Seaweed Farm Options
The basic outline of using deep blue carbon for carbon sequestration is illustrated in the figure. Grow a lot of seaweed, and let some of it fall to the bottom of the deep ocean.
However there are still plenty of details to work out, and depending on what choices you make, the options can look pretty different.
As explained on the 'what seaweed farms need page' the dominate cost of the farm is bringing the nutrient phosphorus (and without on site nitrogen fixation, nitrogen as well) to the farm. If we could tailor the seaweed to our purpose we can eliminate much of this cost. Later on this page we will discuss:
Short Term (Low Tech) solutions
Bio-engineering seaweed the way we want it is not a solved problem at present. In the mean time we need solutions we can deploy today. Here are some possibilities for the short term we will also discuss:
Engineered Seaweed for Carbon Sequestration
If we 'dream big' we should be asking ourselves the question
What would the IDEAL seaweed look like?
And the answer is that it would just do carbon sequestration on its own, without any intervention by humans (thus very low cost). The two places where humans are still involved are
Bringing raw materials (e.g. phosphorus) to the farm
Doing something so that some fraction of biomass of the farm sinks and becomes sequestered carbon (harvesting).
We can solve both of these issues if the seaweed could be tweeked a bit. Imagine
The seaweed naturally creates a 'pod' (think pine cone, or an acorn) that is mostly cellulose, lignin, or other polysaccharide. This pod naturally matures and then falls off. This also roughly what leaves and seed pods do so this is not a stretch to imagine bio-engineering this into seaweed.
The seaweed can be propagated indefinitely vegetatively. This is common in the plant world (think bananas or and in fact many seaweed species). If the seaweed does this it means it effectively 'lives forever' (it regenerates itself)
An important point is that the pod is almost completely just cellulose (or other polysaccharide), which contains ONLY carbon, oxygen and hydrogen (and in particular does NOT contain nitrogen or phosphorus. This means that nutrients like nitrogen and phosphorus are NOT LOST when these pods drop to the bottom of the ocean, so these nutrients do not need to be replaced.
This means that once established the seaweed farm needs very little ongoing phosphorus or nitrogen fertilizer. There is very little ongoing human effort needed at all, even if the farm was very large. The seaweed would simply do its thing, day-in and day-out sequestering carbon. Humans do relatively little, fixing storm damage and insuring that diseases and pest do not get out of control. This is about as cheap and easy as you could imagine.
Engineered Seaweed for Energy
Fuel Instead of Sequestered Carbon
If we engineer the seaweed pods a bit differently than we did when our goal was sequestering carbon, we could optimize the seaweed instead to generate energy (fuel). We no longer get negative carbon, but we do get carbon neutral fuel.
There are numerous proposals for using seaweed (or land plants for that matter) as the input to some process that generates liquid or gaseous fuels. Some use fermentation to make alcohol, others pyrolysis, and still others hydrothermal liquefaction. However all the processes, require moving large amounts of biomass (which is mostly water) to a industrial processor where the fact that seaweed is 90% water is problematic (it is heavy and it has to be dried, or separated somehow).
Let the seaweed do ALMOST ALL the work!
What if we modify the 'pod' so that instead of being made of cellulose, it is filled with oil. Microscopic algae is actually very good at producing oil, and many plants produce seed pods that have a lot of oil (think olives, or sunflower seeds). Now oil is LIGHTER than water, and thus these pods will float to the surface when the mature and break off.
Once on the surface, it is relatively trivial to simply have a boat 'skim' the pods out of the water, and then run them through a mechanical press that would then extract the oil (the husks can be discarded right there on the ocean, sequestering that carbon in the deep sea). The result is a bio-oil that could be used like diesel fuel.
Once again, notice that the output of the process (the pods) is almost exclusively a hydrocarbon (thus no nitrogen or phosphorus was lost so these don't need to be replaced). Also notice that what gets collected and transported by humans (the oil) is not 90% water (unlike the actual seaweed) but is the concentrated fuel that we desired and very little energy and effort was needed to separate it.
Mowing Sargassum Seaweed
The basic idea behind deep blue carbon sequestration is to grow seaweed in the open ocean and have some part of it sink to the deep sea taking carbon with it.
One way of doing that is with bio-engineered seaweed, but there are still unknowns of how exactly to do that to be researched to make that a reality. In the meantime it turns out that nature itself has made a seaweed farm for us that we can leverage.
Nature has Made a Million Ton Seaweed Farm for Us!
The area of the Atlantic ocean a few hundred miles east of Georgia is called the Sargasso Sea. It is named for a type of seaweed called Sargassum, that accumulates there as free-floating seaweed. This seaweed has been present there for as long as humans have sailed that area, but in the past decade, Sargassum has 'gotten out of control' and created huge blooms in the central Atlantic ocean (south of Sargasso Sea), which drift eastward, and then wash up beaches in the Caribbean Islands, Mexico, and the Gulf states. It is a huge problem that is unlikely to change anytime soon.
There are some theories as to the cause of the blooms (maybe dust from Africa fertilizing the sea, maybe runoff from the Amazon basin, maybe changes in ocean currents bringing nutrients up from ocean flow, probably all of the above). But suffice it to say that for whatever the reason, there are literally 10s of millions of tons of Sargassum that grows in the Atlantic each year, and is washing up on shores were we don't want it.
Notice that Nature has done much of the work. It has created a very large 'farm' and fertilized it. The basically problem is that the resulting seaweed simply washes up on shore where not only does not sequester carbon, but people have to invest 10s of millions of dollars hauling it away.
A Seaweed 'Mower'
What we need is a way of sequestering all that seaweed instead of having it wash up on beaches.
Sargassum floats because it has many small floats about 1/4" in diameter that hold gas. Thus if you could create a 'mower' that compromised the floats, the Sargassum would simply sink. If you were to do this out in the Atlantic (or even just a few dozen miles off of most islands), the sea would be quite deep (over 3 KM) and the carbon would be sequestered (and of course, the seaweed would not wash up on beaches).
It turns out in this particular region of the ocean there are strong trade winds that blow consistently from the northeast (see wind map). These winds cause the seaweed to clump into lines (see Langmuir circulation) about a meter or two in width (as shown in the picture). So nature even helps us with the harvest.
Now imagine a 'mower' that is a small catamaran sailboat. Each of the two floats is about 5 meters long or so and there would be about 2 meters between the floats. Between these floats is a roller-shredder mechanism will shred any seaweed that is between the floats. The catamaran comes with a sail, but is unmanned (like SailDrone), and would be powered by the very consistent and significant wind (> 20 KMPH) as well as solar power.
These robots simply spend their days traveling down the lines of Sargassum at a 3-6 kph, 'mowing' the open seas, and letting the seaweed drop to the bottom of the ocean. A fleet of about 1000 of these should be sufficient to sequester millions of tones of carbon each year, and keeping the Caribbean beaches clean. The venture would make money by getting carbon credits (thus the robot needs to keep track of how much seaweed it mows), as well as payments by beach owners for keeping their beaches clean.
Not Ideal, but Not Bad Either
While having bio-engineered seaweed that naturally sheds 'pods' to sequester carbon is ideal from a cost point of view (little fertilizer needed), it requires technology that is in the research stage. However there is nothing that stops us for going 'low tech' now.
The idea would be to set up a farm, probably close to shore, but also in deep water, and simply pay the price of hauling out the needed phosphorus (probably as bio-solids), to make the seaweed grow. We would definitely need to insure that the farm has nitrogen-fixing microbes available to supply the fixed nitrogen. It also would require some effort to 'harvest' the carbon. This amounts to detaching some of it from the floats and and disabling any pneumatocysts that would keep it buoyant) so it will sink to the bottom.
We know from the Redfield ratio) that we will get roughly 106 tons of sequestered carbon for every ton of phosphorus we provide. If we get this phosphorus from bio-solids (sewage treatment), it is basically the cost of transportation. If that can be kept low, we could simply live with that cost (at least in the short term).
Seaweed for Food
Taking the Pressure Off the Land
The primary goal of this web site is to popularize the potential of sequestering carbon in the sea. But our overarching goal is to fight climate change. Agricultural practices are a large part of our current carbon footprint. Seaweed has the potential to grow food more efficiently than is possible than on land, and this can 'take the pressure' off of the forces causing deforestation and other carbon-releasing practices (e.g. intensive farming). In particular
For a given area, seaweed is over FOUR TIMES as productive as any land plant at generating foodstuff. This is mostly because seaweed does not need things like roots, structural parts (e.g stems), circulation systems etc. When we eat seaweed, we eat most of it.
The growing season for seaweed can be continuous. In temperate climates farms are only active 1/2 the year. Growing seaweed in the tropics can double output (winter does have a silver lining, however, it keeps pests down).
Seaweed farms are already very big business in Asia, but most of these farms while large, are still very labor intensive. We need the automation (the equivalent of combines for maize) if we are to scale up to the point seaweed replaces a significant amount of land farming.
While many places already have the culture of eating seaweed directly, seaweed's efficiency and low cost give it the potential of replacing other 'bulk' items like corn (maize) and soybeans that are most often used as feedstock to produce other food products (e.g. sweeteners, tofu, extenders, fake meat, etc). Seaweed should be able to compete well for these applications, lowering costs, and freeing up land for other uses (e.g. reforestation!)
OK those are Interesting Ideas, What's the Plan?
Up until now we have been showing you the 'vision' of what could be done. Hopefully it feels like it 'makes sense'. But there is a big difference between having an idea that feels like it could be implemented, and actually implementing the plan. Here are some details on the plan.