Whales are thought to play a role in the carbon cycle both directly (living biomass and whale falls) and indirectly (the whale pump, the whale conveyor belt, and bioturbation), however the extent of this role remains uncertain^[1]Meynecke J-O, Samanta S, de Bie J, Seyboth E, Prakash Dey S, Fearon G, Vichi M, Findlay K, Roychoudhury A and Mackey B (2023) Do whales really increase the oceanic removal of atmospheric carbon? Front. Mar. Sci. 10:1117409. doi: 10.3389/fmars.2023.1117409 . A 2022 report from The Environmental Defense Fund^[2]Collins, J. R., Boenish, R. E., Fujita, R. M., Rader, D. N., and Moore, L. A. 2022. Natural climate solutions in the open ocean: scientific knowledge and opportunities surrounding four potential pathways for carbon dioxide removal or avoided emissions. Environmental Defense Fund, New York, NY. https://www.edf.org/sites/default/files/2022-10/Natural%20Climate%20Solutions%20in%20the%20Open%20Ocean.pdf  found there to be fewer than 10 scientific studies from which to draw any broad conclusions in this area and cautioned against the creation of a carbon credit system based on whale carbon sequestration. A 2020 study estimates that restoring baleen whale populations to pre-whaling abundances could sequester 0.032 Gt CO2/year, including carbon sequestered from fertilization via whale feces^[3]Durfort, Anaelle, et al. The Collapse and Recovery Potential of Carbon Sequestration by Baleen Whales in the Southern Ocean, 2020, https://doi.org/10.21203/rs.3.rs-92037/v1. . However, rebuilding whale populations is sure to elicit many other environmental and social benefits, explored further on in this road map.

Mechanisms for CDR

Direct Sequestration

• Living Biomass: Due to their size and longevity, whales can store large amounts of carbon for long periods of time in their bodies as biomass. While whaling indeed resulted in a loss of carbon stored in whales, there is not clear evidence to suggest that whaling was a net source of CO2 to the atmosphere^[4]Pearson, Heidi C., et al. “Whales in the Carbon Cycle: Can Recovery Remove Carbon Dioxide?” Trends in Ecology & Evolution, vol. 38, no. 3, 2023, pp. 238–249, https://doi.org/10.1016/j.tree.2022.10.012. .
• Whale Falls: Whale falls, wherein whale carcasses sink to the ocean floor and their carbon-rich biomass is reallocated in various ways, is the “most scientifically comprehensible” of the pathways (direct vs indirect sequestration)^[5]Collins, J. R., Boenish, R. E., Fujita, R. M., Rader, D. N., and Moore, L. A. 2022. Natural climate solutions in the open ocean: scientific knowledge and opportunities surrounding four potential pathways for carbon dioxide removal or avoided emissions. Environmental Defense Fund, New York, NY. https://www.edf.org/sites/default/files/2022-10/Natural%20Climate%20Solutions%20in%20the%20Open%20Ocean.pdf  with a 2010 study estimating that restoration of large baleen whale populations to pre-whaling numbers could sequester 0.0006 Gt CO2e /year.

Indirect Sequestration

• Whale Pump: This is the term often used to describe the role that whales play in cycling nutrients through the ocean via their feces. The whale pump hypothesis sits on two assumptions that have not yet been verified through empirical observations^[6]Collins, J. R., Boenish, R. E., Fujita, R. M., Rader, D. N., and Moore, L. A. 2022. Natural climate solutions in the open ocean: scientific knowledge and opportunities surrounding four potential pathways for carbon dioxide removal or avoided emissions. Environmental Defense Fund, New York, NY. https://www.edf.org/sites/default/files/2022-10/Natural%20Climate%20Solutions%20in%20the%20Open%20Ocean.pdf . The first assumption is around the efficacy of surface water fertilization and subsequent primary production via whale feces. The second assumption concerns the fate of carbon export from primary production.
  • WhaleX Ocean Nourishment synthesizes limiting nutrients (nitrogen, phosphorous, iron, and silica) and disperses them across nutrient poor regions of the ocean, simulating the dispersion of nutrients via whale feces.
• Whale Conveyor Belt: The whale conveyor belt is based on the idea that as whales migrate yearly, they move nutrients around the ocean, potentially increasing iron availability for phytoplankton growth^[7]Roman J, Estes JA, Morissette L, Smith C, Costa D, McCarthy J, Nation JB, Nicol S, Pershing A, Smetacek V. Whales as marine ecosystem engineers. Frontiers in Ecology and the Environment. 2014 Sep;12(7):377-85. .
• Bioturbation: Bioturbation is the process through which whale feeding behaviors stimulate the seabed and resuspend sediments^[8]Meynecke J-O, Samanta S, de Bie J, Seyboth E, Prakash Dey S, Fearon G, Vichi M, Findlay K, Roychoudhury A and Mackey B (2023) Do whales really increase the oceanic removal of atmospheric carbon? Front. Mar. Sci. 10:1117409. doi: 10.3389/fmars.2023.1117409 . Conceptually, this is similar to the whale pump, but the pool of nutrients comes from seafloor sediments instead of whale feces^[9]Nelson, C. H., and Johnson, K. R. (1987). Whales and walruses as tillers of the sea floor. Sci. Am. 256, 112–117. doi: 10.1038/scientificamerican0287-112 ,^[10]Alter, S. E., Rynes, E., and Palumbi, S. R. (2007). DNA Evidence for historic population size and past ecosystem impacts of gray whales. Proc. Natl. Acad. Sci. 104, 15162–15167. doi: 10.1073/pnas.0706056104 .

Rebuilding Whale Populations: Increasing whale populations would likely amplify their role in the carbon cycle, including any sequestration.

• Increasing Krill Abundance:
  • A 2022 article by Savoca^[11]Savoca, Matthew. 2022. “The fall of the great ocean farmers.” The Marine Biologist. ISSN: 2052-5273.  suggests krill as a limiting factor to whale population growth. Savoca points to studies that suggest a close relationship between whales and krill wherein whales provide necessary nutrients for krill to thrive. This is further complicated by competition between krill fisheries and whales in the Southern Ocean.

Reducing Ship Strike: A 2001 study found that in some areas, more than one third of all fin whale and right whale strandings involve ship strike. This can especially impact small populations of whales such as the northern right whale in the western North Atlantic^[12]Laist, David W., et al. “Collisions between Ships and Whales.” Marine Mammal Science, vol. 17, no. 1, 2001, pp. 35–75, https://doi.org/10.1111/j.1748-7692.2001.tb00980.x. . Measures that require large, motorized vessels to slow their speeds in particularly vulnerable areas may be beneficial to whale populations.

CDR Potential

Estimated Sequestration Potential:  0.032 Gt CO2e /year, including carbon sequestered from fertilization^[13]Durfort, A., G. Mariani, M. Troussellier, V. Tulloch, and D. Mouillot. 2021. “The Collapse and Recovery Potential of Carbon Sequestration by Baleen Whales in the Southern Ocean.” Preprint. doi.org/10.21203/rs.3.rs-92037/v1.  

Sequestration Durability: 10 – 100 years^[14]Cross, J.N., Sweeney, C., Jewett, E.B., Feely, R.A., McElhany, P., Carter, B., Stein, T., Kitch, G.D., and Gledhill, D.K., 2023. Strategy for NOAA Carbon Dioxide Removal Research: A white paper documenting a potential NOAA CDR Science Strategy as an element of NOAA’s Climate Interventions Portfolio. NOAA Special Report. NOAA, Washington DC. DOI: 10.25923/gzke-8730  

Challenges

• Difficult to find and track outcomes from whale fertilization events (e.g., feces)
• Tracking the fate of carbon through the water column

Key Knowledge Gaps

Adapted from Pearson et al. 2022

• How effective are whales at creating and maintaining primary production hotspots that lead to enhanced carbon sequestration?
• How bioavailable are whale-derived nutrients?
• What is the carbon flux from cetaceans to the atmosphere?

First-Order Priorities

*Adapted from Pearson et al. 2022

• Investigate primary production hot spots from whales via determination of fecal nutrients to carbon recycling versus export*
• Conduct additional field and laboratory studies to ascertain the bioavailability of krill-derived iron in whale feces*
• Measure the carbon flux from cetaceans to the atmosphere via respiration to understand cetaceans’ net capacity for CO2 removal*

Whales are thought to play a role in the carbon cycle both directly (living biomass and whale falls) and indirectly (the whale pump, the whale conveyor belt, and bioturbation), however the extent of this role remains uncertain^[1]Meynecke J-O, Samanta S, de Bie J, Seyboth E, Prakash Dey S, Fearon G, Vichi M, Findlay K, Roychoudhury A and Mackey B (2023) Do whales really increase the oceanic removal of atmospheric carbon? Front. Mar. Sci. 10:1117409. doi: 10.3389/fmars.2023.1117409 . A 2022 report from The Environmental Defense Fund^[2]Collins, J. R., Boenish, R. E., Fujita, R. M., Rader, D. N., and Moore, L. A. 2022. Natural climate solutions in the open ocean: scientific knowledge and opportunities surrounding four potential pathways for carbon dioxide removal or avoided emissions. Environmental Defense Fund, New York, NY. https://www.edf.org/sites/default/files/2022-10/Natural%20Climate%20Solutions%20in%20the%20Open%20Ocean.pdf  found there to be fewer than 10 scientific studies from which to draw any broad conclusions in this area and cautioned against the creation of a carbon credit system based on whale carbon sequestration. A 2020 study estimates that restoring baleen whale populations to pre-whaling abundances could sequester 0.032 Gt CO2/year, including carbon sequestered from fertilization via whale feces^[3]Durfort, Anaelle, et al. The Collapse and Recovery Potential of Carbon Sequestration by Baleen Whales in the Southern Ocean, 2020, https://doi.org/10.21203/rs.3.rs-92037/v1. . However, rebuilding whale populations is sure to elicit many other environmental and social benefits, explored further on in this road map.

Mechanisms for CDR

Direct Sequestration

• Living Biomass: Due to their size and longevity, whales can store large amounts of carbon for long periods of time in their bodies as biomass. While whaling indeed resulted in a loss of carbon stored in whales, there is not clear evidence to suggest that whaling was a net source of CO2 to the atmosphere^[4]Pearson, Heidi C., et al. “Whales in the Carbon Cycle: Can Recovery Remove Carbon Dioxide?” Trends in Ecology & Evolution, vol. 38, no. 3, 2023, pp. 238–249, https://doi.org/10.1016/j.tree.2022.10.012. .
• Whale Falls: Whale falls, wherein whale carcasses sink to the ocean floor and their carbon-rich biomass is reallocated in various ways, is the “most scientifically comprehensible” of the pathways (direct vs indirect sequestration)^[5]Collins, J. R., Boenish, R. E., Fujita, R. M., Rader, D. N., and Moore, L. A. 2022. Natural climate solutions in the open ocean: scientific knowledge and opportunities surrounding four potential pathways for carbon dioxide removal or avoided emissions. Environmental Defense Fund, New York, NY. https://www.edf.org/sites/default/files/2022-10/Natural%20Climate%20Solutions%20in%20the%20Open%20Ocean.pdf  with a 2010 study estimating that restoration of large baleen whale populations to pre-whaling numbers could sequester 0.0006 Gt CO2e /year.

Indirect Sequestration

• Whale Pump: This is the term often used to describe the role that whales play in cycling nutrients through the ocean via their feces. The whale pump hypothesis sits on two assumptions that have not yet been verified through empirical observations^[6]Collins, J. R., Boenish, R. E., Fujita, R. M., Rader, D. N., and Moore, L. A. 2022. Natural climate solutions in the open ocean: scientific knowledge and opportunities surrounding four potential pathways for carbon dioxide removal or avoided emissions. Environmental Defense Fund, New York, NY. https://www.edf.org/sites/default/files/2022-10/Natural%20Climate%20Solutions%20in%20the%20Open%20Ocean.pdf . The first assumption is around the efficacy of surface water fertilization and subsequent primary production via whale feces. The second assumption concerns the fate of carbon export from primary production.
  • WhaleX Ocean Nourishment synthesizes limiting nutrients (nitrogen, phosphorous, iron, and silica) and disperses them across nutrient poor regions of the ocean, simulating the dispersion of nutrients via whale feces.
• Whale Conveyor Belt: The whale conveyor belt is based on the idea that as whales migrate yearly, they move nutrients around the ocean, potentially increasing iron availability for phytoplankton growth^[7]Roman J, Estes JA, Morissette L, Smith C, Costa D, McCarthy J, Nation JB, Nicol S, Pershing A, Smetacek V. Whales as marine ecosystem engineers. Frontiers in Ecology and the Environment. 2014 Sep;12(7):377-85. .
• Bioturbation: Bioturbation is the process through which whale feeding behaviors stimulate the seabed and resuspend sediments^[8]Meynecke J-O, Samanta S, de Bie J, Seyboth E, Prakash Dey S, Fearon G, Vichi M, Findlay K, Roychoudhury A and Mackey B (2023) Do whales really increase the oceanic removal of atmospheric carbon? Front. Mar. Sci. 10:1117409. doi: 10.3389/fmars.2023.1117409 . Conceptually, this is similar to the whale pump, but the pool of nutrients comes from seafloor sediments instead of whale feces^[9]Nelson, C. H., and Johnson, K. R. (1987). Whales and walruses as tillers of the sea floor. Sci. Am. 256, 112–117. doi: 10.1038/scientificamerican0287-112 ,^[10]Alter, S. E., Rynes, E., and Palumbi, S. R. (2007). DNA Evidence for historic population size and past ecosystem impacts of gray whales. Proc. Natl. Acad. Sci. 104, 15162–15167. doi: 10.1073/pnas.0706056104 .

Rebuilding Whale Populations: Increasing whale populations would likely amplify their role in the carbon cycle, including any sequestration.

• Increasing Krill Abundance:
  • A 2022 article by Savoca^[11]Savoca, Matthew. 2022. “The fall of the great ocean farmers.” The Marine Biologist. ISSN: 2052-5273.  suggests krill as a limiting factor to whale population growth. Savoca points to studies that suggest a close relationship between whales and krill wherein whales provide necessary nutrients for krill to thrive. This is further complicated by competition between krill fisheries and whales in the Southern Ocean.

Reducing Ship Strike: A 2001 study found that in some areas, more than one third of all fin whale and right whale strandings involve ship strike. This can especially impact small populations of whales such as the northern right whale in the western North Atlantic^[12]Laist, David W., et al. “Collisions between Ships and Whales.” Marine Mammal Science, vol. 17, no. 1, 2001, pp. 35–75, https://doi.org/10.1111/j.1748-7692.2001.tb00980.x. . Measures that require large, motorized vessels to slow their speeds in particularly vulnerable areas may be beneficial to whale populations.

CDR Potential

Estimated Sequestration Potential:  0.032 Gt CO2e /year, including carbon sequestered from fertilization^[13]Durfort, A., G. Mariani, M. Troussellier, V. Tulloch, and D. Mouillot. 2021. “The Collapse and Recovery Potential of Carbon Sequestration by Baleen Whales in the Southern Ocean.” Preprint. doi.org/10.21203/rs.3.rs-92037/v1.  

Sequestration Durability: 10 – 100 years^[14]Cross, J.N., Sweeney, C., Jewett, E.B., Feely, R.A., McElhany, P., Carter, B., Stein, T., Kitch, G.D., and Gledhill, D.K., 2023. Strategy for NOAA Carbon Dioxide Removal Research: A white paper documenting a potential NOAA CDR Science Strategy as an element of NOAA’s Climate Interventions Portfolio. NOAA Special Report. NOAA, Washington DC. DOI: 10.25923/gzke-8730  

Challenges

• Difficult to find and track outcomes from whale fertilization events (e.g., feces)
• Tracking the fate of carbon through the water column

Key Knowledge Gaps

Adapted from Pearson et al. 2022

• How effective are whales at creating and maintaining primary production hotspots that lead to enhanced carbon sequestration?
• How bioavailable are whale-derived nutrients?
• What is the carbon flux from cetaceans to the atmosphere?

First-Order Priorities

*Adapted from Pearson et al. 2022

• Investigate primary production hot spots from whales via determination of fecal nutrients to carbon recycling versus export*
• Conduct additional field and laboratory studies to ascertain the bioavailability of krill-derived iron in whale feces*
• Measure the carbon flux from cetaceans to the atmosphere via respiration to understand cetaceans’ net capacity for CO2 removal*

Whales are thought to play a role in the carbon cycle both directly (living biomass and whale falls) and indirectly (the whale pump, the whale conveyor belt, and bioturbation), however the extent of this role remains uncertain^[1]Meynecke J-O, Samanta S, de Bie J, Seyboth E, Prakash Dey S, Fearon G, Vichi M, Findlay K, Roychoudhury A and Mackey B (2023) Do whales really increase the oceanic removal of atmospheric carbon? Front. Mar. Sci. 10:1117409. doi: 10.3389/fmars.2023.1117409 . A 2022 report from The Environmental Defense Fund^[2]Collins, J. R., Boenish, R. E., Fujita, R. M., Rader, D. N., and Moore, L. A. 2022. Natural climate solutions in the open ocean: scientific knowledge and opportunities surrounding four potential pathways for carbon dioxide removal or avoided emissions. Environmental Defense Fund, New York, NY. https://www.edf.org/sites/default/files/2022-10/Natural%20Climate%20Solutions%20in%20the%20Open%20Ocean.pdf  found there to be fewer than 10 scientific studies from which to draw any broad conclusions in this area and cautioned against the creation of a carbon credit system based on whale carbon sequestration. A 2020 study estimates that restoring baleen whale populations to pre-whaling abundances could sequester 0.032 Gt CO2/year, including carbon sequestered from fertilization via whale feces^[3]Durfort, Anaelle, et al. The Collapse and Recovery Potential of Carbon Sequestration by Baleen Whales in the Southern Ocean, 2020, https://doi.org/10.21203/rs.3.rs-92037/v1. . However, rebuilding whale populations is sure to elicit many other environmental and social benefits, explored further on in this road map.

Mechanisms for CDR

Direct Sequestration

• Living Biomass: Due to their size and longevity, whales can store large amounts of carbon for long periods of time in their bodies as biomass. While whaling indeed resulted in a loss of carbon stored in whales, there is not clear evidence to suggest that whaling was a net source of CO2 to the atmosphere^[4]Pearson, Heidi C., et al. “Whales in the Carbon Cycle: Can Recovery Remove Carbon Dioxide?” Trends in Ecology & Evolution, vol. 38, no. 3, 2023, pp. 238–249, https://doi.org/10.1016/j.tree.2022.10.012. .
• Whale Falls: Whale falls, wherein whale carcasses sink to the ocean floor and their carbon-rich biomass is reallocated in various ways, is the “most scientifically comprehensible” of the pathways (direct vs indirect sequestration)^[5]Collins, J. R., Boenish, R. E., Fujita, R. M., Rader, D. N., and Moore, L. A. 2022. Natural climate solutions in the open ocean: scientific knowledge and opportunities surrounding four potential pathways for carbon dioxide removal or avoided emissions. Environmental Defense Fund, New York, NY. https://www.edf.org/sites/default/files/2022-10/Natural%20Climate%20Solutions%20in%20the%20Open%20Ocean.pdf  with a 2010 study estimating that restoration of large baleen whale populations to pre-whaling numbers could sequester 0.0006 Gt CO2e /year.

Indirect Sequestration

• Whale Pump: This is the term often used to describe the role that whales play in cycling nutrients through the ocean via their feces. The whale pump hypothesis sits on two assumptions that have not yet been verified through empirical observations^[6]Collins, J. R., Boenish, R. E., Fujita, R. M., Rader, D. N., and Moore, L. A. 2022. Natural climate solutions in the open ocean: scientific knowledge and opportunities surrounding four potential pathways for carbon dioxide removal or avoided emissions. Environmental Defense Fund, New York, NY. https://www.edf.org/sites/default/files/2022-10/Natural%20Climate%20Solutions%20in%20the%20Open%20Ocean.pdf . The first assumption is around the efficacy of surface water fertilization and subsequent primary production via whale feces. The second assumption concerns the fate of carbon export from primary production.
  • WhaleX Ocean Nourishment synthesizes limiting nutrients (nitrogen, phosphorous, iron, and silica) and disperses them across nutrient poor regions of the ocean, simulating the dispersion of nutrients via whale feces.
• Whale Conveyor Belt: The whale conveyor belt is based on the idea that as whales migrate yearly, they move nutrients around the ocean, potentially increasing iron availability for phytoplankton growth^[7]Roman J, Estes JA, Morissette L, Smith C, Costa D, McCarthy J, Nation JB, Nicol S, Pershing A, Smetacek V. Whales as marine ecosystem engineers. Frontiers in Ecology and the Environment. 2014 Sep;12(7):377-85. .
• Bioturbation: Bioturbation is the process through which whale feeding behaviors stimulate the seabed and resuspend sediments^[8]Meynecke J-O, Samanta S, de Bie J, Seyboth E, Prakash Dey S, Fearon G, Vichi M, Findlay K, Roychoudhury A and Mackey B (2023) Do whales really increase the oceanic removal of atmospheric carbon? Front. Mar. Sci. 10:1117409. doi: 10.3389/fmars.2023.1117409 . Conceptually, this is similar to the whale pump, but the pool of nutrients comes from seafloor sediments instead of whale feces^[9]Nelson, C. H., and Johnson, K. R. (1987). Whales and walruses as tillers of the sea floor. Sci. Am. 256, 112–117. doi: 10.1038/scientificamerican0287-112 ,^[10]Alter, S. E., Rynes, E., and Palumbi, S. R. (2007). DNA Evidence for historic population size and past ecosystem impacts of gray whales. Proc. Natl. Acad. Sci. 104, 15162–15167. doi: 10.1073/pnas.0706056104 .

Rebuilding Whale Populations: Increasing whale populations would likely amplify their role in the carbon cycle, including any sequestration.

• Increasing Krill Abundance:
  • A 2022 article by Savoca^[11]Savoca, Matthew. 2022. “The fall of the great ocean farmers.” The Marine Biologist. ISSN: 2052-5273.  suggests krill as a limiting factor to whale population growth. Savoca points to studies that suggest a close relationship between whales and krill wherein whales provide necessary nutrients for krill to thrive. This is further complicated by competition between krill fisheries and whales in the Southern Ocean.

Reducing Ship Strike: A 2001 study found that in some areas, more than one third of all fin whale and right whale strandings involve ship strike. This can especially impact small populations of whales such as the northern right whale in the western North Atlantic^[12]Laist, David W., et al. “Collisions between Ships and Whales.” Marine Mammal Science, vol. 17, no. 1, 2001, pp. 35–75, https://doi.org/10.1111/j.1748-7692.2001.tb00980.x. . Measures that require large, motorized vessels to slow their speeds in particularly vulnerable areas may be beneficial to whale populations.

CDR Potential

Estimated Sequestration Potential:  0.032 Gt CO2e /year, including carbon sequestered from fertilization^[13]Durfort, A., G. Mariani, M. Troussellier, V. Tulloch, and D. Mouillot. 2021. “The Collapse and Recovery Potential of Carbon Sequestration by Baleen Whales in the Southern Ocean.” Preprint. doi.org/10.21203/rs.3.rs-92037/v1.  

Sequestration Durability: 10 – 100 years^[14]Cross, J.N., Sweeney, C., Jewett, E.B., Feely, R.A., McElhany, P., Carter, B., Stein, T., Kitch, G.D., and Gledhill, D.K., 2023. Strategy for NOAA Carbon Dioxide Removal Research: A white paper documenting a potential NOAA CDR Science Strategy as an element of NOAA’s Climate Interventions Portfolio. NOAA Special Report. NOAA, Washington DC. DOI: 10.25923/gzke-8730  

Challenges

• Difficult to find and track outcomes from whale fertilization events (e.g., feces)
• Tracking the fate of carbon through the water column

Key Knowledge Gaps

Adapted from Pearson et al. 2022

• How effective are whales at creating and maintaining primary production hotspots that lead to enhanced carbon sequestration?
• How bioavailable are whale-derived nutrients?
• What is the carbon flux from cetaceans to the atmosphere?

First-Order Priorities

*Adapted from Pearson et al. 2022

• Investigate primary production hot spots from whales via determination of fecal nutrients to carbon recycling versus export*
• Conduct additional field and laboratory studies to ascertain the bioavailability of krill-derived iron in whale feces*
• Measure the carbon flux from cetaceans to the atmosphere via respiration to understand cetaceans’ net capacity for CO2 removal*

Whales are thought to play a role in the carbon cycle both directly (living biomass and whale falls) and indirectly (the whale pump, the whale conveyor belt, and bioturbation), however the extent of this role remains uncertain^[1]Meynecke J-O, Samanta S, de Bie J, Seyboth E, Prakash Dey S, Fearon G, Vichi M, Findlay K, Roychoudhury A and Mackey B (2023) Do whales really increase the oceanic removal of atmospheric carbon? Front. Mar. Sci. 10:1117409. doi: 10.3389/fmars.2023.1117409 . A 2022 report from The Environmental Defense Fund^[2]Collins, J. R., Boenish, R. E., Fujita, R. M., Rader, D. N., and Moore, L. A. 2022. Natural climate solutions in the open ocean: scientific knowledge and opportunities surrounding four potential pathways for carbon dioxide removal or avoided emissions. Environmental Defense Fund, New York, NY. https://www.edf.org/sites/default/ files/2022-10/Natural%20Climate%20Solutions%20in%20the%20Open%20Ocean.pdf  found there to be fewer than 10 scientific studies from which to draw any broad conclusions in this area and cautioned against the creation of a carbon credit system based on whale carbon sequestration. A 2020 study estimates that restoring baleen whale populations to pre-whaling abundances could sequester 0.032 Gt CO2/year, including carbon sequestered from fertilization via whale feces^[3]Durfort, Anaelle, et al. The Collapse and Recovery Potential of Carbon Sequestration by Baleen Whales in the Southern Ocean, 2020, https://doi.org/10.21203/rs.3.rs-92037/v1. . However, rebuilding whale populations is sure to elicit many other environmental and social benefits, explored further on in this road map.

Mechanisms for CDR

Direct Sequestration

• Living Biomass: Due to their size and longevity, whales can store large amounts of carbon for long periods of time in their bodies as biomass. While whaling indeed resulted in a loss of carbon stored in whales, there is not clear evidence to suggest that whaling was a net source of CO2 to the atmosphere^[4]Pearson, Heidi C., et al. “Whales in the Carbon Cycle: Can Recovery Remove Carbon Dioxide?” Trends in Ecology & Evolution, vol. 38, no. 3, 2023, pp. 238–249, https://doi.org/10.1016/j.tree.2022.10.012. .
• Whale Falls: Whale falls, wherein whale carcasses sink to the ocean floor and their carbon-rich biomass is reallocated in various ways, is the “most scientifically comprehensible” of the pathways (direct vs indirect sequestration)^[5]Collins, J. R., Boenish, R. E., Fujita, R. M., Rader, D. N., and Moore, L. A. 2022. Natural climate solutions in the open ocean: scientific knowledge and opportunities surrounding four potential pathways for carbon dioxide removal or avoided emissions. Environmental Defense Fund, New York, NY. https://www.edf.org/sites/default/ files/2022-10/Natural%20Climate%20Solutions%20in%20the%20Open%20Ocean.pdf  with a 2010 study estimating that restoration of large baleen whale populations to pre-whaling numbers could sequester 0.0006 Gt CO2e /year.

Indirect Sequestration

• Whale Pump: This is the term often used to describe the role that whales play in cycling nutrients through the ocean via their feces. The whale pump hypothesis sits on two assumptions that have not yet been verified through empirical observations^[6]Collins, J. R., Boenish, R. E., Fujita, R. M., Rader, D. N., and Moore, L. A. 2022. Natural climate solutions in the open ocean: scientific knowledge and opportunities surrounding four potential pathways for carbon dioxide removal or avoided emissions. Environmental Defense Fund, New York, NY. https://www.edf.org/sites/default/ files/2022-10/Natural%20Climate%20Solutions%20in%20the%20Open%20Ocean.pdf . The first assumption is around the efficacy of surface water fertilization and subsequent primary production via whale feces. The second assumption concerns the fate of carbon export from primary production.
  • WhaleX Ocean Nourishment synthesizes limiting nutrients (nitrogen, phosphorous, iron, and silica) and disperses them across nutrient poor regions of the ocean, simulating the dispersion of nutrients via whale feces.
• Whale Conveyor Belt: The whale conveyor belt is based on the idea that as whales migrate yearly, they move nutrients around the ocean, potentially increasing iron availability for phytoplankton growth^[7]Roman J, Estes JA, Morissette L, Smith C, Costa D, McCarthy J, Nation JB, Nicol S, Pershing A, Smetacek V. Whales as marine ecosystem engineers. Frontiers in Ecology and the Environment. 2014 Sep;12(7):377-85. .
• Bioturbation: Bioturbation is the process through which whale feeding behaviors stimulate the seabed and resuspend sediments^[8]Meynecke J-O, Samanta S, de Bie J, Seyboth E, Prakash Dey S, Fearon G, Vichi M, Findlay K, Roychoudhury A and Mackey B (2023) Do whales really increase the oceanic removal of atmospheric carbon? Front. Mar. Sci. 10:1117409. doi: 10.3389/fmars.2023.1117409 . Conceptually, this is similar to the whale pump, but the pool of nutrients comes from seafloor sediments instead of whale feces^[9]Nelson, C. H., and Johnson, K. R. (1987). Whales and walruses as tillers of the sea floor. Sci. Am. 256, 112–117. doi: 10.1038/scientificamerican0287-112 ,^[10]Alter, S. E., Rynes, E., and Palumbi, S. R. (2007). DNA Evidence for historic population size and past ecosystem impacts of gray whales. Proc. Natl. Acad. Sci. 104, 15162–15167. doi: 10.1073/pnas.0706056104 .

Rebuilding Whale Populations: Increasing whale populations would likely amplify their role in the carbon cycle, including any sequestration.

• Increasing Krill Abundance:
  • A 2022 article by Savoca^[11]Savoca, Matthew. 2022. “The fall of the great ocean farmers.” The Marine Biologist. ISSN: 2052-5273.  suggests krill as a limiting factor to whale population growth. Savoca points to studies that suggest a close relationship between whales and krill wherein whales provide necessary nutrients for krill to thrive. This is further complicated by competition between krill fisheries and whales in the Southern Ocean.

Reducing Ship Strike: A 2001 study found that in some areas, more than one third of all fin whale and right whale strandings involve ship strike. This can especially impact small populations of whales such as the northern right whale in the western North Atlantic^[12]Laist, David W., et al. “Collisions between Ships and Whales.” Marine Mammal Science, vol. 17, no. 1, 2001, pp. 35–75, https://doi.org/10.1111/j.1748-7692.2001.tb00980.x. . Measures that require large, motorized vessels to slow their speeds in particularly vulnerable areas may be beneficial to whale populations.

CDR Potential

Estimated Sequestration Potential:  0.032 Gt CO2e /year, including carbon sequestered from fertilization^[13]Durfort, A., G. Mariani, M. Troussellier, V. Tulloch, and D. Mouillot. 2021. “The Collapse and Recovery Potential of Carbon Sequestration by Baleen Whales in the Southern Ocean.” Preprint. doi.org/10.21203/rs.3.rs-92037/v1.  

Sequestration Durability: 10 – 100 years^[14]Cross, J.N., Sweeney, C., Jewett, E.B., Feely, R.A., McElhany, P., Carter, B., Stein, T., Kitch, G.D., and Gledhill, D.K., 2023. Strategy for NOAA Carbon Dioxide Removal Research: A white paper documenting a potential NOAA CDR Science Strategy as an element of NOAA’s Climate Interventions Portfolio. NOAA Special Report. NOAA, Washington DC. DOI: 10.25923/gzke-8730  

Challenges

• Difficult to find and track outcomes from whale fertilization events (e.g., feces)
• Tracking the fate of carbon through the water column

Key Knowledge Gaps

Adapted from Pearson et al. 2022

• How effective are whales at creating and maintaining primary production hotspots that lead to enhanced carbon sequestration?
• How bioavailable are whale-derived nutrients?
• What is the carbon flux from cetaceans to the atmosphere?

First-Order Priorities

*Adapted from Pearson et al. 2022

• Investigate primary production hot spots from whales via determination of fecal nutrients to carbon recycling versus export*
• Conduct additional field and laboratory studies to ascertain the bioavailability of krill-derived iron in whale feces*
• Measure the carbon flux from cetaceans to the atmosphere via respiration to understand cetaceans’ net capacity for CO2 removal*

Whales are thought to play a role in the carbon cycle both directly (living biomass and whale falls) and indirectly (the whale pump, the whale conveyor belt, and bioturbation), however the extent of this role remains uncertain. A 2022 report from The Environmental Defense Fund found there to be fewer than 10 scientific studies from which to draw any broad conclusions in this area and cautioned against the creation of a carbon credit system based on whale carbon sequestration. A 2020 study estimates that restoring baleen whale populations to pre-whaling abundances could sequester 0.032 Gt CO2/year, including carbon sequestered from fertilization via whale feces. However, rebuilding whale populations is sure to elicit many other environmental and social benefits, explored further on in this road map.

Mechanisms for CDR

Direct Sequestration

• Living Biomass: Due to their size and longevity, whales can store large amounts of carbon for long periods of time in their bodies as biomass. While whaling indeed resulted in a loss of carbon stored in whales, there is not clear evidence to suggest that whaling was a net source of CO2 to the atmosphere.
• Whale Falls: Whale falls, wherein whale carcasses sink to the ocean floor and their carbon-rich biomass is reallocated in various ways, is the “most scientifically comprehensible” of the pathways (direct vs indirect sequestration) with a 2010 study estimating that restoration of large baleen whale populations to pre-whaling numbers could sequester 0.0006 Gt CO2e /year.

Indirect Sequestration

• Whale Pump: This is the term often used to describe the role that whales play in cycling nutrients through the ocean via their feces. The whale pump hypothesis sits on two assumptions that have not yet been verified through empirical observations. The first assumption is around the efficacy of surface water fertilization and subsequent primary production via whale feces. The second assumption concerns the fate of carbon export from primary production.
  • WhaleX Ocean Nourishment synthesizes limiting nutrients (nitrogen, phosphorous, iron, and silica) and disperses them across nutrient poor regions of the ocean, simulating the dispersion of nutrients via whale feces.
• Whale Conveyor Belt: The whale conveyor belt is based on the idea that as whales migrate yearly, they move nutrients around the ocean, potentially increasing iron availability for phytoplankton growth.
• Bioturbation: Bioturbation is the process through which whale feeding behaviors stimulate the seabed and resuspend sediments. Conceptually, this is similar to the whale pump, but the pool of nutrients comes from seafloor sediments instead of whale feces,.

Rebuilding Whale Populations: Increasing whale populations would likely amplify their role in the carbon cycle, including any sequestration.

• Increasing Krill Abundance:
  • A 2022 article by Savoca suggests krill as a limiting factor to whale population growth. Savoca points to studies that suggest a close relationship between whales and krill wherein whales provide necessary nutrients for krill to thrive. This is further complicated by competition between krill fisheries and whales in the Southern Ocean.

Reducing Ship Strike: A 2001 study found that in some areas, more than one third of all fin whale and right whale strandings involve ship strike. This can especially impact small populations of whales such as the northern right whale in the western North Atlantic. Measures that require large, motorized vessels to slow their speeds in particularly vulnerable areas may be beneficial to whale populations.

CDR Potential

Estimated Sequestration Potential:  0.032 Gt CO2e /year, including carbon sequestered from fertilization 

Sequestration Durability: 10 – 100 years 

Challenges

• Difficult to find and track outcomes from whale fertilization events (e.g., feces)
• Tracking the fate of carbon through the water column

Key Knowledge Gaps

Adapted from Pearson et al. 2022

• How effective are whales at creating and maintaining primary production hotspots that lead to enhanced carbon sequestration?
• How bioavailable are whale-derived nutrients?
• What is the carbon flux from cetaceans to the atmosphere?

First-Order Priorities

*Adapted from Pearson et al. 2022

• Investigate primary production hot spots from whales via determination of fecal nutrients to carbon recycling versus export*
• Conduct additional field and laboratory studies to ascertain the bioavailability of krill-derived iron in whale feces*
• Measure the carbon flux from cetaceans to the atmosphere via respiration to understand cetaceans’ net capacity for CO2 removal*

Whales are thought to play a role in the carbon cycle both directly (living biomass and whale falls) and indirectly (the whale pump, the whale conveyor belt, and bioturbation), however the extent of this role remains uncertain^[1]Meynecke J-O, Samanta S, de Bie J, Seyboth E, Prakash Dey S, Fearon G, Vichi M, Findlay K, Roychoudhury A and Mackey B (2023) Do whales really increase the oceanic removal of atmospheric carbon? Front. Mar. Sci. 10:1117409. doi: 10.3389/fmars.2023.1117409 . A 2022 report from The Environmental Defense Fund^[2]Collins, J. R., Boenish, R. E., Fujita, R. M., Rader, D. N., and Moore, L. A. 2022. Natural climate solutions in the open ocean: scientific knowledge and opportunities surrounding four potential pathways for carbon dioxide removal or avoided emissions. Environmental Defense Fund, New York, NY. www.edf.org/sites/default/ files/2022-10/Natural%20Climate%20Solutions%20in%20the%20Open%20Ocean.pdf  found there to be fewer than 10 scientific studies from which to draw any broad conclusions in this area and cautioned against the creation of a carbon credit system based on whale carbon sequestration. A 2020 study estimates that restoring baleen whale populations to pre-whaling abundances could sequester 0.032 Gt CO2/year, including carbon sequestered from fertilization via whale feces^[3]Durfort, Anaelle, et al. The Collapse and Recovery Potential of Carbon Sequestration by Baleen Whales in the Southern Ocean, 2020, https://doi.org/10.21203/rs.3.rs-92037/v1. . However, rebuilding whale populations is sure to elicit many other environmental and social benefits, explored further on in this road map.

Mechanisms for CDR

Direct Sequestration

• Living Biomass: Due to their size and longevity, whales can store large amounts of carbon for long periods of time in their bodies as biomass. While whaling indeed resulted in a loss of carbon stored in whales, there is not clear evidence to suggest that whaling was a net source of CO2 to the atmosphere^[4]Pearson, Heidi C., et al. “Whales in the Carbon Cycle: Can Recovery Remove Carbon Dioxide?” Trends in Ecology & Evolution, vol. 38, no. 3, 2023, pp. 238–249, https://doi.org/10.1016/j.tree.2022.10.012. .
• Whale Falls: Whale falls, wherein whale carcasses sink to the ocean floor and their carbon-rich biomass is reallocated in various ways, is the “most scientifically comprehensible” of the pathways (direct vs indirect sequestration)^[5]Collins, J. R., Boenish, R. E., Fujita, R. M., Rader, D. N., and Moore, L. A. 2022. Natural climate solutions in the open ocean: scientific knowledge and opportunities surrounding four potential pathways for carbon dioxide removal or avoided emissions. Environmental Defense Fund, New York, NY. www.edf.org/sites/default/ files/2022-10/Natural%20Climate%20Solutions%20in%20the%20Open%20Ocean.pdf  with a 2010 study estimating that restoration of large baleen whale populations to pre-whaling numbers could sequester 0.0006 Gt CO2e /year.

Indirect Sequestration

• Whale Pump: This is the term often used to describe the role that whales play in cycling nutrients through the ocean via their feces. The whale pump hypothesis sits on two assumptions that have not yet been verified through empirical observations^[6]Collins, J. R., Boenish, R. E., Fujita, R. M., Rader, D. N., and Moore, L. A. 2022. Natural climate solutions in the open ocean: scientific knowledge and opportunities surrounding four potential pathways for carbon dioxide removal or avoided emissions. Environmental Defense Fund, New York, NY. www.edf.org/sites/default/ files/2022-10/Natural%20Climate%20Solutions%20in%20the%20Open%20Ocean.pdf . The first assumption is around the efficacy of surface water fertilization and subsequent primary production via whale feces. The second assumption concerns the fate of carbon export from primary production.
  • WhaleX Ocean Nourishment synthesizes limiting nutrients (nitrogen, phosphorous, iron, and silica) and disperses them across nutrient poor regions of the ocean, simulating the dispersion of nutrients via whale feces.
• Whale Conveyor Belt: The whale conveyor belt is based on the idea that as whales migrate yearly, they move nutrients around the ocean, potentially increasing iron availability for phytoplankton growth^[7]Roman J, Estes JA, Morissette L, Smith C, Costa D, McCarthy J, Nation JB, Nicol S, Pershing A, Smetacek V. Whales as marine ecosystem engineers. Frontiers in Ecology and the Environment. 2014 Sep;12(7):377-85. .
• Bioturbation: Bioturbation is the process through which whale feeding behaviors stimulate the seabed and resuspend sediments^[8]Meynecke J-O, Samanta S, de Bie J, Seyboth E, Prakash Dey S, Fearon G, Vichi M, Findlay K, Roychoudhury A and Mackey B (2023) Do whales really increase the oceanic removal of atmospheric carbon? Front. Mar. Sci. 10:1117409. doi: 10.3389/fmars.2023.1117409 . Conceptually, this is similar to the whale pump, but the pool of nutrients comes from seafloor sediments instead of whale feces^[9]Nelson, C. H., and Johnson, K. R. (1987). Whales and walruses as tillers of the sea floor. Sci. Am. 256, 112–117. doi: 10.1038/scientificamerican0287-112 ,^[10]Alter, S. E., Rynes, E., and Palumbi, S. R. (2007). DNA Evidence for historic population size and past ecosystem impacts of gray whales. Proc. Natl. Acad. Sci. 104, 15162–15167. doi: 10.1073/pnas.0706056104 .

Rebuilding Whale Populations: Increasing whale populations would likely amplify their role in the carbon cycle, including any sequestration.

• Increasing Krill Abundance:
  • A 2022 article by Savoca^[11]Savoca, Matthew. 2022. “The fall of the great ocean farmers.” The Marine Biologist. ISSN: 2052-5273.  suggests krill as a limiting factor to whale population growth. Savoca points to studies that suggest a close relationship between whales and krill wherein whales provide necessary nutrients for krill to thrive. This is further complicated by competition between krill fisheries and whales in the Southern Ocean.

Reducing Ship Strike: A 2001 study found that in some areas, more than one third of all fin whale and right whale strandings involve ship strike. This can especially impact small populations of whales such as the northern right whale in the western North Atlantic^[12]Laist, David W., et al. “Collisions between Ships and Whales.” Marine Mammal Science, vol. 17, no. 1, 2001, pp. 35–75, https://doi.org/10.1111/j.1748-7692.2001.tb00980.x. . Measures that require large, motorized vessels to slow their speeds in particularly vulnerable areas may be beneficial to whale populations.

CDR Potential

Estimated Sequestration Potential:  0.032 Gt CO2e /year, including carbon sequestered from fertilization^[13]Durfort, A., G. Mariani, M. Troussellier, V. Tulloch, and D. Mouillot. 2021. “The Collapse and Recovery Potential of Carbon Sequestration by Baleen Whales in the Southern Ocean.” Preprint. doi.org/10.21203/rs.3.rs-92037/v1.  

Sequestration Durability: 10 – 100 years^[14]Cross, J.N., Sweeney, C., Jewett, E.B., Feely, R.A., McElhany, P., Carter, B., Stein, T., Kitch, G.D., and Gledhill, D.K., 2023. Strategy for NOAA Carbon Dioxide Removal Research: A white paper documenting a potential NOAA CDR Science Strategy as an element of NOAA’s Climate Interventions Portfolio. NOAA Special Report. NOAA, Washington DC. DOI: 10.25923/gzke-8730  

Challenges

• Difficult to find and track outcomes from whale fertilization events (e.g., feces)
• Tracking the fate of carbon through the water column

Key Knowledge Gaps

Adapted from Pearson et al. 2022

• How effective are whales at creating and maintaining primary production hotspots that lead to enhanced carbon sequestration?
• How bioavailable are whale-derived nutrients?
• What is the carbon flux from cetaceans to the atmosphere?

First Order Priorities

*Adapted from Pearson et al. 2022

• Investigate primary production hot spots from whales via determination of fecal nutrients to carbon recycling versus export*
• Conduct additional field and laboratory studies to ascertain the bioavailability of krill-derived iron in whale feces*
• Measure the carbon flux from cetaceans to the atmosphere via respiration to understand cetaceans’ net capacity for CO2 removal*

Whales are thought to play a role in the carbon cycle both directly (living biomass and whale falls) and indirectly (the whale pump, the whale conveyor belt, and bioturbation), however the extent of this role remains uncertain. A 2022 report from The Environmental Defense Fund found there to be fewer than 10 scientific studies from which to draw any broad conclusions in this area and cautioned against the creation of a carbon credit system based on whale carbon sequestration. A 2020 study estimates that restoring baleen whale populations to pre-whaling abundances could sequester 0.032 Gt CO2/year, including carbon sequestered from fertilization via whale feces. However, rebuilding whale populations is sure to elicit many other environmental and social benefits, explored further on in this road map.

Mechanisms for CDR

Direct Sequestration

• Living Biomass: Due to their size and longevity, whales can store large amounts of carbon for long periods of time in their bodies as biomass. While whaling indeed resulted in a loss of carbon stored in whales, there is not clear evidence to suggest that whaling was a net source of CO2 to the atmosphere.
• Whale Falls: Whale falls, wherein whale carcasses sink to the ocean floor and their carbon-rich biomass is reallocated in various ways, is the “most scientifically comprehensible” of the pathways (direct vs indirect sequestration) with a 2010 study estimating that restoration of large baleen whale populations to pre-whaling numbers could sequester 0.0006 Gt CO2e /year.

Indirect Sequestration

• Whale Pump: This is the term often used to describe the role that whales play in cycling nutrients through the ocean via their feces. The whale pump hypothesis sits on two assumptions that have not yet been verified through empirical observations. The first assumption is around the efficacy of surface water fertilization and subsequent primary production via whale feces. The second assumption concerns the fate of carbon export from primary production.
  • WhaleX Ocean Nourishment synthesizes limiting nutrients (nitrogen, phosphorous, iron, and silica) and disperses them across nutrient poor regions of the ocean, simulating the dispersion of nutrients via whale feces.
• Whale Conveyor Belt: The whale conveyor belt is based on the idea that as whales migrate yearly, they move nutrients around the ocean, potentially increasing iron availability for phytoplankton growth.
• Bioturbation: Bioturbation is the process through which whale feeding behaviors stimulate the seabed and resuspend sediments. Conceptually, this is similar to the whale pump, but the pool of nutrients comes from seafloor sediments instead of whale feces,.

Rebuilding Whale Populations: Increasing whale populations would likely amplify their role in the carbon cycle, including any sequestration.

• Increasing Krill Abundance:
  • A 2022 article by Savoca suggests krill as a limiting factor to whale population growth. Savoca points to studies that suggest a close relationship between whales and krill wherein whales provide necessary nutrients for krill to thrive. This is further complicated by competition between krill fisheries and whales in the Southern Ocean.

Reducing Ship Strike: A 2001 study found that in some areas, more than one third of all fin whale and right whale strandings involve ship strike. This can especially impact small populations of whales such as the northern right whale in the western North Atlantic. Measures that require large, motorized vessels to slow their speeds in particularly vulnerable areas may be beneficial to whale populations.

CDR Potential

Estimated Sequestration Potential:  0.032 Gt CO2e /year, including carbon sequestered from fertilization 

Sequestration Durability: 10 – 100 years 

Challenges

• Difficult to find and track outcomes from whale fertilization events (e.g., feces)
• Tracking the fate of carbon through the water column

Key Knowledge Gaps

Adapted from Pearson et al. 2022

• How effective are whales at creating and maintaining primary production hotspots that lead to enhanced carbon sequestration?
• How bioavailable are whale-derived nutrients?
• What is the carbon flux from cetaceans to the atmosphere?

First Order Priorities

*Adapted from Pearson et al. 2022

• Investigate primary production hot spots from whales via determination of fecal nutrients to carbon recycling versus export*
• Conduct additional field and laboratory studies to ascertain the bioavailability of krill-derived iron in whale feces*
• Measure the carbon flux from cetaceans to the atmosphere via respiration to understand cetaceans’ net capacity for CO2 removal*

Whales are thought to play a role in the carbon cycle both directly (living biomass and whale falls) and indirectly (the whale pump, the whale conveyor belt, and bioturbation), however the extent of this role remains uncertain. A 2022 report from The Environmental Defense Fund found there to be fewer than 10 scientific studies from which to draw any broad conclusions in this area and cautioned against the creation of a carbon credit system based on whale carbon sequestration. A 2020 study estimates that restoring baleen whale populations to pre-whaling abundances could sequester 0.032 Gt CO2/year, including carbon sequestered from fertilization via whale feces. However, rebuilding whale populations is sure to elicit many other environmental and social benefits, explored further on in this road map.

Mechanisms for CDR

Direct Sequestration

• Living Biomass: Due to their size and longevity, whales can store large amounts of carbon for long periods of time in their bodies as biomass. While whaling indeed resulted in a loss of carbon stored in whales, there is not clear evidence to suggest that whaling was a net source of CO2 to the atmosphere.
• Whale Falls: Whale falls, wherein whale carcasses sink to the ocean floor and their carbon-rich biomass is reallocated in various ways, is the “most scientifically comprehensible” of the pathways (direct vs indirect sequestration) with a 2010 study estimating that restoration of large baleen whale populations to pre-whaling numbers could sequester 0.0006 Gt CO2e /year.

Indirect Sequestration

• Whale Pump: This is the term often used to describe the role that whales play in cycling nutrients through the ocean via their feces. The whale pump hypothesis sits on two assumptions that have not yet been verified through empirical observations. The first assumption is around the efficacy of surface water fertilization and subsequent primary production via whale feces. The second assumption concerns the fate of carbon export from primary production.
  • WhaleX Ocean Nourishment synthesizes limiting nutrients (nitrogen, phosphorous, iron, and silica) and disperses them across nutrient poor regions of the ocean, simulating the dispersion of nutrients via whale feces.
• Whale Conveyor Belt: The whale conveyor belt is based on the idea that as whales migrate yearly, they move nutrients around the ocean, potentially increasing iron availability for phytoplankton growth.
• Bioturbation: Bioturbation is the process through which whale feeding behaviors stimulate the seabed and resuspend sediments. Conceptually, this is similar to the whale pump, but the pool of nutrients comes from seafloor sediments instead of whale feces,.

Rebuilding Whale Populations: Increasing whale populations would likely amplify their role in the carbon cycle, including any sequestration.

• Increasing Krill Abundance:
  • A 2022 article by Savoca suggests krill as a limiting factor to whale population growth. Savoca points to studies that suggest a close relationship between whales and krill wherein whales provide necessary nutrients for krill to thrive. This is further complicated by competition between krill fisheries and whales in the Southern Ocean.

Reducing Ship Strike: A 2001 study found that in some areas, more than one third of all fin whale and right whale strandings involve ship strike. This can especially impact small populations of whales such as the northern right whale in the western North Atlantic. Measures that require large, motorized vessels to slow their speeds in particularly vulnerable areas may be beneficial to whale populations.

CDR Potential

Estimated Sequestration Potential:  0.032 Gt CO2e /year, including carbon sequestered from fertilization 

Sequestration Durability: 10 – 100 years 

Challenges

• Difficult to find and track outcomes from whale fertilization events (e.g., feces)
• Tracking the fate of carbon through the water column

Key Knowledge Gaps

Adapted from Pearson et al. 2022

• How effective are whales at creating and maintaining primary production hotspots that lead to enhanced carbon sequestration?
• How bioavailable are whale-derived nutrients?
• What is the carbon flux from cetaceans to the atmosphere?

First Order Priorities

*Adapted from Pearson et al. 2022

• Investigate primary production hot spots from whales via determination of fecal nutrients to carbon recycling versus export*
• Conduct additional field and laboratory studies to ascertain the bioavailability of krill-derived iron in whale feces*
• Measure the carbon flux from cetaceans to the atmosphere via respiration to understand cetaceans’ net capacity for CO2 removal*

Whales are thought to play a role in the carbon cycle both directly (living biomass and whale falls) and indirectly (the whale pump, the whale conveyor belt, and bioturbation), however the extent of this role remains uncertain. A 2022 report from The Environmental Defense Fund found there to be fewer than 10 scientific studies from which to draw any broad conclusions in this area and cautioned against the creation of a carbon credit system based on whale carbon sequestration. A 2020 study estimates that restoring baleen whale populations to pre-whaling abundances could sequester 0.032 Gt CO2/year, including carbon sequestered from fertilization via whale feces. However, rebuilding whale populations is sure to elicit many other environmental and social benefits, explored further on in this road map.

Mechanisms for CDR

Direct Sequestration

• Living Biomass: Due to their size and longevity, whales can store large amounts of carbon for long periods of time in their bodies as biomass. While whaling indeed resulted in a loss of carbon stored in whales, there is not clear evidence to suggest that whaling was a net source of CO2 to the atmosphere.
• Whale Falls: Whale falls, wherein whale carcasses sink to the ocean floor and their carbon-rich biomass is reallocated in various ways, is the “most scientifically comprehensible” of the pathways (direct vs indirect sequestration) with a 2010 study estimating that restoration of large baleen whale populations to pre-whaling numbers could sequester 0.0006 Gt CO2e /year.

Indirect Sequestration

• Whale Pump: This is the term often used to describe the role that whales play in cycling nutrients through the ocean via their feces. The whale pump hypothesis sits on two assumptions that have not yet been verified through empirical observations. The first assumption is around the efficacy of surface water fertilization and subsequent primary production via whale feces. The second assumption concerns the fate of carbon export from primary production.
  • WhaleX Ocean Nourishment synthesizes limiting nutrients (nitrogen, phosphorous, iron, and silica) and disperses them across nutrient poor regions of the ocean, simulating the dispersion of nutrients via whale feces.
• Whale Conveyor Belt: The whale conveyor belt is based on the idea that as whales migrate yearly, they move nutrients around the ocean, potentially increasing iron availability for phytoplankton growth.
• Bioturbation: Bioturbation is the process through which whale feeding behaviors stimulate the seabed and resuspend sediments. Conceptually, this is similar to the whale pump, but the pool of nutrients comes from seafloor sediments instead of whale feces,.

Rebuilding Whale Populations: Increasing whale populations would likely amplify their role in the carbon cycle, including any sequestration.

• Increasing Krill Abundance:
  • A 2022 article by Savoca suggests krill as a limiting factor to whale population growth. Savoca points to studies that suggest a close relationship between whales and krill wherein whales provide necessary nutrients for krill to thrive. This is further complicated by competition between krill fisheries and whales in the Southern Ocean.

Reducing Ship Strike: A 2001 study found that in some areas, more than one third of all fin whale and right whale strandings involve ship strike. This can especially impact small populations of whales such as the northern right whale in the western North Atlantic. Measures that require large, motorized vessels to slow their speeds in particularly vulnerable areas may be beneficial to whale populations.

CDR Potential

Estimated Sequestration Potential:  0.032 Gt CO2e /year, including carbon sequestered from fertilization 

Sequestration Durability: 10 – 100 years 

Challenges

• Difficult to find and track outcomes from whale fertilization events (e.g., feces)
• Tracking the fate of carbon through the water column

Key Knowledge Gaps

Adapted from Pearson et al. 2022

• How effective are whales at creating and maintaining primary production hotspots that lead to enhanced carbon sequestration?
• How bioavailable are whale-derived nutrients?
• What is the carbon flux from cetaceans to the atmosphere?

First Order Priorities

*Adapted from Pearson et al. 2022

• Investigate primary production hot spots from whales via determination of fecal nutrients to carbon recycling versus export*
• Conduct additional field and laboratory studies to ascertain the bioavailability of krill-derived iron in whale feces*
• Measure the carbon flux from cetaceans to the atmosphere via respiration to understand cetaceans’ net capacity for CO2 removal*

While fishes have not traditionally been considered as important parts of the ocean carbon cycle / biological pump^[1]Sarmiento, Jorge L., and Nicolas Gruber. 2006. “Organic Matter Production.” In Ocean Biogeochemical Dynamics, 117–72. Princeton, N.J.: Princeton University Press. , there are several recent studies, as highlighted in the 2022 Environmental Defense Fund report “Natural Climate Solutions in the Open Ocean”, that focus on the geochemical contributions of fishes to the global carbon cycle^[2]Wilson, Rod W., F. J. Millero, J. R. Taylor, P. J. Walsh, V. Christensen, S. Jennings, and M. Grosell. 2009. “Contribution of Fish to the Marine Inorganic Carbon Cycle.” Science 323 (5912): 359–62. doi.org/10.1126/ science.1157972. ^[3]Boyd, Philip W., Hervé Claustre, Marina Levy, David A. Siegel and Thomas Weber. 2019. “Multi-Faceted Particle Pumps Drive Carbon Sequestration in the Ocean.” Nature 568 (7752): 327–35. doi.org/10.1038/s41586-019-1098-2. ^[4]Mariani, Gaël, William W. L. Cheung, Arnaud Lyet, Enric Sala, Juan Mayorga, Laure Velez, Steven D. Gaines, Tony Dejean, Marc Troussellier, and David Mouillot. 2020. “Let More Big Fish Sink: Fisheries Prevent Blue Carbon SequestrationHalf in Unprofitable Areas.” Science Advances 6 (44): eabb4848. doi.org/10.1126/sciadv.abb4848. ^[5]Bianchi, Daniele, David A. Carozza, Eric D. Galbraith, Jérôme Guiet, and Timothy DeVries. 2021. “Estimating Global Biomass and Biogeochemical Cycling of Marine Fish with and without Fishing.” Science Advances 7 (41): eabd7554. doi.org/10.1126/sciadv.abd7554. ^[6]Saba, Grace K., Adrian B. Burd, John P. Dunne, Santiago Hernández-León, Angela H. Martin, Kenneth A. Rose, Joseph Salisbury, et al., 2021. “Toward a Better Understanding of Fish-Based Contribution to Ocean Carbon Flux.” Limnology and Oceanography 66 (5): 1639–64. doi.org/10.1002/ lno.11709. . Many of the mechanisms by which fish are thought to contribute to carbon cycling are similar to whales (carbon stored in living biomass, bioturbation, carcasses falling to ocean floor, fertilization through feces) but also include contribution by intestinal precipitation of calcium carbonates^[7]Wilson, Rod W., F. J. Millero, J. R. Taylor, P. J. Walsh, V. Christensen, S. Jennings, and M. Grosell. 2009. “Contribution of Fish to the Marine Inorganic Carbon Cycle.” Science 323 (5912): 359–62. doi.org/10.1126/ science.1157972. .

There is still uncertainty around the specifics of mesopelagic fish-mediated carbon export, however the 2022 Environmental Defense Fund report suggests there is enough evidence of these species’ large contributions to global sequestration to warrant “the immediate pursuit of limitations or prohibitions on their harvest”.

Mechanism for CDR

CDR Potential

Estimated Sequestration Potential: Unclear, due to large knowledge gaps around biomass estimates of marine fish stocks, uncertainties in direct and indirect carbon export and overall carbon fluxes, few studies observing natural senescence / dead falls of fishes, and a poor understanding of the life cycle emissions of most fish species^[9]Collins, J. R., Boenish, R. E., Fujita, R. M., Rader, D. N., and Moore, L. A. 2022. Natural climate solutions in the open ocean: scientific knowledge and opportunities surrounding four potential pathways for carbon dioxide removal or avoided emissions. Environmental Defense Fund, New York, NY. https://www.edf.org/sites/default/files/2022-10/Natural%20Climate%20Solutions%20in%20the%20Open%20Ocean.pdf .

Sequestration Durability: Unknown.

Challenges

• More research is needed to understand carbon fluxes and life cycle emissions before developing strategies to increase carbon uptake and sequestration.

Key Knowledge Gaps

Adapted from EDF Natural Climate Solutions in the Open Ocean

• Lack of knowledge around the natural senescence or resulting deadfalls of fishes
• What is the contribution of fishes to inorganic carbon export via carbonate excretion?
• What is the total biomass of fishes, the fluxes in these communities, and conversion factors to go from biomass to units of carbon?
• How to discern between active carbon transport from mesopelagic fish versus from zooplankton?
• What is the composition of mesopelagic communities and what are the differences in roles played by small fishes versus other species such as cephalopods?

First-Order Priorities

*Adapted from EDF Natural Climate Solutions in the Open Ocean

• Conduct studies observing the natural senescence or resulting deadfalls of fishes*
• Conduct additional studies to understand the contribution of fishes to inorganic carbon export via carbonate excretion^[10]Salter, Michael A., et al. “Calcium carbonate production by fish in temperate Marine Environments.” Limnology and Oceanography, vol. 64, no. 6, 2019, pp. 2755–2770, https://doi.org/10.1002/lno.11339. *
• Create new models, observing technologies, and data to better constrain the total biomass of fishes, the fluxes in these communities, and conversion factors to go from biomass to units of carbon*
• Create new observational methods and models to better discern between active carbon transport from mesopelagic fish versus from zooplankton*
• Conduct studies to better understand the composition of mesopelagic communities to determine the difference in roles played by small fishes versus other species such as cephalopods*

While fishes have not traditionally been considered as important parts of the ocean carbon cycle / biological pump^[1]Sarmiento, Jorge L., and Nicolas Gruber. 2006. “Organic Matter Production.” In Ocean Biogeochemical Dynamics, 117–72. Princeton, N.J.: Princeton University Press. , there are several recent studies, as highlighted in the 2022 Environmental Defense Fund report “Natural Climate Solutions in the Open Ocean”, that focus on the geochemical contributions of fishes to the global carbon cycle^[2]Wilson, Rod W., F. J. Millero, J. R. Taylor, P. J. Walsh, V. Christensen, S. Jennings, and M. Grosell. 2009. “Contribution of Fish to the Marine Inorganic Carbon Cycle.” Science 323 (5912): 359–62. doi.org/10.1126/ science.1157972. ^[3]Boyd, Philip W., Hervé Claustre, Marina Levy, David A. Siegel and Thomas Weber. 2019. “Multi-Faceted Particle Pumps Drive Carbon Sequestration in the Ocean.” Nature 568 (7752): 327–35. doi.org/10.1038/s41586-019-1098-2. ^[4]Mariani, Gaël, William W. L. Cheung, Arnaud Lyet, Enric Sala, Juan Mayorga, Laure Velez, Steven D. Gaines, Tony Dejean, Marc Troussellier, and David Mouillot. 2020. “Let More Big Fish Sink: Fisheries Prevent Blue Carbon SequestrationHalf in Unprofitable Areas.” Science Advances 6 (44): eabb4848. doi.org/10.1126/sciadv.abb4848. ^[5]Bianchi, Daniele, David A. Carozza, Eric D. Galbraith, Jérôme Guiet, and Timothy DeVries. 2021. “Estimating Global Biomass and Biogeochemical Cycling of Marine Fish with and without Fishing.” Science Advances 7 (41): eabd7554. doi.org/10.1126/sciadv.abd7554. ^[6]Saba, Grace K., Adrian B. Burd, John P. Dunne, Santiago Hernández-León, Angela H. Martin, Kenneth A. Rose, Joseph Salisbury, et al., 2021. “Toward a Better Understanding of Fish-Based Contribution to Ocean Carbon Flux.” Limnology and Oceanography 66 (5): 1639–64. doi.org/10.1002/ lno.11709. . Many of the mechanisms by which fish are thought to contribute to carbon cycling are similar to whales (carbon stored in living biomass, bioturbation, carcasses falling to ocean floor, fertilization through feces) but also include contribution by intestinal precipitation of calcium carbonates^[7]Wilson, Rod W., F. J. Millero, J. R. Taylor, P. J. Walsh, V. Christensen, S. Jennings, and M. Grosell. 2009. “Contribution of Fish to the Marine Inorganic Carbon Cycle.” Science 323 (5912): 359–62. doi.org/10.1126/ science.1157972. .

There is still uncertainty around the specifics of mesopelagic fish-mediated carbon export, however the 2022 Environmental Defense Fund report suggests there is enough evidence of these species’ large contributions to global sequestration to warrant “the immediate pursuit of limitations or prohibitions on their harvest”.

Mechanism for CDR

CDR Potential

Estimated Sequestration Potential: Unclear, due to large knowledge gaps around biomass estimates of marine fish stocks, uncertainties in direct and indirect carbon export and overall carbon fluxes, few studies observing natural senescence / dead falls of fishes, and a poor understanding of the life cycle emissions of most fish species^[9]Collins, J. R., Boenish, R. E., Fujita, R. M., Rader, D. N., and Moore, L. A. 2022. Natural climate solutions in the open ocean: scientific knowledge and opportunities surrounding four potential pathways for carbon dioxide removal or avoided emissions. Environmental Defense Fund, New York, NY. https://www.edf.org/sites/default/files/2022-10/Natural%20Climate%20Solutions%20in%20the%20Open%20Ocean.pdf .

Sequestration Durability: Unknown.

Challenges

• More research is needed to understand carbon fluxes and life cycle emissions before developing strategies to increase carbon uptake and sequestration.

Key Knowledge Gaps

Adapted from EDF Natural Climate Solutions in the Open Ocean

• Lack of knowledge around the natural senescence or resulting deadfalls of fishes
• What is the contribution of fishes to inorganic carbon export via carbonate excretion?
• What is the total biomass of fishes, the fluxes in these communities, and conversion factors to go from biomass to units of carbon?
• How to discern between active carbon transport from mesopelagic fish versus from zooplankton?
• What is the composition of mesopelagic communities and what are the differences in roles played by small fishes versus other species such as cephalopods?

First-Order Priorities

*Adapted from EDF Natural Climate Solutions in the Open Ocean

• Conduct studies observing the natural senescence or resulting deadfalls of fishes*
• Conduct additional studies to understand the contribution of fishes to inorganic carbon export via carbonate excretion^[10]Salter, Michael A., et al. “Calcium carbonate production by fish in temperate Marine Environments.” Limnology and Oceanography, vol. 64, no. 6, 2019, pp. 2755–2770, https://doi.org/10.1002/lno.11339. *
• Create new models, observing technologies, and data to better constrain the total biomass of fishes, the fluxes in these communities, and conversion factors to go from biomass to units of carbon*
• Create new observational methods and models to better discern between active carbon transport from mesopelagic fish versus from zooplankton*
• Conduct studies to better understand the composition of mesopelagic communities to determine the difference in roles played by small fishes versus other species such as cephalopods*

While fishes have not traditionally been considered as important parts of the ocean carbon cycle / biological pump^[1]Sarmiento, Jorge L., and Nicolas Gruber. 2006. “Organic Matter Production.” In Ocean Biogeochemical Dynamics, 117–72. Princeton, N.J.: Princeton University Press. , there are several recent studies, as highlighted in the 2022 Environmental Defense Fund report “Natural Climate Solutions in the Open Ocean”, that focus on the geochemical contributions of fishes to the global carbon cycle^[2]Wilson, Rod W., F. J. Millero, J. R. Taylor, P. J. Walsh, V. Christensen, S. Jennings, and M. Grosell. 2009. “Contribution of Fish to the Marine Inorganic Carbon Cycle.” Science 323 (5912): 359–62. doi.org/10.1126/ science.1157972. ^[3]Boyd, Philip W., Hervé Claustre, Marina Levy, David A. Siegel and Thomas Weber. 2019. “Multi-Faceted Particle Pumps Drive Carbon Sequestration in the Ocean.” Nature 568 (7752): 327–35. doi.org/10.1038/s41586-019-1098-2. ^[4]Mariani, Gaël, William W. L. Cheung, Arnaud Lyet, Enric Sala, Juan Mayorga, Laure Velez, Steven D. Gaines, Tony Dejean, Marc Troussellier, and David Mouillot. 2020. “Let More Big Fish Sink: Fisheries Prevent Blue Carbon SequestrationHalf in Unprofitable Areas.” Science Advances 6 (44): eabb4848. doi.org/10.1126/sciadv.abb4848. ^[5]Bianchi, Daniele, David A. Carozza, Eric D. Galbraith, Jérôme Guiet, and Timothy DeVries. 2021. “Estimating Global Biomass and Biogeochemical Cycling of Marine Fish with and without Fishing.” Science Advances 7 (41): eabd7554. doi.org/10.1126/sciadv.abd7554. ^[6]Saba, Grace K., Adrian B. Burd, John P. Dunne, Santiago Hernández-León, Angela H. Martin, Kenneth A. Rose, Joseph Salisbury, et al., 2021. “Toward a Better Understanding of Fish-Based Contribution to Ocean Carbon Flux.” Limnology and Oceanography 66 (5): 1639–64. doi.org/10.1002/ lno.11709. . Many of the mechanisms by which fish are thought to contribute to carbon cycling are similar to whales (carbon stored in living biomass, bioturbation, carcasses falling to ocean floor, fertilization through feces) but also include contribution by intestinal precipitation of calcium carbonates^[7]Wilson, Rod W., F. J. Millero, J. R. Taylor, P. J. Walsh, V. Christensen, S. Jennings, and M. Grosell. 2009. “Contribution of Fish to the Marine Inorganic Carbon Cycle.” Science 323 (5912): 359–62. doi.org/10.1126/ science.1157972. .

There is still uncertainty around the specifics of mesopelagic fish-mediated carbon export, however the 2022 Environmental Defense Fund report suggests there is enough evidence of these species’ large contributions to global sequestration to warrant “the immediate pursuit of limitations or prohibitions on their harvest”.

Mechanism for CDR

CDR Potential

Estimated Sequestration Potential: Unclear, due to large knowledge gaps around biomass estimates of marine fish stocks, uncertainties in direct and indirect carbon export and overall carbon fluxes, few studies observing natural senescence / dead falls of fishes, and a poor understanding of the life cycle emissions of most fish species^[9]Collins, J. R., Boenish, R. E., Fujita, R. M., Rader, D. N., and Moore, L. A. 2022. Natural climate solutions in the open ocean: scientific knowledge and opportunities surrounding four potential pathways for carbon dioxide removal or avoided emissions. Environmental Defense Fund, New York, NY. https://www.edf.org/sites/default/files/2022-10/Natural%20Climate%20Solutions%20in%20the%20Open%20Ocean.pdf .

Sequestration Durability: Unknown.

Challenges

• More research is needed to understand carbon fluxes and life cycle emissions before developing strategies to increase carbon uptake and sequestration.

Key Knowledge Gaps

Adapted from EDF Natural Climate Solutions in the Open Ocean

• Lack of knowledge around the natural senescence or resulting deadfalls of fishes
• What is the contribution of fishes to inorganic carbon export via carbonate excretion?
• What is the total biomass of fishes, the fluxes in these communities, and conversion factors to go from biomass to units of carbon?
• How to discern between active carbon transport from mesopelagic fish versus from zooplankton?
• What is the composition of mesopelagic communities and what are the differences in roles played by small fishes versus other species such as cephalopods?

First-Order Priorities

*Adapted from EDF Natural Climate Solutions in the Open Ocean

• Conduct studies observing the natural senescence or resulting deadfalls of fishes*
• Conduct additional studies to understand the contribution of fishes to inorganic carbon export via carbonate excretion^[10]Salter, Michael A., et al. “Calcium carbonate production by fish in temperate Marine Environments.” Limnology and Oceanography, vol. 64, no. 6, 2019, pp. 2755–2770, https://doi.org/10.1002/lno.11339. *
• Create new models, observing technologies, and data to better constrain the total biomass of fishes, the fluxes in these communities, and conversion factors to go from biomass to units of carbon*
• Create new observational methods and models to better discern between active carbon transport from mesopelagic fish versus from zooplankton*
• Conduct studies to better understand the composition of mesopelagic communities to determine the difference in roles played by small fishes versus other species such as cephalopods*

While fishes have not traditionally been considered as important parts of the ocean carbon cycle / biological pump^[1]Sarmiento, Jorge L., and Nicolas Gruber. 2006. “Organic Matter Production.” In Ocean Biogeochemical Dynamics, 117–72. Princeton, N.J.: Princeton University Press. , there are several recent studies, as highlighted in the 2022 Environmental Defense Fund report “Natural Climate Solutions in the Open Ocean”, that focus on the geochemical contributions of fishes to the global carbon cycle^[2]Wilson, Rod W., F. J. Millero, J. R. Taylor, P. J. Walsh, V. Christensen, S. Jennings, and M. Grosell. 2009. “Contribution of Fish to the Marine Inorganic Carbon Cycle.” Science 323 (5912): 359–62. doi.org/10.1126/ science.1157972. ^[3]Boyd, Philip W., Hervé Claustre, Marina Levy, David A. Siegel and Thomas Weber. 2019. “Multi-Faceted Particle Pumps Drive Carbon Sequestration in the Ocean.” Nature 568 (7752): 327–35. doi.org/10.1038/s41586-019-1098-2. ^[4]Mariani, Gaël, William W. L. Cheung, Arnaud Lyet, Enric Sala, Juan Mayorga, Laure Velez, Steven D. Gaines, Tony Dejean, Marc Troussellier, and David Mouillot. 2020. “Let More Big Fish Sink: Fisheries Prevent Blue Carbon SequestrationHalf in Unprofitable Areas.” Science Advances 6 (44): eabb4848. doi.org/10.1126/sciadv.abb4848. ^[5]Bianchi, Daniele, David A. Carozza, Eric D. Galbraith, Jérôme Guiet, and Timothy DeVries. 2021. “Estimating Global Biomass and Biogeochemical Cycling of Marine Fish with and without Fishing.” Science Advances 7 (41): eabd7554. doi.org/10.1126/sciadv.abd7554. ^[6]Saba, Grace K., Adrian B. Burd, John P. Dunne, Santiago Hernández-León, Angela H. Martin, Kenneth A. Rose, Joseph Salisbury, et al., 2021. “Toward a Better Understanding of Fish-Based Contribution to Ocean Carbon Flux.” Limnology and Oceanography 66 (5): 1639–64. doi.org/10.1002/ lno.11709. . Many of the mechanisms by which fish are thought to contribute to carbon cycling are similar to whales (carbon stored in living biomass, bioturbation, carcasses falling to ocean floor, fertilization through feces) but also include contribution by intestinal precipitation of calcium carbonates^[7]Wilson, Rod W., F. J. Millero, J. R. Taylor, P. J. Walsh, V. Christensen, S. Jennings, and M. Grosell. 2009. “Contribution of Fish to the Marine Inorganic Carbon Cycle.” Science 323 (5912): 359–62. doi.org/10.1126/ science.1157972. .

There is still uncertainty around the specifics of mesopelagic fish-mediated carbon export, however the 2022 Environmental Defense Fund report suggests there is enough evidence of these species’ large contributions to global sequestration to warrant “the immediate pursuit of limitations or prohibitions on their harvest”.

Mechanism for CDR

CDR Potential

Estimated Sequestration Potential: Unclear, due to large knowledge gaps around biomass estimates of marine fish stocks, uncertainties in direct and indirect carbon export and overall carbon fluxes, few studies observing natural senescence / dead falls of fishes, and a poor understanding of the life cycle emissions of most fish species^[9]Collins, J. R., Boenish, R. E., Fujita, R. M., Rader, D. N., and Moore, L. A. 2022. Natural climate solutions in the open ocean: scientific knowledge and opportunities surrounding four potential pathways for carbon dioxide removal or avoided emissions. Environmental Defense Fund, New York, NY. https://www.edf.org/sites/default/ files/2022-10/Natural%20Climate%20Solutions%20in%20the%20Open%20Ocean.pdf .

Sequestration Durability: Unknown.

Challenges

• More research is needed to understand carbon fluxes and life cycle emissions before developing strategies to increase carbon uptake and sequestration.

Key Knowledge Gaps

Adapted from EDF Natural Climate Solutions in the Open Ocean

• Lack of knowledge around the natural senescence or resulting deadfalls of fishes
• What is the contribution of fishes to inorganic carbon export via carbonate excretion?
• What is the total biomass of fishes, the fluxes in these communities, and conversion factors to go from biomass to units of carbon?
• How to discern between active carbon transport from mesopelagic fish versus from zooplankton?
• What is the composition of mesopelagic communities and what are the differences in roles played by small fishes versus other species such as cephalopods?

First-Order Priorities

*Adapted from EDF Natural Climate Solutions in the Open Ocean

• Conduct studies observing the natural senescence or resulting deadfalls of fishes*
• Conduct additional studies to understand the contribution of fishes to inorganic carbon export via carbonate excretion^[10]Salter, Michael A., et al. “Calcium carbonate production by fish in temperate Marine Environments.” Limnology and Oceanography, vol. 64, no. 6, 2019, pp. 2755–2770, https://doi.org/10.1002/lno.11339. *
• Create new models, observing technologies, and data to better constrain the total biomass of fishes, the fluxes in these communities, and conversion factors to go from biomass to units of carbon*
• Create new observational methods and models to better discern between active carbon transport from mesopelagic fish versus from zooplankton*
• Conduct studies to better understand the composition of mesopelagic communities to determine the difference in roles played by small fishes versus other species such as cephalopods*

While fishes have not traditionally been considered as important parts of the ocean carbon cycle / biological pump^[1]Sarmiento, Jorge L., and Nicolas Gruber. 2006. “Organic Matter Production.” In Ocean Biogeochemical Dynamics, 117–72. Princeton, N.J.: Princeton University Press. , there are several recent studies, as highlighted in the 2022 Environmental Defense Fund report “Natural Climate Solutions in the Open Ocean”, that focus on the geochemical contributions of fishes to the global carbon cycle^[2]Wilson, Rod W., F. J. Millero, J. R. Taylor, P. J. Walsh, V. Christensen, S. Jennings, and M. Grosell. 2009. “Contribution of Fish to the Marine Inorganic Carbon Cycle.” Science 323 (5912): 359–62. doi.org/10.1126/ science.1157972. ,^[3]Boyd, Philip W., Hervé Claustre, Marina Levy, David A. Siegel and Thomas Weber. 2019. “Multi-Faceted Particle Pumps Drive Carbon Sequestration in the Ocean.” Nature 568 (7752): 327–35. doi.org/10.1038/s41586-019-1098-2. ,^[4]Mariani, Gaël, William W. L. Cheung, Arnaud Lyet, Enric Sala, Juan Mayorga, Laure Velez, Steven D. Gaines, Tony Dejean, Marc Troussellier, and David Mouillot. 2020. “Let More Big Fish Sink: Fisheries Prevent Blue Carbon SequestrationHalf in Unprofitable Areas.” Science Advances 6 (44): eabb4848. doi.org/10.1126/sciadv.abb4848. ,^[5]Bianchi, Daniele, David A. Carozza, Eric D. Galbraith, Jérôme Guiet, and Timothy DeVries. 2021. “Estimating Global Biomass and Biogeochemical Cycling of Marine Fish with and without Fishing.” Science Advances 7 (41): eabd7554. doi.org/10.1126/sciadv.abd7554. ,^[6]Saba, Grace K., Adrian B. Burd, John P. Dunne, Santiago Hernández-León, Angela H. Martin, Kenneth A. Rose, Joseph Salisbury, et al., 2021. “Toward a Better Understanding of Fish-Based Contribution to Ocean Carbon Flux.” Limnology and Oceanography 66 (5): 1639–64. doi.org/10.1002/ lno.11709. . Many of the mechanisms by which fish are thought to contribute to carbon cycling are similar to whales (carbon stored in living biomass, bioturbation, carcasses falling to ocean floor, fertilization through feces) but also include contribution by intestinal precipitation of calcium carbonates^[7]Wilson, Rod W., F. J. Millero, J. R. Taylor, P. J. Walsh, V. Christensen, S. Jennings, and M. Grosell. 2009. “Contribution of Fish to the Marine Inorganic Carbon Cycle.” Science 323 (5912): 359–62. doi.org/10.1126/ science.1157972. .

There is still uncertainty around the specifics of mesopelagic fish-mediated carbon export, however the 2022 Environmental Defense Fund report suggests there is enough evidence of these species’ large contributions to global sequestration to warrant “the immediate pursuit of limitations or prohibitions on their harvest”.

Mechanism for CDR

CDR Potential

Estimated Sequestration Potential: Unclear, due to large knowledge gaps around biomass estimates of marine fish stocks, uncertainties in direct and indirect carbon export and overall carbon fluxes, few studies observing natural senescence / dead falls of fishes, and a poor understanding of the life cycle emissions of most fish species^[9]Collins, J. R., Boenish, R. E., Fujita, R. M., Rader, D. N., and Moore, L. A. 2022. Natural climate solutions in the open ocean: scientific knowledge and opportunities surrounding four potential pathways for carbon dioxide removal or avoided emissions. Environmental Defense Fund, New York, NY. www.edf.org/sites/default/ files/2022-10/Natural%20Climate%20Solutions%20in%20the%20Open%20Ocean.pdf .

Sequestration Durability: Unknown.

Challenges

• More research is needed to understand carbon fluxes and life cycle emissions before developing strategies to increase carbon uptake and sequestration.

Key Knowledge Gaps

Adapted from EDF Natural Climate Solutions in the Open Ocean

• Lack of knowledge around the natural senescence or resulting deadfalls of fishes
• What is the contribution of fishes to inorganic carbon export via carbonate excretion?
• What is the total biomass of fishes, the fluxes in these communities, and conversion factors to go from biomass to units of carbon?
• How to discern between active carbon transport from mesopelagic fish versus from zooplankton?
• What is the composition of mesopelagic communities and what are the differences in roles played by small fishes versus other species such as cephalopods?

First-Order Priorities

*Adapted from EDF Natural Climate Solutions in the Open Ocean

• Conduct studies observing the natural senescence or resulting deadfalls of fishes*
• Conduct additional studies to understand the contribution of fishes to inorganic carbon export via carbonate excretion^[10]Salter, Michael A., et al. “Calcium carbonate production by fish in temperate Marine Environments.” Limnology and Oceanography, vol. 64, no. 6, 2019, pp. 2755–2770, https://doi.org/10.1002/lno.11339. *
• Create new models, observing technologies, and data to better constrain the total biomass of fishes, the fluxes in these communities, and conversion factors to go from biomass to units of carbon*
• Create new observational methods and models to better discern between active carbon transport from mesopelagic fish versus from zooplankton*
• Conduct studies to better understand the composition of mesopelagic communities to determine the difference in roles played by small fishes versus other species such as cephalopods*

While fishes have not traditionally been considered as important parts of the ocean carbon cycle / biological pump^[1]Sarmiento, Jorge L., and Nicolas Gruber. 2006. “Organic Matter Production.” In Ocean Biogeochemical Dynamics, 117–72. Princeton, N.J.: Princeton University Press. , there are several recent studies, as highlighted in the 2022 Environmental Defense Fund report “Natural Climate Solutions in the Open Ocean”, that focus on the geochemical contributions of fishes to the global carbon cycle^[2]Wilson, Rod W., F. J. Millero, J. R. Taylor, P. J. Walsh, V. Christensen, S. Jennings, and M. Grosell. 2009. “Contribution of Fish to the Marine Inorganic Carbon Cycle.” Science 323 (5912): 359–62. doi.org/10.1126/ science.1157972. ,^[3]Boyd, Philip W., Hervé Claustre, Marina Levy, David A. Siegel and Thomas Weber. 2019. “Multi-Faceted Particle Pumps Drive Carbon Sequestration in the Ocean.” Nature 568 (7752): 327–35. doi.org/10.1038/s41586-019-1098-2. ,^[4]Mariani, Gaël, William W. L. Cheung, Arnaud Lyet, Enric Sala, Juan Mayorga, Laure Velez, Steven D. Gaines, Tony Dejean, Marc Troussellier, and David Mouillot. 2020. “Let More Big Fish Sink: Fisheries Prevent Blue Carbon SequestrationHalf in Unprofitable Areas.” Science Advances 6 (44): eabb4848. doi.org/10.1126/sciadv.abb4848. ,^[5]Bianchi, Daniele, David A. Carozza, Eric D. Galbraith, Jérôme Guiet, and Timothy DeVries. 2021. “Estimating Global Biomass and Biogeochemical Cycling of Marine Fish with and without Fishing.” Science Advances 7 (41): eabd7554. doi.org/10.1126/sciadv.abd7554. ,^[6]Saba, Grace K., Adrian B. Burd, John P. Dunne, Santiago Hernández-León, Angela H. Martin, Kenneth A. Rose, Joseph Salisbury, et al., 2021. “Toward a Better Understanding of Fish-Based Contribution to Ocean Carbon Flux.” Limnology and Oceanography 66 (5): 1639–64. doi.org/10.1002/ lno.11709. . Many of the mechanisms by which fish are thought to contribute to carbon cycling are similar to whales (carbon stored in living biomass, bioturbation, carcasses falling to ocean floor, fertilization through feces) but also include contribution by intestinal precipitation of calcium carbonates^[7]Wilson, Rod W., F. J. Millero, J. R. Taylor, P. J. Walsh, V. Christensen, S. Jennings, and M. Grosell. 2009. “Contribution of Fish to the Marine Inorganic Carbon Cycle.” Science 323 (5912): 359–62. doi.org/10.1126/ science.1157972. .

There is still uncertainty around the specifics of mesopelagic fish-mediated carbon export, however the 2022 Environmental Defense Fund report suggests there is enough evidence of these species’ large contributions to global sequestration to warrant “the immediate pursuit of limitations or prohibitions on their harvest”.

Mechanism for CDR

CDR Potential

Estimated Sequestration Potential: Unclear, due to large knowledge gaps around biomass estimates of marine fish stocks, uncertainties in direct and indirect carbon export and overall carbon fluxes, few studies observing natural senescence / dead falls of fishes, and a poor understanding of the life cycle emissions of most fish species^[9]Collins, J. R., Boenish, R. E., Fujita, R. M., Rader, D. N., and Moore, L. A. 2022. Natural climate solutions in the open ocean: scientific knowledge and opportunities surrounding four potential pathways for carbon dioxide removal or avoided emissions. Environmental Defense Fund, New York, NY. www.edf.org/sites/default/ files/2022-10/Natural%20Climate%20Solutions%20in%20the%20Open%20Ocean.pdf .

Sequestration Durability: Unknown.

Challenges

• More research is needed to understand carbon fluxes and life cycle emissions before developing strategies to increase carbon uptake and sequestration.

Key Knowledge Gaps

Adapted from EDF Natural Climate Solutions in the Open Ocean

• Lack of knowledge around the natural senescence or resulting deadfalls of fishes
• What is the contribution of fishes to inorganic carbon export via carbonate excretion?
• What is the total biomass of fishes, the fluxes in these communities, and conversion factors to go from biomass to units of carbon?
• How to discern between active carbon transport from mesopelagic fish versus from zooplankton?
• What is the composition of mesopelagic communities and what are the differences in roles played by small fishes versus other species such as cephalopods?

First Order Priorities

*Adapted from EDF Natural Climate Solutions in the Open Ocean

• Conduct studies observing the natural senescence or resulting deadfalls of fishes*
• Conduct additional studies to understand the contribution of fishes to inorganic carbon export via carbonate excretion^[10]Salter, Michael A., et al. “Calcium carbonate production by fish in temperate Marine Environments.” Limnology and Oceanography, vol. 64, no. 6, 2019, pp. 2755–2770, https://doi.org/10.1002/lno.11339. *
• Create new models, observing technologies, and data to better constrain the total biomass of fishes, the fluxes in these communities, and conversion factors to go from biomass to units of carbon*
• Create new observational methods and models to better discern between active carbon transport from mesopelagic fish versus from zooplankton*
• Conduct studies to better understand the composition of mesopelagic communities to determine the difference in roles played by small fishes versus other species such as cephalopods*

While fishes have not traditionally been considered as important parts of the ocean carbon cycle / biological pump^[1]Sarmiento, Jorge L., and Nicolas Gruber. 2006. “Organic Matter Production.” In Ocean Biogeochemical Dynamics, 117–72. Princeton, N.J.: Princeton University Press. , there are several recent studies, as highlighted in the 2022 Environmental Defense Fund report “Natural Climate Solutions in the Open Ocean”, that focus on the geochemical contributions of fishes to the global carbon cycle^[2]Wilson, Rod W., F. J. Millero, J. R. Taylor, P. J. Walsh, V. Christensen, S. Jennings, and M. Grosell. 2009. “Contribution of Fish to the Marine Inorganic Carbon Cycle.” Science 323 (5912): 359–62. doi.org/10.1126/ science.1157972. ,^[3]Boyd, Philip W., Hervé Claustre, Marina Levy, David A. Siegel and Thomas Weber. 2019. “Multi-Faceted Particle Pumps Drive Carbon Sequestration in the Ocean.” Nature 568 (7752): 327–35. doi.org/10.1038/s41586-019-1098-2. ,^[4]Mariani, Gaël, William W. L. Cheung, Arnaud Lyet, Enric Sala, Juan Mayorga, Laure Velez, Steven D. Gaines, Tony Dejean, Marc Troussellier, and David Mouillot. 2020. “Let More Big Fish Sink: Fisheries Prevent Blue Carbon SequestrationHalf in Unprofitable Areas.” Science Advances 6 (44): eabb4848. doi.org/10.1126/sciadv.abb4848. ,^[5]Bianchi, Daniele, David A. Carozza, Eric D. Galbraith, Jérôme Guiet, and Timothy DeVries. 2021. “Estimating Global Biomass and Biogeochemical Cycling of Marine Fish with and without Fishing.” Science Advances 7 (41): eabd7554. doi.org/10.1126/sciadv.abd7554. ,^[6]Saba, Grace K., Adrian B. Burd, John P. Dunne, Santiago Hernández-León, Angela H. Martin, Kenneth A. Rose, Joseph Salisbury, et al., 2021. “Toward a Better Understanding of Fish-Based Contribution to Ocean Carbon Flux.” Limnology and Oceanography 66 (5): 1639–64. doi.org/10.1002/ lno.11709. . Many of the mechanisms by which fish are thought to contribute to carbon cycling are similar to whales (carbon stored in living biomass, bioturbation, carcasses falling to ocean floor, fertilization through feces) but also include contribution by intestinal precipitation of calcium carbonates^[7]Wilson, Rod W., F. J. Millero, J. R. Taylor, P. J. Walsh, V. Christensen, S. Jennings, and M. Grosell. 2009. “Contribution of Fish to the Marine Inorganic Carbon Cycle.” Science 323 (5912): 359–62. doi.org/10.1126/ science.1157972. .

There is still uncertainty around the specifics of mesopelagic fish-mediated carbon export, however the 2022 Environmental Defense Fund report suggests there is enough evidence of these species’ large contributions to global sequestration to warrant “the immediate pursuit of limitations or prohibitions on their harvest”.

Mechanism for CDR

CDR Potential

Estimated Sequestration Potential: Unclear, due to large knowledge gaps around biomass estimates of marine fish stocks, uncertainties in direct and indirect carbon export and overall carbon fluxes, few studies observing natural senescence / dead falls of fishes, and a poor understanding of the life cycle emissions of most fish species^[9]Collins, J. R., Boenish, R. E., Fujita, R. M., Rader, D. N., and Moore, L. A. 2022. Natural climate solutions in the open ocean: scientific knowledge and opportunities surrounding four potential pathways for carbon dioxide removal or avoided emissions. Environmental Defense Fund, New York, NY. www.edf.org/sites/default/ files/2022-10/Natural%20Climate%20Solutions%20in%20the%20Open%20Ocean.pdf .

Sequestration Durability: Unknown.

Challenges

• More research is needed to understand carbon fluxes and life cycle emissions before developing strategies to increase carbon uptake and sequestration.

Key Knowledge Gaps

Adapted from EDF Natural Climate Solutions in the Open Ocean

• Lack of knowledge around the natural senescence or resulting deadfalls of fishes
• What is the contribution of fishes to inorganic carbon export via carbonate excretion?
• What is the total biomass of fishes, the fluxes in these communities, and conversion factors to go from biomass to units of carbon?
• How to discern between active carbon transport from mesopelagic fish versus from zooplankton?
• What is the composition of mesopelagic communities and what are the differences in roles played by small fishes versus other species such as cephalopods?

First Order Priorities

*Adapted from EDF Natural Climate Solutions in the Open Ocean

• Conduct studies observing the natural senescence or resulting deadfalls of fishes*
• Conduct additional studies to understand the contribution of fishes to inorganic carbon export via carbonate excretion^[10]Salter, Michael A., et al. “Calcium carbonate production by fish in temperate Marine Environments.” Limnology and Oceanography, vol. 64, no. 6, 2019, pp. 2755–2770, https://doi.org/10.1002/lno.11339. *
• Create new models, observing technologies, and data to better constrain the total biomass of fishes, the fluxes in these communities, and conversion factors to go from biomass to units of carbon*
• Create new observational methods and models to better discern between active carbon transport from mesopelagic fish versus from zooplankton*
• Conduct studies to better understand the composition of mesopelagic communities to determine the difference in roles played by small fishes versus other species such as cephalopods*

While fishes have not traditionally been considered as important parts of the ocean carbon cycle / biological pump^[1]Sarmiento, Jorge L., and Nicolas Gruber. 2006. “Organic Matter Production.” In Ocean Biogeochemical Dynamics, 117–72. Princeton, N.J.: Princeton University Press. , there are several recent studies, as highlighted in the 2022 Environmental Defense Fund report “Natural Climate Solutions in the Open Ocean”, that focus on the geochemical contributions of fishes to the global carbon cycle^[2]Wilson, Rod W., F. J. Millero, J. R. Taylor, P. J. Walsh, V. Christensen, S. Jennings, and M. Grosell. 2009. “Contribution of Fish to the Marine Inorganic Carbon Cycle.” Science 323 (5912): 359–62. doi.org/10.1126/ science.1157972. ,^[3]Boyd, Philip W., Hervé Claustre, Marina Levy, David A. Siegel and Thomas Weber. 2019. “Multi-Faceted Particle Pumps Drive Carbon Sequestration in the Ocean.” Nature 568 (7752): 327–35. doi.org/10.1038/s41586-019-1098-2. ,^[4]Mariani, Gaël, William W. L. Cheung, Arnaud Lyet, Enric Sala, Juan Mayorga, Laure Velez, Steven D. Gaines, Tony Dejean, Marc Troussellier, and David Mouillot. 2020. “Let More Big Fish Sink: Fisheries Prevent Blue Carbon SequestrationHalf in Unprofitable Areas.” Science Advances 6 (44): eabb4848. doi.org/10.1126/sciadv.abb4848. ,^[5]Bianchi, Daniele, David A. Carozza, Eric D. Galbraith, Jérôme Guiet, and Timothy DeVries. 2021. “Estimating Global Biomass and Biogeochemical Cycling of Marine Fish with and without Fishing.” Science Advances 7 (41): eabd7554. doi.org/10.1126/sciadv.abd7554. ,^[6]Saba, Grace K., Adrian B. Burd, John P. Dunne, Santiago Hernández-León, Angela H. Martin, Kenneth A. Rose, Joseph Salisbury, et al., 2021. “Toward a Better Understanding of Fish-Based Contribution to Ocean Carbon Flux.” Limnology and Oceanography 66 (5): 1639–64. doi.org/10.1002/ lno.11709. . Many of the mechanisms by which fish are thought to contribute to carbon cycling are similar to whales (carbon stored in living biomass, bioturbation, carcasses falling to ocean floor, fertilization through feces) but also include contribution by intestinal precipitation of calcium carbonates^[7]Wilson, Rod W., F. J. Millero, J. R. Taylor, P. J. Walsh, V. Christensen, S. Jennings, and M. Grosell. 2009. “Contribution of Fish to the Marine Inorganic Carbon Cycle.” Science 323 (5912): 359–62. doi.org/10.1126/ science.1157972. .

There is still uncertainty around the specifics of mesopelagic fish-mediated carbon export, however the 2022 Environmental Defense Fund report suggests there is enough evidence of these species’ large contributions to global sequestration to warrant “the immediate pursuit of limitations or prohibitions on their harvest”.

Mechanism for CDR

• Limitations or prohibitions on harvest may increase the living biomass of fish, inducing higher natural long-term carbon sequestration by increasing carcass deadfall. Previous studies that evaluate the effectiveness of reducing fishing and establishing marine protected areas to address climate change suggest that these efforts support climate adaptation^[8]J.-P. Gattuso, A. K. Magnan, L. Bopp, W. W. L. Cheung, C. M. Duarte, J. Hinkel, E. McLeod, F. Micheli, A. Oschlies, P. Williamson, R. Bille, V. I. Chalastani, R. D. Gates, J. O. Irisson, J. J. Middelburg, H. O. Portner, G. H. Rau, Ocean solutions to address climate change and its effects on marine ecosystems. Front. Mar. Sci. 5, 337 (2018). .

CDR Potential

Estimated Sequestration Potential: Unclear, due to large knowledge gaps around biomass estimates of marine fish stocks, uncertainties in direct and indirect carbon export and overall carbon fluxes, few studies observing natural senescence / dead falls of fishes, and a poor understanding of the life cycle emissions of most fish species^[9]Collins, J. R., Boenish, R. E., Fujita, R. M., Rader, D. N., and Moore, L. A. 2022. Natural climate solutions in the open ocean: scientific knowledge and opportunities surrounding four potential pathways for carbon dioxide removal or avoided emissions. Environmental Defense Fund, New York, NY. www.edf.org/sites/default/ files/2022-10/Natural%20Climate%20Solutions%20in%20the%20Open%20Ocean.pdf .

Sequestration Durability: Unknown.

Challenges

• More research is needed to understand carbon fluxes and life cycle emissions before developing strategies to increase carbon uptake and sequestration.

Key Knowledge Gaps

Adapted from EDF Natural Climate Solutions in the Open Ocean

• Lack of knowledge around the natural senescence or resulting deadfalls of fishes
• What is the contribution of fishes to inorganic carbon export via carbonate excretion?
• What is the total biomass of fishes, the fluxes in these communities, and conversion factors to go from biomass to units of carbon?
• How to discern between active carbon transport from mesopelagic fish versus from zooplankton?
• What is the composition of mesopelagic communities and what are the differences in roles played by small fishes versus other species such as cephalopods?

First Order Priorities

*Adapted from EDF Natural Climate Solutions in the Open Ocean

• Conduct studies observing the natural senescence or resulting deadfalls of fishes*
• Conduct additional studies to understand the contribution of fishes to inorganic carbon export via carbonate excretion^[10]Salter, Michael A., et al. “Calcium carbonate production by fish in temperate Marine Environments.” Limnology and Oceanography, vol. 64, no. 6, 2019, pp. 2755–2770, https://doi.org/10.1002/lno.11339. *
• Create new models, observing technologies, and data to better constrain the total biomass of fishes, the fluxes in these communities, and conversion factors to go from biomass to units of carbon*
• Create new observational methods and models to better discern between active carbon transport from mesopelagic fish versus from zooplankton*
• Conduct studies to better understand the composition of mesopelagic communities to determine the difference in roles played by small fishes versus other species such as cephalopods*

While fishes have not traditionally been considered as important parts of the ocean carbon cycle / biological pump^[1]Sarmiento, Jorge L., and Nicolas Gruber. 2006. “Organic Matter Production.” In Ocean Biogeochemical Dynamics, 117–72. Princeton, N.J.: Princeton University Press. , there are several recent studies, as highlighted in the 2022 Environmental Defense Fund report “Natural Climate Solutions in the Open Ocean”, that focus on the geochemical contributions of fishes to the global carbon cycle^[2]Wilson, Rod W., F. J. Millero, J. R. Taylor, P. J. Walsh, V. Christensen, S. Jennings, and M. Grosell. 2009. “Contribution of Fish to the Marine Inorganic Carbon Cycle.” Science 323 (5912): 359–62. doi.org/10.1126/ science.1157972. ,^[3]Boyd, Philip W., Hervé Claustre, Marina Levy, David A. Siegel and Thomas Weber. 2019. “Multi-Faceted Particle Pumps Drive Carbon Sequestration in the Ocean.” Nature 568 (7752): 327–35. doi.org/10.1038/s41586-019-1098-2. ,^[4]Mariani, Gaël, William W. L. Cheung, Arnaud Lyet, Enric Sala, Juan Mayorga, Laure Velez, Steven D. Gaines, Tony Dejean, Marc Troussellier, and David Mouillot. 2020. “Let More Big Fish Sink: Fisheries Prevent Blue Carbon SequestrationHalf in Unprofitable Areas.” Science Advances 6 (44): eabb4848. doi.org/10.1126/sciadv.abb4848. ,^[5]Bianchi, Daniele, David A. Carozza, Eric D. Galbraith, Jérôme Guiet, and Timothy DeVries. 2021. “Estimating Global Biomass and Biogeochemical Cycling of Marine Fish with and without Fishing.” Science Advances 7 (41): eabd7554. doi.org/10.1126/sciadv.abd7554. ,^[6]Saba, Grace K., Adrian B. Burd, John P. Dunne, Santiago Hernández-León, Angela H. Martin, Kenneth A. Rose, Joseph Salisbury, et al., 2021. “Toward a Better Understanding of Fish-Based Contribution to Ocean Carbon Flux.” Limnology and Oceanography 66 (5): 1639–64. doi.org/10.1002/ lno.11709. . Many of the mechanisms by which fish are thought to contribute to carbon cycling are similar to whales (carbon stored in living biomass, bioturbation, carcasses falling to ocean floor, fertilization through feces) but also include contribution by intestinal precipitation of calcium carbonates^[7]Wilson, Rod W., F. J. Millero, J. R. Taylor, P. J. Walsh, V. Christensen, S. Jennings, and M. Grosell. 2009. “Contribution of Fish to the Marine Inorganic Carbon Cycle.” Science 323 (5912): 359–62. doi.org/10.1126/ science.1157972. .

There is still uncertainty around the specifics of mesopelagic fish-mediated carbon export, however the 2022 Environmental Defense Fund report suggests there is enough evidence of these species’ large contributions to global sequestration to warrant “the immediate pursuit of limitations or prohibitions on their harvest”.

Mechanism for CDR

• Limitations or prohibitions on harvest may increase the living biomass of fish, inducing higher natural long-term carbon sequestration by increasing carcass deadfall. Previous studies that evaluate the effectiveness of reducing fishing and establishing marine protected areas to address climate change suggest that these efforts support climate adaptation^[8]J.-P. Gattuso, A. K. Magnan, L. Bopp, W. W. L. Cheung, C. M. Duarte, J. Hinkel, E. McLeod, F. Micheli, A. Oschlies, P. Williamson, R. Bille, V. I. Chalastani, R. D. Gates, J. O. Irisson, J. J. Middelburg, H. O. Portner, G. H. Rau, Ocean solutions to address climate change and its effects on marine ecosystems. Front. Mar. Sci. 5, 337 (2018). .

CDR Potential

Estimated Sequestration Potential: Unclear, due to large knowledge gaps around biomass estimates of marine fish stocks, uncertainties in direct and indirect carbon export and overall carbon fluxes, few studies observing natural senescence / dead falls of fishes, and a poor understanding of the life cycle emissions of most fish species^[9]Collins, J. R., Boenish, R. E., Fujita, R. M., Rader, D. N., and Moore, L. A. 2022. Natural climate solutions in the open ocean: scientific knowledge and opportunities surrounding four potential pathways for carbon dioxide removal or avoided emissions. Environmental Defense Fund, New York, NY. www.edf.org/sites/default/ files/2022-10/Natural%20Climate%20Solutions%20in%20the%20Open%20Ocean.pdf .

Sequestration Durability: Unknown.

Challenges

• More research is needed to understand carbon fluxes and life cycle emissions before developing strategies to increase carbon uptake and sequestration.

Key Knowledge Gaps

Adapted from EDF Natural Climate Solutions in the Open Ocean

• Lack of knowledge around the natural senescence or resulting deadfalls of fishes
• What is the contribution of fishes to inorganic carbon export via carbonate excretion?
• What is the total biomass of fishes, the fluxes in these communities, and conversion factors to go from biomass to units of carbon?
• How to discern between active carbon transport from mesopelagic fish versus from zooplankton?
• What is the composition of mesopelagic communities and what are the differences in roles played by small fishes versus other species such as cephalopods?

First Order Priorities

*Adapted from EDF Natural Climate Solutions in the Open Ocean

• Conduct studies observing the natural senescence or resulting deadfalls of fishes*
• Conduct additional studies to understand the contribution of fishes to inorganic carbon export via carbonate excretion^[10]Salter, Michael A., et al. “Calcium carbonate production by fish in temperate Marine Environments.” Limnology and Oceanography, vol. 64, no. 6, 2019, pp. 2755–2770, https://doi.org/10.1002/lno.11339. *
• Create new models, observing technologies, and data to better constrain the total biomass of fishes, the fluxes in these communities, and conversion factors to go from biomass to units of carbon*
• Create new observational methods and models to better discern between active carbon transport from mesopelagic fish versus from zooplankton*
• Conduct studies to better understand the composition of mesopelagic communities to determine the difference in roles played by small fishes versus other species such as cephalopods*

• Nutrient cycling
• Restoring the role of marine organisms in the carbon cycle

• Nutrient cycling^[1]Ratnarajah L, Bowie AR, Lannuzel D, Meiners KM, Nicol S (2014) The Biogeochemical Role of Baleen Whales and Krill in Southern Ocean Nutrient Cycling. PLoSONE9(12):e114067. doi:10.1371/journal.pone.0114067
• Restoring the role of marine organisms in the carbon cycle^[2]National Academies of Sciences, Engineering, and Medicine 2022. A Research Strategy for Ocean-based Carbon Dioxide Removal and Sequestration. Washington, DC: The National Academies Press. https://doi.org/10.17226/26278.

1. Open systems where the open ocean is directly manipulated to enhance biological production, capture atmospheric CO₂, and export the captured carbon to the deep ocean. In open systems, CO₂ fixation is facilitated by the addition of limiting macronutrients (e.g., phosphorus, nitrogen, silica) and/or micronutrients (e.g., iron) to the ocean’s surface to augment biological production . Open system techniques accelerate natural processes already occurring in the ocean. Most approaches in the open ocean fall into the following two categories (some proposals that do not fit into these categories are also explored).
   1. Surface nutrient addition: the direct addition of nutrients (macro or micro) into ocean waters in situ to increase microalgal growth 
   2. Nutrient upwelling: artificial upwelling of nutrient-rich deep ocean waters to the surface to increase microalgal growth
2. Closed systems where inputs and growth conditions are controlled, and outputs (microalgae) are harvested within the confines of a pond or a photobioreactor. In closed systems, CO₂ fixation is facilitated by the mixing of required inputs (sunlight, nutrients, CO₂, water) and the introduction of microalgae culture with the intention of reproduction and continuous fixation in a contained system . This can be accomplished on shore in cultivation ponds or photobioreactors, or afloat in photobioreactors either stationary or towed at sea .

1. 1. Onshore: encompasses more established methods of microalgae cultivation, including photobioreactors, cultivation ponds, and hybrid onshore configurations. In these systems, all inputs are tightly controlled and regulated, and outputs must be directly managed through either storage or utilization of byproducts. While cultivation techniques are well-established and show high technological readiness, storage and utilization pathways remain underdeveloped and scale is a major consideration. Social and environmental risks for closed onshore systems are easier to monitor and mitigate due to the controlled nature of the system. 
   2. Offshore: includes floating photobioreactors (PBRs) that are incorporated into a floating platform which can be stationary or towed behind a ship. In these systems, cultivation occurs in the photobioreactor, inputs are regulated, and outputs can be actively managed or directed. While at sea, these photobioreactors operate much like their onshore counterparts to cultivate microalgae, however nutrients and energy are provided by the ocean water and wave action, respectively. After microalgae are cultivated, they can be sunk into the deep ocean for sequestration or hauled to shore to be used as biomass. This is an area that has garnered much attention in startup communities (see this Y Combinator request for startups), however, little is available about the technologies in the open-sourced or peer reviewed literature.

1. Open systems where the open ocean is directly manipulated to enhance biological production, capture atmospheric CO₂, and export the captured carbon to the deep ocean. In open systems, CO₂ fixation is facilitated by the addition of limiting macronutrients (e.g., phosphorus, nitrogen, silica) and/or micronutrients (e.g., iron) to the ocean’s surface to augment biological production . Open system techniques accelerate natural processes already occurring in the ocean. Most approaches in the open ocean fall into the following two categories (some proposals that do not fit into these categories are also explored).
   1. Surface nutrient addition: the direct addition of nutrients (macro or micro) into ocean waters in situ to increase microalgal growth 
   2. Nutrient upwelling: artificial upwelling of nutrient-rich deep ocean waters to the surface to increase microalgal growth
2. Closed systems where inputs and growth conditions are controlled, and outputs (microalgae) are harvested within the confines of a pond or a photobioreactor. In closed systems, CO₂ fixation is facilitated by the mixing of required inputs (sunlight, nutrients, CO₂, water) and the introduction of microalgae culture with the intention of reproduction and continuous fixation in a contained system . This can be accomplished on shore in cultivation ponds or photobioreactors, or afloat in photobioreactors either stationary or towed at sea .

1. 1. Onshore: encompasses more established methods of microalgae cultivation, including photobioreactors, cultivation ponds, and hybrid onshore configurations. In these systems, all inputs are tightly controlled and regulated, and outputs must be directly managed through either storage or utilization of byproducts. While cultivation techniques are well-established and show high technological readiness, storage and utilization pathways remain underdeveloped and scale is a major consideration. Social and environmental risks for closed onshore systems are easier to monitor and mitigate due to the controlled nature of the system. 
   2. Offshore: includes floating photobioreactors (PBRs) that are incorporated into a floating platform which can be stationary or towed behind a ship. In these systems, cultivation occurs in the photobioreactor, inputs are regulated, and outputs can be actively managed or directed. While at sea, these photobioreactors operate much like their onshore counterparts to cultivate microalgae, however nutrients and energy are provided by the ocean water and wave action, respectively. After microalgae are cultivated, they can be sunk into the deep ocean for sequestration or hauled to shore to be used as biomass. This is an area that has garnered much attention in startup communities (see this Y Combinator request for startups), however, little is available about the technologies in the open-sourced or peer reviewed literature.

Restoration of marine animal populations may generate many benefits for surrounding communities and economies. While we are calling these “co-benefits” here, it should be noted that some of these benefits may be so significant (while carbon sequestration feasibility and efficacy remain unknown) that these may in fact be the main benefits of restoration. Many of the environmental benefits relate directly to social benefits, such as fisheries enhancement and coastal protection. (Note that there are significantly more co-benefits in “blue carbon” than any of the other CDR Road Maps.)

• Potential for economic stimulation and job creation from enhanced tourism (e.g., whale watching - of particular value to coastal communities that are dependent on marine-based livelihoods)
• Cultural / intrinsic / recreational value
• Education and research – the pursuit of restoring blue carbon for CDR will naturally add value to the existing body of research and can provide valuable educational experiences for the upcoming generation of scientists and conservationists.

Restoration of whale stocks may generate many benefits for surrounding communities and economies. While we are calling these “co-benefits” here, it should be noted that some of these benefits may be so significant (while carbon sequestration feasibility and efficacy remain unknown) that these may in fact be the main benefits of restoration. Many of the environmental benefits relate directly to social benefits, such as fisheries enhancement and coastal protection. (Note that there are significantly more co-benefits in “blue carbon” than any of the other CDR Road Maps.)

• Potential for economic stimulation and job creation from enhanced tourism (e.g., whale watching - of particular value to coastal communities that are dependent on marine-based livelihoods)
• Cultural / intrinsic / recreational value
• Education and research – the pursuit of restoring blue carbon for CDR will naturally add value to the existing body of research and can provide valuable educational experiences for the upcoming generation of scientists and conservationists.

1. Open systems where the open ocean is directly manipulated to enhance biological production, capture atmospheric CO₂, and export the captured carbon to the deep ocean. In open systems, CO₂ fixation is facilitated by the addition of limiting macronutrients (e.g., phosphorus, nitrogen, silica) and/or micronutrients (e.g., iron) to the ocean’s surface to augment biological production . Open system techniques accelerate natural processes already occurring in the ocean. Most approaches in the open ocean fall into the following two categories (some proposals that do not fit into these categories are also explored).
   1. Surface nutrient addition: the direct addition of nutrients (macro or micro) into ocean waters in situ to increase microalgal growth 
   2. Nutrient upwelling: artificial upwelling of nutrient-rich deep ocean waters to the surface to increase microalgal growth
2. Closed systems where inputs and growth conditions are controlled, and outputs (microalgae) are harvested within the confines of a pond or a photobioreactor. In closed systems, CO₂ fixation is facilitated by the mixing of required inputs (sunlight, nutrients, CO₂, water) and the introduction of microalgae culture with the intention of reproduction and continuous fixation in a contained system . This can be accomplished on shore in cultivation ponds or photobioreactors, or afloat in photobioreactors either stationary or towed at sea .

1. 1. Onshore: encompasses more established methods of microalgae cultivation, including photobioreactors, cultivation ponds, and hybrid onshore configurations. In these systems, all inputs are tightly controlled and regulated, and outputs must be directly managed through either storage or utilization of byproducts. While cultivation techniques are well-established and show high technological readiness, storage and utilization pathways remain underdeveloped and scale is a major consideration. Social and environmental risks for closed onshore systems are easier to monitor and mitigate due to the controlled nature of the system. 
   2. Offshore: includes floating photobioreactors (PBRs) that are incorporated into a floating platform which can be stationary or towed behind a ship. In these systems, cultivation occurs in the photobioreactor, inputs are regulated, and outputs can be actively managed or directed. While at sea, these photobioreactors operate much like their onshore counterparts to cultivate microalgae, however nutrients and energy are provided by the ocean water and wave action, respectively. After microalgae are cultivated, they can be sunk into the deep ocean for sequestration or hauled to shore to be used as biomass. This is an area that has garnered much attention in startup communities (see this Y Combinator request for startups), however, little is available about the technologies in the open-sourced or peer reviewed literature.

Efforts around restoration efforts are often met with social acceptance and public support, especially when compared to other climate solutions seen as “tampering with nature”^[1]Wolske, K. S., K. T. Raimi, V. Campbell-Arvai, and P. S. Hart. 2019. “Public support for carbon dioxide removal strategies: the role of tampering with nature perceptions.” Climatic Change 152 (3-4):345-361. doi:10.1007/s10584-019-02375-z. . This may be in part due to the minimal risks (real and perceived) associated with restoration efforts. While some risks, outlined below, do exist, there may be a higher tolerance for such risks given the long list of potential benefits and co-benefits (both environmentally and socially).

• Potential for negative economic impacts to some industries such as oil and gas, fisheries, and mining^[2]National Academies of Sciences, Engineering, and Medicine 2022. A Research Strategy for Ocean-based Carbon Dioxide Removal and Sequestration. Washington, DC: The National Academies Press. https://doi.org/10.17226/26278.
• Stricter fisheries management to increase species abundances can cause impacts on food security, displacement, and economic strain. (for example, Marine Protected Areas can cause varied impacts among communities and social groups and can be met with opposition)^[3]Mascia, M. B., C. A. Claus, and R. Naidoo. 2010. Impacts of marine protected areas on fishing communities. Conservation Biology 24(5):1424-1429. doi:10.1111/j.1523-1739.2010.01523.x.

Efforts around restoring natural ecosystems are often met with social acceptance and public support, especially when compared to other climate solutions seen as “tampering with nature”^[1]Wolske, K. S., K. T. Raimi, V. Campbell-Arvai, and P. S. Hart. 2019. “Public support for carbon dioxide removal strategies: the role of tampering with nature perceptions.” Climatic Change 152 (3-4):345-361. doi:10.1007/s10584-019-02375-z. . This may be in part due to the minimal risks (real and perceived) associated with restoring natural ecosystems. While some risks, outlined below, do exist, there may be a higher tolerance for such risks given the long list of potential benefits and co-benefits (both environmentally and socially).

• Potential for negative economic impacts to some industries such as oil and gas, fisheries, and mining^[2]National Academies of Sciences, Engineering, and Medicine 2022. A Research Strategy for Ocean-based Carbon Dioxide Removal and Sequestration. Washington, DC: The National Academies Press. https://doi.org/10.17226/26278.
• Stricter fisheries management to increase species abundances can cause impacts on food security, displacement, and economic strain. (for example, Marine Protected Areas can cause varied impacts among communities and social groups and can be met with opposition)^[3]Mascia, M. B., C. A. Claus, and R. Naidoo. 2010. Impacts of marine protected areas on fishing communities. Conservation Biology 24(5):1424-1429. doi:10.1111/j.1523-1739.2010.01523.x.

Efforts around restoring natural ecosystems are often met with social acceptance and public support, especially when compared to other climate solutions seen as “tampering with nature”^[1]Wolske, K. S., K. T. Raimi, V. Campbell-Arvai, and P. S. Hart. 2019. “Public support for carbon dioxide removal strategies: the role of tampering with nature perceptions.” Climatic Change 152 (3-4):345-361. doi:10.1007/s10584-019-02375-z. . This may be in part due to the minimal risks (real and perceived) associated with restoring natural ecosystems. While some risks, outlined below, do exist, there may be a higher tolerance for such risks given the long list of potential benefits and co-benefits (both environmentally and socially).

• Potential for negative economic impacts to some industries such as oil and gas, fisheries, and mining^[2]National Academies of Sciences, Engineering, and Medicine 2022. A Research Strategy for Ocean-based Carbon Dioxide Removal and Sequestration. Washington, DC: The National Academies Press. https://doi.org/10.17226/26278.
• Stricter fisheries management to increase species abundances can cause impacts on food security, displacement, and economic strain. (for example, Marine Protected Areas can cause varied impacts among communities and social groups and can be met with opposition)^[3]Mascia, M. B., C. A. Claus, and R. Naidoo. 2010. Impacts of marine protected areas on fishing communities. Conservation Biology 24(5):1424-1429. doi:10.1111/j.1523-1739.2010.01523.x.

1. Open systems where the open ocean is directly manipulated to enhance biological production, capture atmospheric CO₂, and export the captured carbon to the deep ocean. In open systems, CO₂ fixation is facilitated by the addition of limiting macronutrients (e.g., phosphorus, nitrogen, silica) and/or micronutrients (e.g., iron) to the ocean’s surface to augment biological production . Open system techniques accelerate natural processes already occurring in the ocean. Most approaches in the open ocean fall into the following two categories (some proposals that do not fit into these categories are also explored).
   1. Surface nutrient addition: the direct addition of nutrients (macro or micro) into ocean waters in situ to increase microalgal growth 
   2. Nutrient upwelling: artificial upwelling of nutrient-rich deep ocean waters to the surface to increase microalgal growth
2. Closed systems where inputs and growth conditions are controlled, and outputs (microalgae) are harvested within the confines of a pond or a photobioreactor. In closed systems, CO₂ fixation is facilitated by the mixing of required inputs (sunlight, nutrients, CO₂, water) and the introduction of microalgae culture with the intention of reproduction and continuous fixation in a contained system . This can be accomplished on shore in cultivation ponds or photobioreactors, or afloat in photobioreactors either stationary or towed at sea .

1. 1. Onshore: encompasses more established methods of microalgae cultivation, including photobioreactors, cultivation ponds, and hybrid onshore configurations. In these systems, all inputs are tightly controlled and regulated, and outputs must be directly managed through either storage or utilization of byproducts. While cultivation techniques are well-established and show high technological readiness, storage and utilization pathways remain underdeveloped and scale is a major consideration. Social and environmental risks for closed onshore systems are easier to monitor and mitigate due to the controlled nature of the system. 
   2. Offshore: includes floating photobioreactors (PBRs) that are incorporated into a floating platform which can be stationary or towed behind a ship. In these systems, cultivation occurs in the photobioreactor, inputs are regulated, and outputs can be actively managed or directed. While at sea, these photobioreactors operate much like their onshore counterparts to cultivate microalgae, however nutrients and energy are provided by the ocean water and wave action, respectively. After microalgae are cultivated, they can be sunk into the deep ocean for sequestration or hauled to shore to be used as biomass. This is an area that has garnered much attention in startup communities (see this Y Combinator request for startups), however, little is available about the technologies in the open-sourced or peer reviewed literature.