Carbon removal spotlight — ocean carbon dioxide removal

Running tide image with their carbon dioxide removing ocean cakes

This is the fourth instalment of our Spotlight series where we explore some of the main nature-based carbon removal methods and offer a deep dive interview with one of our industry partners. If you’d like to discover more about other carbon capture and removal technologies, check out our articles on direct air capture (DAC), concrete mineralisation and reforestation.

Additionally, we’ll speak to our partner Running Tide, a company that is rebalancing the natural carbon cycle through carbon removal, restoration, and biodiversity solution, as opposed to offsets. They’ll be discussing their projects, the carbon removal landscape and what the future looks like for ocean-based carbon dioxide removal (CDR).

What role do oceans play in removing carbon?

We live on a blue planet. For billions of years, the oceans — not the atmosphere — have been the centre of our climate system. The deep ocean is the largest slow carbon reservoir on the planet that, by current estimates, stores 39,000 gigatons of dissolved carbon. Each year through natural processes the oceans move ten billion tonnes of CO₂ from the fast carbon cycle to the deep ocean, making it our most powerful ally in the effort to rebalance the carbon cycle and stop global warming. 

The ocean removes carbon in three simple ways — chemistry, photosynthesis, and gravity. Nearly 50 billion tons of carbon is absorbed through photosynthesis each year by phytoplankton — tiny microscopic plants that serve as the fundamental building blocks of life in the ocean. Once they die, a small percentage of marine plants sink to the ocean floor and either become food for marine organisms or are buried and turned into fossil fuels over several million years. Leveraging this natural mechanism, the ocean works like a biological pump, removing carbon from its surface in what’s called the "fast carbon cycle", to its bottom where it enters the "slow carbon cycle". 

The ocean is Earth’s biggest carbon sink — 30-40% of all carbon dioxide released by humans, primarily through the burning of fossil fuels, ends up in the upper ocean. But absorbing these manmade emissions has come at a high price to ocean health and its capacity to balance the carbon cycle. Ocean acidification caused by an increase in dissolved carbon dioxide significantly damages coral reefs and negatively impacts biodiversity, putting approximately 90% of marine life at risk of extinction.

But ocean acidification isn’t just a concern for life beneath the waves, it also has a huge impact on humans — and several key industries are already feeling the effects. Fish stocks are at their lowest ever, and while overfishing is a massive contributor to this, ocean acidification reduces the ability and rate at which fish stocks can recover. In Europe, the shellfish industry could lose over $1 billion by 2100 as a direct impact of ocean acidification.

What is ocean CDR?

There are only two ways to remove carbon from the fast carbon cycle - you can transform fast carbon into a stable mineral, or you can bury organic carbon and put it into slow carbon reservoirs (deep ocean, rock formations, etc.). The ocean naturally utilises both pathways through the solubility pump (mineralisation) and biological carbon pump (plant growth and sinking to the deep ocean). 

  • Mineralisation or ocean alkalinity enhancement: Currently there are two ways being researched to understand how to work with the solubility pump of the ocean. The first is through the use of an electrochemical process, and the second is through the dissolution of alkaline minerals in the surface of the ocean. Both of these processes leverage ocean chemistry to transform fast carbon in the surface ocean into the stable bicarbonate mineral reservoir. 

  • Biological carbon pump enhancement or grow and sink: There are a number of methods being researched including growing and sinking terrestrial plants and growing and sinking marine plants from the smallest phytoplankton to the largest and fastest growing seaweeds like kelp. 

Both methods leverage existing natural processes, are highly scalable and efficient, and have the potential to offer numerous co-benefits to communities and to restoring ocean health. Seaweeds are weirdly great at absorbing carbon -  the challenge is growing enough, sinking it reliably, and measuring the amount of carbon that was removed. All of challenges that are currently being worked through by companies and researchers to drive the industry forward.

How does ocean CDR work?

The process of ocean CDR can vary depending on the specific technique used. However, the general principle is the same — to capture carbon dioxide from the atmosphere or upper layers of the ocean and store it. These are the potential methods for ocean CDR:

  • Mineralisation and ocean alkalinity enhancement (OAE): This involves accelerating the natural process of mineral weathering, which removes carbon dioxide from the upper layers of the ocean through chemical reactions with rocks. Grinding rocks of particular mineral content and spreading them on coasts or on the ocean floor is one technique to accelerate this process and enhance the ocean's carbon sequestration capacity.

  • Macroalgae open-ocean mariculture and sinking (MOS): MOS replicates the natural carbon sequestration of phytoplankton. There are several techniques to MOS, including adding biomass that pushes carbon downwards or introducing alkaline substances such as limestone that naturally convert CO2 into more stable compounds while providing a place for marine plants to anchor and naturally sequester carbon.

  • Ocean fertilisation: This technique involves adding nutrients, such as iron, to the ocean to stimulate the growth of phytoplankton. The phytoplankton absorbs carbon dioxide through photosynthesis and the carbon is then stored in the ocean as the phytoplankton die and sink to the ocean floor.

  • Blue carbon ecosystems: These ecosystems, which include mangroves, salt marshes, seagrasses and coastal kelp forests, are highly efficient at sequestering carbon dioxide from the ocean and storing it in their biomass and sediments. By restoring and protecting these ecosystems, we can increase their carbon sequestration capacity.

What are the benefits of ocean CDR?

While reforestation and direct air capture have received most of the limelight when it comes to the voluntary carbon market, ocean CDR boasts a variety of distinct advantages. Ultimately, it’ll take the development of numerous approaches to mitigate and reverse the worst effects of global warming. Ocean CDR will have a crucial role to play in reaching that goal, for reasons that include:

  • Limited land requirements: Unlike reforestation, ocean CDR does not require large amounts of arable land. It’s also more resilient to natural and man-made disasters than land-based carbon removal projects. As the planet warms, more intense and frequent droughts and wildfires will increasingly threaten reforestation projects, in addition to the constant threat of human intervention such as illegal logging.

  • Cost-effective: Ocean CDR methods are relatively cost-effective when compared to other carbon removal methods such as direct air capture, and have the capacity to increase in their affordability as methods are advanced and refined. 

  • Scalable: The ocean is vast, covering over 70% of the Earth’s surface. This means there’s significant potential to scale up ocean CDR methods to remove large amounts of carbon dioxide from the atmosphere and upper layers of the ocean while minimising the potential for negative localised impacts. Some models have estimated that the open-ocean growth and sinking of macroalgae could sequester up to 270 Gt of carbon dioxide by 2100.

  • Biodiversity and ecosystem restoration: Ocean CDR techniques can provide numerous benefits for marine biodiversity and ecosystems. MOS, for example, provides important habitat for a range of marine species, while ocean fertilisation can increase fish populations.

What are the barriers to scaling ocean CDR?

Like any new technology, ocean CDR faces barriers to its development. Examples of key considerations to maximise its potential on a global scale include:

  • Scientific uncertainty: While there is no uncertainty about the negative effects of man-made emissions on the health of the oceans, there is still some scientific uncertainty surrounding the effectiveness of ocean CDR methods, particularly in terms of the capacity for novel techniques to remove and store carbon at climatically relevant scales. Additionally, there is a need for further study of the potential positive or negative environmental impacts. The scientific community, alongside carbon removal practitioners, are engaged in ongoing research to explore these areas of uncertainty, and to build upon scientific understanding and consensus.

  • Regulatory frameworks: There is a need to develop robust regulatory frameworks to ensure that ocean CDR methods are implemented safely and effectively across the globe without negatively impacting marine or human ecosystems. These frameworks are less developed than those regulating land-based carbon removal techniques, however, a number of governments and regulatory bodies around the world are developing and implementing new frameworks to guide the deployment of these solutions. As these regulatory pathways advance, this opens the door for permitting and research for both existing and future solutions.

  • Public perception: There is a lack of public education and awareness surrounding ocean CDR, due in part to the novelty of the solution, as well as a lack of understanding of the scale and scientific rigour behind these solutions. As such, practitioner transparency and community engagement are key elements of a responsible project.

  • Investment in infrastructure: While ocean CDR methods have the potential to sequester significant amounts of carbon dioxide, scaling these methods up to a meaningful level will require significant investment and infrastructure development. The work of carbon removal is necessary to safeguard planetary health. To make this work a reality, global investments - including the purchase of carbon removal credits - must scale accordingly.

Ocean CDR is a promising solution in the fight against climate change. While there are still uncertainties to be addressed, the potential benefits of reducing carbon emissions, preserving marine biodiversity and promoting sustainable economic development make it a valuable tool in the transition to a more sustainable future. As the world continues to grapple with the impacts of climate change, it’s clear that innovative and effective solutions like ocean CDR will be essential in achieving a more sustainable and resilient future for us all.

Partner spotlight: Running Tide

Runningtide employees standing in front of an ocean cargo ship.Since 2017, Running Tide has been working to develop and deploy solutions that amplify the ocean’s natural pathways for removing and storing carbon. The company implemented its first macroalgae and shellfish aquaculture in 2018, and began growing macroalgae in the ocean for research purposes in 2019. We sat down with Kristen Hammer to discuss Running Tide’s journey, how its solution removes carbon and the future of ocean CDR.

Can you give us an overview of Running Tide? Who are you? What is your mission? And how did you get to where you are today?

Running Tide is a global ocean health company. Our work focuses on developing tools to monitor and diagnose key ocean health indicators (think ocean acidification, increasing temperatures, biodiversity loss), and then designing and deploying interventions that improve ocean and planetary health. Our primary focus is carbon removal and ocean alkalinity enhancement, and we also are working on a number of solutions that utilise macroalgae and bivalves to improve biodiversity and marine and coastal habitats, including by designing nature-inclusive infrastructure, and tackling excess nutrients in coastal environments. 

Our CEO and Founder, Marty Odlin, is from a fourth-generation commercial fishing family. After a successful career in systems engineering, he returned to Maine to get back into the family business. However, Marty quickly realised that due to a warming and increasingly acidified ocean, fish populations were being decimated, as were the lives and livelihoods of his community — and he knew that the same thing was happening to coastal communities around the world. As a systems engineer, Marty understood that any effective solution had to be nature-based, scalable and rooted in the wisdom of ocean operators and coastal communities, which led him to founding Running Tide. The team started by building an innovative, world-class shellfish aquaculture system, which uses machine vision and a variety of sensors to understand what’s happening in the water and with the animals in a much more detailed way than traditional aquaculture. This foundational technology and scientific understanding is also applied to our carbon removal work, which involves sinking terrestrial biomass, ocean alkalinity enhancement, and eventually growing and sinking macroalgae. We deploy into the open ocean, and amplify natural processes  — including ocean currents, gravity, and photosynthesis — to sustainably scale our system. In 2023, we’ve been deploying our first credit-generating carbon removal deployments out of Iceland. 

My role at Running Tide is within our growth team, so I spend a lot of time talking with customers and potential customers, explaining Running Tide’s work and answering questions. I also work closely with our scientists and engineers, as well as with external partners, managing our work on any grants that we’re working on.  

Can you tell us about Running Tide's innovative approach to ocean carbon removal and how it differs from other carbon removal solutions currently available in the market?

Runningtide employee holding Runningtide carbon removal cake

Our nature-based multipathway system — including terrestrial biomass, ocean alkalinity enhancement, and marine biomass — is completely unique in its approach and scalability. Our system is purposefully designed to be iterative, allowing us to increase complexity and scale over time. The system is free-floating, far from shore in the open ocean, allowing materials to disperse via ocean currents. Our deployment locations are carefully chosen such that our system floats for a predetermined amount of time, and then sinks into the deep ocean — 1000m depths or greater, which is key to the durability of our system. 

One of the really exciting things about our system is that, once deployed into the open ocean, the only energy inputs required already exist in nature — meaning we don’t have to emit any extra carbon. Since carbon removal efficiency means removing much more carbon than you emit, this is extremely important. In addition, shipping is one of the most carbon-efficient ways to move mass in today’s world — another purposeful element of our system design. Overall, we’re building a supply chain that is not only carbon neutral, but carbon negative. 

How has Running Tide's technology been tested and proven effective in removing carbon? Can you share any success stories or case studies that highlight the impact of your solution?

Research and testing are integral and ongoing components of our work. We are continually testing our carbon removal system and the sensors and processes used to quantify the amount of carbon removed — in laboratory settings, coastal ocean environments, and in the open ocean. We have a number of research partnerships with scientists around the world that are advancing our understanding of our system’s interactions with the ocean. Of course, all of this research and testing has given us the opportunity to learn, iterate upon our systems, and improve our designs. This year, we delivered our first carbon removal credits to customers - the first ever ocean carbon removal credits!

In addition to measuring the amount of carbon removed and designing a system that is as efficient and scalable as possible, our team has put in a lot of work to rigorously evaluate and monitor the ways that our interventions might interact with ocean ecosystems. As an ocean health company, it's extremely important to us that our system maximises positive impacts to the environment while minimising negative impacts. 

Given the growing demand for carbon credits, how do you see Running Tide's solution fitting into the larger carbon market? How can businesses verify and track the carbon removal achieved through your technology?

One thing that makes our solution really unique is the ability to scale very rapidly, leveraging natural pathways and existing technology and infrastructure to meet the size of the problem. That is one of the many things that sets our solution apart from others in the durable carbon removal space — the ease of scale, and that scaling doesn’t require a huge additional investment of energy (and carbon emissions) or infrastructure. 

We quantify our credits using an integrated combination of models, lab and coastal testing, and in-situ open-ocean measurements taken during deployments. We’ve designed and built a suite of sensors that are deployed alongside our carbon removal operations, collecting data and feeding our models and learning platform for continuous learning and improvement.

When Running Tide delivers credits to our customers, they will receive a report which outlines all of the details around how the carbon that generated their credit was removed and quantified. As time goes on, this report may grow to include additional resources, such as an interactive dashboard. We also track all of our deployments and credits internally on a ledger, to ensure that no credits are double counted.  

Running Tide has worked with Deloitte to assure that our processes for quantifying the carbon removed from our system, detailed in our Framework Protocol, are in conformance with the highest industry standards — specifically ISO 14064-2. Deloitte has also reviewed Running Tide's environmental review plans and determined that our environmental monitoring scope is comprehensive.

How can businesses best integrate Running Tide's ocean carbon removal solution into their overall sustainability strategy, and what kind of support does your company offer to help them do so?

Running Tide’s high-quality carbon removal credits can play a strong role in any company’s sustainability strategy — not only by neutralising their emissions but by enabling them to actively contribute to improving ocean health and safeguarding critical ecosystems. Advance purchases also serve as an excellent market signal that catalyses the carbon removal industry as a whole. A strong voluntary carbon market not only advances our collective climate goals, but encourages regulatory bodies and policymakers to implement the necessary frameworks to ensure that all actors are behaving responsibly. Running Tide works closely with customers to ensure they understand not only how our system works, but how their support can impact the future of the carbon removal industry. 

Can you discuss the scalability of Running Tide's technology? How does it compare to other carbon removal solutions in terms of scalability and cost-effectiveness?

The ocean is already the Earth’s largest carbon sink and the most efficient way to move huge amounts of mass around the world — commercial shipping alone moves over 10 billion tonnes of goods per year. Our system is designed with this in mind, using the power of the ocean and its biological pump, along with gravity, wave energy and photosynthesis to do much of the carbon removal work of our system. We also use native materials in our system that can be sourced sustainably and at scale, including wood and alkaline materials. As we scale up algae growth on our carbon buoys, we expect to be able to remove a significant additional amount of carbon using these natural processes. 

The unique scalability and efficiency of our system is precisely what allows us to sell Running Tide carbon removal credits at a lower price than many competing carbon removal solutions. 

As an ocean-based carbon removal company, what are some of the unique challenges you face in this industry? How have you addressed these challenges?

Our carbon removal system, like others in the ocean, operates in what is what’s considered an “open system”, which is inherently harder to measure than a closed system (think measuring changes in a glass of water versus a pond versus the ocean —- the larger and more complex the system, the more difficult it is to measure changes to that system). 

The ecosystems within an open system are also inherently interconnected — which is why we thoughtfully consider our system design and the impact of all of our interventions upon the entire ocean ecosystem. We perform detailed reviews of the potential environmental impacts of our interventions — both positive and negative — and use that information to further inform and refine our system design. Running Tide has a strong internal team of scientists focusing on this work, and we partner with an independent Scientific Advisory Board and a number of external scientists and leading research institutions as well.  

Because the ocean is an open system, we can’t rely on direct measurement alone to quantify the carbon that our interventions remove — as such, we use rigorous models and testing to support our direct measurements and we have sought out external partners to audit and validate our work as well. We are constantly expanding our scope of scientific research to answer current open questions. 

Someone with gloves touching kelp

Looking ahead, what do you envisage for the future of ocean-based carbon removal? How will Running Tide continue to innovate and contribute to this growing industry?

As documented by the Intergovernmental Panel on Climate Change (IPCC), all reasonable scenarios that limit global warming to 1.5°C — the globally accepted limit beyond which the planet is likely to face dire and unpredictable effects — require the immediate reduction of emissions across all economic sectors, combined with large-scale carbon removal. 

The longer we wait to reduce emissions, the faster we must scale carbon removal. Alongside other hard-working companies in the carbon removal space, Running Tide is determined to build this industry into a strong, robust climate solution. As we grow, we look forward to continuing to partner with other industries to reduce and remove emissions at a global scale, and bring the ocean — and the entire planet — back to a healthy, productive, thriving state. 

Thank you Kristen

If you’d like to support Running Tide’s work and remove your company’s carbon emissions, sign up to our carbon removals marketplace. We have a range of different projects and project portfolios that suit a variety of business needs.