Biomass Sinking
Biomass sinking is a method that taps into the carbon sequestration potential of biomass and the power of our oceans’ currents. CO₂ is permanently removed from the atmosphere by transporting seaweed or other plants to the middle of the ocean and sinking the carbon-rich biomass to its depths.
Introduction
Biomass sinking is a great example of utilising natural processes, like ocean currents and existing carbon cycles, to safely store carbon at the bottom of the ocean. This can occur via currents alone, gravity, or assisted means engineered by humans.
This method taps into uncharted potential of deep oceans to store carbon. As 83% of the global carbon cycle circulates through oceans, there is huge potential for CO2 removal.
The Process
The general processes involved in ocean blue carbon are outlined below:
Carbon Capture
CO₂ is trapped by seaweed growing in surface waters and is then converted to carbon-rich biomass in a process called photosynthesis.
Seaweed Transport
The floatation devices, upon which the seaweed forests grow, move with the currents out into the ocean.
Seaweed Sinking
Once the seaweed growth hits a critical mass the flotation device breaks down and the biomass sinks to the bottom of the ocean floor.
How it works
Photosynthesis
Seaweed sequesters carbon via a process called photosynthesis. CO₂ is dissolved in ocean water and is then absorbed by seaweed. Pigments in the seaweed use energy from the sun to convert the CO₂ and water to oxygen and carbohydrates. Terrestrial plants mostly rely on the pigment, chlorophyll, but seaweeds use a variety of pigments, as it allows them to take advantage of many more wavelengths of light. The carbohydrates are transported around the seaweed and used to build carbon-rich biomass.
Ocean Currents
Ocean currents are the constant and predictable movement of seawater around the globe. They are both driven by our climate, via wind (Coriolis Effect) and are hugely important for regulating it. Heat is distributed more evenly around the globe on ocean currents as they act as a conveyor belt of heat from the Equator to the Poles. Now, ocean blue carbon projects are tapping into the power of these currents to carry seaweed biomass away from coastal areas and out into the deep ocean to securely store the carbon they contain.
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Carbon Storage
The storage process begins with the biomass sinking. Gravity drags the seaweed down, many hundreds of meters, to the ocean floor. Over time, the carbon either becomes embedded in the ocean floor sediments or is consumed by deep ocean organisms and removed from the fast carbon cycle for centuries. Even if gases escape from these sediments, the low temperature and high pressure near the ocean floor turn CO₂ into a liquid denser than the surrounding water, ensuring its retention.
Tapping into uncharted potential
Biomass sinking is at a relatively nascent stage compared to other carbon dioxide removal technologies. However, research is continuing and it does represent an opportunity to mobilize vast swathes of the Earth’s previously underutilized surface to tackle climate change. Therefore, it should be recognized as a viable and impactful solution. All this while providing invaluable environmental co-benefits that ensure the sustained healthy functioning of our oceans.
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One of biomass sinking's most powerful climate impacts is its rapidity. Seaweeds are some of the fastest-growing species on Earth and therefore can help oceans sequester CO₂ more rapidly and efficiently than other ecosystems.
Research has shown that a kelp forest removes 3 times more CO₂ from the atmosphere per unit area than a pine forest. Biomass sinking is also a very scalable solution as there is no space limitation to its deployment (2/3 of the globe’s surface is available for use). The high permanence (likely thousands, but potentially millions of years) of the biomass once it reaches the ocean’s depths, is also a big contributor to biomass sinking’s climate impact.
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One of the greatest environmental problems we face is coastal eutrophication. This occurs when too much nitrogen and phosphorus run off the land and into the ocean, e.g., from agricultural activities.
These nutrients cause algal blooms which deplete oxygen and prevent sunlight from penetrating the water surface, which in turn results in ocean ‘dead zones’. Biomass sinking methods counteract this as seaweeds regulate nutrient levels when they take up nitrogen and phosphorus to grow. Research shows that seaweed production also reduces ocean acidity, improves biodiversity, and helps protect our coasts from storm surges and erosion.
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