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Carbon sequestration in the sea: Is it the largest soda factory in human history?

By Gadi Kolker

Carbon sequestration in oceans and other water bodies is emerging as a critical strategy in the fight against climate change. These methods are gaining momentum among scientists, policymakers, and environmentalists due to their potential to absorb vast amounts of greenhouse gases. This article reviews current techniques, incentives, challenges, and leading activities in the field, including the controversial work of Russ George, and asks: is this the largest soda plant in human history?

Russ George and the fertilization of the oceans - to what extent are we allowed to engineer nature? In 2012, Russ George, known for controversial ocean-fertilization projects, led a large-scale iron-fertilization experiment off the coast of British Columbia, arguing it would boost salmon populations, capture carbon, and support the region’s Indigenous community. While some reports pointed to increases in phytoplankton and salmon, the project faced significant opposition due to potential environmental risks and the lack of regulatory approval under frameworks such as the Convention on the Prevention of Marine Pollution and Canadian law. No charges were filed against George, but his activities highlight the need for rigorous oversight and scientific validation of ocean carbon-sequestration efforts.

With boundaries and responsibilities outlined, the following sections survey leading methods, beginning with ocean fertilization.

1. Fertilizing the sea

As illustrated by the George case, this method adds nutrients, such as iron, to stimulate phytoplankton growth that absorbs CO2 via photosynthesis; when these organisms die, they sink, theoretically sequestering carbon in the deep ocean. Significant concerns remain about ecological impacts and the long-term effectiveness and permanence of this approach.

2. Improve alkalinity

Adding alkaline materials to seawater increases its capacity to absorb CO2, aiming to mimic natural processes that lock away carbon for millennia. CO2 dissolves into seawater and can re-emit to the atmosphere; its dissolution forms carbonic acid, which can react with marine ions to create stable bicarbonate and carbonate species. Rising atmospheric CO2 increases ocean acidity because alkalinity does not rise in tandem, contributing to phenomena such as coral bleaching; research continues to optimize materials and assess environmental impacts.

3. Restoration of Ecosystems Near the Shores-Blue Carbon

Mangroves, seagrasses, and salt marshes - known as blue-carbon ecosystems - store carbon in both biomass and underlying sediments. Conserving and restoring these habitats offers dual benefits: durable carbon storage alongside biodiversity gains and coastal protection. Similar restoration occurs in freshwater systems such as seasonal wetlands, enhancing biodiversity and bird migration stopovers year after year.

4. Fixation of biomass in the deep sea

This approach cultivates biomass and deposits it in the deep ocean, where carbon can remain stored for thousands of years, without dispersing nutrients as in fertilization. The focus is on macroalgae that absorb CO2 and whose biomass is proactively sunk at end of life to enhance permanence. One startup in the field is Gigablue, which uses inert flakes on which algae grow; as mass increases, the flakes sink to the seabed, theoretically locking carbon for millennia, and its AI identifies optimal ocean sites. Another company, BlueGreen, developed a proprietary treatment for nuisance algae in freshwater, causing them to sink while maintaining potable-water quality; this supports both carbon sequestration and increased drinking-water availability, with operations in Florida and several African sites.

Incentives and Market Dynamics

1. Research Grants: Programs such as the EU’s Horizon and the U.S. Department of Energy’s Ocean Carbon and Biogeochemistry Program fund innovative marine carbon-sequestration research.

2. Policy and Support: Initiatives like the Blue Carbon Initiative and the UNFCCC Paris Agreement encourage integrating ocean sequestration into national climate strategies; the London Convention provides a regulatory framework for responsible research and deployment.

3. Carbon Markets: The voluntary carbon market (VCM) shows renewed interest in high-quality, nature-based credits; as of 2024, some prices reached up to $500 per tonne, particularly under CORSIA’s aviation-offset criteria, with a similar trend emerging at the IMO (International Maritime Organization), which until recently did not recognize offsets in its mitigation strategy.

Conclusion