Rivers help lock carbon from fires into oceans for thousands of years


Date:
June 3, 2020
Source:
University of East Anglia
Summary:
The extent to which rivers transport burned carbon to oceans -
where it can be stored for tens of millennia - is revealed in new
research. The study calculates how much burned carbon is being
flushed out by rivers and locked up in the oceans. Oceans store a
surprising amount of carbon from burned vegetation, for example as a
result of wildfires and managed burning. The research team describe
it as a natural - if unexpected - quirk of the Earth system.



FULL STORY ==========================================================================
The extent to which rivers transport burned carbon to oceans -- where
it can be stored for tens of millennia -- is revealed in new research
led by the University of East Anglia (UEA).


==========================================================================
The study, published today in Nature Communications, calculates how much
burned carbon is being flushed out by rivers and locked up in the oceans.

Oceans store a surprising amount of carbon from burned vegetation, for
example as a result of wildfires and managed burning. The research team describe it as a natural -- if unexpected -- quirk of the Earth system.

The international interdisciplinary team, including collaborators from
the Universities of Exeter, Swansea, Zurich, Oldenburg and Florida International, studied the amount of dissolved carbon flowing through
78 rivers on every continent except Antarctica.

Lead researcher Dr Matthew Jones, of the Tyndall Centre for Climate
Change Research at UEA, said: "Fires leave behind carbon-rich materials,
like charcoal and ash, which break down very slowly in soils. 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.

"We know that this burned carbon takes about 10 times longer to break
down in the oceans than on land. 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." Based on a large dataset
of 409 observations from 78 rivers around the world, the researchers
analysed how the burned fraction of dissolved carbon in rivers varies
at different latitudes and in different ecosystems. They then upscaled
their findings to estimate that 18 million tonnes of dissolved burned
carbon are transported annually by rivers. When combined with the burned
carbon that is exported with sediments, the estimate rises to 43 million
tonnes of burned carbon per year.



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Dr Jones said: "We found that a surprising amount -- around 12% per cent
-- of all carbon flowing through rivers comes from burned vegetation.

"While fires emit two billion tonnes of carbon each year, they also
leave behind around 250 million tonnes 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." "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. By comparison, only about one per cent of
carbon taken up by land plants ends up in the ocean.

"With wildfires anticipated to increase in the future because of climate change, we can expect more burned carbon to be flushed out by rivers
and locked up in the oceans.

"It's a natural quirk of the Earth system -- a moderating 'negative
feedback' of the warming climate that could trap some extra carbon
in a more fire-prone world." This study was principally funded by
the Natural Environmental Research Council (NE/L002434/1), with other
financial support from the Tyndall Centre for Climate Change Research
and the Swiss National Science Foundation (PZ00P2_185835).


========================================================================== Story Source: Materials provided by University_of_East_Anglia. Note:
Content may be edited for style and length.


========================================================================== Journal Reference:
1. Matthew W. Jones, Alysha I. Coppola, Cristina Santi'n, Thorsten
Dittmar,
Rudolf Jaffe', Stefan H. Doerr, Timothy A. Quine. Fires
prime terrestrial organic carbon for riverine export to
the global oceans. Nature Communications, 2020; 11 (1) DOI:
10.1038/s41467-020-16576-z ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/06/200603100514.htm https://www.sciencedaily.com/releases/2020/06/200603100514.htm

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