Marine Carbon Dioxide Removal (mCDR)

Deep Sea Storage

Our planet is being transformed by climate disruption, with some of the worst impacts occurring in the ocean. Currently, most efforts to address climate change are focused on reducing emissions of greenhouse gases. While those efforts remain vital, they’re no longer enough. We must also clean up the “legacy” greenhouse gas pollution already in our atmosphere.

Ocean Visions believes that we may be able to harness the power of the ocean to restore the climate and the ocean itself. The ocean already holds more carbon than any other part of the biosphere and has the potential to contribute even more. The sheer scale of the ocean means that any marine carbon dioxide removal (mCDR) solutions proven to be viable and safe would have the potential to clean up billions of tons of CO₂.

A number of marine mCDR approaches are being explored—including deep sea storage.

Deep Sea Storage Overview

Marine Carbon capture and storage (CCS) is the process of capturing and storing carbon dioxide (CO₂) before it is released into the atmosphere. Usually, the CO₂ is captured from large point sources, such as coal-fired power plants, and then stored in an underground geological formation. Captured CO₂ could also be stored in the ocean water column or on the sea bed—if done so at a sufficient depth. Captured CO₂ could also be mineralized via reation with seafloor rocks, enabling permanent carbon storage. Similarly, plant waste from agricultural production or seaweed farming could be sunk to the deep ocean for long-term sequestration.

Technical Potential

The technical potential for deep sea storage is constrained by the availability of CO₂. While emissions from point sources are estimated at approximately 15 billion tons per year, less than 30 million tons of CO₂ are currently captured and stored. Transportation of CO₂ is another bottleneck, as pipeline infrastructure remains very limited.

Environmental Co-Benefits and Concerns

Environmental impacts will differ significantly depending on the final carbon storage form (liquid or solid) and location (water column, seafloor or sub-seabed geological formation). Currently, all operational and planned marine CCS projects store their CO₂ in saline aquifers or depleted gas fields, both of which are deemed highly leakage-proof. Liquid CO₂ injected in the water column, however, will diffuse into the surrounding seawater and cause regional hotspots of ocean acidification at levels that might be detrimental to marine life. At the centuries to millennia scale, this CO₂ could resurface and be released into the atmosphere. Carbon storage in solid forms may result in local habitat destruction.

Cost Considerations

Sinking biomass to the ocean floor has never been tested at scale but recent estimates suggest costs of $10-80 per ton of CO₂ removed. In contrast, the costs of CCS have been examined in detail: A 2019 analysis by the National Petroleum Council*, for example, suggests that only a fraction of stationary emissions could be captured, liquified, transported, and stored for under $50 per ton of CO₂. The large majority of CCS will exceed $100 per ton of avoided emissions. In CCS, capture costs make up the lion share of the technology; costs are particularly high when older plants have to be retrofitted for CO₂ capture and when the purity of CO₂ in the captured gas is lower than 95 percent, which is the case 98 percent of the time.

Dive Deeper

Explore mCDR Road Maps

Ocean Visions’ mCDR road maps provide overviews of potential technologies, obstacles they face, and first-order priorities needing attention to advance the field. The road maps are intended to catalyze global collaboration and engagement and will be updated and refined as advances emerge in science, technology, governance, and policy.