Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Tropical rivers breathe carbon

16.08.2016

New study reveals previously underestimated carbon source

About half of the carbon dioxide that is produced by humankind, and which plays an important role in global warming, is taken up by seas and oceans. In addition to the oceans, however, large tropical river systems can also store substantial amounts of carbon, which are released when the climate changes.


A branch of the Congo River in the Congo Basin. The area is not, as once thought, completely covered by rain forest, but consists partially of swamp forests.

Credit: Jordon Hemingway, WHOI

This has been verified in a new scientific publication by Dr. Enno Schefuß of MARUM, the Center for Marine Environmental Sciences at the University of Bremen, who studied an older sediment core using advanced methods. Results of the work by Schefuß and his team have been published in the journal Nature Geoscience.

In the warm and humid environments of the tropics, such as the rain forests, plants take up a large amount of carbon dioxide (CO2). At the same time, microbial activity in the soil is very pronounced under these conditions, which means that organic material is rapidly broken down again and converted back to CO2. Thus, in marine sediments directly offshore from tropical river estuaries no aged plant material should actually be deposited. At least this has been generally assumed so far, according to Dr. Enno Schefuß.

The sediment core investigated, however, comprising deposits off the mouth of the Congo River, contains some very old organic material. Using radiocarbon methods, the scientists have determined the age of molecular fossils, which are specific chemical components of plants, and of microscopically small wood particles.

“The organic components were much older than the depositional age of the sediments, which surprised us at first,” says Schefuß. The core was retrieved during an expedition in 2002 and was studied using highly sophisticated analytical methods. Only the topmost, or youngest, sample from the core showed a relatively young age. The reason for this, according to Schefuß, was atmospheric nuclear testing carried out through the year 1963. These drastically increased the content of atmospheric radioactive carbon (14C), which is used to determine the age.

“These high 14C levels overprint all modern samples,” explains the geoscientist, “and the true age is masked by this effect.” So the rivers actually transport older organic material, whose true age is simply not detected. “This fact changes our view of the carbon cycle.”

But where does the old organic material come from? The wood particles, for example, which were 3,000 years old when they were deposited? “We found a systematic relationship between age and humidity,” says Schefuß. Even under the relatively dry present-day conditions in the Congo, the conversion processes occur rapidly. It is thus impossible that they are directly regulated by humidity. It can only be explained, in fact, by a different source, which releases carbon when aridity increases.

Special analytical techniques by the English colleagues helped in answering this question. In the samples, the remains of specific, methane-consuming bacteria were discovered, which provided the crucial evidence: the Congo Basin is not completely covered by rain forest. In the center, where several tributaries flow into the Congo, there is an area that is continuously covered by water like a swamp. “The area is about the size of Switzerland and was relatively unknown until recently because it is hidden beneath a dense forest. All of the organic material that goes into the swamp remains fairly well preserved under the oxygen-free conditions. The methane oxidizers live here,” explains Schefuß.

The study suggests that the swamp must have been significantly larger in the past. As it dried out the old organic material was released. “What we see in the sediment record, in the stable components that survived decay and transport, are merely the indicators of large CO2 releases,” says Schefuß. The significantly greater portion of released carbon goes directly into the atmosphere as CO2.

“This illustrates the fact that wetland areas in tropical river systems are an important storehouse for carbon. If they dry out, either by natural causes or human activity, CO2 is released,” summarizes Schefuß. The Bremen geochemist is convinced that, in the future, the role of tropical wetland areas will have to be more persistently considered in CO2 models. The new interpretation of these data could also serve as a model for comparable areas, such as the Amazon.

Furthermore, the study highlights the importance of sediment cores from the sea floor as climate archives. “There are no climate archives on land that can record these processes. In the areas that dry out the material is transported away. In the remaining swamp areas the material continues to be conserved,” stresses Schefuß. These processes can only be observed offshore near river mouths, where the released stable organic material is finally deposited. “Climate fluctuations in the past thus serve as natural experiments to help us better assess the impacts of the current climate change.”

Publication:
Enno Schefuß, Timothy I. Eglinton, Charlotte L. Spencer-Jones, Jürgen Rullkötter,
Ricardo De Pol-Holz, Helen M. Talbot, Pieter M. Grootes, Ralph R. Schneider: Hydrologic control of carbon cycling and aged carbon discharge in the Congo River basin.
Published in: Nature Geoscience, DOI: 10.1038/ngeo2778

Contact:
Dr. Enno Schefuß
Telephone: 0421 218 65526
E-Mail: eschefuss@marum.de

Further information / photo material:
Ulrike Prange
MARUM Public Relation
Telefon: 0421 218 65540
E-Mail: medien@marum.de

Ulrike Prange | idw - Informationsdienst Wissenschaft
Further information:
http://www.marum.de

Further reports about: CO2 Congo MARUM Nature Geoscience carbon dioxide organic material wetland areas

More articles from Life Sciences:

nachricht 127 at one blow...
18.01.2017 | Stiftung Zoologisches Forschungsmuseum Alexander Koenig, Leibniz-Institut für Biodiversität der Tiere

nachricht How gut bacteria can make us ill
18.01.2017 | Helmholtz-Zentrum für Infektionsforschung

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: How gut bacteria can make us ill

HZI researchers decipher infection mechanisms of Yersinia and immune responses of the host

Yersiniae cause severe intestinal infections. Studies using Yersinia pseudotuberculosis as a model organism aim to elucidate the infection mechanisms of these...

Im Focus: Interfacial Superconductivity: Magnetic and superconducting order revealed simultaneously

Researchers from the University of Hamburg in Germany, in collaboration with colleagues from the University of Aarhus in Denmark, have synthesized a new superconducting material by growing a few layers of an antiferromagnetic transition-metal chalcogenide on a bismuth-based topological insulator, both being non-superconducting materials.

While superconductivity and magnetism are generally believed to be mutually exclusive, surprisingly, in this new material, superconducting correlations...

Im Focus: Studying fundamental particles in materials

Laser-driving of semimetals allows creating novel quasiparticle states within condensed matter systems and switching between different states on ultrafast time scales

Studying properties of fundamental particles in condensed matter systems is a promising approach to quantum field theory. Quasiparticles offer the opportunity...

Im Focus: Designing Architecture with Solar Building Envelopes

Among the general public, solar thermal energy is currently associated with dark blue, rectangular collectors on building roofs. Technologies are needed for aesthetically high quality architecture which offer the architect more room for manoeuvre when it comes to low- and plus-energy buildings. With the “ArKol” project, researchers at Fraunhofer ISE together with partners are currently developing two façade collectors for solar thermal energy generation, which permit a high degree of design flexibility: a strip collector for opaque façade sections and a solar thermal blind for transparent sections. The current state of the two developments will be presented at the BAU 2017 trade fair.

As part of the “ArKol – development of architecturally highly integrated façade collectors with heat pipes” project, Fraunhofer ISE together with its partners...

Im Focus: How to inflate a hardened concrete shell with a weight of 80 t

At TU Wien, an alternative for resource intensive formwork for the construction of concrete domes was developed. It is now used in a test dome for the Austrian Federal Railways Infrastructure (ÖBB Infrastruktur).

Concrete shells are efficient structures, but not very resource efficient. The formwork for the construction of concrete domes alone requires a high amount of...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

12V, 48V, high-voltage – trends in E/E automotive architecture

10.01.2017 | Event News

2nd Conference on Non-Textual Information on 10 and 11 May 2017 in Hannover

09.01.2017 | Event News

Nothing will happen without batteries making it happen!

05.01.2017 | Event News

 
Latest News

Explaining how 2-D materials break at the atomic level

18.01.2017 | Materials Sciences

Data analysis optimizes cyber-physical systems in telecommunications and building automation

18.01.2017 | Information Technology

Reducing household waste with less energy

18.01.2017 | Ecology, The Environment and Conservation

VideoLinks
B2B-VideoLinks
More VideoLinks >>>