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-Scenarios for OMA to remove anthropomorphic CO 2 .
Source publication
Ocean Afforestation, more precisely Ocean Macroalgal Afforestation (OMA), has the potential to reduce atmospheric carbon dioxide concentrations through expanding natural populations of macroalgae, which absorb carbon dioxide, then are harvested to produce biomethane and biocarbon dioxide via anaerobic digestion. The plant nutrients remaining after...
Contexts in source publication
Context 1
... extensive analysis of harvest production data for many macroalgae from around the world ( Gao et al., 1991;Chung et al., 2011;Oilgae, 2011;Roesijadi et al., 2008Roesijadi et al., , 2010Bruton et al., 2009;Lenstra et al., 2011; and references therein) indicates a conservative harvestable projection of about 18 ash-free tons per hectare per year, pro- viding sufficient nutrients are available. Note that Table 28 of Chynoweth (2002) reports yields of 11-50 ash-free t/ha/yr are reasonable. More examination of the validity of 18 ash-free t/ha/yr is included in the online supplementary information, "OMA Discussion of Macroalgae Production and Density." ...
Context 2
... online supplementary information "OMA Process Concepts" presents a conceptual outline of the process designs and many of the numbers used in the LCA, which are summa- rized in Table 1. Table 2 presents a scenario to attain a 2035 objective of net zero carbon emissions. The U.S. Energy Information Administration presents current projections as 600 quadrillion Btu/yr (176 million GWh/yr) global fossil fuel use by 2035, pro- ducing 43 metric tons of CO 2 . ...
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Citations
... They generally require an attachment point and therefore commonly grow naturally in shallow coastal waters particularly of rocky shores, with free floating Sargassum fluitans and natans being two noteworthy exceptions. Farming of macroalgae has been proposed as mCDR approach via farming along floating structures providing attachment points, in the coastal and even open ocean, sometimes called ocean afforestation (N'Yeurt et al., 2012). By now several initiatives are exploring macroalgae cultivation and sinking. ...
The Paris Agreement to limit global warming to well below 2°C requires drastic reductions in greenhouse gas emissions and the balancing of any remaining emissions by carbon dioxide removal (CDR). Due to uncertainties about the potential and durability of many land-based approaches to deliver sufficient CDR, marine CDR options are receiving more and more interest. We present the current state of knowledge regarding the potentials, risks, side effects as well as challenges associated with technical feasibility, governance, monitoring, reporting and accounting of marine CDR, covering a range of biotic and geochemical approaches. We specifically discuss to what extent a comparison with direct injection of CO 2 into seawater, which had been proposed decades ago and is now prohibited by international agreements, may provide guidance for evaluating some of the biotic marine CDR approaches.
... At the large scale, seaweed aquaculture may alter the environment by providing climate regulation services and other ES related to nutrient cycling and sequestration, thus producing both positive and negative impacts on natural communities and ecosystem functioning at a global scale that are often difficult to predict (Campbell et al. 2019). In fact, given their high growth and carbon uptake rates, there is a current growing interest in seaweed aquaculture as a way to reach carbon net zero (Hughes et al. 2012;N'Yeurt et al. 2012;Laurens et al. 2020;Hurd et al. 2022;Ould and Caldwell 2022). Due to the complexity of the topic (e.g., Hurd et al. 2022, Gallagher et al. 2022, Troell et al. 2022, Paine et al. 2023) and many unknowns surrounding the potential environmental impacts, it is still questionable whether it will be feasible and successful at the scales necessary to reduce carbon emissions. ...
... Due to the complexity of the topic (e.g., Hurd et al. 2022, Gallagher et al. 2022, Troell et al. 2022, Paine et al. 2023) and many unknowns surrounding the potential environmental impacts, it is still questionable whether it will be feasible and successful at the scales necessary to reduce carbon emissions. Initial estimates suggest that it would be necessary to cover 9% (N'Yeurt et al. 2012) or even more (Hurd et al. 2022) of global oceans with seaweed farms to significantly reduce CO 2 emissions, accompanied by sinking the biomass in the deep ocean, which would require massive increases in investment and technology and could lead to major conflicts of interest regarding marine spatial planning. Moreover, it opens up the question -why discard a resource that can be used for food, feed, biostimulants and biomaterials? ...
The potential of seaweed as a renewable resource is becoming increasingly recognized by diverse
stakeholders in Europe. Currently, several initiatives are working on accelerating the development
of the European algae industry. Seaweed cultivation can be an important cornerstone in
developing EU aquaculture and achieving the European Green Deal. An expert working group
was selected and established in February 2021 by the European knowledge brokering mechanism
Eklipse. This group was tasked to explore and map the current state of knowledge regarding
ecosystem services (ES) provided by seaweed cultivation, including knowledge gaps, constraints,
potential negative impacts and tradeoffs. The study was based on the Delphi process and a Quick
Scoping Review (QSR). The results of each method showed differences in constraints, negative
impacts and knowledge gaps, revealing the need for better communication and collaboration
between the involved stakeholders. Both methods identified the following six ES provided by
seaweed cultivation: (i) provisioning food, (ii) provisioning hydrocolloids and feed, (iii) regulating
water quality, (iv) provisioning habitats, (v) provisioning of nurseries and (vi) regulating climate.
Nevertheless, the specific ES identified differed between seaweed taxa. In addition, both methods
highlighted also potential negative environmental impacts (e.g., wider ecosystem effects),
technological constraints and knowledge gaps (e.g., production). The identified knowledge gaps
and constraints were further discussed and prioritized with stakeholders in a workshop in Brussels.
This workshop identified the structural research needs for future investigations, including: improved
knowledge of environmental impacts; better management of genetic diversity and clear definitions
of legal frameworks to support the development of the EU initiative on seaweed sustainable use.
This paper summarizes the findings of the investigations of the expert group and future challenges
for seaweed cultivation under current and near-future climatic scenarios.
... So, macroalgal aquaculture shows a remarkable role in carbon storage although the present distribution of marine farms covers only sheltered bays located in coastal areas. However, the marine areas cultivated with seaweed farmings is just 1.600 Km 2 , as 0.004% of the whole marine areas covered by wild populations [35,36]. It has been valued that about 48 million Km 2 could be suitable for the cultivation of macroalgae [37] while only 0.01% of the whole ocean surface is used for marine farms, all located in coastal seawaters [34]. ...
... Amongst them, Oceans 2050 (https://www.oceans2050. com) has recently launched a novel planning to value the amount of CO 2 stored in twenty-three farming seaweeds widespread in ocean waters, suggesting, also, some actions to promote seaweed aquaculture for climate restoration [36]. In conclusion, wild and farming seaweeds could be a potential solution to reduce the atmospheric concentration of CO 2 , but further studies are necessary to fully understand the nutrient reallocation, the real quantification of carbon sequestration by natural and farming seaweeds and the potential of cost-effective infrastructures for ocean afforestation. ...
Global warming is the result of an increasing trend in the concentration of Green House Gases, especially of carbon dioxide, in the terrestrial atmosphere. To date, there is a great interest by science and policy in the potential of marine vegetation, as a carbon sink, to remove part of the organic carbon soluted in ocean waters. This important role could be realized by wild and farming seaweed that could sequester, altogether, large amounts of carbon dioxide in ocean sediments, within a blue carbon strategy. Amongst vegetated coastal ecosystems, the meadows of marine phanerogams, tidal salt marshes and mangroves are hot spots for carbon storage. Side by side, seaweed farming is increasing worldwide and represents an important storage of organic carbon buried in coastal sediments. So, ocean afforestation could be a viable pathway for the mitigation of climate changes. However, there are some constraints that must be solved to extend farming seaweed in the deep ocean. In conclusions, wild and farming seaweeds are a potential solution to reduce the concentration of carbon dioxide in the terrestrial atmosphere but further studies are necessary to quantify the amount of carbon sequestration stored, from wild and farming seaweeds, in deep ocean sediments.
... The former relies on hitherto unproved technology for growing seaweed in the deep ocean and also would require a considerable amount of the global ocean surface (approximately 1%-3% to achieve the range of potential carbon sequestration in Figure 3), with all the associated risks and trade-offs. This area is only one-tenth of the 9%-33% of the global ocean coverage proposed by the source papers (de Ramon N'Yeurt et al., 2012;Lehahn et al., 2016), with carbon sequestration scaled accordingly, but is still, in our opinion, pushing the limits of what might be feasible, environmentally sound, or socially acceptable (noting that publication of a negative emissions "solution" in the peerreviewed literature does not mean that it is safe, feasible, or even worth pursuing; e.g., Johnson et al., 2008). Nonetheless, as with coastal macroalgal aquaculture, this open ocean approach at some scale could potentially provide a relatively safe and low risk, measurable carbon sequestration and is therefore likely to be a subject of increasing study and commercial development in the coming years. ...
... A governance and evaluation framework would be necessary, which would evaluate continually the social and environmental impacts and ensure net benefits, while prioritizing research and upscaling activities for the most promising selection of potential technologies (e.g., Bellamy, 2018). Furthermore, as with other aspects of climate policy and management, full and proper engagement with the public would be an essential part of ensuring a just and democratic utilization of globally shared environmental resources (e.g., Bellamy, 2018;Nemet et al., 2018;Cox et al., 2021;Cooley et al., 2023) and to prevent vested interests in powerful economies from benefiting disproportionately (e.g., Dunlap and Fairhead, 2014). Such a governance effort cannot be achieved without extensive investment at all levels in the knowledge exchange, brokerage, and management necessary to facilitate it (e.g., Johnson et al., 2020). ...
In this Policy Bridge, we present the key issues regarding the safety, efficacy, funding, and governance of coastal and marine systems in support of climate change mitigation. Novel insights into the likely potential of these systems for use in mitigating excess carbon dioxide emissions are presented. There may be potential for coastal blue carbon and marine carbon dioxide removal (mCDR) actions to impact climate change mitigation significantly over the rest of the 21st century, particularly post 2050. However, governance frameworks are needed urgently to ensure that the potential contribution from coastal and ocean systems to climate change mitigation can be evaluated properly and implemented safely. Ongoing research and monitoring efforts are essential to ensure that unforeseen side effects are identified and corrective action is taken. The co-creation of governance frameworks between academia, the private sector, and policymakers will be fundamental to the safe implementation of mCDR in the future. Furthermore, a radical acceleration in the pace of development of mCDR governance is needed immediately if it is to contribute significantly to the removal of excess carbon dioxide emissions by the latter half of this century. To what extent large-scale climate interventions should be pursued is a decision for policymakers and wider society, but adaptive legal, economic, policy, research, and monitoring frameworks are needed urgently to facilitate informed decision-making around any implementation of mCDR in the coming decades. Coastal and ocean systems cannot be relied upon to deliver significant carbon dioxide removal until further knowledge of specific management options is acquired and evaluated.
... Ocean Macroalgal Afforestation (OMA), or the process of cultivating macroalgae in the ocean, offers the potential to decrease atmospheric carbon dioxide levels by increasing the natural growth of macroalgae. These macroalgae naturally absorb carbon dioxide, and they can be harvested for the production of biomethane and biocarbon dioxide using anaerobic digestion (N'Yeurt et al., 2012;Capron et al., 2020). Seaweed has a remarkable capacity to absorb carbon dioxide (CO2) from the atmosphere through photosynthesis, making it a powerful tool for carbon sequestration (Duarte et al., 2017;Krause-Jensen et al., 2018). ...
As global demand for sustainable biomass and need to mitigate global warming begin to rise, cultivation of seaweed has gained significant attention in recent years due to its potential for carbon recycling. However, limited availability of suitable coastal areas for large-scale seaweed cultivation has led to exploration of offshore environments as a viable alternative. The nature of many offshore environments often exposes seaweed farming systems to harsh environmental conditions, including strong waves, currents, and wind. These factors can lead to structural failures, kelp losses, and significant financial losses for seaweed farmers. The main objective of this study is to present a robust design and numerical analysis of an economically viable floating offshore kelp farm facility, and evaluate its stability and mooring system performance. A numerical method of preliminary designs of the offshore aquaculture systems were developed using the OrcaFlex software. The models were subjected to a series of dynamic environmental loading scenarios representing extreme events. These simulations aimed to forecast the overall dynamic response of an offshore kelp farm at a depth of 50m and to determine the best possible farm design with structural integrity for a selected offshore environment. Furthermore, to assess the economic feasibility of establishing offshore seaweed farms, a comprehensive capital expenses analysis was conducted. The results revealed that, in terms of the kelp farms with the same number of the kelp cultivating lines, the cost of building kelp farms will be strongly affected by the cost of mooring lines. The present study may help to understand the dynamic response and economic feasibility of offshore kelp farms. KEYWORDS offshore, mooring systems, kelp cultivation, seaweed farm, dynamical response analysis, economic analysis, capital expenses analysis of offshore seaweed farms Frontiers in Marine Science SC (2024) Engineering design and economic analysis of offshore seaweed farm.
... Ocean Macroalgal Afforestation (OMA), or the process of cultivating macroalgae in the ocean, offers the potential to decrease atmospheric carbon dioxide levels by increasing the natural growth of macroalgae. These macroalgae naturally absorb carbon dioxide, and they can be harvested for the production of biomethane and biocarbon dioxide using anaerobic digestion (N'Yeurt et al., 2012;Capron et al., 2020). Seaweed has a remarkable capacity to absorb carbon dioxide (CO2) from the atmosphere through photosynthesis, making it a powerful tool for carbon sequestration (Duarte et al., 2017;Krause-Jensen et al., 2018). ...
As global demand for sustainable biomass and need to mitigate global warming begin to rise, cultivation of seaweed has gained significant attention in recent years due to its potential for carbon recycling. However, limited availability of suitable coastal areas for large-scale seaweed cultivation has led to exploration of offshore environments as a viable alternative. The nature of many offshore environments often exposes seaweed farming systems to harsh environmental conditions, including strong waves, currents, and wind. These factors can lead to structural failures, kelp losses, and significant financial losses for seaweed farmers. The main objective of this study is to present a robust design and numerical analysis of an economically viable floating offshore kelp farm facility, and evaluate its stability and mooring system performance. A numerical method of preliminary designs of the offshore aquaculture systems were developed using the OrcaFlex software. The models were subjected to a series of dynamic environmental loading scenarios representing extreme events. These simulations aimed to forecast the overall dynamic response of an offshore kelp farm at a depth of 50m and to determine the best possible farm design with structural integrity for a selected offshore environment. Furthermore, to assess the economic feasibility of establishing offshore seaweed farms, a comprehensive capital expenses analysis was conducted. The results revealed that, in terms of the kelp farms with the same number of the kelp cultivating lines, the cost of building kelp farms will be strongly affected by the cost of mooring lines. The present study may help to understand the dynamic response and economic feasibility of offshore kelp farms.
... Macroalgae (seaweed) cultivation is receiving growing attention as a potential carbon dioxide removal (CDR) strategy to mitigate climate change (Duarte et al., 2017;Gattuso et al., 2021;National Academies of Sciences, E. and Medicine, 2022;de Ramon N'Yeurt et al., 2012). The motivation behind this strategy stems from the high rate of primary production and biomass accumulation of seaweed (Duarte and Cebriań, 1996;Schiel and Foster, 2015;Duarte et al., 2017;Smale et al., 2020), the immense size of the ocean, the buffering capacity of seawater, and the durability of the ocean as carbon storage (Gruber et al., 2019;Siegel et al., 2021). ...
Macroalgae cultivation is receiving growing attention as a potential carbon dioxide removal (CDR) strategy. Macroalgae biomass harvesting and/or intentional sinking have been the main focus of research efforts. A significant amount of biomass is naturally lost through erosion and breakage of cultivated or naturally growing seaweed, but the contribution of the resulting particulates to carbon sequestration is relatively unexplored. Here, we use a fully coupled kelp-biogeochemistry model forced by idealized parameters in a closed system to estimate the potential of macroalgal-derived particulate organic carbon (POC) sinking as a CDR pathway. Our model indicates that at a kelp density of 1.1 fronds m⁻³, macroalgal POC sinking can export 7.4 times more carbon to the deep sea (depths > 500m) and remove 5.2 times more carbon from the atmosphere (equivalent to an additional 336.0 gC m⁻² yr⁻¹) compared to the natural biological pump without kelp in our idealized closed system. The results suggest that CDR associated with POC sinking should be explored as a possible benefit of seaweed farming and point to the need for further study on organic carbon partitioning and its bioavailability to quantify the effectiveness and impacts of macroalgal cultivation as a CDR strategy.
... Although not all countries have reported the area under seaweed cultivation, the global areal extent is likely to be under 4000 km 2 , as China, Indonesia and Korea (i.e. 90 % of the world's production) report a cultivated area of 3680 km 2 ( Table 5). Estimates of the total area potentially farmable range from 100,000 to 48,000,000 km 2 globally Froehlich et al., 2019;Lehahn et al., 2016;N'Yeurt et al., 2012;Wu et al., 2023), being mostly offshore or in open ocean waters. These estimates, however, rarely consider growth limitation by micronutrients (e.g., iron, Paine et al., 2023), nor the economic costs or the logistical and technical feasibility of farming in open waters (Coleman et al., 2022;DeAngelo et al., 2022), and should therefore be considered as overestimates of the actual realizable potential. ...
... Once it ends up in deep ocean currents or seafloor sediments hundreds of meters below the surface, the carbon is prevented from being exchanged with the atmosphere over several hundred to several thousand years (Volk and Hoffert, 2013). Traditionally, seagrasses and mangroves have been considered the dominant form of oceanic carbon sequestration (Duarte and Cebriá n, 1996); however, in recent years researchers have been looking at seaweeds like Sargassum's role as important carbon sinks (N'Yeurt et al., 2012;Raven, 2017;Kokubu et al., 2019). ...
The North Atlantic Ocean features high seasonal productivity of the brown seaweed Sargassum, which floats on the ocean surface and accumulates in large numbers in the Sargasso Sea. Sargassum blooms can stretch from the west coast of Africa to the Gulf of Mexico, and have created the largest seaweed blooms ever observed. Sargassum blooms have increased in intensity in recent years, and can negatively impact coastal communities when they wash up onshore in large quantities and decay. While seaweed sinking from surface waters to the seafloor may be an important carbon sink by removing carbon from the atmosphere, the magnitude of carbon sequestration by Sargassum and other macroalgae remains poorly understood. Given the magnitude of Sargassum blooms in the North Atlantic, they may pose a significant mechanism for carbon sequestration in the deep sea, though direct observations are rare. In this study, we documented the presence and distribution of Sargassum seaweed on the seafloor using video from ten remotely operated vehicle dives conducted on NOAA Ship Okeanos Explorer. Locations included sites in the Gulf of Mexico, in the Caribbean Sea, and off the Southeastern United States. Sargassum was observed in numbers ranging from 0 to over 112 per dive, and a frequency of between 0-11.23 observations for every 100 meters of horizontal distance. These observations suggest that Sargassum does make its way to the deep sea in potentially significant amounts. Natural systems like Sargassum sinking could serve as natural laboratories for understanding and managing seaweed burial as a climate mitigation strategy. Long-term monitoring of the fate of sunken Sargassum on the seabed is needed in order to determine how much is ultimately sequestered rather than recycled back into the system. Such observations would inform the feasibility of Sargassum farming and/or facilitated sinking as potential carbon dioxide removal strategies.
... They are being considered as a biological method of CDR and for eventual use in carbon trading as carbon removal offsets (Coleman et al., 2022;Cooley et al., 2022;Ross et al., 2023;Vanderklift et al., 2022;Figures S1-S7 in the Supporting Information): Indeed, some companies and NGOs are already selling seaweed carbon as offsets on the voluntary carbon market ( Figures S2-S4). Ongoing projects include enhancing the scale of natural seaweed beds by restoring those that have been lost from climate change and local anthropogenic activities , protecting existing seaweed beds (Pessarrodona et al., 2023), and expanding the scale of seaweed aquaculture, including in the open ocean (N'Yeurt et al., 2012;Froehlich et al., 2019). Numerous start-up companies and NGOs are trialing growing seaweeds, particularly kelps (order Laminariales) but also pelagic Sargassum spp. ...
To limit global warming below 2°C by 2100, we must drastically reduce greenhouse gas emissions and additionally remove ~100–900 Gt CO 2 from the atmosphere (carbon dioxide removal, CDR) to compensate for unavoidable emissions. Seaweeds (marine macroalgae) naturally grow in coastal regions worldwide where they are crucial for primary production and carbon cycling. They are being considered as a biological method for CDR and for use in carbon trading schemes as offsets. To use seaweeds in carbon trading schemes requires verification that seaweed photosynthesis that fixes CO 2 into organic carbon results in CDR, along with the safe and secure storage of the carbon removed from the atmosphere for more than 100 years (sequestration). There is much ongoing research into the magnitude of seaweed carbon storage pools (e.g., as living biomass and as particulate and dissolved organic carbon in sediments and the deep ocean), but these pools do not equate to CDR unless the amount of CO 2 removed from the atmosphere as a result of seaweed primary production can be quantified and verified. The draw‐down of atmospheric CO 2 into seawater is via air‐sea CO 2 equilibrium, which operates on time scales of weeks to years depending upon the ecosystem considered. Here, we explain why quantifying air‐sea CO 2 equilibrium and linking this process to seaweed carbon storage pools is the critical step needed to verify CDR by discrete seaweed beds and nearshore and open ocean aquaculture systems prior to their use in carbon trading.
