Madison Churchill & Rebecca Daniel, The Marine Diaries
Giant kelp off the coast of California. Photo: Hannah Gabrielson.
In the face of the global climate crisis, the race is on to find new and innovative ways of capturing carbon. New technologies (such as Direct Air Capture) aim to reduce the amount of greenhouse gases in our atmosphere, but there are already many carbon capture systems that exist naturally on our planet. These systems have been in place for millions of years, regulating and balancing our atmosphere. On land, rainforests and dense stands of trees work to cycle carbon out of the air, and back into the earth. Similar regulatory systems exist in our ocean, known as blue carbon. In fact, some blue carbon ecosystems are better carbon sinks than rainforests - once thought of as the ‘lungs of the Earth’.
One of the tools we have in the fight against climate change is kelp.
What is Kelp?
So, what is kelp, and how does it capture carbon? Kelp are large brown algae. All kelps are a type of seaweed, but not all seaweeds are kelp. These macro algae contain four distinct components.
A holdfast - a root-like system that affixes the kelp to the ocean floor.
The stipe - a long stem-like stalk that connects the base of the kelp to the ocean’s surface.
Pneumatocysts - gas-filled bulbs, attach to the stipe, allowing the kelp to stay buoyant and upright in the water column.
Spanning out from the stipe, are the blades. These long leafy structures can be seen from the surface. Much like a land plant, they utilise sunlight during photosynthesis.
How does Kelp Capture Carbon?
Kelp grows rapidly - giant kelp is the fastest, growing over half a metre per day (much faster than trees)! Growing in large underwater stands, kelp forests are thought to play a key role as a blue carbon store. Through the process of photosynthesis, kelp absorbs CO2 into its tissues. Because of their rapid growth, they have incredible capacity to store ~200 million tons of CO2 per year. But their potential for natural carbon sequestration has been estimated to be 1-10 billion tons annually!
Kelps differ from other coastal ecosystems, which typically store carbon in their soils. Their sequestration potential lies in their ability to transport carbon to the open ocean and deep sea. When parts of kelp break off, they can drift for thousands of kilometers because of their pneumatocysts, which help them stay afloat. Eventually they may sink to the seafloor, sequestering carbon in the deep sea.
Cultivating Kelp for Carbon Capture
Some organisations have begun cultivating kelp to help fight the climate crisis. Farms are popping up along the American West Coast, and elsewhere around the globe. An organisation in Maine is experimenting with growing kelp in the open ocean on biodegradable buoys, which will drop to the ocean floor once the kelp reaches maturity. Other organisations are looking to do the same, whilst some suggest that kelp would be better used for food or biofuel.
It’s still unclear what the impacts of mass carbon storage at the sea floor might entail, or whether it's viable, but most agree it’s worth researching further.
The Benefits of Kelp
Kelp forests provide the foundation for an entire ocean ecosystem to thrive, and thus promote local biodiversity. Hundreds of fish, invertebrates, birds, and marine mammals seek refuge in kelp forests. This is crucial in an era of mass extinctions. But kelp forests are already under threat, jeopardising their ability to support species and sequester carbon.
Not only do they help to alleviate some of the burden of greenhouse gases, kelp forests are also a sustainable food source, used for millennia by indigenous peoples. Unlike planting trees, kelp does not require water or fertiliser inputs. At the end of the growing season, once they begin to die off, these nutrient-rich organisms can even be composted and used as fertiliser.
This super-alga serves many purposes that can help us create a more sustainable future. If we invest in nature-based solutions to climate change, the benefits to people and planet are endless.
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