Coastal Blue Carbon

Making Waves: Episode 124

canoes on the shore; image credit: NY Department of Environmental Conservation

Do Not Disturb

Coastal salt marshes, mangroves, and seagrass beds are incredibly efficient at absorbing and storing large quantities of the greenhouse gas carbon dioxide from the atmosphere. These habitats contain large stores of carbon accumulated over hundreds to thousands of years. But if we disturb or destroy these coastal areas, enormous amounts of carbon stored in the soil are released back to the atmosphere, contributing to climate change.


Healthy coastal habitat is not only important for seafood and recreation, it also plays an important role in reducing climate change. In this podcast, we talk with NOAA environmental scientist Ariana Sutton-Grier about Coastal Blue Carbon.


This is Making Waves from NOAA's National Ocean Service. I'm Troy Kitch.

Imagine you're on vacation. You're out early — before anyone else is awake — paddling through a quiet marsh. You startle a duck as you round a corner. As you float over a bed of sea grass, you see a school of small fish dart away. It doesn't seem like there's much going on here. It's a peaceful place. But in fact there's something really important happening here that you can't see, hear, or feel. You're floating over a vast warehouse of sorts — for hundreds or even thousands of years, the sea grass you're floating over has been quitely sucking carbon dioxide from the air and transporting it to the soil beneath the water. You're floating over a vast reservoir of carbon, locked away just below your canoe. That carbon? It's called coastal blue carbon. And as you'll going to hear today, it's something quite special.

To lead us on our journey of discovery with this thing called coastal Blue Carbon, we have a NOAA expert on hand: ecosystem ecologist and biogeochemist Dr. Ariana Sutton-Grier.

That coastal area we just visited in the canoe? It's called a carbon sink. It's not the kind of sink you wash your hands in. Ariana explains:

[Ariana Sutton-Grier] "So a carbon sink is a mechanism by which carbon in the atmosphere is removed from the atmosphere for a long period of time. Decades, if not hundreds, or thousands, or millions of years. So there are efforts to build or create human engineered carbon sinks, but these have really not been so successful so far. It's very challenging to do this. So the most effective carbon sinks on the planet right now are the natural sinks."

And these sinks are important to us because we're putting too much CO2 in the atmosphere and that's causing climate change. Ariana explains climate change this way: imagine you have a greenhouse behind your house. Your greenhouse stays warm all year round because it traps some of the sun's energy and keeps it inside.

[Ariana Sutton-Grier] "Our atmosphere on Earth functions very much like that greenhouse. The gases from our atmosphere trap some of the sun's energy and help to keep our planet livable — not too hot, not too cold. One of the primary greenhouse gases that's in our atmosphere is carbon dioxide, or CO2. So we are all dependant on these greenhouse gases to make Earth a livable environment."

The problem we have, she said, is that we're burning vast quantities of fossil fuels — the coal, oil, and gas that power our society. And when we burn these fuels, we're releasing carbon that was buried millions of years ago back into the atmosphere in the form of carbon dioxide.

[Ariana Sutton-Grier] "This additional CO2 acts to trap more of the sun's energy. So our atmosphere has more energy in it. This has been described as global warming. And it's true that on average temperatures are increasing in many parts of the world. But it isn't just about temperature. Because there's more energy in the atmosphere, this also changes our weather and our climate patterns. This can lead to changes in many critical processes, including how frequent and intense storms may be, and how much rainfall we can expect in different parts of the world."

Ariana said that what all these changes add up to is this: environmental conditions on Earth are changing, and they're changing at a very rapid rate. So why should we care?

[Ariana Sutton-Grier] "There are concerns about species that will not be able to adapt to these changing conditions fast enough and may go extinct. There's also a lot of concern about water shortages and food shortages because rainfall, and climate, and weather patterns are changing. So it's very challenging to predict all of the interactions that are likely to occur as a result of this changing climate, but it is very clear that these changes are already occuring and that these changes are putting more stresses on both natural ecosystems and human communities alike."

And with that mind, now we can turn our attention back to the importance of carbon sinks — because these sinks help get all this excess carbon out of the atmosphere. Ariana said that many people think of forests when they think of carbon sinks, but few people think of coastal ecosystems.

[Ariana Sutton-Grier] "Forests are good natural carbon sinks. Trees take up carbon from the atmosphere, they photosynthesize, they store that carbon, and they turn it into wood. But forests are not the only ecosystems that store a lot of carbon. In fact, coastal ecosystems — and here I'm thinking mainly of mangroves, salt marshes, and sea grasses — they take up and store large amounts of carbon as well. And I think one of the reasons that these coastal ecosystems are just now being recognized as important carbon sinks is because most of the carbon in these ecosystems is stored below ground in the soils. So it's not in the biomass of the trees the way it is in a forest, where we can see that carbon. In these coastal systems, it's almost entirely below ground where we can't see it. These soil under these coastal ecosystems tend to be several meters deep and they often store carbon that is decades if not thousands of years old."

And that's coastal blue carbon. And coastal blue carbon ecosystems are places that Ariana and many others at NOAA — along with many other groups — are trying to conserve and protect.

[Ariana Sutton-Grier] "So when I say 'blue carbon,' it's called blue because I'm talking about the fraction of carbon that is taken up and stored in ocean and coastal ecosystems. So this is in comparison to green and black carbon. Green carbon is the carbon that is taken up by terrestrial ecosystems, so ecosystems on land. Black carbon is the carbon that's released in the production and burning of fossil fuels, such as coal, oil, and gas. That produces black carbon. So NOAA's efforts have really focused on blue carbon, but not just all of blue carbon, really the coastal fraction of blue carbon — and that's the part that's taken up and stored in mangroves, sea grasses, and salt marshes."

So it's not just that these coastal blue carbon ecosystems are lesser known than, say, rainforests when it comes to serving as carbon sinks. It's that they're really, really good carbon sinks. They're great at sucking carbon from the atmosphere — a process that scientists call sequestering carbon.

[Ariana Sutton-Grier] "These coastal systems are sequestering carbon at rates ten times higher than most forested systems. And what that means is that even though they represent a much smaller fraction of the land area of the Earth, because they're really just along the fringe of the coast, and they aren't any near as large as our forested areas. But because their rates of sequestration are ten times higher, they actually represent an equivalent carbon sink annually to our forested systems on the planet. They're also incredibly efficient. You protect a small amount of land area when it's these coastal habitats and you get a very impressive natural carbon sink. When you add to that story the fact that they're already storing usually hundreds or thousands of years worth of carbon in their soils, so that if we do disturb them, we get an enormous amount of carbon that contributes to climate change. That just makes the story that much more impressive that protecting or restoring these systems where possible is a really effective climate mitigation opportunity."

Did you catch that last part? When you disturb these coastal habitats, you aren't only halting sequestration — the ability of the sea grasses, mangroves, or salt marshes to take in carbon. You're also releasing potentially thousands of years of stored carbon into the atmosphere.

[Ariana Sutton-Grier] "This distinction between sequestration and storage is really important. When we disturb these coastal habitats — we destroy them, we develop them — that store of old carbon gets released into the atmosphere. So this means that when we destroy these coastal ecosystems, not only do lose their continued ability to sequester carbon each year, but we also lose that enormous pool of carbon, that stored carbon in the soils that's very old carbon. So that's why when we disturb these ecosystems, there tends to be a very big release of carbon out of the system within that first few months or years after the disturbance because we're disturbing not only the sequestration but also the old stored carbon."

So here's the good news. Ariana said that the only thing we have to do to keep these coastal powerhouses working for us every year and to keep their stored carbon locked away ... is to leave them alone and ensure these areas stay in tact and healthy.

[Ariana Sutton-Grier] "And when you protect that healthy, in tact system you get all these other co-benefits. You get nursery habitat for fisheries that help support both commercial and recreational fishing, you get storm protection in terms of reduced waves and storm surge activity during major storms, you get recreational opportunities, educational opportunities, cultural opportunities — things like bird watching, snorkeling, etc. So these habitats really ... it's just a win-win-win if you can get the climate benefits and then all the other co-benefits for coastal habitats."

You just can't beat a win, win, win. That's why NOAA is very involved in conserving coastal ecosystems in many different ways. Ariana said that one way is by working with partners to manage marine protected areas.

[Ariana Sutton-Grier] "A marine protected area, or MPA, is a place like a marine park that protects natural places for conservation, recreation, and other sustainable uses. MPA's can include national parks, national marine sanctuaries, and similar state-level programs. Most MPAs are open to the public and allow a wide range of recreational and other sustainable uses."

A good example of this, she said, is the Florida Keys National Marine Sanctuary, which includes 1,800 miles of shoreline lined with mangroves and thousands of acres of sea grasses. And yet another type of MPA is called a national estuarine research reserves, or NERRS sites.

[Ariana Sutton-Grier] "The NERRS are systems of coastal protected areas that include many blue carbon habitats such as salt marshes in the Waquoit Bay, Massachusetts, NERR, which is doing ground-breaking research on blue carbon. And mangroves in the Apalachicola, Florida, NERR site, where scientists are working to develop appropriate protocols to estimate mangrove biomass."

But Ariana added that NOAA is also working with local communities to identify new marine protected areas — special places that are destinations for tourism, help sustain fisheries, and generally help make communities healthier and happier — but places that also need long-term protection to protect valuable marine ecosystems and sensitive species.

[Ariana Sutton-Grier] "For example, the office of national marine sanctuaries is working on a new process to allow communities to nominate areas for consideration as new sanctuaries. So NOAA continues to work to create more protected areas in our coastal and marine ecosystems."

And the more coastal ecosystems we can protect and conserve, the more coastal blue carbon areas we'll have. But while the Earth's capacity to store carbon from the atmosphere is really important, Ariana stressed that it's just one part of a bigger picture:

[Ariana Sutton-Grier] "We get so many benefits from coastal ecosystems. Coastal blue carbon is just one more reason to love the oceans and the coasts. I never want people to think that I'm just talking about the carbon. The carbon is the motivation to draw attention to the importance of coastal and marine ecosystems. But isn't just about the carbon. It's about the fact that in protecting the carbon, which is great for the planet, for climate, etc. It's great. But really it is another tool, it's another way to draw attention to the importance of protecting and restoring these absolutely essential habitats that provide all these wonderful benefits to people."

That was Ariana Sutton-Grier, a scientist with NOAA's coastal blue carbon effort.

And this is Making Waves from NOAA's National Ocean Service. Thanks for tuning in to the podcast. Send us feedback at We'll be back in a few weeks with a new episode.

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