Running Tide’s Carbon Buoy: Engineering In Partnership With Nature

Shane Scranton
minute read

Key Takeaways

  • One mechanism for packaging this carbon removal approach is the “carbon buoy." Running Tide has multiple carbon buoy designs being researched and tested simultaneously, and we are not solely focused on the carbon removal pathway that utilizes macroalgae. Research deployments are currently being conducted in the North Atlantic throughout the summer of 2023 with carbon buoys made of wood coated with alkaline minerals. Additional carbon buoy designs are in various stages of development in lab and coastal settings. 
  • Our carbon buoy development process follows design and governance principles that serve as guardrails, allowing Running Tide to scale deployments as the team increases its understanding of these interventions' ecological, socioeconomic, and carbon impacts.


Following the publication of Running Tide’s Ocean Carbon Removal Research Roadmap – and in line with our commitment to promote transparency around our work as detailed in our Framework Protocol for open ocean carbon removal – we are sharing additional detail into our research and development efforts that have informed our current research deployments being conducted out of Iceland.

Functionally, there are two primary mechanisms by which you can remove carbon and store it in the slow carbon cycle:

  1. You can fix carbon biologically (i.e., via photosynthesis) and put it under immense pressure such that it cannot be re-released (i.e., the deep ocean, stored underground, etc.), or
  2. You can create a chemical reaction that transfers fast carbon into a more stable form, such as bicarbonate.

While there are a number of different carbon removal pathways, from enhanced rock weathering to direct air capture and storage (each with its own fun acronym), all carbon removal solutions can be distilled into one of these two approaches.

The ocean is the largest natural carbon sink on our planet, and provides a range of biological and chemical pathways by which this natural fast-to-slow carbon transfer occurs. Running Tide’s carbon removal system is designed to amplify these natural processes, specifically the ocean’s biological carbon pump and solubility pump, moving additional carbon from the fast carbon cycle to the slow carbon cycle. 

Embracing Complexity

Open systems such as the ocean are inherently complex – the end state of billions of years of geological, physical, chemical, biological, and now anthropogenic interactions at both the macro and micro scale. Any carbon removal approach that seeks to intervene into these complex systems in a climatically-relevant way must embrace that complexity, and understand that myriad factors will influence an intervention’s success. 

But embracing complexity does not mean designing complex systems to match. Gall’s Law states that a complex system that works is invariably found to have evolved from a simple system that worked. Our carbon removal approach embraces this philosophy, and we work to design and operationalize simple interventions that can layer in complexity over time. 

In this ocean context, this means starting with interventions designed to utilize well-understood physical processes – ocean transport, sinking, wind and wave action – before layering in more complex chemical pathways and living biological systems. 

What is a Carbon Buoy?

One mechanism to operationalize this carbon removal approach is via the deployment of “carbon buoys” into the surface of the ocean.

The carbon buoy represents Running Tide’s primary interaction point with the natural environment – i.e., the object by which a carbon removal intervention is packaged and delivered. Carbon buoys are a calibrated combination of organic and inorganic matter that is commonly found in the ocean. Under consideration are various carbon-rich or alkaline natural materials that are responsibly sourced, processed, and then deployed into the open ocean, where they passively drift on ocean currents. These materials float – hence the “buoy” in carbon buoy – and once they absorb enough water to lose buoyancy, they rapidly sink.

In doing so, carbon buoys utilize basic physical oceanographic processes to durably move carbon from the fast cycle to the slow cycle, following the process described in our Framework Protocol.

Figure 1: One of Running Tide’s first research deployments in 2023 off the coast of Iceland, representing several hundred net tons of CO2e removal via one of our current carbon buoy designs: wood coated with alkaline minerals. Workers are visible in yellow in the foreground for scale. 

Mitigation by Design

While the carbon buoy is a key component of Running Tide’s carbon removal efforts, creating a “perfect” carbon buoy is not the goal; the goal is to durably remove carbon as efficiently, safely, and cost-effectively as possible. 

As our Framework Protocol states, “a carbon removal system, especially one that intervenes in the natural environment, should seek to achieve the highest climatic benefit while minimizing any adverse localized impacts. The system should be designed to have a net positive impact, inclusive of benefits to the climate, ecosystem, and affected communities; it should be designed to be deployed safely, with appropriate safeguard mechanisms and controls in place; and, while starting small, it should be designed for scalability, such that it has the potential to scale to the size of the problem.”

Running Tide’s carbon removal approach and carbon buoy designs embody this systems-level thinking. The buoys are the product of tuned performance parameters optimizing material combinations and physical, chemical, and biological interactions. In designing carbon buoys, we are engineering in partnership with nature: we’re building a flexible platform with multiple carbon buoy designs – sometimes referred to as recipes – that allows us to dynamically respond to changing ocean conditions, environmental considerations, and geographic differences. 

In practice, mitigation by design is demonstrated by the carbon buoys’ form factor. The small unit size enables efficient manufacturing that can integrate a range of substances and components, which are dispersed by natural processes over a widely distributed geographic area. This low-density distribution of buoys limits the potential for negative localized impact while maximizing potential scale. 

Carbon Buoy System Design and Progression 

We follow core system design and governance principles and consider potential environmental impacts when evaluating our carbon buoys to ensure our system is safe, scalable, flexible, and has a net positive impact on the planet and the communities we’re operating within. These principles guide our design cycles as we explore material feasibility, engineering feasibility, and environmental considerations, and they provide guardrails as the team pursues scaling promising carbon buoy designs toward larger deployments. These principles may be best represented in our selection of carbon buoy materials: a combination of naturally occurring substances that are prevalent in the ocean, can be handled and introduced in various inert forms, and present no more than a minor or transitory impact to ocean ecosystems when deployed thoughtfully – while also removing carbon effectively. 

We rely on materials that have the capacity to amplify the two natural carbon removal processes described above: biological growth and storage, and chemical dissolution (i.e., grow and dissolve). The first process, grow, involves biomass-based materials that capture carbon via photosynthesis, which is transferred into the slow carbon cycle for durable storage once sunk into the deep ocean. Biomass materials can be further differentiated into a) terrestrial materials, such as wood that is sustainably sourced from suppliers, and b) marine materials, such as macroalgae grown on the carbon buoy while it is floating in the ocean. The second carbon removal process, dissolve, involves alkaline minerals that fix carbon in the bicarbonate pool through chemical processes in the surface ocean, ensuring movement to the slow carbon cycle. 

Figure 2: Running Tide’s primary materials.

Each design must balance tradeoffs between deployment and production efficiency, cost, and impact. As an example, an initial design for a “long line” carbon buoy tested by Running Tide in 2020 and 2021 provided significant potential efficiencies in terms of algae yield (high yields were observed in fixed research locations with high wave energy, low-nutrient conditions), but presented potential challenges at scale in terms of deployability and potential ecological impacts (both in the ocean and within the supply chain) based on scientific and engineering review. Though these reviews determined the risk was minimal, and long lines are commonly used in marine aquaculture, we tested a number of more conservative alternative approaches, leading to the development of the lower density, distributed carbon buoy designs used in research deployments today. 

2023 Carbon Buoy Designs

A range of carbon buoys designs are currently being tested and evaluated so we can learn, iterate, and improve. This “learning loop” enables us to discover – and correct for – any potential negative secondary effects while still at small scales, and helps to improve system design for removing carbon at larger scales. Several carbon buoy designs at various levels of maturity are below: 

Wood Coated with Alkaline Minerals

Figure 3: Wood coated with alkaline materials at Running Tide’s operational facilities in Iceland. For initial research deployments, residue biomass was sourced from Canada, processed, and combined with a mixture of CaCO3 and Ca(OH)2 onsite.

  • Status: Operationalized in open ocean research deployments.
  • Material types: Terrestrial Biomass; Alkaline Minerals
  • Description: Running Tide is deploying this design in 2023 research pilot deployments out of Iceland, consisting of mixtures of sustainably sourced forestry residues (both hardwood and softwood), calcium carbonate, lime kiln dust, and water that is mixed and passively cured. This carbon buoy recipe floats for up to three weeks, with the alkaline coating rapidly dissolving on the surface ocean before the buoys sink below 1,000 meters in depth – out of contact with the fast carbon cycle for centuries to millennia. The primary carbon removal pathway for this buoy design is terrestrial biomass sinking, with a secondary ocean alkalinity enhancement benefit.

Naturally-Bound Wood Seeded with Macroalgae

Figure 4: Several iterations of Running Tide’s naturally-bound wood carbon buoy design. Top: naturally-bound woody biomass seeded with sugar kelp. This coastal experiment utilized seeded cotton lines wrapped around carbon buoys in a low wave, high nutrient environment, which is not reflective of open ocean conditions or expected commercial production processes, but helps to test and refine carbon buoy feasibility. Bottom: an unseeded, naturally-bound wood carbon buoy design.

  • Status: Being tested in Running Tide’s labs and in coastal experiments.
  • Material types: Terrestrial Biomass; Macroalgae
  • Description: A wood-based carbon buoy, formed using an organic hydrophobic binder, allows the carbon buoy to float for 1-3 months and provides a suitable substrate for macroalgae growth. Saccharina latissima (sugar kelp) and Ulva lactuca are fast-growing macroalgae species endemic to many ocean regions around the globe. Aquatic biomass growth is expected to be the primary carbon removal pathway for this carbon buoy recipe with a secondary terrestrial biomass sinking benefit, dependent on float times and macroalgae growth rates.

Mineral-Bound Wood Seeded with Macroalgae

Figure 5: Running Tide’s naturally alkaline, mineral-bound wood carbon buoy design with Ulva lactuca growth in a laboratory setting. 

  • Status: Being tested in Running Tide’s labs
  • Material types: Terrestrial Biomass; Alkaline Minerals; Macroalgae
  • Description: A three-pathway carbon buoy utilizing naturally alkaline cementitious binder and wood. This carbon buoy design is described internally as “tums for the ocean”, with the goal to maximize the ocean alkalinity enhancement removal pathway and the ability to float for three-plus months, providing a suitable substrate for longer-term macroalgae growth. This float time is advantageous for cultivating algae species and provides the potential for higher yield, while the binder dissolves more slowly than an alkaline coating, providing distributed slow dissolution ocean alkalinity enhancement. Both carbon removal pathways – ocean alkalinity enhancement and terrestrial and aquatic biomass sinking – are utilized in this design.

Many additional carbon buoy designs are at various levels of bench-scale development and are part of active laboratory and controlled coastal testing. 

Guardrails, Not Gates 

Running Tide’s carbon buoys system, coupled with our open ocean verification fleet, enables us to scale a carbon removal solution while monitoring impact, tuning the designs, and ensuring any unexpected issues are resolved along the way. The carbon buoy’s conceptual simplicity gives us the flexibility to combine the right materials to suit the specific needs of each location. Different designs will be best suited for different seasons and operational constraints, and we can adjust the system as the ocean continues to change. 

As reported by the Intergovernmental Panel on Climate Change (IPCC) in their Sixth Assessment Report, 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 large-scale carbon removal to the effect of hundreds to thousands of gigatons by the end of the century, along with the immediate reduction of CO2 emissions across all economic sectors. The speed and scale required for this endeavor lack historical precedent, leaving us to draw analogies to the COVID-19 vaccine effort, World War II mobilization, or to building the oil industry in reverse. However, even those extreme analogies break when we consider the scale that must be achieved on such a rapid timeframe across the entire Earth system. 

We need to test, measure, iterate, and learn rapidly to determine which approaches truly have the potential to reach a climatically relevant scale. This can only be done with responsible research following a staged progression approach, with clear guardrails that individual practitioners and the industry writ large can follow. In the long term, third-party governance, clear regulation, and codified codes of conduct will enable the carbon removal industry to verify its impact using standardized and regulated processes. However, the absence of this market infrastructure can not be used as justification to delay critical research, and real-world learnings can be used to inform the rules that are set. Running Tide’s Governance Principles inform our own progression, and we hope will offer a pathway for other practitioners to follow. 

Earth ecosystems are rapidly declining, and the barometer we need to consider most in our system design is the long-lasting negative damage of ongoing anthropogenic emissions on these ecosystems. The activity of carbon removal will result in changes to the planet, and it is our responsibility to ensure that these environmental, social, and cultural changes are positive. We believe our carbon buoy system design offers the simplicity and flexibility required to enlist natural systems in this critical effort. 

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