Rivers ensure one-third of carbon from fires is stored in the ocean

June 3 (UPI) -- Rivers help carry as much as a third of the black carbon generated by wildfires to the ocean, according to new research.

For the study, scientists analyzed the dissolved carbon flowing through 78 rivers located all over the world. Their analysis has offered scientists new insights into one of Earth's many carbon cycles.

When wildfires and managed burns scorch vegetation, the latest findings -- published Wednesday in the journal Nature Communications -- suggest a surprisingly large amount of carbon ends up stored in the ocean.

"Fires leave behind carbon-rich materials, like charcoal and ash, which break down very slowly in soils," Matthew Jones, climate change researcher at the University of East Anglia, said in a news release. "We care about this burned carbon because it is essentially 'locked out' of the atmosphere for the distant future -- it breaks down to greenhouse gases extremely slowly in comparison to most unburned carbon."

The research suggests a lot of the carbon in the ocean is produced by fire.

"We know that this burned carbon takes about 10 times longer to break down in the oceans than on land," Jones said. "Rivers are the conveyor belts that shift carbon from the land to the oceans, so they determine how long it takes for burned carbon to break down. So, we set out to estimate how much burned carbon reaches the oceans via rivers."

Scientists collected more than 409 carbon samples from dozens of rivers, including freshwater sources on every continent but Antarctica. The measurements showed the planet's rivers carry more than 18 million metric tons of dissolved carbon into the ocean annually. Previous studies suggests as much as 43 million tons of sedimentary carbon is also carried by rivers to the ocean each year.

The authors of the study estimate at least 12 percent of all carbon flowing in rivers consists of burned vegetation.

"While fires emit two billion tons of carbon each year, they also leave behind around 250 million tons of carbon as burned residues, like charcoal and ash. Around half of the carbon in these residues is in the particularly long-lived form of 'black carbon', and we show that about one-third of all black carbon reaches the oceans," Jones said.

"This is a good thing because that carbon gets locked up and stored for very long periods -- it takes tens of millennia for black carbon to degrade to carbon dioxide in the oceans," Jones added.

Climate change is expected to lead to an increase in the frequency, intensity and size of wildfires, which the new research suggests is likely to result in larger amounts of black carbon getting washed into and stored in the oceans. The phenomena is an example of one of the warming climate's few helpful feedback loops.