As the global race to net zero intensifies, carbon dioxide removal (CDR) technologies are becoming critical tools — not just for governments, but for corporations under pressure to act credibly on climate. Now, a new frontier is gaining serious attention: the ocean.
ClimeFi and the World Ocean Council have partnered to produce a landmark series exploring marine-based CDR technologies. In Part One of their three-part series, they explore what mCDR actually is, why it’s gaining ground, and how it compares to its land-based counterparts.
Why Marine CDR Matters Now
The case for durable CDR — solutions that store CO₂ for centuries or more — is well established. Buyers are increasingly seeking high-integrity removals that go beyond traditional offsets. Until now, most attention has been focused on land-based CDR like biochar, direct air capture (DAC), and enhanced rock weathering.
But to reach the IPCC’s target of 10 gigatonnes of annual removals by 2050, land-based solutions have to be supported by ocean-based solutions. The ocean, covering 71% of Earth’s surface and already absorbing 30% of anthropogenic CO₂, will play a vital role.
Remarkably, meeting the entire 2050 removal target through mCDR would change the ocean’s inorganic carbon content by just 0.007%. The potential is enormous—and largely untapped.
What Is mCDR?
Marine CDR (mCDR) includes both natural-process enhancements and engineered approaches that accelerate CO₂ uptake or remove previously dissolved carbon from the ocean, resulting in net atmospheric drawdown.
There are two main types of systems:
- Open systems: Leverage natural oceanic processes. These are typically more scalable and lower-cost but present challenges in measurement, reporting, and verification (MRV).
- Closed systems: Contain the process in controlled environments, enabling easier MRV but often requiring higher upfront investment.
As modeling tools and verification methods evolve, MRV challenges for open systems are expected to ease, while closed systems should benefit from economies of scale.
The Five Key mCDR Pathways
Here’s a breakdown of the five main mCDR approaches:
- Electro-Chemical / CO₂ Stripping (Closed)
Uses electrochemistry to extract CO₂ from seawater, sometimes producing alkalinity-enhancing byproducts. - Ocean Alkalinity Enhancement (OAE) (Open)
Adds alkaline materials like olivine to seawater, enhancing its ability to absorb CO₂. - Artificial Upwelling / Downwelling (Open)
Mimics oceanic currents to sequester CO₂ in deep water or stimulate plankton growth. - Ocean Fertilization (Open)
Introduces nutrients to trigger phytoplankton blooms, which draw down CO₂ through the biological carbon pump. - Biomass Sinking (Open/Hybrid)
Involves growing and sinking seaweed or biomass into deep ocean layers or sediments for long-term storage.
Each has its own profile in terms of durability, cost, and technological maturity.
The CDR Market Is Growing
In short: cautiously, but increasingly.
Durable CDR purchases jumped 70% in 2024 to 7.6 million tonnes of CO₂ — but only 4% were actually delivered (most deliveries are biocharCDR). The rest of those purchases were future-dated offtake agreements.
As of early 2025, mCDR accounts for just 3.5% of durable CDR volumes. However, Q1 2025 saw a record quarter: 230,000 tonnes of mCDR credits purchased, making up 33% of all durable CDR buys.
That’s a clear signal of rising confidence — and a maturing marketplace.
An Ocean Future For Carbon Removal Markets
As marine carbon removal continues this trajectory, it will form a vital part of global net-zero strategies, especially as technology costs fall and MRV frameworks mature.
The partnership between ClimeFi and the World Ocean Council is timely, helping to demystify a complex and sometimes controversial space. As new buyers enter the market and ocean-based solutions scale, mCDR will over the years become a mainstream climate asset class.