Hopeful rays paint the morning sky as our research vessel playfully bobs on the waves off Jersey’s coastline. I stand beside Dr Ben Harris, postdoc and the Convex Seascape Survey (CSS) lead field scientist, as he meticulously checks the equipment. This dedicated team of researchers has a shared mission: to explore the ocean’s vast carbon reserves and unlock the secrets hidden in the seafloor. “There’s a whole world beneath the waves that we rarely consider,” Harris says. “The seafloor is not merely sand and rocks; it is teeming with organisms and processes that play a critical role in regulating the planet’s carbon.”

The Intergovernmental Panel on Climate Change warns that, alongside rapid decarbonisation, we must remove an additional five billion tonnes of CO₂ annually to stay within the 2°C target set by the Paris Agreement. While the ocean absorbs 50 times more carbon than the atmosphere, seabed carbon remains largely unprotected and unaccounted for in global inventories. The Convex Seascape Survey is a partnership between the University of Exeter and the Blue Marine Foundation, funded by Convex Group Ltd. Professor Callum Roberts, the overall lead scientist and principal investigator, along with fellow academics, developed the aim of bridging this knowledge gap. Together, they seek to provide credible science and open-source data on the ocean’s carbon-sequestration capabilities.

This ambitious five-year study involves some of the world’s leading marine scientists and seeks to answer vital questions: How much carbon does the ocean floor store, and how can we protect this largely unseen carbon sink? By investigating carbon-storing habitats on the seabed, CSS researchers hope to provide valuable scientific data that can shape future marine protection policies and elevate the importance of blue carbon on the climate agenda by 2027.

“If we can prove that these ecosystems store significant carbon, it could change our approach to ocean conservation and lead to stronger protections for these habitats,” Harris says as he prepares the sediment sampling equipment.

While coastal ecosystems such as mangroves and seagrass meadows are recognised as carbon sinks, the deep seafloor remains an unknown frontier. It comprises a complex web of organic life, sediment, and carbon-rich deposits formed over centuries. Yet human activities such as fishing, dredging, and pollution are disturbing these seafloor carbon stores, potentially releasing vast amounts of carbon back into the water and atmosphere. For Harris and his team, this research is more than an academic exercise; it’s about understanding the ocean’s silent contribution to stabilising the global climate and ensuring it can continue to do so. “Our work is urgent,” Harris says. “If we can prove that these ecosystems store significant carbon, it could change how we think about ocean conservation and lead to protections for habitats often overlooked in policy discussions.”

The CSS team’s research has taken them from the depths within the Cable Protection Zone of New Zealand to the Marine Protected Areas (MPA) of the rocky coasts of Jersey where we are today. Their approach is multifaceted, combining the expertise of biologists, oceanographers, and data analysts. Tara Williams, a marine biologist and PhD researcher on the CSS team, explains the importance of studying these habitats holistically. “This isn’t just about sediment samples or isolated carbon data,” Williams says. “It’s about understanding how carbon storage interacts with biodiversity, water chemistry, and even human communities that rely on these areas.”

Our boat slows to a gentle hum as the skipper locates our first dive site, known as ‘E Inside’. “You’d best jump in now, team,” he calls from the helm. “The tide is slack for the next 30 minutes; it’s go time!” The team swiftly gears up, executing a well-rehearsed dance as they slip into warm undergarments and heavy dry suits, preparing for the chilly waters ahead. The urgency stems from the relentless currents generated by 12-metre tides that race around Jersey’s coastline.

Over coffee, Harris recalls their first dive here, racing along the seabed in a fierce 3-knot current before having to abort the mission. “The currents can be brutal here, making fieldwork challenging. But don’t worry, that won’t happen today,” he assures me with a cheeky smile. With coring tubes and sampling equipment in hand, we dive beneath the waves, swiftly descending to a depth of 25 metres while clinging to the line to avoid being swept out into the English Channel. As my eyes adjust to the seemingly lifeless seafloor, I’m astonished to find it peppered with catsharks, shells, and spider crabs. The team quickly gets to work on the coring; Ben begins hammering the first metre-long plastic tube into the muddy sea floor below. A cloud of sediment rises, resembling smoke, and envelops the team, the thick mud lingering heavily in the water column. Eventually, only their focused expressions behind scuba masks remain visible as they embark on this crucial step of the project.

As we resurface from the first dive, Mara Fischer, fellow CSS PhD researcher, meticulously logs the sediment samples at the back of the boat. “The first metre of sediment can tell us a lot,” she explains. “We analyse the organic content, carbon levels, and even the microbial communities, all of which help us understand the health of the ecosystem.”

The team employs cutting-edge techniques to gather and analyse samples from the seafloor, navigating the challenges of planning, weather conditions, and the operation of specialised equipment. As Mara explains: “Our specific area of investigation within the CSS focuses on the role that life and biodiversity play in the movement of organic carbon in and out of the seabed and how this is affected by protecting these habitats from human disturbance.”

To address these questions, the researchers utilise several key methods. Firstly, one-metre sediment cores are collected to determine the amount of organic carbon stored within the seabed. Changes in organic carbon through these cores reflect carbon accumulation over time, with each core potentially representing hundreds to thousands of years of sedimentation. Sediment grabs are also employed to extract samples from the top 15 centimetres of sediment. These samples are then sieved in the lab to study infaunal communities, organisms that play a crucial role in carbon flux by mixing sediment and facilitating long-term carbon storage.

The team also investigates the animal communities residing on the seabed, including sponges and corals, by employing a remotely operated vehicle (ROV) to film these habitats. This method enables the assessment of abundance and diversity over large areas of the seafloor. As Harris explains: “The ROV is an effective and efficient way of filming large areas of the seafloor. From this footage, we estimate the abundance and diversity of animals living on, and growing out of, the seabed.” Baited remote underwater video systems (BRUVS) are also deployed to capture footage of fish communities, which interact closely with the seabed in their hunting and nesting behaviours. This innovative approach provides valuable insights into the ecosystems that contribute to the ocean’s carbon dynamics.

Conducting this research at sea is filled with challenges, from unpredictable weather to the difficulty of finding ideal sampling conditions. Securing a truly undisturbed study area remains tough, as soft sediment habitats are often overlooked in the establishment of MPAs. “Despite having all the world’s continental shelves to choose from, finding an undisturbed area has been surprisingly tough,” Harris explains.

Even when the perfect site is found, sampling can be delayed by wildlife encounters, equipment issues, human activities or rough seas. As the sun dips below the horizon and the researchers’ time in Jersey draws to a close, a shared sense of accomplishment fills the air. Embedded within these sediment samples are answers to essential questions about the mysteries of blue carbon.

As I step into the research labs at Exeter University’s Penryn Campus, I’m greeted by Anna Smith, a PhD student and the project’s ‘core splitter’. Her research, in collaboration with the Jersey International Centre of Advanced Studies, examines how macroalgae like kelp contribute to sediment carbon storage.

Her meticulous job involves slicing each one-metre frozen sediment core in half and extracting small samples every few centimetres. This role is a vital link in the conveyor belt of blue carbon analysis, as she carefully prepares samples for the team to examine. She opens a freezer filled with hundreds of tiny samples from diverse habitats and locations.

“It’s fascinating to see the layers of sediment and what they reveal about the past,” she says, holding a sample to the light, where the colours, textures, and stories come to life in a single tube.

I’m then led deeper into the heart of the research labs, where I meet Dr Torsa Sengupta, who is responsible for sample analysis. She opens a drawer filled with freeze-dried sediment core samples, each containing valuable answers about blue carbon. Selecting a sample labelled ‘Location 3, Site 2’, she removes the dried sediment and grinds it into a fine powder using a pestle and mortar. The powdered sample is placed into a glass beaker and transferred to a fume hood, where she adds concentrated hydrochloric acid to dissolve the inorganic carbon, primarily from calcium carbonate shells. This process leaves behind only the organic carbon, which she can then measure accurately. Next, she feeds the mixture into the Carbon Determination Element Analyser, a powerful machine designed to yield critical data for the CSS project. After a few minutes, the machine outputs a series of numbers and colourful graphs representing carbon and nitrogen levels.

“That’s it?” I ask, feeling somewhat anticlimactic. “Yep, that’s it,” Sengupta giggles as she jots down the results. Having witnessed the entire process, from diving into cold, unpredictable seas to meticulous analysis, I’m reminded of the immense effort behind these crucial numbers. This data is vital for understanding how to protect not just our oceans but all life on this planet.

“The seabed holds centuries’ worth of organic carbon,” Harris notes. “If we disturb it, that carbon could be re-released into the ocean and atmosphere, counteracting our efforts to reduce emissions. Our research isn’t just about measuring carbon; it’s about understanding how to protect it.”

An inspiring aspect of the CSS project is its collaboration with local communities at on-site locations. From divers to sailors, these partners provide invaluable knowledge about tides, currents, and bathymetry, enhancing the project’s conservation aims. Their insights offer a unique perspective on how the seabed has evolved over generations. “Locals understand these waters better than anyone,” Harris notes.

“Their knowledge has guided us to sample sites and highlighted changes they’ve observed over the years. This is as much their project as it is ours.” With a shared commitment to protecting their waters, this research advocates for policies that support both local livelihoods and marine ecosystem health.

The CSS’ fieldwork has already transformed our understanding of seafloor ecosystems, revealing that burrowing creatures like worms, clams, and brittle stars contribute significantly to carbon storage. This new knowledge is offering groundbreaking insights into the role of these often-overlooked species in capturing and stabilising carbon on the seabed. As CSS pushes forward, the stakes are clear: protecting these ecosystems can become a vital strategy in reducing atmospheric carbon. With continued research, CSS hopes to drive policies that not only value marine biodiversity but also leverage it to address our warming climate.

“We’ve just scratched the surface of what the seafloor can tell us,” Harris explains. “In the next two and a half years, we’ll have a clearer picture of how carbon, biodiversity, and human activity interact under the waves. And with that knowledge, we can make informed decisions that support a sustainable future.”

Hidden beneath the waves, the seafloor quietly supports life on Earth. Through the work of the CSS team, these unsung ecosystems are beginning to find a voice. By protecting the seafloor, we’re safeguarding a vital part of the carbon cycle, adding a powerful tool in the fight against climate change