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Researching the oceans’ capacity to fix carbon

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As a child, Isaac Santos played in the clear blue seas of Brazil. Now, as a recently arrived Gothenburger, he plans to return to his old homeland to do research in the deep mud of the Amazon. The goal is to measure on site how crabs in mangroves are helping to mitigate the climate crisis.

Isaac Santos is the ultimate global citizen. He first moved from his homeland of Brazil to the USA to become a student, and he stayed until he had obtained his doctorate. His next place of residence was Australia. He stayed there for eleven years where he also fitted in starting a family and becoming an Australian citizen.

When he and his family chose to move to Gothenburg a year ago, it was actually primarily a ship that was the drawcard. The University’s new research vessel, the R/V Skagerak, which is due to enter service next year, is a fairly unique initiative, even internationally.

“I would say that this ship was one of the most significant factors in persuading me to move here. It’s a very clear indicator that we are committed to marine research here,” says Santos, who is professor of marine chemistry in the Department of Marine Sciences.

Another key driver was that the University of Gothenburg is positive to conducting research in other countries. In Australia, he had to study marine chemistry on site.

In november, he’s off to the Amazon. Along with a new research team, he is going to set up a high-tech mini-laboratory in the field. Once they have installed their instruments in the trees, mud and water, they will be able to make combined measurements in a way that has not been possible previously, for example measuring radon, carbon dioxide, methane and carbon isotopes.

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Issac Santos och student Justin Gleeson sitting i a swamp all muddy
Everyday life for field workers in the mangrove swamp. During a previous study in Australia, Isaac Santos, on the right, and student Justin Gleeson are covered in mud during sampling
Photo: Issac Santos

Isaac Santos is looking for an important piece of the puzzle in understanding the capacity of mangrove swamps to capture carbon dioxide. To date, the research has focused on transfer to the soil. He aims to show that these areas also transfer a large proportion to coastal waters, where it is stored as ‘blue carbon’.

it means that the seawater captures twice as much carbon in mangrove swamps than we estimate today.

This is where the small crabs living in the mud play a crucial role.

“The tunnels the crabs dig in the mud mean that the coastal waters can be filtered. When the water travels into and out of the holes, it acts like a carbon pump, because the carbon compounds in the mangrove mud get pumped into the seawater.”

The process is known as outwelling and contributes alkalinity to the ocean. This is also what gives the ocean its buffer capacity against becoming too acidic. The project will also study how the interaction between the mangrove trees and the water affects the acidity.

As yet Santos does not know precisely what quantities of carbon are contributed to the ocean in this process. Only that it is more than we think.

“Our first results showed that it exceeds previous calculations. If that proves to be the case, it means that the seawater captures twice as much carbon in mangrove swamps than we estimate today.

Ultimately he also wants to map the interaction between mangrove swamps and the oceans on a global scale by bringing together his studies from across the world. If his hypotheses prove to be correct, it may become necessary to re-assess how important the oceans are for storing carbon dioxide. Besides boosting the value of terrestrial and marine environments, Santos believes that this would also be significant for economically weak countries where mangroves are often located.

“If we can demonstrate a greater ecological contribution from countries with mangroves, a greater share of environmental requirements might be borne by wealthier countries. More poor countries will have weightier economic arguments on their side,” says Santos.

Blue carbon

Organic carbon stored in seabeds and marine species is referred to as blue carbon. The three types of ecosystems that make the greatest contributions are mangrove swamps, eelgrass meadows, and marine wetlands. Taken together, they account for almost half the planet’s capacity to store carbon.

In the form of carbon sinks, blue carbon reduces the amount of carbon dioxide in the atmosphere. It consequently plays a key role in the Earth’s ability to resist climate change.

The ocean as a carbon sink 

ThenResearchers have been able to identify the mechanisms behind the global carbon cycle for many decades. What is regarded as our most important carbon sink or storage place for carbon dioxide in nature has changed however. It used to be thought that most carbon was stored in the biomass of the Earth’s living organisms, in vegetation. It was theorised that the oceans and the soil could also capture and store carbon, but no one was able to prove that was the case. 

Now: Research teams around the world have identified soils and sediments as the biggest carbon sinks. It is estimated that ten times more carbon is fixed in the soil than in living biomass. It has also been proven that carbon can be stored there for hundreds of years. The term ‘blue carbon’ – carbon that is fixed in the oceans – did not gain a foothold in research until the 2010s. There is however still a lack of agreement on how big this carbon sink is.

In the future: The development of analytical methods will enable researchers to calculate how much carbon from the land is captured by the oceans. This is based on the theory of outwelling, which dates back to the 1960s, but which it has not been possible to test previously. Initial research suggests that large quantities are involved. It is estimated for example that through outwelling of alkalinity, the oceans are capable of fixing twice as much carbon as the land (soils). Researchers will also be able to calculate the global quantity.

Isaac Santos

Title: Professor of marine chemistry
Age: 38
Family: Married to Ana and has two sons, aged 10 and 12. Has a cat and a dog. 
Best memory from fieldwork: Loves collecting samples at night in mangrove swamps and on coral reefs. Night-time always provides a completely different perspective on the system we are studying.
How he likes to spend his spare time: Enjoying nature with his family.

Favourite place: Any beach.