When Life Hands You Seaweed
on sargassum, sequestration, whales & climate
Sargassum is having a moment. A golden brown seaweed that only marine biologists used to pay much attention to is now a regular on the evening news. For the last dozen years, the annual blooms in the Atlantic have grown bigger and lasted longer, with 2023 shaping up to be the biggest of all. So big, in fact, that the Great Atlantic Sargassum Belt can be seen from space, massive patches of free-floating macro-algae stretching 5,000 miles from the east coast of the Americas to the west coast of Africa.
It is just as impressive up close, piled to depths of three feet or more as it washes ashore, burying beaches in a smelly, rotting mass of sliminess, laced with bits of plastic, flesh-eating bacteria and toxins, including lead and arsenic. If all that weren’t bad enough, it smells like rotten eggs as it decays, thanks to emissions of asthma-inducing hydrogen sulfide.
Sargassum chases aways tourists. It buries turtle nests. It clogs up water intake valves, mucks up marinas and traps boats. It blocks the sun, threatening coral reefs. It soaks up the oxygen in the water, creating dead zones, forcing fish to flee or die, and driving fishermen to despair.
A patch of sargassum can double its biomass in ten days. Like Audrey II, the fast-growing, ravenous, singing plant from The Little Shop of Horrors, sargassum is a glutton, though one that doesn’t need to say, “Feed me!”
Gorging on an all-you-can-eat buffet of nutrient-rich run-off without a predator in sight, sargassum is an full on climate change success story.
“You have the Congo, the Amazon, the Orinoco, the Mississippi—the largest rivers on the planet, which have been affected by things like deforestation, increasing fertilizer use and burning biomass. All of that is increasing the nitrogen concentrations in these rivers and so we’re now seeing these blooms as kind of a manifestation of the changing nutrient cycles on our planet.”
This is a well-fed monster largely of our own making, basking in record warm waters made possible by human-triggered climate change.
Beyond the Sea
Since 2011, sargassum has spread well beyond its historic home, the eponymous Sargasso Sea, a roughly 3.5 million sq km area in the North Atlantic between the US and the Canary Islands. It is only sea in the world completely surrounded by water, bounded by four strong ocean currents that collectively keep it contained.
The Sargasso Sea is an ecological treasure, a marine nursery, sheltering and feeding young turtles, fish and other sea creatures; an idyllic pit stop for birds to grab a quick snack. For eels that spend most of their lives slithering in the rivers of Europe, North America, the Caribbean and North Africa, it is the romantic, tropical getaway of choice for mating.
So what happened? In 2009 / 2010, thanks to a dramatic shift in wind patterns, a sizable chunk of sargassum escaped from the confines of the ocean current “fence.” This big blob of seaweed then drifted west toward the Iberian Peninsula and from there floated south to warmer waters off the coast of Africa where it found itself in sargassum heaven. The population exploded, with patches of sargassum expanding westward across the Atlantic to the Caribbean, then Florida, then south to Mexico and Brazil. Depending on seasonal currents, the seaweed can travel even further east, slipping into the Gulf of Mexico.
Burying Carbon Where the Sun Don’t Shine
Almost always, too much of a good thing is a bad thing, but there is one notable good that comes from too much sargassum. Seaweed soaks up vast amounts of carbon. In fact, not only does the Great Atlantic Sargassum Belt soak up more carbon than a tropical rain forest, but it also soaks it up faster. This year’s bumper crop, expected to top last year’s June tally of 24 million tons (that’s about 5 million African elephants-worth), is a massive carbon sink.
At least for as long as it out there floating in open water.
As soon as the seaweed hits the sand, it begins to rot, turning into a smelly, prodigious carbon emitter.
Two companies, both startups based in the U.K., are currently testing out schemes to harvest sargassum before it hits the shore. They want to bale it up, then sink the bales to the bottom of the ocean where cold temperatures and low oxygen levels should slow decay. The CO2 tapped in the sargassum, unceremoniously buried at sea, should, it is hoped, be sequestered for millennia. Out of sight. Out of mind. Out of the atmosphere.
Technically, sargassum soaks up CO2 that is dissolved in water, so doesn’t draw it in from the air. Still, removing waterborne CO2 from surface waters should open up room for more atmospheric carbon to stored in the ocean. It’s a bit of a chemical dance, but the net effect ought to be a reduction in atmospheric carbon. Exactly how big a reduction has yet to be determined, but looks like we will soon find out.
A company with a big vision, Seaweed Generation, is building floating robots called “AlgaRays” and “AlgaVators” that are designed to munch through sargassum like PAC-MAN™ and tidy up the ocean surface like a Roomba®. The prototype, “Alfie,” is 2 x 4 x 0.5 meters. If a pilot project off the coast of Antigua proves successful, a full-size version (10 x 4 x 1.5 meters) will be built, capable of gobbling and sinking a much as 16 tons of sargassum at a time, four to six times per hour.
Co-founder and former Google software engineer, Patricia Estridge, estimates that a fleet of a 1,000 of these sargassum-bundling bots could be enough to keep the seaweed in check and beaches safe. The company doesn’t plan to stop there. They are also looking into growing seaweed specifically for carbon dioxide removal (CDR), potentially co-locating seaweed farms near off-shore wind installations near coast of England. Farmed seaweed offers co-benefits, such as creating habitat to increase biodiversity, and also revenue streams from useful materials (e.g., for making bioplastics) harvested before sinking the waste.
Another startup, Seafields, has similar ambitions but hopes to build a 55,000 sq km ocean “farm” in the South Atlantic to grow, process and bury sargassum. This “largest farm on Earth” could be located in a vast gyre that, like the Sargasso Sea, is surrounded by strong ocean currents. But unlike the Sargasso Sea, it is considered to be a marine desert because the warm surface waters are too salty to support life.
The ambitious scheme involves installing long plastic tubes to bring nutrient rich waters up from the bottom. According to Seafields, any sargassum that escapes a moat of bobbing plastic buoys would quickly die of starvation in the salty surface waters out in the wild.
Still, one wonders whether deserts, on land or water, might serve an unacknowledged purpose when viewed within a larger system. Are these areas really “unproductive,” or is there more to the story?
It is hard to think of anything in nature that doesn’t serve a purpose. For example, until a few years ago, scientists referred to sections of genomes that weren’t functioning as genes as “junk DNA.” Now we know that without the “junk,” chromosomes don’t “bundle” correctly.
Likewise, no one really knows what the long term effects of bringing bottom waters to the surface at scale within the South Atlantic gyre might be. But we do now know that altering the mix of waters can have all sorts of sobering, climate-altering implications.
It was recently reported that a critical globe-spanning current known as “the Southern Ocean overturning circulation” that delivers nutrient-rich bottom waters from off the coast of Antartica to surface waters in the Arctic has slowed by an astonishing 30% over the last few decades. Thanks to global warming, the rate of polar ice melt has dramatically accelerated, adding vast amounts of freshwater to the mix altering the dynamics of the current.
Indeed, no one knows what littering the sea floor with tons of trussed up sargassum bundles might lead to.
These are still early days in the sargassum sequestration business, full of hype, hope and wishful business models involving the somewhat dicey world of carbon credits. However, storing carbon in Davy Jones’ Locker actually has a compelling ecological precedent.
Whale Fall
When a whale dies and sinks to the bottom of the ocean, tons of carbon are sequestered for millennia. During its life, which can last as long as century, a whale processes vast amounts of carbon as it dines on krill and plankton, the tiny organisms at the base of the marine food chain that collectively absorb around 40 percent of annual carbon dioxide emissions. Nutrient-rich whale poop, in turn, nourishes plankton, so the more whales, the more plankton, the more CO2 absorbed, and around it goes.
In death, a “whale fall” becomes a decades-long feast for dozens of species, a whale-size speck of astonishing biodiversity in the crushing darkness of the abyss.
Of course, not all dead whales drift to the bottom. And today, there are simply fewer whales left to fall thanks to the industrial-scale hunting of the 18th and 19th centuries.
Just as Aldo Leopold understood that a mountain without its wolves would not lead to a “hunter’s paradise,” but rather to too many deer and a mountain stripped bare of vegetation, there are consequences for an ocean—and a planet—without its whales.
It seems that we are the “future generations” that no one was thinking about when whale products were scaled up and sold as oil to light lamps and grease the machinery of the industrial revolution, or used to fashion corsets from baleen. We are the ones left with the legacy of a poorer planet.
It is no small irony that the commercialization of cheap fossil fuels “saved” whales by crashing the market for whale-derived products, but by then the damage had been done. By the time the first whale fall was spotted in 1977 via submersible robot, whale populations were a small fraction of what they once had been.
Would more whales mean less sargassum? It is hard to say. More whales—and more whales falling—would certainly have taken a significant amount of carbon out the equation and perhaps kept the climate a little less feverish, the weather a little less extreme, and polar ice caps a little more frozen for at least a little while longer.
In Norway, a Direct Air Capture (DAC) installation designed to suck carbon straight out of the thin air, can pull in 0.5 million tons of CO2 annually. DAC sounds straightforward (since the problem is too much CO2 in the air, it makes sense to take it out of the air), but it’s a complicated process involving solvents, heat, the embedded carbon of plant construction, the cost of converting the gas into a form that can either be buried underground or pumped into a marine aquifer, and, of course, transporting it.
The tech will get better, but by comparison, it has been estimated that single 40-ton dead whale at the bottom of the ocean sequesters two tons of carbon for free, with “biodiversity services” thrown in as a bonus. This doesn’t include the vast amounts of carbon a whale circulates within a biotic system during its lifetime, keeping it from escaping into the atmosphere.
If we had the whales that once were, we might also have the climate that once was. That is logic behind efforts to restore whale populations by assigning a monetary value for the ecosystem services they provide. It is hoped that by packaging whales as a financial asset, the funds raised could be used for conservation.
Back at the Beach
Cottage industries have sprung up to deal with the gooey, stinky mess of rotting seaweed. There are entrepreneurs making everything from sargassum bricks and biogas to fertilizers and ingredients for cosmetics.
Cleaning beaches can provide steady employment for months on end for anyone who can stand the smell. There are special machines to scrub the sand. Trucks are needed to haul it away. And there is demand for giant booms to block the muck from reaching the shore at all.
Keeping the “beach” in Miami Beach now comes with a multi-million dollar annual price tag. “It is a lot of money,” notes Miami-Dade County Mayor Daniela Levine Cava. “But look, our environment is our economy here. So it’s money well spent.”
Perhaps the money would have been better spent years ago on reducing greenhouse gas emissions, improving energy efficiency, protecting and expanding tropical rainforests, investing in regenerative agriculture, building more and better sewage treatment plants and, yes, saving whales.
Resilience is about bouncing forward. It is still worth investing in all of the above. It is worth trying to figure out how to turn an explosion of seaweed into an opportunity.
But it is also worth taking a moment to understand what the Great Atlantic Sargassum Belt really is: a degraded ecosystem in the process of rebuilding and rebalancing. The loss of biodiversity over the last couple of centuries is incalculable. Literally. We don’t fully know all the species whose populations have crashed or that have gone extinct. Nor do we understand the impacts of their disappearance on systems dynamics. Lose the whales and there is a cost to everything that relied on them.
We have only known about whale falls since the late 1970s, which was about the same time Coca-Cola began using plastic bottles, sending the first bits of micro-plastics into the gyre of the Sargasso Sea, and into the gyres of every other ocean, too.
The chemistry of the water has changed. The temperature of the water has changed. Global currents have changed. The weather has changed.
The question is not whether nature can work with what’s left, but rather whether there will be a place for us in a world transformed.