🌊 Happy World Ocean’s Day 🌊

💙 The ocean’s biodiversity and beauty are not the only thing that make the ocean remarkable. The ocean covers 70% of our planet and serves as its largest carbon sink, holding 42 times the carbon in the atmosphere.

🔦 I wanted to mark the occasion by SINKING deeper into marine carbon dioxide removal (aka hashtag#mCDR) which could play a critical role in fighting climate change.

So what do we mean when we say mCDR? There is actually an ever increasing range of methods:

👉 Ocean Alkalinity Enhancement (hashtag#OAE): enhances the ocean’s natural carbon sink by adding alkaline materials (e.g. olivine, lime, magnesium hydroxide) to seawater, increasing its capacity to convert atmospheric CO₂ into long-lived bicarbonate ions. TRL: 3-4. Costs: $300-$600/t today, could go to $50-$150/t. Example: Ebb Carbon

👉 Direct Ocean Capture (hashtag#DOC): extracts CO₂ from seawater using energy and membranes or electrodes, either converting it into solid carbonate minerals or capturing it as a gas for geological storage, while returning treated alkaline water to the ocean to boost future uptake. TRL: 5-6. Costs: $400-$1,500/t today, could go to <$150/t. Example: Captura

👉 Deep Ocean Sinking: cultivates fast-growing macroalgae (e.g. kelp, sargassum), which absorb CO₂ via photosynthesis and are then intentionally sunk to the deep ocean, isolating the carbon from the atmosphere for centuries. TRL: 3-4. Costs: $465-$1,000/t today. Example: Gigablue

👉 Ocean Iron Fertilisation (hashtag#OIF): triggers phytoplankton blooms in iron-limited regions of the ocean (e.g. the Southern Ocean), which absorb CO₂ and may export some organic carbon to the deep sea via the biological pump. TRL: 1-2. Costs: none current, could be as low as $5-$20/t. No examples yet.

🤔 It is important to note that there are still major uncertainties around monitoring, reporting and verification (MRV), unresolved international legal questions (e.g. London Protocol), and ecological risks such as deoxygenation, acidification, and biodiversity disruption.

📈 As a result, mCDR is rightly ramping up slowly, with only 23,000t of deliveries to date. But corporate interest in these approaches is high, with almost 440,000t already purchased.

🌍 So where does that leave us? I see huge potential in mCDR due to the sheer size of the opportunity and potentially low costs. I also think we need to start clearly differentiating between the different methods more, as their risk and potential vary vastly.

👏 Finally, a big shout-out to all the companies working in the space and Carbon to Sea Initiative in particular, who are continuously pushing the research agenda in the space and helping us understand mCDR better.

⁉️ Your thoughts? Will mCDR be a key part of the solution? What is

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