I recently spent a sunny morning aboard Falcon Spirit, a University of Plymouth research vessel. As the boat motored along the south Devon coast, I spoke to Joan Edwards, director of marine policy for The Wildlife Trusts, about some exciting new research that maps blue carbon habitats in UK seas.
It’s long been understood that ocean habitats play a key role in storing carbon from the atmosphere, but until now, nobody has known exactly how much ends up in kelp, seagrass meadows, salt marshes and sediment in the seabed. Quantifying this, Edwards says, is the first step to minimising any damage caused by human activities such as commercial trawling to the most carbon-rich ecosystems in the ocean.
Today, Mike Burrows and other scientists at the Scottish Association for Marine Science reveal that 244 million tonnes of organic carbon are stored in just the top 10cm of seabed habitats around the UK. Most (98%) of that is in mud or silt that’s quite easily overlooked when it comes to conservation measures.
I’m Anna Turns, senior environment editor, and you’re reading the Imagine newsletter – a weekly synthesis of academic insight on solutions to climate change, brought to you by The Conversation.
This week, I’ve set sail from Plymouth Sound to explore the significance of blue carbon, while Jack Marley searches for razor shells on Northumberland’s tidal mudflats.
So what does blue carbon actually mean? In simple terms, it’s the carbon that is captured and stored by ocean habitats. The new report from scientists at the Scottish Association of Marine Science gives the UK “an opportunity to show the rest of the world just how important blue carbon is and why we need to protect it” as Michael Burrows says. That’s because, “when unharmed, marine habitats naturally absorb carbon and prevent it being released into the atmosphere,” explains Burrows, the professor of marine ecology who led this Scottish Association of Marine Sciences project.
New data from this blue carbon mapping project shows that UK seabed habitats could capture almost three times as much carbon as UK forests do per year. This has huge implications – knowing where the biggest blue carbon stores are will influence decisions about which areas should be prioritised as marine-protected areas and which may be better suited for future developments such as offshore wind.
As the Falcon Spirit passed Cawsand Bay, where seagrass meadows thrive beneath the waves (partly thanks to advanced mooring systems that allow these marine plants to regenerate), I was amazed to learn that these beautiful habitats are only part of the story.
Carbon superhighways
Just like leaf litter in a forest, the fronds of seagrass or kelp that break off in the shallows get transported further offshore. When they sink, carbon gets incorporated into the sediment. Edwards explained that “plankton snow” is another major source of carbon – when these tiny plants and animals die, they sink to the seabed and the carbon they contain ends up being stored as blue carbon.
In the Southern Ocean, small shrimp-like crustaceans called krill are fished commercially. A recent study found that these Antarctic krill store at least 20 million tonnes of carbon annually as their poo and other waste products sink to the deep ocean.
Angus Atkinson, a professor of marine ecology at Plymouth Marine Laboratory, describes the potential of this “carbon superhighway”: “For the first time, we used a computer model of ocean currents to show these waste products don’t need to reach great depths to achieve storage for at least 100 years, further enhancing the carbon storage potential of krill habitats,” he writes. Remarkably, this makes carbon storage from krill equivalent to that of the world’s mangroves, salt marshes and seagrass beds.
Scratching the surface
As research goes, marine scientists are only just scratching the surface of life in the seabed. Marine ecologists from the Convex Seascape Survey, a multidisciplinary research project exploring blue carbon stored in the world’s seabed, describe this ecosystem as a “bustling metropolis” where burrowing lugworms, sea potatoes and bobbit worms mix sediments.
“Convex Seascape Survey scientist Adam Porter is developing pioneering techniques for photographing and measuring the sediment moved by urchins and other species in the lab,” writes Benjamin Harris, a researcher at the University of Exeter. “Results from these experiments allow us to estimate the amount of carbon being moved downward into the seabed and stored by these animals on a seascape scale, which could be colossal.”
Protecting global hotspots
For South Africa’s first national blue carbon sink assessment, Jacqueline L Raw, marine researcher at the Nelson Mandela University, focused on mangroves, salt marshes and seagrass, which she calls “the definitive blue carbon ecosystems”. While mud and silt weren’t covered by her study, Raw explains how the soils of those other blue carbon ecosystems are waterlogged with salty seawater: “This prevents the stored organic carbon from being converted back to CO₂ through remineralisation,” she says. “If left undisturbed and subject to certain conditions, these carbon stocks can build up over centuries.”
Now that blue carbon is being measured, albeit in discrete patches around the globe, the question moves on to how best to manage the sea to protect those precious stores. With goals to protect 30% of the world’s oceans by 2030, the UK’s new blue carbon map is timely.
Blue carbon only emerged as a mainstream global climate solution relatively recently, with substantial discussions about blue carbon gaining momentum in the run-up to the COP27 climate summit in Egypt in 2023.
As William Austin, professor of marine geology at the University of St Andrews and Rebecca J McLeod, senior research fellow in marine ecology at the University of Otago, ask: “Marine sediments provide the largest store of organic carbon on Earth, so why aren’t we looking to the sea as we plan our way out of the climate crisis?”
It turns out that fjords in temperate areas such as New Zealand have some of the highest potential for carbon storage and are “hotspots of carbon burial”. Scotland’s sea lochs need robust protection for this same reason and the Scottish government is leading the way – blue carbon potential is now part of the selection criteria for sites designated as Highly Protected Marine Areas.
Indonesia may soon take similar steps. With 22% of the world’s mangroves and 5% of seagrass meadows, protection from industrial fishing, mass tourism and mining is set to increase across this archipelago. But critically, protecting seagrass is “quite tricky” because an Indonesian seagrass map has not yet been completed, as Brurce Muhammad Mecca and Astra Rushton-Allan from Australia-based research organisation Climateworks Centre, point out.
Only with baseline data and ongoing mapping can the amount (and potential decline) of blue carbon be properly monitored. So the bottom of the ocean needs to become a top priority, and quickly.
Thanks to everyone who pointed out the glaring error in last week’s newsletter: methane is composed of four hydrogen atoms and one carbon atom, not the other way around as I suggested. One shudders at the thought of an atmosphere capable of harbouring such a monstrous compound. It may interest you to know, kind reader, that your humble author got a D in A-level chemistry – Jack.
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