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Woody biomass sinking

From £301/tonne · Questions? Talk to sales


Woody biomass sinking is a method that sequesters carbon by submerging leftover woody materials in the oxygen-depleted layer of the Black Sea (the anoxic layer), which is approximately 2 kilometers deep.

In this unique environment, the woody biomass remains preserved - the lack of oxygen means it doesn’t decompose. And it doesn’t disrupt the local ecosystem since there's no life other than specialized microbes.

Two sources of woody biomass are used: The first is forestry waste biomass collected from a hydroelectric reservoir or directly from forestry operations, addressing potential issues for dam operators and aquatic ecosystems. The second source consists of woody offcuts from fruit and nut orchards surrounding the Black Sea.

This sinking process is done by a crane that pushes the biomass deep enough for the sea’s pressure to take over, and the biomass sinks into the anoxic zone.

Activities are fully measured, monitored, and accounted for by an end-to-end Measurement, Reporting and Verification system, including deep-sea sensors, cameras and truck-mounted devices, providing complete visibility from the field to the bottom of the sea.

The science

The Black Sea is the largest anoxic basin in the world and already serves as a large, natural carbon sink.

Woody biomass sinking is a method of removing carbon that essentially accelerates and improves a natural solution. In nature, the woody biomass tends to decompose in fragile environments like rivers and oxygenated waters at the surface of the sea. Woody biomass sinking allows us to bypass those fragile environments.

The natural anoxic zone in the Black Sea starts around a depth of 150m. It lacks oxygen and is saturated with sulfide. We consider the permanence of carbon removal to be at least 100 years, which is a conservative estimate. With ongoing scientific research underway, we expect that figure will be updated to 1,000 years. Evidence from preserved sunken ships dating back to Roman times also reinforces the idea that lignin, a key component of wood, resists decomposition without oxygen.

The stability of the Black Sea's stratification over the past 5,000 years, a result of its unique geological formation, effectively prevents the mixing of anoxic deepwater with oxygen-rich surface waters. As a result, even if the wood does decompose, the organic carbon stored at the bottom of the Black Sea is likely to remain there for thousands of years.

Research papers 5

Supercritical‘s view

At Supercritical, we've historically been cautious about partnering with a biomass sinking provider, mainly because we’re conscious of the potential ecosystem impacts of sinking biomass to the ocean floor.

However, we’re confident in this specific project for two reasons:

1. The unique conditions in the anoxic zone of the Black Sea give us confidence that there will be no to minimal effects on the ecosystem.

2. Overall, the impact on the ecosystem is positive, as it prevents foreign woody biomass, such as forestry waste, from decomposing in the reservoirs, rivers and the oxygen-rich surface waters.

Furthermore, we were impressed with our providers’ approach to Measurement, Reporting and Verification. There's also considerable scaling potential, given the high agricultural and forestry production in this area, where substantial amounts of waste biomass could be sustainably removed by sinking - without harming soil productivity or the ecosystem.

Our supplier's solution not only provides carbon removal, but also offers safe storage for unused agricultural residue (a waste management problem), manages river runoff (addressing eutrophication in the oxic layer of the Black Sea), and mitigates the fire hazard posed by forest ground biomass.

Bojana Bajzelj

Head of Climate

Project locations 3

  • Map of The Black Sea
    The Black Sea
  • Map of Georgia
  • Map of Turkey


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  • Remove carbon

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