic nitrogen inputs could support ~3.5 million km2 of macroalgal cultivation, corresponding with an estimated CDR range of 5- 10 Gt CDR annually{{6}}, alleviating competition for “natural” nutrient supplies with phytoplankton and alleviating the need for an upwelled supply of nutrients (and the associated risks of releasing CO2 from upwelled deep ocean waters).
- It is hypothesized that macroalgae-based pathways could supply CDR at moderate cost ($25-125 per ton of CO2 removed){{7}},{{8}},{{22}}, but these cost estimates are preliminary and subject to change as macroalgae-based pathways advance in technological readiness{{9}}.
- Researchers at UC Irvine are developing a biophysical-economic model to better understand the geophysical, biological, and economic sensitivities of macroalgae-based CDR pathways{{10}}
2. Sequestration Permanence -For cultivated macroalgae to contribute to CDR, the carbon captured in the macroalgal tissue needs to be sequestered to prevent its decomposition and return to the atmosphere. Sequestration pathways include:
-
- Intentionally sinking the macroalgae (pre- or post-processing) into the deep ocean (>1000 meters depth) where it can be sequestered from contact with the atmosphere for hundreds to a few thousand years{{11}} (if remineralized in the deep ocean) or for thousands-to-millions of years (if buried in marine sediments).{{12}}
- There are natural analogues to this process already. In macroalgal systems, already ~50% of natural macroalgal production breaks off and becomes dissolved or particulate organic matter. Some of the particulate organic matter is transported to the deep ocean, where the carbon is sequestered.{{13}}
- Relying on sedimentary burial below or adjacent to the farm (typically more applicable for farms not located over deep water).
- Oceans2050 is working to determine the permanence of burial under coastal farms
- Harvesting the macroalgae for:
- Bioenergy{{14}}
- Combining combustion pathways with carbon capture and storage{{15}} (thousands-to-millions of years if stored in a geologic reservoir)
- Pyrolysis, resulting in biochar{{16}},{{17}} (hundreds-to-thousands of years)
- Production of long-lived bioproducts, such as bioplastics, that are capable of permanent (>100 years) sequestration{{18}
- Bioenergy{{14}}
- Intentionally sinking the macroalgae (pre- or post-processing) into the deep ocean (>1000 meters depth) where it can be sequestered from contact with the atmosphere for hundreds to a few thousand years{{11}} (if remineralized in the deep ocean) or for thousands-to-millions of years (if buried in marine sediments).{{12}}
3. Differentiating from Avoided Emissions - Macroalgae can provide a number of other services that either reduce or replace greenhouse gas emissions, but do not remove legacy carbon dioxide pollution from the atmosphere. One example of reducing emissions: red algal supplements added to cattle feed may play a key role in reducing enteric methane emissions from cattle by over 50%{{19}},{{20}}. Given methane’s potency as a greenhouse gas, such emissions reductions may play an outsized role in slowing planetary temperature increases through the reduction of greenhouse gases. Macroalgae biomass may also be converted into short-lived, high-value bioproducts, such as food and nutritional supplements{{21}}. This process may contribute to avoided emissions if it substitutes for carbon-intensive feedstocks, but it does not represent CDR because of the short timescale over which these products sequester carbon before it returns to the atmosphere. Although the focus of this roadmap is on macroalgae pathways for CDR, many of the obstacles faced, development needs, and near-term opportunities for advancement are relevant to these associated pathways for avoided greenhouse gas emissions.
[post_title] => CDR Potential [post_excerpt] => [post_status] => publish [comment_status] => closed [ping_status] => closed [post_password] => [post_name] => cdr-potential [to_ping] => [pinged] => [post_modified] => 2023-02-14 16:42:23 [post_modified_gmt] => 2023-02-14 16:42:23 [post_content_filtered] => [post_parent] => 536 [guid] => https://oceanvisions.org/?page_id=1744 [menu_order] => 1 [post_type] => page [post_mime_type] => [comment_count] => 0 [filter] => raw )- Localized buffering/reductions in ocean acidification due to CO2 uptake. {{1}},{{2}},{{3}},{{4}},{{5}}
- Nutrient remediation and metal uptake in eutrophied, polluted coastal waters {{6}}
- Building macroalgae cultivation facilities near shellfish or fish aquaculture facilities may alleviate negative impacts from such activities{{9}} (e.g., deoxygenation, eutrophication)
- Macroalgae farms may attenuate wave energy {{7}}
- Creation of habitat with resulting nurseries for fish and other marine life {{8}}
- Carbon capture at sea may reduce the demand for terrestrial-based CDR alternatives that compete for land and/or freshwater
- Macroalgae are known to release bromoform and other halomethanes{{4}},{{5}}, and thus, large-scale macroalgae cultivation seems likely to increase the release of these substances. This needs additional research as the natural marine sources of these gases are currently estimated to be responsible for around 9% of stratospheric ozone loss, including depletion due to anthropogenic causes{{6}}.
- Production of methane, nitrous oxide, and other potentially hazardous gases by the macroalgae
- The potential for CO2 outgassing from pumping deep water to the surface (artificial upwelling) to supply needed nutrients for the macroalgae{{3}}.
- Ecological and biogeochemical (especially acidification and hypoxia) impacts in the deep sea from sinking large quantities of macroalgae into the deep ocean
- Such effects are likely to be location-specific
- Impacts to biodiversity and ecosystem function from large-scale cultivation operations, including{{1}},{{2}}:
- Enhanced disease and parasite risk
- Alteration of population genetics
- Introduction of non-native species into new environments
- Enhancement in epiphytic calcifiers that could offset carbon sequestration through calcification-induced CO2 release
- Reduced phytoplankton production in and around large macroalgae farms due to competition for nutrients and light
- Ecological and biogeochemical (especially acidification and hypoxia) impacts in the deep sea from sinking large quantities of macroalgae into the deep ocean
- Such effects are likely to be location-specific
- Changes in light and nutrient availability (including possible changes in ocean albedo)
- In near-coastal zones, changes in circulation patterns due to drag by the seaweed could change residence time in nearshore environments
- Changes in coastal residence time may affect the prevalence and intensity of harmful algal blooms (HABs)
- Entanglement of marine megafauna (e.g., whales)
- Job Creation: Seaweed farming could also present new job opportunities for fishers whose work is threatened by climate change{{4}}.
- Value-Added Products: High-value bioproducts (pigments, lipids, proteins, etc) can replace more carbon-intensive alternatives in feed, food, fuel, and other commodities.
- Competition for Space: Competition for space with existing ocean stakeholders – commercial shipping, commercial fishing, indigenous rights, marine protected areas, non-seaweed aquaculture, etc.
- Potential for entanglement of macroalgae cultivation equipment with shipping, commercial fishing gear, aquaculture farms etc, particularly if the macroalgae farm is free floating
- Financing: Financing any CDR approach brings with it the risk of creating inequity and decreasing social welfare{{4}}. With macroalgae cultivation, this may be especially applicable to coastal dwelling communities who rely on the ocean for their livelihoods, food, and cultural meaning.
- Proof-of-concept field experiments have not been conducted in open ocean conditions to test growth rates, sequestration potential, and environmental impacts of macroalgal CDR pathways (Accelerate Design and Permitting of Controlled Field Trials)
- Siting analyses are needed to identify optimal nutrient, light, and wave conditions for growth; as well as potential conflicts with other marine industries (such as the NOAA Coastal Aquaculture Siting and Sustainability toolkit) (Develop New Modeling Tools to Support Design and Evaluation)
- A suite of tools and methodologies to estimate productivity, carbon capture, export, and sequestration, including direct and remote sensing approaches{{1}} needs to be built (Develop New Modeling Tools to Support Design and Evaluation, Measure the Scale and Impacts of CDR via Macroalgae Sinking, Develop New In-Water Tools for Autonomous CDR Operations).
- For sinking pathways, the challenges of following the carbon from source (farm) to deposition (seafloor) in energetically active environments (horizontal and vertical currents, turbulent areas, etc.)
- We do not understand enough about the net CDR benefit from a life cycle perspective (Develop New Modeling Tools to Support Design and Evaluation, Accelerate Design and Permitting of Controlled Field Trials, Develop New In-Water Tools for Autonomous CDR Operations, Develop CDR Monitoring and Verification Protocols)
- Challenges exist verifying additional CO2 uptake from the atmosphere to the ocean in a dynamic background as a result of macroalgae cultivation and sequestration CDR pathways (Develop New Modeling Tools to Support Design and Evaluation, Accelerate Design and Permitting of Controlled Field Trials, Develop New In-Water Tools for Autonomous CDR Operations)
- Inclusion of various macroalgal CDR into integrated assessment models to simulate and predict complex, global responses to macroalgal CDR. Examples include changes in CO2 fluxes in other ecosystems via teleconnections (connections in Earth processes and non-continuous geographic regions, which are often caused by processes not immediately apparent from first principles), and to estimate permanence via the various macroalgal CDR pathways (Develop New Modeling Tools to Support Design and Evaluation)
- Increased knowledge base regarding the physiology (including heat tolerance) and genomics of a broader array of potential cultivars – beyond the ten most common - to understand their growth and carbon sequestration potential is needed (Develop New Modeling Tools to Support Design and Evaluation, Accelerate Design and Permitting of Controlled Field Trials)
- Better understanding of how large-scale macroalgae cultivation affects the partitioning of carbon between particulate and dissolved phases, and its implications for CDR (Develop New Modeling Tools to Support Design and Evaluation, Accelerate Design and Permitting of Controlled Field Trials)
- Advances are needed in offshore mooring design, as well as viable, durable, and cost-effective farming systems for offshore cultivation technology{{1}} (Develop New In-Water Tools for Autonomous CDR Operations)
- Current observational technologies (sensors, ROVs, AUVs, etc.) and modeling tools are not widespread or easily available to support field trials with the necessary spatial and temporal frequency of monitoring and sampling (Develop New In-Water Tools for Autonomous CDR Operations)
- Technologies to accelerate macroalgal sinking are not well explored or understood (Accelerate Design and Permitting of Controlled Field Trials, Develop New In-Water Tools for Autonomous CDR Operations)
- Wave-powered devices (both for electrical power and upwelling) are in their infancy (Develop New In-Water Tools for Autonomous CDR Operations)
- Upwelling systems must be designed and tested to access deeper water nutrients and keep them in the euphotic zone where they can support macroalgal growth (as opposed to immediately sinking out of the euphotic zone)
- Harvesting and processing technologies that minimize environmental impact and energy use are needed (Develop New In-Water Tools for Autonomous CDR Operations)
- More efficient means of drying the harvested crop (for non-sinking pathways)
- Technologies to scale shore-based hatcheries to produce more juvenile kelp ready for outplanting are needed (Develop New In-Water Tools for Autonomous CDR Operations)
- Training, skills development, and technology transfers are needed globally to expand available workforce for macroalgal cultivation and sequestration (Accelerate RD&D Through New Partnerships, Broaden Funding Base for RD&D, Growing & Maintaining Public Support)
- Stable, increased research and development funding to build capacity in this sector, such as has been seen with the ARPA-E MARINER program in the US (Broaden Funding Base for RD&D)
- Certification standards for macroalgal carbon sequestration are needed to support developing markets for macroalgae CO2 sequestration (Develop CDR Monitoring and Verification Protocols)
- Scalable business models and markets to support demand for the multitude of potential products that can be derived from macroalgae (nutritional supplements, high value food items, additives, biochar, bioenergy, etc.) are needed to support this industry (Accelerate RD&D Through New Partnerships, Broaden Funding Base for RD&D, Growing & Maintaining Public Support)
Many of the obstacles and needs around building and maintaining public support are not specific to macroalgal cultivation and sequestration, but there are a few points of interest specific to macroalgal cultivation pathways (Growing & Maintaining Public Support):
- Industrial-scale farms could have a negative public connotation (e.g. corn fields/monoculture in the ocean)
- If genetically modified macroalgae were to be used to increase cultivation yields and sequestration potential, especially in the context of industrial-scale macroalgae farms, that might be perceived negatively by the public given public views on genetically modified organisms
- Public perceptions of sinking macroalgal may differ from perceptions about conversion of cultivated macroalgae into high value bio products
High-resolution data-assimilative models are needed to support real-world testing of macroalgal CDR pathways. These modeling tools must:
- Account for complex interactions in the vicinity of the farm and downstream impacts{{1}}{{2}}
- Provide four-dimensional (space and time) estimates of biogeochemistry in zone of influence both in the presence and absence of macroalgae cultivation. The difference between these two simulations can be used to inform CDR estimates that account for background variability in the ocean.
- CDR estimates from macroalgae must include estimates of the “opportunity cost” of macroalgal carbon sequestration (how much production and export would have occurred in natural phytoplankton communities in the absence of a macroalgal farm?) as well as any enhancements to marine ecosystem productivity due to the presence of a macroalgal farm (is phytoplankton production enhanced above background levels due to the presence of macroalgae farms?).
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 macroalgae cultivation, 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.
Proof-of-concept field trials are urgently needed to test both cultivation and sequestration technologies, as well as the full array of impacts. Field trials are needed to test predictions regarding:
- Cultivation yields and their dependence on species, ocean basin, nutrient availability, and farm design among others
- Performance of deep-water moorings
- Impacts to pelagic marine ecosystems
- Performance of harvesting technologies
- Additional CO2 uptake from the atmosphere into the macroalgae
Specific field experiments around the impacts of sinking seaweed in the deep ocean are urgently needed. Given the extensive amount of macroalgae cultivated and harvested in the coastal zone, we have more advanced knowledge of the scale impacts of natural accretion into sediments. We now need a global research effort around the fate and impacts of sinking seaweed in the deep ocean. To advance this agenda we need to convene scientists, engineers, seaweed farmers, and more to:
- Identify existing deep-sea observatories, facilities, and vehicles to accelerate research on the fate of macroalgal carbon intentionally sunk in the deep ocean
- Develop a standardized list of biological indicators to measure during field trials to facilitate intercomparison between field trials
- Collaborate with existing farms to conduct field trials. This may be especially important for offshore farms that may be more representative of the open ocean conditions necessary to scale cultivation to achieve globally relevant CDR.
- Evaluate the potential to conduct sinking trials with portions of the supply of floating Sargassum patches to evaluate CDR and environmental impacts of sinking. Globally, there are ~10 gigatons of carbon in these Sargassum patches{{1}}, much of which is otherwise destined to end up on beaches, where it may become an environmental nuisance and will decompose, returning its carbon to the atmosphere. This may also serve as a way of generating public support for macroalgae CDR given the considerable social, economic, and environmental issues caused by Sargassum patches.
- Review oceanographic data from past cruises, coastal observing systems, and buoy data to acquire needed physical, chemical, and biological information to assess site potential for field experiments.
- Data from pilot studies investigating the effects of kelp on local mitigation of ocean acidification (e.g., in the state of Washington, USA) may also provide useful information on macroalgae growth rates/carbon sequestration rates, as well as environmental co-benefits and risks.
A new suite of durable, seagoing technologies are needed to support macroalgae CDR 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] => 2023-08-08 16:33:38 [post_modified_gmt] => 2023-08-08 16:33:38 [post_content_filtered] => [post_parent] => 549 [guid] => https://oceanvisions.org/roadmaps/macroalgae-cultivation-carbon-sequestration/first-order%e2%80%a8-priorities/develop-new-in-water-tools-for-autonomous-cdr-operations/ [menu_order] => 3 [post_type] => page [post_mime_type] => [comment_count] => 0 [filter] => raw )Standardized methodologies from third parties to verify uptake of atmospheric CO2 resulting from macroalgae carbon sequestration will ultimately need to be developed to enable trading of carbon removal credits. Key first steps to support development of these protocols include:
[post_title] => Develop CDR Monitoring and Verification Protocols [post_excerpt] => [post_status] => publish [comment_status] => closed [ping_status] => closed [post_password] => [post_name] => develop-cdr-monitoring-and-verification-protocols [to_ping] => [pinged] => [post_modified] => 2023-08-02 14:41:35 [post_modified_gmt] => 2023-08-02 14:41:35 [post_content_filtered] => [post_parent] => 549 [guid] => https://oceanvisions.org/roadmaps/macroalgae-cultivation-carbon-sequestration/first-order%e2%80%a8-priorities/develop-cdr-monitoring-and-verification-protocols/ [menu_order] => 4 [post_type] => page [post_mime_type] => [comment_count] => 0 [filter] => raw )Research, development, and demonstration of macrolgae CDR may be accelerated and strengthened by creating partnerships with key industries/sectors, including:
- Integrated multi-trophic aquaculture{{1}}: Integration with finfish and shellfish to leverage cost savings with operations and achieve permaculture-style benefits (macroalgae can take up waste products generated by fish; fish can feed on macroalgae, the increase in pH from the presence of algae can also be beneficial for shellfish whose growth is already threatened by ocean acidification).
- Offshore wind farms are often viewed as “dead space” for other marine spatial uses, but could provide power sources and platforms for macroalgal farms
- Microalgae companies to adopt best practices for shore-based nursery facilities, such as nutrient and light needs to optimize growth and facility design(s) that maximize growth potential and minimize cost.
Developing and strengthening relationships with partner industries may also help promote 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] => 2023-08-02 14:41:52 [post_modified_gmt] => 2023-08-02 14:41:52 [post_content_filtered] => [post_parent] => 549 [guid] => https://oceanvisions.org/roadmaps/macroalgae-cultivation-carbon-sequestration/first-order%e2%80%a8-priorities/accelerate-rdd-through-new-partnerships/ [menu_order] => 5 [post_type] => page [post_mime_type] => [comment_count] => 0 [filter] => raw )Injection of significant funding is critical to move forward needed RD&D projects for CDR generally, for ocean-based CDR, and for macroalgae CDR specifically. In addition to national and subnational governmental support that is vitally needed and has been outlined in the Expanding Finance and Investment road map, additional stakeholders that need to be engaged include:
[post_title] => Broaden Funding Base for RD&D [post_excerpt] => [post_status] => publish [comment_status] => closed [ping_status] => closed [post_password] => [post_name] => broaden-funding-base-for-rdd [to_ping] => [pinged] => [post_modified] => 2023-08-02 14:42:17 [post_modified_gmt] => 2023-08-02 14:42:17 [post_content_filtered] => [post_parent] => 549 [guid] => https://oceanvisions.org/roadmaps/macroalgae-cultivation-carbon-sequestration/first-order%e2%80%a8-priorities/broaden-funding-base-for-rdd/ [menu_order] => 6 [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, but there are some specific elements that can be emphasized to cultivate public support around macroalgae-based CDR:
These include:
- The perceived advantage of nature-based approaches for macroalgae pathways{{1}}
- Identification and quantification of the co-benefits associated with macroalgae cultivation
- Inclusion of coastal blue carbon ecosystems as part of a campaign to build broad public support for macroalgae.
Macroalgae Cultivation and Carbon Sequestration
Cultivating seaweed to capture and sequester CO2