Biogeosciences Research Spotlight

Simulating a Warmer, Drier Arctic

Field experiments examine the effect of rising temperatures and drying soils on carbon dynamics in the Arctic.

Source: Journal of Geophysical Research: Biogeosciences

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The Arctic tundra is a natural carbon sink. As temperatures continue to rise around the globe, more vegetation will spring up in the frigid region, potentially pulling even more carbon dioxide from the atmosphere due to increased plant productivity.

However, the warming carries other consequences, too. Even though carbon uptake during the growing season increased in recent years, observations show annual net losses of carbon to the atmosphere—as Arctic soils thaw, a vast reservoir of carbon locked up in the permafrost can be released to the atmosphere as greenhouse gases. Continued releases could shift the region from a carbon sink to a source by the end of this century.

Automated flux chamber collects continuous measurements of carbon dioxide exchange at a drying and permafrost thaw experiment in Alaskan sub-arctic tundra. Credit: Sue Natali
Automated flux chamber collects continuous measurements of carbon dioxide exchange at a drying and permafrost thaw experiment in Alaskan subarctic tundra. Credit: Sue Natali

Previous research has shown that soil moisture plays a critical part in both permafrost thaw and carbon exchange with the atmosphere—as the permafrost breaks down, surface water may drain away to deeper soil layers, leaving the topsoil high and dry. However, this kind of soil drying is often overlooked in research on the impacts of thawing permafrost.

Recognizing this oversight, Natali et al. took a first look at how thawing permafrost and soil moisture dynamics combined will affect carbon in the Arctic tundra.  The team documented carbon dioxide exchange during 3 years of growing seasons in an upland tundra ecosystem in the northern foothills of the Alaska Range.

Critically, the research team manipulated some plots to experimentally induce warming and drying. They simulated winter warming by insulating vegetation with increased snowpack and summer warming by covering plants with open-topped greenhouses. They also manipulated water table levels with an automated pumping system. The team then measured the effects of their changes on fluxes of both carbon dioxide and methane.

The warming treatment increased ground thaw by approximately 15% compared to controls and caused an increase in carbon dioxide released from plant and microbial respiration. The authors found that, together, warming and drying increased ecosystem respiration by 20% over the 3-year experiment, the same amount that warming and drying increased respiration individually. The results indicate that temperature and moisture levels may disparately affect carbon release from plants and microbes within the plots when they work in concert.

In addition, the amount of decomposition in the top 10 centimeters of soil was nearly 2 times greater in the warming condition and in the dry condition compared with controls. The study also detected methane emissions—which can have a much larger impact on global warming than carbon dioxide—across all plots, even controls, but emissions were highest for the warmed plots. (Journal of Geophysical Research: Biogeosciences, doi:10.1002/2014JG002872, 2015)

—Kate Wheeling, Freelance Writer

Citation: Wheeling, K. (2015), Simulating a warmer, drier Arctic, Eos, 96, doi:10.1029/2015EO033087. Published on 27 July 2015.

© 2015. The authors. CC BY-NC 3.0
  • Casa Quicc

    “However, this kind of soil drying is often overlooked in research on the impacts of thawing permafrost. Recognizing this oversight, Natali et al. took a first look at how thawing permafrost and soil moisture dynamics combined will affect carbon in the Arctic tundra.” This is a gross exaggeration. There have been many previous field studies on this topic. Hardly the “first look” at thawing in the Arctic. The writer owes an apology to many previous investigators in Alaska.

    • Kate Wheeling

      You’re absolutely right that thawing in the Arctic has been widely studied. This new paper builds off of what is already known about permafrost thaw. What Dr. Natali and her colleagues add to this body of research is how thawing permafrost and changes in soil moisture in warming ecosystems interact to influence the carbon cycle in the Arctic.

    • Sue Natali

      Dear Dr. Potter,
      Thank you for your comment. I agree that there is a strong body of research in this area. To clarify, our study experimentally manipulated permafrost thaw and soil moisture in combination to examine impacts on carbon cycling in upland tundra. In the full manuscript I have cited several papers that examine these processes individually and through observational studies, combined. I am happy to send the full manuscript, and can also provide some of those references and others in this discussion.
      Sue