When you think about the bottom of the ocean what do you think of – shipwrecks, sharks, or seabed sediments secretly tackling the climate crisis? Did that last point make your list? Well, it’s not surprising if it didn’t as scientists are just starting to understand it themselves. It is part of a relatively new field of scientific study, blue carbon, which is helping to make that last point not so secret anymore.
Blue carbon is a term used to describe the carbon stored in marine and coastal ecosystems. Just like plants on land can remove carbon dioxide from our atmosphere via photosynthesis, so do many marine plants and algae. These blue carbon habitats also happen to be some of the most awe-inspiring on the planet, with meadows of underwater seagrass, kelp forests home to utterly adorable animals, mangroves, and marshes. These are just some examples of the habitats that qualify for the title as they are good at capturing carbon.
Actually, just using the word ‘good’ is entirely underplaying it, they are extraordinary at it. Compared to forests on land, saltmarshes can sequester (the process of capturing and storing) carbon at rates 43-55 times more per unit area. Seagrass covers less than 0.1% of the seafloor but is responsible for 10-18% of the total carbon stored by our oceans and can capture carbon 35 times faster than a rainforest. There would be no turf war when it comes to land vs sea grass here, there’s a clear winner. And as carbon dioxide is a greenhouse gas, by removing it from the atmosphere these habitats are helping to reduce the effects of climate change.
There’s also an extra bonus to the initial reduction in carbon dioxide from our atmosphere as the carbon can become ‘locked’ in these habitats, such as in seabed sediments, and radiocarbon dating has confirmed it can be locked away for millennia. How much carbon can be buried away in sediments is complex to measure with many factors, such as hydrodynamics, primary producers, sedimentation, and temperature, influencing how much is actually locked away. However, compared to terrestrial ecosystems, blue carbon ecosystems can bury carbon at a rate that is a whole order of magnitude greater. And it is estimated that seagrass, saltmarshes, mangroves, and seaweeds are responsible for 50% of the carbon locked away in marine sediments. These carbon capture cities have been secretly storing carbon all over the world since their existence, but it’s only recently humans have started to pay attention. The term blue carbon was only coined in 2009 and with habitats like seagrass and saltmarshes being found around the coasts of all continents except Antarctica, it’s really something we should all be paying attention to.
Blue carbon is a very novel field of research, but we are seeing blue carbon come through in environmental impact assessments for offshore wind farms, only very recently within the past year, whereas that wasn’t a consideration before.
Caitlin Cunningham
These habitats have got carbon capture sorted, but what about capturing our hearts? Caitlin Cunningham, Marine Sustainability Advisor from NatureScot in Scotland, explains that “blue carbon habitats provide an important climate regulation service but they also play an important role in the wider ecosystems they exist in. They support high levels of biodiversity and other vital ecosystem services such as coastal flood defence, water filtration, and nursery habitats for juvenile fish species, which increases food security”. Seagrass meadows alone are estimated to support fishing grounds that feed over 3 billion people. These habitats are quietly tackling the issues humanity is facing and all whilst being hubs of marine health. How could you not fall in love with these habitats hook, line, and sinker?
But research has revealed a worrying catch. With so much carbon stored in a small area, the destruction or disturbance of these habitats can unlock the carbon stored up over all that time — and that can be a lot. Part of the problem is that blue carbon habitats are typically found in coastal environments, places where threats such as developments, pollution, and rising sea levels have all led to devastating losses of these habitats. Pressures such as coastal development have caused over 50% of salt marshes and seagrasses to be lost in Europe (where we have long-term data to record this). Although the importance of these areas is now more widely recognized, globally between 2000-2019 we still lost an area of saltmarsh twice the size of Singapore. Mangrove ecosystems don’t fare any better, they cover around 15% of the world’s coast and more than half are threatened to collapse.
To put into context just how much carbon that could have released we can look at this on a smaller scale of a single bay, in a single country. Between 1885 and 2019, Jamaica Bay, NY, USA lost 95% of the carbon stored in its wetlands, which released around the annual carbon emission of 4.5 million average US cars. Cunningham adds that there is a double blow with the loss of blue carbon habitats; not only does this initially release carbon dioxide which “exacerbates the current climate crisis but then we are also potentially losing whatever future carbon sequestration potential they hold”.
It is clear that these ecosystems are enormously valuable. So how are they being protected? “They might already be protected,” Cunningham answers, “because we acknowledge seagrass is an important habitat from a biodiversity perspective”. So in some cases, we might already be in luck because we recognize the value of other services they provide, allowing for protections to be put in place.
The field of blue carbon research has also stepped up, knowing there’s little time to spare, with scientific papers released on blue carbon research increasing by 20 percent every year. Research into blue carbon has allowed us to quantify the amount of carbon released and this greater understanding allows for better protections and management to be integrated into marine policy. As a result of these findings, the United Nations Framework Convention on Climate Change has begun to discuss blue carbon at an international policy level. We are then seeing blue carbon being considered right down to individual developments. Cunningham explains that “blue carbon is a very novel field of research, but we are seeing blue carbon come through in environmental impact assessments for offshore wind farms, only very recently within the past year, whereas that wasn’t a consideration before”. It is refreshing to see this chance for carbon impacts to be considered right at the start rather than the afterthought.
It’s about the right development in the right place: the development of marine renewable energy is important to help us tackle the climate crisis but we’re also in a biodiversity crisis, it’s important that we maximise climate change mitigation whilst minimising impacts to nature.
Caitlin Cunningham
A recent win in our understanding of blue carbon came in 2024 as the UK became the first country to map and estimate the carbon of 885,000 square kilometers (341,700 square miles) of its seabed. The Blue Carbon Mapping Project has estimated that 244 million tonnes of carbon are stored in just the top 10 centimeters of UK seabed habitat. That’s over half of the entire UK’s emissions in 2022. Given that 70% of the Earth’s surface is covered by marine sediments, it’s both a reminder of just how important a role the oceans play in the climate crisis and a worrying thought of what happens if that carbon becomes unlocked. So how are we navigating developing our ocean now we know the secret of just how much carbon seabed sediments could be storing?
Cunningham explains that firstly there is still much to learn. “We need to better understand the pressure interactions of the different industries and activities and what they have on blue carbon habitats — many uses of our oceans actually have a limited impact on these blue carbon habitats and can coexist.” But Cunningham continues providing a very insightful peek behind the curtain at how decisions on developing our ocean alongside these issues can be made: “It’s about the right development in the right place. For example, the development of marine renewable energy is important to help us tackle the climate crisis but given we’re also in a biodiversity crisis, it’s important that we maximise climate change mitigation whilst minimising impacts to nature.”
“The number one thing is to reduce and limit pressures such as bottom contact fishing, pollution, and developments,” says Cunningham. It is estimated that the equivalent of 3% of global annual greenhouse gas emissions could be removed from the atmosphere by protecting and providing large-scale restoration of blue carbon habitats. “But success isn’t always guaranteed,” Cunningham notes “so our preference is protecting existing stores”.
The potential of restoration projects to offset carbon emissions has brought blue carbon to the attention of industries looking to invest in carbon credit schemes. The use of blue carbon credits is new, with the first voluntary blue carbon credit being purchased in 2022 by aquaculture company Urchinomics for a kelp restoration scheme. But there are still many questions that need to be addressed through collaborations between research, governments, industry, investors, and community voices. One of these questions is how to ensure the carbon is stored long-term, especially if other activities the industries continue alongside this offset further exacerbate the climate crisis which would increase the likelihood of restored habitats becoming degraded through impacts such as sea level rise or storms, ultimately unlocking the carbon again.
Blue carbon is no longer a secret and with that, there is another reason to mourn the loss of these habitats. But with this knowledge, we have also gained ways to create better guidance and motivation to protect and restore these habitats. With the continuing climate crisis we now just have to make the decision – do we carbon sink or swim?
Source Link: Blue Carbon: The Secret We Might Not Want To Unlock?
