Ocean-assisted carbon removal

A deep dive into ocean alkalinity enhancement and direct ocean capture

By Irene Polnyi · January 13, 2023

Originally published on Substack

This article examines two ocean-based carbon dioxide removal (oCDR) methods: Ocean Alkalinity Enhancement (OAE) and electrochemical Direct Ocean Capture (DOC).

The Ocean's Carbon Storage Capacity

The ocean is a grand carbon reservoir containing 38,000 Gt of carbon in its deep interior. According to ClimateWorks Foundation research, returning atmospheric CO2 to preindustrial levels would increase ocean carbon by only 0.7%.

How Ocean CDR Works

Unlike direct air capture, ocean methods leverage natural sea-air gas exchange. By manipulating surface conditions—particularly pH levels—these techniques trigger chemical reactions that draw CO2 from the atmosphere.

Ocean Alkalinity Enhancement

This approach adds alkaline minerals to raise water pH, enhancing CO2 absorption. The resulting bicarbonate ions cannot return to the atmosphere and remain permanently stored (~10,000 years). Planetary Technology leads commercialization through electrochemical processing of mine waste.

Direct Ocean Capture

Using renewable electricity to split seawater into acidic and basic solutions, this method directly strips CO2 from seawater. It requires pairing with long-term storage solutions like deep-ocean injection or mineralization.

Notable Companies

Primary Challenges