Princeton University findet unerwartete bakterielle Methansenke: Arktische Böden nehmen mehr Methan auf als sie freisetzen

Lange hatte man gefürchtet, der tauende Dauerfrostboden in der Arktis könnte große Mengen an Methan in die Atmosphäre freisetzen, was den Treibhauseffekt anheizt. Umso größer war nun die Überraschung, als eine von der Universität Princeton angeführte Forschergruppe das glatte Gegenteil herausfand. Der allergrößte Teil der Arktis wirkt nämlich offenbar als Methan-Senke, nimmt mehr Methan auf als er abgibt. Erstaunliche 87% aller Arktisböden sind Kohlenstoff-untersättigt. Die Wissenschaftler fanden dort Methan-hungige Bakterien, die nur darauf warten, Methan aufzunehmen und zu absorbieren. Und noch besser: Die Fähigkeit der Bakterien zur Methanaufnahme steigert sich mit zunehmender Temperatur.

Im Folgenden die Pressemitteilung im Blog der Princeton University vom 14. August 2015:

On warmer Earth, most of Arctic may remove, not add, methane

In addition to melting icecaps and imperiled wildlife, a significant concern among scientists is that higher Arctic temperatures brought about by climate change could result in the release of massive amounts of carbon locked in the region’s frozen soil in the form of carbon dioxide and methane. Arctic permafrost is estimated to contain about a trillion tons of carbon, which would potentially accelerate global warming. Carbon emissions in the form of methane have been of particular concern because on a 100-year scale methane is about 25-times more potent than carbon dioxide at trapping heat.

However, new research led by Princeton University researchers and published in The ISME Journal in August suggests that, thanks to methane-hungry bacteria, the majority of Arctic soil might actually be able to absorb methane from the atmosphere rather than release it. Furthermore, that ability seems to become greater as temperatures rise.

The researchers found that Arctic soils containing low carbon content — which make up 87 percent of the soil in permafrost regions globally — not only remove methane from the atmosphere, but also become more efficient as temperatures increase. During a three-year period, a carbon-poor site on Axel Heiberg Island in Canada’s Arctic region consistently took up more methane as the ground temperature rose from 0 to 18 degrees Celsius (32 to 64.4 degrees Fahrenheit). The researchers project that should Arctic temperatures rise by 5 to 15 degrees Celsius over the next 100 years, the methane-absorbing capacity of “carbon-poor” soil could increase by five to 30 times.

The researchers found that this ability stems from an as-yet unknown species of bacteria in carbon-poor Arctic soil that consume methane in the atmosphere. The bacteria are related to a bacterial group known as Upland Soil Cluster Alpha, the dominant methane-consuming bacteria in carbon-poor Arctic soil. The bacteria the researchers studied remove the carbon from methane to produce methanol, a simple alcohol the bacteria process immediately. The carbon is used for growth or respiration, meaning that it either remains in bacterial cells or is released as carbon dioxide.

First author Chui Yim “Maggie” Lau, an associate research scholar in Princeton’s Department of Geosciences, said that although it’s too early to claim that the entire Arctic will be a massive methane “sink” in a warmer world, the study’s results do suggest that the Arctic could help mitigate the warming effect that would be caused by a rising amount of methane in the atmosphere. In immediate terms, climate models that project conditions on a warmer Earth could use this study to more accurately calculate the future methane content of the atmosphere, Lau said.

“At our study sites, we are more confident that these soils will continue to be a sink under future warming. In the future, the Arctic may not have atmospheric methane increase as much as the rest of the world,” Lau said. “We don’t have a direct answer as to whether these Arctic soils will offset global atmospheric methane or not, but they will certainly help the situation.”

The researchers want to study the bacteria’s physiology as well as test the upper temperature threshold and methane concentrations at which they can still efficiently process methane, Lau said. Field observations showed that the bacteria are still effective up to 18 degrees Celsius (64.4 degrees Fahrenheit) and can remove methane down to one-quarter of the methane level in the atmosphere, which is around 0.5 parts-per-million.

“If these bacteria can still work in a future warmer climate and are widespread in other Arctic permafrost areas, maybe they could regulate methane for the whole globe,” Lau said. “These regions may seem isolated from the world, but they may have been doing things to help the world.”

From Princeton, Lau worked with geoscience graduate student and second author Brandon Stackhouse; Nicholas Burton, who received his bachelor’s degree in geosciences in 2013; David Medvigy, an assistant professor of geosciences; and senior author Tullis Onstott, a professor of geosciences. Co-authors on the paper were from the University of Tennessee-Knoxville; the Oak Ridge National Laboratory; McGill University; Laurentian University in Canada; and the University of Texas at Austin.

The research was supported by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research (DE-SC0004902); the National Science Foundation (grant no. ARC-0909482); the Canada Foundation for Innovation (grant no. 206704); the Natural Sciences and Engineering Research Council of Canada Discovery Grant Program (grant no. 298520-05); and the Northern Research Supplements Program (grant no. 305490-05)

Read the abstract.

M.C.Y. Lau, B.T. Stackhouse, A.C. Layton, A. Chauhan, T. A. Vishnivetskaya, K. Chourey, J. Ronholm, N.C.S. Mykytczuk, P.C. Bennett, G. Lamarche-Gagnon, N. Burton, W.H. Pollard, C.R. Omelon, D.M. Medvigy, R.L. Hettich, S.M. Pfiffner, L.G. Whyte, and T.C. Onstott. 2015. An active atmospheric methane sink in high Arctic mineral cryosols. The ISME Journal. Article published in print August 2015. DOI:10.1038/ismej.2015.13.

Erstaunlicherweise nahm die deutschsprachige Presse von der wichtigen Studie keine Notiz.

Bereits Ende 2014 hatte eine Gruppe der Universität Kopenhagen um Christian Juncher Jørgensen in Nature Geoscience über ähnliche Methansenken aus Grönland berichtet:

Net regional methane sink in High Arctic soils of northeast Greenland
Arctic tundra soils serve as potentially important but poorly understood sinks of atmospheric methane (CH4), a powerful greenhouse gas1, 2, 3, 4, 5. Numerical simulations project a net increase in methane consumption in soils in high northern latitudes as a consequence of warming in the past few decades3, 6. Advances have been made in quantifying hotspots of methane emissions in Arctic wetlands7, 8, 9, 10, 11, 12, 13, but the drivers, magnitude, timing and location of methane consumption rates in High Arctic ecosystems are unclear. Here, we present measurements of rates of methane consumption in different vegetation types within the Zackenberg Valley in northeast Greenland over a full growing season. Field measurements show methane uptake in all non-water-saturated landforms studied, with seasonal averages of − 8.3 ± 3.7 μmol CH4 m−2 h−1 in dry tundra and − 3.1 ± 1.6 μmol CH4 m−2 h−1 in moist tundra. The fluxes were sensitive to temperature, with methane uptake increasing with increasing temperatures. We extrapolate our measurements and published measurements from wetlands with the help of remote-sensing land-cover classification using nine Landsat scenes. We conclude that the ice-free area of northeast Greenland acts as a net sink of atmospheric methane, and suggest that this sink will probably be enhanced under future warmer climatic conditions.

Auch hier fiel die mediale Berichterstattung mager aus. Interessanterweise griff jedoch Planet Erde am 21. Juni 2016 im Rahmen einer Konferenzberichterstattung die Ergebnisse der dänischen Arbeitsgruppe auf.

Auch in Alaska sieht die Lage ähnlich aus. Am 1. Juni 2016 veröffentlichte der Geologische Dienst der USA (USGS) eine Studie zum Kohlenstofhaushalt in Alaska. Climate Central berichtete darüber:

Warming Could Boost Carbon Storage in Alaska Forests
Climate change may dramatically increase carbon storage in Alaska’s temperate forests, possibly offsetting the climate impacts of melting permafrost and wildfires, new research from the U.S. Geological Survey shows.

Weiterlesen auf Climate Central