Marine carbon dioxide removal, or mCDR, covers a wide and varied set of approaches that use the ocean in some way to remove carbon dioxide from the atmosphere. The term is broad enough to include everything from restoring coastal wetlands to manipulating ocean chemistry at scale. That breadth is one of the field’s strengths, but also one of its central challenges.
This post is intended as a short primer for anyone coming to this forum without a deep mCDR background, or for anyone who wants a shared starting point for the discussions in this section.
mCDR techniques generally fall into a few broad categories:
- Ocean alkalinity enhancement (OAE): Adding alkaline minerals to seawater to increase its capacity to absorb and store CO₂.
- Macroalgae cultivation: Growing kelp and other seaweeds to absorb CO₂, then sinking or processing the biomass so that the carbon does not return quickly to the atmosphere.
- Artificial upwelling: Bringing nutrient-rich deep water to the surface to stimulate phytoplankton growth and biological carbon uptake.
- Direct ocean capture: Extracting dissolved CO₂ directly from seawater, which can increase the ocean’s capacity to absorb more CO₂ from the air.
- Coastal blue carbon: Protecting and restoring mangroves, saltmarshes, and seagrass beds, ecosystems that store large amounts of carbon in sediments and biomass.
- Ocean iron fertilisation (OIF): Adding iron to stimulate phytoplankton blooms and drive biological uptake of CO₂.
The ocean already absorbs around 25-30% of the CO₂ humans emit each year. mCDR approaches aim to amplify or make use of that capacity, but most techniques are still at the research or pilot stage. Questions around permanence, ecological impact, scalability, monitoring, and cost remain largely unresolved.
The SEAO2-CDR project sits precisely in this space: building the evaluation tools and evidence base needed to address those questions in a systematic way.