Potential role of seaweeds in climate change mitigation

Ross, Finnley W.R.; Boyd, Philip W.; Filbee‐Dexter, Karen; Watanabe, Kazuo; Ortega, Alejandra; Lovelock, Catherine E.; Sondak, Calvyn Fredrik Aldus; Bach, Lennart T.; Duarte, Carlos Marmolejo; Serrano, Óscar; Beardall, John; Tarbuck, Patrick; Macreadie, Peter I.

doi:10.1016/j.scitotenv.2023.163699

Cited by 17 publications

(12 citation statements)

References 150 publications

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“…In addition to the natural fluxes of seaweed carbon beyond the continental shelf, there is considerable interest in enhancing these processes by growing seaweeds on artificial structures in the open ocean, termed “ocean (macroalgal) afforestation,” and sinking resulting biomass to the deep ocean (Figure 1b; Arzeno‐Soltero et al., 2023; Ocean Visions and Monterey Bay Aquarium Research Institute, 2022; Ross et al., 2023; Figures S1, S4, S5, S7). As seaweeds sink, a range of processes (as above) will affect their degradation and the amount of biomass that reaches the deep ocean floor (Figure 1b).…”

Section: Seaweed Carbon Storage Poolsmentioning

confidence: 99%

“…Various strategies are being proposed for CDR. Ocean-based CDR includes ocean alkalinity enhancement (Renforth & Henderson, 2017) and increasing the amount of seaweed-derived carbon storage on a global scale via the expansion of aquaculture, including into the open oceans (ocean afforestation; Ross et al, 2023), by restoring seaweed ecosystems that have been lost due to climate change (Smale et al, 2019;Wernberg et al, 2011) and conserving existing seaweed ecosystems (Pessarrodona et al, 2023).…”

Section: Introductionmentioning

confidence: 99%

“…Seaweeds are highly productive primary producers of temperate rocky shores worldwide where they form substantial biomass in natural beds, provide energy to higher trophic levels, and create a habitat for invertebrates and fish (Hurd et al., 2014; Pessarrodona, Assis, et al., 2022; Pessarrodona, Filbee‐Dexter, et al., 2022). 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 (Filbee‐Dexter et al., 2022), 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).…”

Section: Introductionmentioning

confidence: 99%

“…;Arzeno- Soltero et al, 2023; Ocean Visions and Monterey Bay Aquarium Research Institute, 2022;Ross et al, 2023; Figures …”

mentioning

confidence: 99%

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Air‐sea carbon dioxide equilibrium: Will it be possible to use seaweeds for carbon removal offsets?

Hurd,

Gattuso,

Boyd

2023

Journal of Phycology

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To limit global warming below 2°C by 2100, we must drastically reduce greenhouse gas emissions and additionally remove ~100–900 Gt CO2 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 CO2 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 CO2 removed from the atmosphere as a result of seaweed primary production can be quantified and verified. The draw‐down of atmospheric CO2 into seawater is via air‐sea CO2 equilibrium, which operates on time scales of weeks to years depending upon the ecosystem considered. Here, we explain why quantifying air‐sea CO2 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.

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Section: Seaweed Carbon Storage Poolsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

“…;Arzeno- Soltero et al, 2023; Ocean Visions and Monterey Bay Aquarium Research Institute, 2022;Ross et al, 2023; Figures …”

mentioning

confidence: 99%

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Air‐sea carbon dioxide equilibrium: Will it be possible to use seaweeds for carbon removal offsets?

Hurd,

Gattuso,

Boyd

2023

Journal of Phycology

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“…Seaweeds provide numerous advantages, including carbon dioxide remediation, substitution of fossil fuels, reduction of marine eutrophication, and mitigation of ocean acidification. 10,11 Alginate, an unbranched linear polysaccharide, is present in the cell wall and intercellular matrix of various genera of brown seaweed. Alginate consists of two uronic acid monomers, β-Dmannuronic acid (M) and α-L-guluronic acid (G), arranged in three conformations of either homopolymeric (MM, GG) or heteropolymeric (MG) blocks (Figure 1).…”

Section: ■ Introductionmentioning

confidence: 99%

Green Alginate Extraction from Macrocystis pyrifera for Bioplastic Applications: Physicochemical, Environmental Impact, and Chemical Hazard Analyses

Smith,

Cabling,

Leonard

et al. 2024

ACS Sustainable Resour. Manage.

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To scale alginate production for widespread use, a focus on advancing sustainable extraction methods is needed. This study investigates greener extraction methods and their effect on alginate properties to advance sustainable methods suitable for bio-based plastic applications. Three alginate extraction protocols were selected by evaluating the hazard levels to human and environmental health of solvents and reagents used in 23 alginate extraction methods. The three methods were tested on samples of Macrocystis pyrifera algae and evaluated based on the efficiency of extraction, uronic acid composition (M/G ratio), molecular weight, and carbohydrate composition. Finally, the extraction methods were assessed using a partial life cycle assessment, assessing the water, chemical, and energy consumption and respective greenhouse gas emissions. The study found that the choice of extraction protocol significantly influenced the properties of the resulting alginate. Protocols 1 and 2, using operating conditions of high pH and temperature and short alkaline extraction times, produced alginates with a high M/G ratio (1.23 and 1.53, respectively) and comparable molecular weight to commercial alginate, but they had increased energy and water consumption and emissions (987 and 389 kg CO2-eq (CO2 equivalents), respectively) compared to the other protocol evaluated. Protocol 3, using ambient conditions and an alkaline chelating sodium citrate treatment, resulted in alginates with a decreased M/G ratio (0.63), reduced greenhouse gas emissions (177 kg CO2-eq), and high yield (26.7%) but produced alginates with lower molecular weight (59.5 kDa). This research highlights the adaptability of extraction protocols for achieving the desired alginate properties and evaluates the safety and environmental implications of the selected methods.

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Contribution of marine macrophytes to pCO2 and DOC variations in human-impacted coastal waters

Watanabe,

Tokoro,

Moki

et al. 2024

Biogeochemistry

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Carbon cycles in coastal waters are highly sensitive to human activities and play important roles in global carbon budgets. CO2 sink–source behavior is regulated by spatiotemporal variations in net biological productivity, but the contribution of macrophyte habitats including macroalgae aquaculture to atmospheric CO2 removal has not been well quantified. We investigated the variations in the carbonate system and dissolved organic carbon (DOC) in human-impacted macrophyte habitats and analyzed the biogeochemical drivers for the variations of these processes. Cultivated macroalgal metabolism (photosynthesis, respiration, calcification, and DOC release) was quantified by in situ field-bag experiments. Cultivated macroalgae took up dissolved inorganic carbon (DIC) (16.2–439 mmol-C m−2 day−1) and released DOC (1.2–146 mmol-C m−2 day−1). We estimated that seagrass beds and macroalgae farming contributed 0.8 and 0.4 mmol-C m−2 day−1 of the in situ total CO2 removal (5.7 and 6.7 mmol-C m−2 day−1, respectively) during their growing period in a semi-enclosed embayment but efficient water exchange (i.e., short residence time) in an open coastal area precluded detection of the contribution of macrophyte habitats to the CO2 removal. Although hydrological processes, biological metabolism, and organic carbon storage processes would contribute to the net CO2 sink–source behavior, our analyses distinguished the contribution of macrophytes from other factors. Our findings imply that macroalgae farming, in addition to restoring and creating macrophyte habitats, has potential for atmospheric CO2 removal.

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Potential role of seaweeds in climate change mitigation

Cited by 17 publications

References 150 publications

Air‐sea carbon dioxide equilibrium: Will it be possible to use seaweeds for carbon removal offsets?

Air‐sea carbon dioxide equilibrium: Will it be possible to use seaweeds for carbon removal offsets?

Green Alginate Extraction from Macrocystis pyrifera for Bioplastic Applications: Physicochemical, Environmental Impact, and Chemical Hazard Analyses

Contribution of marine macrophytes to pCO2 and DOC variations in human-impacted coastal waters

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