🥼Scientific Overview of Carbon Removal Approach
In 2022, we published an overview of some of the science underpinning our approach to marine carbon dioxide removal. This concise summary is followed by a link to the full text.
Understanding Carbon Cycles
We think of the global carbon cycle consisting of two primary components:
Fast Carbon Cycle: This cycle involves the rapid exchange of carbon through living organisms, the atmosphere, and the surface ocean. Processes such as photosynthesis and respiration are key parts of this cycle, which operates on timescales from days to decades.
Slow Carbon Cycle: This cycle involves the long-term storage of carbon in geological formations, deep ocean sediments, and deep waters, operating over centuries to millions of years. It includes processes like the burial of organic matter and the formation of fossil fuels.
Human activities, like burning fossil fuels, have disrupted the balance by transferring large amounts of carbon from the slow cycle to the fast cycle. Running Tide aims to counteract this by siphoning carbon from the fast cycle back to the slow cycle via deep ocean storage.
We focus on three primary mechanisms of ocean-based carbon removal, amplifications of mechanisms which naturally work to balance the Earth's carbon cycles:
Ocean Transport Amplification: In the Earth system, rivers carry wood from forests into the deep ocean to be buried. Strategic and targeted removal of carbon-rich biomass by-products from forestry and agriculture amplifies the carbon drawdown of land use projects. Durably storing fast-cycle biomass in the deep ocean is sometimes known as "Terrestrial Biomass Sinking" or "Ocean Storage of Biomass."
Ocean Alkalinity Enhancement: Much of the ocean’s natural ability to absorb carbon comes from the dissolution of alkaline minerals, such as Calcium, in seawater. In our system, the introduction of an alkaline payload into the ocean surface alkalinizes that water and increases the capacity of the ocean to absorb carbon from the atmosphere.
Photosynthetic Carbon Fixation: Macroalgae grows rapidly given the right combination of sunlight and nutrients. Just like plants, these organisms build themselves out of carbon from their environment through photosynthesis. When this happens in ocean surface water it perturbs the carbon equilibrium between the air and sea, inducing novel carbon dioxide flux. Meanwhile if the macroalgae ultimately sinks to the deep ocean, any accumulated growth gets exported out of the fast-cycle, preventing this carbon from remixing into the surface waters and atmosphere and durably storing it in the deep ocean.
Running Tide’s Ocean Carbon Dioxide Removal (CDR) Approach
All of our intervention designs consist of passively drifting material, which requires less novel infrastructure to maintain than anchored or tethered farms, and dispersed systems reduce instances of acute shading or light attenuation effects.
Our initial deployments used wood chips processed with an alkaline mineral coating ("coated wood") to remove carbon by exporting fast-cycle wood residue that would otherwise decompose or burn to the seafloor. The mineral coating was designed to offset any organic acids leached by the wood, and likely produced a net-alkaline effect over the course of our first deployment season.
Research and development efforts expanded on what we learned about the properties of various coated wood recipes. We focused on designing and testing different wood species, modifying the form factors, coating materials, and processing techniques to achieve float times that would support macroalgae growth to maturity. We also developed various composite, formed buoys consisting of organic material (e.g. wood chips, mycelium, psyllium, cotton) and alkaline mineral (e.g. calcium carbonate, lime kiln dust) which could be similarly seeded with macroalgae. We called these "carbon buoys." Essentially, carbon buoys were engineered to float at the surface of the ocean for a designated period of time, providing a substrate for macroalgae growth and/or a delivery mechanism for alkaline materials to the surface ocean. The idea was that the buoy would become negatively buoyant over time, sinking and exporting carbon to the deep ocean.
Beyond buoy design, the trick to carbon removal via any of these passively drifting, dispersed systems was predicting, assessing, and verifying how deployed material would drift in the ocean, when it would sink, and what its terminal distribution on the seafloor would be. Measurement and monitoring of CDR effects in the open ocean is massively challenging, so our scientific research was primarily focused on building computational models to quantify removal uncertainties and secondary effects on interconnected, dynamic Earth systems. Additionally, multiple programs aimed to identify and resolve open questions related to macroalgae growth and cultivation and assessing our broader environmental impact.
Research Program
Key areas of ongoing research and development include:
Quantification methods: Developing models and measurement techniques to accurately assess carbon removal across various pathways.
Ecological impact assessments: Studying potential effects on marine ecosystems, from surface waters to the deep sea floor.
Deep sea research program: Understanding the complex biological and chemical consequences of introducing novel biological material to various deep sea environments
Macroalgae breeding and cultivation: Selecting and improving strains for open ocean conditions and optimal carbon sequestration.
Durability of sequestration: Investigating the fate of sunk biomass, including remineralization rates and sediment burial processes.
Ocean transport modeling: Refining predictions of substrate dispersal and sinking behavior.
Alkalinity enhancement dynamics: Quantifying dissolution rates, reaction kinetics, and CO2 uptake in real-world conditions.
Baselining and monitoring: Developing tools, techniques, and procedures for capturing reliable in-situ data to validate models and lab-based experiments and insights
Goals and Future Directions
Running Tide aimed to incrementally scale the ocean-based carbon removal system to make a significant impact on global CO2 levels. To demonstrate carbon removal efficacy so that we could responsibly, iteratively increase deployment scale, we needed to continuously improve and tune a variety of models, identify and research open questions, and refine our quantification approach to meet the challenge of measuring and monitoring phenomena in the open ocean.
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