The greatest carbon sink of all


—One of the brightest hopes for carbon sequestration lies in the darkest place on earth: the abyssal depths of the deep ocean. For millennia, dead plants and animals have sunk to the sea floor, where they form sediment that eventually turns into rock (and sometimes fossil fuels).

Some climatologists believe we can now speed up this natural process and clean up our modern carbon mess by deliberately sinking millions of tons of algae and fish.

But is the carbon sink the climate equivalent of sweeping dirt under the rug? Our knowledge of deep-sea ecosystems is still sketchy; and even if the carbon math works, the logistics of sinking carbon could disrupt the marine systems we depend on for food, transportation and recreation.

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Such a vast natural solution
Like the problem

1. Sinking seaweed. A paper 2016 in Nature Geoscience estimated that marine macroalgae – aka seaweed or kelp – could store around 175 million tonnes of carbon each year, either by burying it in coastal sediments or exporting it to the deep sea. In 2020, the Energy Futures Initiative, a non-profit climate technology organization, published a report that found that marine carbon dioxide removal could one day sequester CO2 on a billion-ton scalethanks to the huge amount of space available in the ocean and the lack of land use complications.

Ways of sequestration carbon from macroalgae in the deep sea.
The figure was adapted from Krause-Jensen and Duarte, 2016.

2. Just add water (and money). There do not appear to be any major technical barriers to algae cultivation, that can grow at almost 3 centimeters per hour. Several start-ups are already experimenting with growing or moving coastal kelp far out to sea, where it would settle to the ocean floor instead of washing up on shore. running tide uses carbon buoys to suspend “microforests” of kelp over deep water: when the buoys are deflated, the kelp sinks naturally. Pull to refresh wants to use semi-autonomous solar-powered vessels to grow and sink its carbon-sucking algae.

3. Reduce industrial fishing. Gaël Mariani, marine ecologist at the University of Montpellier calculated that big fish like tuna also sink to the sea floor when they die – and that global fishing has interrupted this natural process to the tune of 730 million tonnes of CO2 since 1950. Letting the big ones get away can be a victory for carbon.

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The numbers are still murky

1. Science comes and goes. The 2016 Nature article estimated that one square kilometer of algae absorbs about 50 tons of carbon. But when University of Tasmania scientist John Barry Gallagher ran the numbers, he was surprised to find thkelp forests are actually a net source of carbon. He calculated that tiny algae-eating sea creatures exhale their own CO2, which means that one square kilometer of kelp emits an average of 20 tonnes. His useful article from March suggests that more research is needed before developing seaweed farms.

2. The detail is in the weeds. In this great article from the MIT Technology Review from last year, James Temple attempts to unravel the prospects for carbon removal from kelp. He notes that researchers are concerned about a billion-ton blue carbon effort blocking the paths of marine mammals, disrupting local ecosystems, interfering with shipping and encroaching on protected areas and indigenous territories.

3. Don’t Sink It, Eat It. Any discussion of kelp is complicated by its growing popularity as a climate-friendly product. agricultural commodity, biofuel and replacement of plastics. These reduce the global carbon footprint but are only carbon-neutral solutions: recycling the carbon dioxide already present in the atmosphere rather than eliminating it permanently. To sink and sequester the kelp instead, a generous carbon price (or other incentive) would be needed to make it a more attractive option.

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What to keep an eye on

1. First experiences. Running Tide has already deployed about 1600 kelp buoys, and now you can buy “carbon negative” oysters online.

2. Piece of kelps. What you considered “a unique serialized digital security token comprising a futures contract for one ton of seaweed“To be a great way to build natural capital based on marine permaculture, or another example of cryptocurrency gone crazy, it will be interesting to see what happens to the $200 face value of the kelp coin. when it matures (at some as yet unspecified point in the future).

3. Public and political rejection. In 1990, protesters succeeded in prevent a seaweed farm destined to produce nori for Washington State’s hottest sushi food trend. Permission is still a big issue for kelp farming, although Washington recently introduced a bill streamline regulation.

Image: @jasondecaairestaylor |


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