Ocean-Based Natural Climate Solutions: Open Ocean


SOA Blog

Sustainable Ocean Alliance is accelerating ocean solutions around the world. Here are their stories.

The ocean, covering 71% of the Earth's surface, is a remarkable planetary system that stores more carbon than all soil and forest systems combined. Its vastness, remote nature, and intricate biogeochemical and physical characteristics make it both captivating and challenging to study. 

In our active fight against climate change, natural climate solutions (NCS) have emerged as valuable strategies to offset, mitigate, and reverse the impacts of our changing planet. These solutions restore and conserve various ecosystems to sequester carbon and provide additional benefits, including supporting livelihoods in fishing and tourism, protecting coastal regions, preserving biodiversity, and offering recreational opportunities. Natural climate solutions present a holistic approach with multiple advantages.


In this blog series, we're diving into the fascinating world of natural climate solutions (NCS) by exploring the findings of three reports by the Environmental Defense Fund, which shine a light on different interventions for carbon sequestration in various ecosystems. We'll also highlight real-life examples of individuals and organizations SOA has supported with grants that drive positive change through NCS.

Read Part 1 of this blog series: Ocean-Based Natural Climate Solutions: Seaweed.

Blue Carbon Blog Series Blog Headers (2)

Types of Ocean-Based Natural Climate Solutions 

Within the ocean system specifically, the following reports from EDF examine three points of potential intervention for natural climate solutions: 

  • EDF Report on Seaweed: Various interventions to conserve, restore, and increase the productivity of macroalgal (seaweed) systems (natural beds and farms) to avoid greenhouse gas emissions and sequester more carbon.

  • EDF Report on Open Ocean: Interventions in the open ocean, including carbon sequestration via the rebuilding of biomass in large marine mammals and epipelagic fishes, and the potential for avoided emissions by restricting or limiting new fishing in the mesopelagic ocean and/or benthic trawling

  • EDF Report on Coastal Ecosystems: Interventions to conserve, restore, and manage vegetated, coastal blue carbon ecosystems such as mangroves, marshes, and seagrasses to avoid greenhouse gas emissions and increase carbon sequestration.

It is crucial to note that no approach for removing existing carbon from the Earth's atmosphere can replace the importance of avoiding or reducing emissions. Even if removal is achieved through natural climate solutions or any other method, emission reduction remains paramount.

Part 2 of the series focuses on Natural Climate Solutions in the Open Ocean.


Carbon in the Open Ocean

The ocean plays a vital role in carbon storage, storing 50 times more carbon than the atmosphere, and 20 times more than land plants and soil combined (Source: NOAA). 

Carbon is absorbed, cycled, and sequestered in the ocean through multiple processes:

  1. Carbon dioxide (CO2) is absorbed from the atmosphere by the surface ocean

  2. A portion of that carbon in the absorbed CO2 is transported to deeper ocean waters where it can be locked away from the atmosphere in various forms for periods ranging from months to millennia. We call this process the "biological pump."

Models have shown the ocean actually served as a source of CO2 to the atmosphere before the Industrial Revolution, and nearly all of the CO2 absorbed by the ocean today is generated by human activity. In fact, 23% of all anthropogenic CO2 emissions from 2010 to 2019 have ended up in the ocean, with the rest remaining in the atmosphere or being stored by terrestrial ecosystems (Canadell et al., 2021).

The continued rise in atmospheric CO2 concentrations continues to “push” more and more carbon into the ocean, with evidence showing that the ocean’s natural ability to absorb CO2 may be weakening (Canadell et al., 2021).

In this section, we will examine four proposed ocean solution pathways that aim to enhance and preserve one or more biogeochemical processes that make up the ocean’s biological pump:

  1. Carbon sequestration via epipelagic fish

  2. Avoided emission/carbon sequestration via mesopelagic fish

  3. Rebuilding of large marine mammal communities, including whales

  4. Avoiding deep-sea mining & benthic trawling 


Natural Climate Solution: Storage, uptake, and sequestration of carbon in the ocean

Carbon in the ocean is absorbed and stored through physical and biogeochemical processes. It can be divided into two main subsystems: the surface ocean absorbing CO2 from the atmosphere, and some of that carbon being exported to deeper waters for long-term storage.

Phytoplankton and Zooplankton

One way the ocean cycles carbon is through phytoplankton and zooplankton. Phytoplankton—small marine algae and cyanobacteria—are the cornerstone of productivity in the global ocean. When nutrients and sunlight are abundant, these organisms act as the biological engines of the surface ocean and support the biosphere’s primary energy source (Field et al., 1998). 

Zooplankton, along with heterotrophic bacteria (organisms that cannot produce their own food), are the ocean’s secondary producers. They consume, repackage, and process the carbon fixed by the billions of phytoplankton that drive the biological pump. When zooplankton graze on phytoplankton, it keeps the phytoplankton population in check, and in turn, zooplankton serve as prey for higher trophic-level organisms like whales and fish. 

The effects of climate change and anthropogenic mobilization of CO2—particularly those associated with ocean acidification and increases in sea surface temperatures—have already been observed in both phytoplankton and zooplankton populations. Given their crucial role as the primary food source for numerous species, any shifts in algal populations can have substantial impacts on the ecological structure, function, carbon export, and overall ecosystem health of the ocean.


Natural Climate Solution: Fisheries

Epipelagic Fisheries

Epipelagic fish inhabit the ocean's epipelagic zone, otherwise known as the "sunlight zone." This is considered the upper layer of the ocean, where sunlight is able to penetrate—up to about 200 meters deep.

There is potential for strengthening carbon sequestration through the rebuilding of epipelagic fish populations. Currently, the most promising and immediate climate action involving epipelagic fish is through reducing fuel consumption used by the fishing fleets that target these species.     

Nearly 82% of the emissions associated with fishing large pelagic species came directly from fuel use, and only 57% of the global offshore catch would be profitable without current fuel subsidies (Mariani et al., 2020). Emissions could also be reduced by:

  • Lowering fish catches

  • Improving nearshore fishery production to disincentivize transit further offshore in response to stock depletion

  • Improving catch efficiency

  • Reducing the amount of bottom trawling

  • Ending overcapitalization and fuel subsidies

Mesopelagic Fisheries

Mesopelagic fish inhabit the ocean's mesopelagic zone, otherwise known as the "twilight zone." The area is between 200 and 1,000 meters where light intensity is severely reduced.

The science surrounding the carbon export mediated by mesopelagic fish populations is also uncertain, yet we find these species present contributions to global carbon sequestration massive enough to warrant immediate pursuit of limitations or prohibitions on their harvest. 

Large-scale biomass removal through commercial fishing would therefore almost certainly disrupt one of the most significant zoogeochemical transfers of carbon on the planet.

Limiting the harvest of these species is a conservative policy intervention that could be taken today to prevent further deterioration of the ocean’s capacity to sequester atmospheric carbon and avoid greenhouse gas (GHG) emissions.

SOA Grantee Spotlights: Fisheries

Seafar: AI for IUU Fishing | Cape Town, South Africa


Seafar is an Africa-based startup that seeks to mitigate illegal, unregulated, and unreported (IUU) fishing through software that utilizes radar data and artificial intelligence (AI) to identify when fishing vessels turn off their radar or otherwise behave in ways implying unlawful fishing activity is taking place.

The global cost of IUU fishing is estimated at $10-23.5 billion per year and it weakens food security, particularly in developing nations (40% occurs in West Africa alone).

As a software-based service, Seafar’s solution requires low capital expense and holds promise for rapid scaling to under-served and under-policed areas of the world.

Bahari Remedies: Community Approach to Fisheries Resilience | Dar es Salaam, Tanzania

Kunduchi picSmall-scale fisheries are vital for livelihoods and food security in Tanzania, but they face challenges from climate change, overfishing, and unsustainable practices.

This project promotes climate-resilient fisheries in Kunduchi by enhancing the capacity of the fishing community in sustainable fisheries practices and climate change adaptation measures. Through a community-based approach, training and support are provided to adopt sustainable fishing practices, raise awareness, and adapt to climate change impacts.


Natural Climate Solution: Rebuilding of large marine mammal communities, including whales

Rebuilding whale populations has benefits beyond carbon sequestration, and there is evidence that whales can assist in carbon flow to the deep ocean through different stages in their life cycles.

There are two primary pathways through which whales contribute to carbon flux:

  1. The natural sinking of deceased whales to the ocean floor, known as "whale falls"

  2. The redistribution of iron-rich, buoyant whale feces within the water column through the "whale pump" fertilization mechanism

The increase in whale populations could lead to more carbon sequestration in living biomass. Nevertheless, there remain many uncertainties surrounding these pathways, including whether whales act as carbon sources or sinks, the amount of carbon a single whale can sequester, and how to track and attribute such sequestration.

Further scientific research is required to fully grasp the potential carbon sequestration pathway related to marine mammals.


Natural Climate Solution: Avoided Emissions through Reductions in Seafloor Trawling 

Bottom trawling is a fishing practice that herds and captures target species, like seafloor fish or crabs, by towing a net along the ocean floor (Source: NOAA). Restrictions or prohibitions on bottom trawling—or other sediment-disturbing activities such as deep-sea mining—may be effective in reducing or avoiding carbon emissions. However, research is still needed to better understand the movement of carbon from sediments as a result of these activities, and the longer-term fate of resuspended organic matter. 

To read more about deep-sea mining, the implications, and how you can take action, visit SOA’s Campaign Against Deep Seabed Mining

SOA Grantee Spotlights: Deep-Sea Mining

Earthlanka: Awareness of Seabed Mining | Colombo, Sri Lanka


EarthLanka is currently running a campaign advocating for a moratorium on deep-sea mining, collecting data, soliciting youth contributions for research, and building awareness of the issue in Sri Lanka to influence government protection of marine resources.



Te Ipukarea: Rethinking Our Blue Future | Auckland, New ZealandCook_Islands_787992297

Blue Cradle Foundation produced a short video about deep-sea mining, including indigenous perspectives and the voices of Pacific Islanders, which premiered at the 2022 UN Ocean Conference.

The Cook Islands could be one of the first nations to issue exploratory licenses for deep-sea mining in its exclusive economic zone

Deep Sea Defenders | Vancouver, British Columbia, Canada


Deep Sea Defenders organized a demonstration outside the Metals Company HQ—the parent company of Nauru Ocean Resources, Inc. and a primary instigator of the “2-year rule” of the International Seabed Authority (ISA)—in Vancouver on June 8 for World Oceans Day 2022 and produced a documentary and social media campaign about deep-sea mining utilizing the content and media attention it generates.



Key Points and Takeaways

None of the open ocean climate solution pathways we reviewed are scientifically mature enough to support high-quality carbon credit schemes, however, EDF identified several significant research needs that could accelerate the development of sufficiently precise estimates of sequestration or avoided emissions from all four of these natural climate solution pathways to support high-quality carbon credits and justify other investments to protect or accelerate them. 

The research needed to accelerate the development of open ocean climate solution pathways includes:

  • Greater scientific collaboration among ocean scientists

  • Improved statistical methods for estimating carbon sequestration

  • Development of new models and technologies to measure fish biomass and carbon fluxes

  • Creation of biogeochemical models for marine mammals

  • Further studies on the impact of krill-derived iron on carbon export

  • Development of robust estimates for carbon emissions from disturbed seafloor sediments



Many of these marine ecosystems store carbon at rates far exceeding those of other global ecosystems. Additionally, there are many co-benefits associated with the preservation or restoration of these blue carbon ecosystems. 

Addressing the limitations requires the development of new frameworks that conceive individual blue carbon ecosystems as interconnected elements within broader seascapes, rather than as self-contained entities. Such a shift in perspective would enable a more holistic approach to harnessing the potential of these ecosystems.

High-quality blue carbon projects should accurately sequester and store carbon, restore ecological integrity, and provide opportunities for local and Indigenous communities to participate fairly and benefit from the voluntary carbon market. Through an open and consultative research process, a set of principles and guidance was developed to define high-quality blue carbon projects and credit development. 




Other Articles

Show All

Ocean-Based Natural Climate Solutions: Coastal Ecosystems

The ocean, covering 71% of the Earth's surface, is a remarkable planetary system that stores more...

Ocean-Based Natural Climate Solutions: Seaweed

The ocean, covering 71% of the Earth's surface, is a remarkable planetary system that stores more...

Leadership for Climate-Resilient Fisheries Fellowship: Meet the 2023 Global Fellows

Since 2021, Sustainable Ocean Alliance and the Environmental Defense Fund (EDF) Fisheries Solution...