Introducing Sediment Carbon Storage (SCS)

In efforts to expand Marine Anoxic Carbon Storage to a globally available solution, a new initiative in Rewind’s biomass storage projects portfolio is emerging. Relying on natural processes, existing infrastructure, and a deep understanding of marine environments to safely and durably store carbon, we are excited to introduce Sediment Carbon Storage (SCS).

What is SCS?

SCS is a novel carbon storage method that preserves biomass in anoxic marine sediments. Instead of allowing organic matter to decompose (breakdown) and release carbon back into the atmosphere, SCS mimics the natural process whereby terrestrial organic matter is carried out by rivers and sunk to the seabed, where natural sedimentation will bury and protect it for thousands of years.

How it works:

Terrestrial biomass — preferably woody material that has no alternative use — is transported to existing designated underwater storage sites where dredged marine sediments are actively being deposited. These sites already receive massive volumes of sediment as part of a global, gigaton-scale marine management routine called dredging: cleaning out the seabed of ports, rivers, and waterways. As the dredged sediments are deposited, they bury the biomass, isolating it from oxygen and creating the conditions necessary for geological preservation.

Why it works:

Oxygen in the sea water reaches only a few inches into the sediment, so even a a thin layer of sediment creates an anoxic environment. In anoxic (oxygen-free) environments, microbial activity slows down dramatically. This inhibits decomposition and prevents the transformation of biomass into CO₂ and methane. In short: no oxygen, no decomposition, no carbon release. Strong evidence for this process comes from the remarkable preservation of ancient wooden shipwrecks discovered buried in anoxic marine sediments — their structural integrity and carbon content intact after millennia underwater.

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Closing the carbon loop:

Sediment dredging is a widespread and necessary practice used to maintain shipping lanes and manage coastal areas. However, it unintentionally disrupts buried carbon stores — exposing ancient organic matter to oxygen and causing it to oxidize into CO₂. SCS turns this liability into an opportunity. By introducing new biomass into these sedimentation sites, we leverage the same dredged material to re-bury fresh carbon. This closes the carbon loop, restoring — and even enhancing — the ocean's role as a long-term carbon sink. 

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Durability & Safety:

Marine sediments are naturally designed to store carbon over geological timescales. By leveraging their physical and chemical properties, we achieve long-term, low-risk storage without the need for industrial-scale processing or synthetic materials. This approach is grounded in natural processes and requires minimal intervention once burial occurs. Natural analogues demonstrate the efficacy of this method. For instance, river deltas act as significant carbon sinks by trapping and burying organic material transported from terrestrial environments. Similarly, sapropels—organic-rich sediment layers found in the Mediterranean Sea—have formed during periods of enhanced productivity and anoxic conditions, leading to increased carbon burial. While methane generation can occur in anoxic sediments, the slow diffusion of methane through compacted sediments, combined with natural aerobic and anaerobic oxidation processes, significantly reduces the likelihood of its release to the atmosphere.

Why is this Good?

SCS integrates with an existing human activity — sediment dredging — making it energy efficient, cost-effective, and easy to regulate within existing marine permitting frameworks. It also has a minimal added impact on marine ecosystems when designed thoughtfully and may present an opportunity to restore large areas of the marine environments that have been previously disturbed by human activity.

Where is Rewind going with this?

As with everything Rewind does, we lead with science. We started with a thorough literature review, and then designed a series of experiments ranging from the lab environment, through a mesocosm, and to a small-scale field trial. We are measuring oxygen, sulfide, and methane dynamics, as well as biomass preservation and environmental changes to chemistry and biodiversity in both the water and the sediment. This marks a critical step toward validating SCS as a scientifically sound and scalable CDR strategy. We are sharing a few images from our work today, and the full scientific reports will be published as experiments are completed and analyzed. 

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Meanwhile, are you a Marine Expert? We want you to dive deeper!

Our comprehensive literature review on the science and practice underpinning SCS, including sediment chemistry, oxygen profiles, biomass degradation pathways, and global dredging practices, is ready for scrutiny! We're sharing this review publicly and inviting external experts to help us refine, challenge, and strengthen the scientific foundation of this approach.