The Role of Snow Cover and Soil Freeze/Thaw Cycles Affecting Boreal-Arctic Soil Carbon Dynamics

Yonghong Yi, University of Montana, yonghong.yi@ntsg.umt.edu (Presenter)
John Kimball, University of Montana, johnk@ntsg.umt.edu
Michael Rawlins, University of Massachusetts, rawlins@geo.umass.edu
Mahta Moghaddam, USC, mahta@usc.edu
Eugenie Euskirchen, University of Alaska Fairbanks, seeuskirchen@alaska.edu

Northern Hemisphere permafrost affected landscapes contain about twice as much carbon as the global atmosphere, largely stored in permafrost and seasonally thawed soil active layers. This vast carbon pool is vulnerable to accelerated losses through mobilization and decomposition under regional warming, with potentially large global carbon and climate impacts. Satellite data records spanning the past 3 decades indicate widespread reductions (~0.8-1.3 days decade-1) in mean annual snow cover extent and frozen season duration across the boreal-Arctic domain, coincident with regional warming. How the soil carbon pool responds to these changes will have a large impact on regional and global climate. Here, we coupled a hydrology model( integrated with a detailed 1-D soil heat transfer model) with a terrestrial carbon model to investigate the sensitivity of soil organic carbon stocks and soil decomposition to changes in snow cover and soil freeze/thaw processes in the Pan-Arctic region from 1979 to 2010. The simulated carbon fluxes are generally consistent with selected boreal and Arctic tower eddy covariance measurements (GPP: RMSE ≤ 1.56 g C/m2/day; NEE: RMSE ≤ 0.89 g C/m2/day). The simulated temperature and moisture fields are also consistent with the in-situ measurements, but subject to large uncertainties in surface meteorology inputs (particularly precipitation/snow), and soil parameters including soil texture and peat fraction. Our results indicate widespread soil active layer deepening across the pan-Arctic, with a mean regional trend of 0.68cm/yr and ranging from a 7.50cm/yr increase to -1.71cm/yr decrease. The simulated active layer changes coincide with regional warming and increasing non-frozen season trends observed from the satellite record. Warming promotes vegetation growth and soil heterotrophic respiration, particularly within surface (≤25 cm) soil layers. The model simulations also show that seasonal snow cover has a large impact on soil temperatures, whereby a deeper snowpack cools surface soil layers and inhibits soil decomposition, but enhances deeper soil temperatures and soil respiration rates, especially in tundra ecosystems. Our results demonstrate the important control of snow cover in affecting northern soil freeze/thaw and decomposition processes, and the necessity of considering both warming, and changing precipitation and snow cover regimes in characterizing permafrost soil carbon dynamics.

Presentation Type:  Poster

Session:  General Contributions   (Tue 4:35 PM)

Associated Project(s): 

• Kimball, John: Carbon Cycle applications of the Soil Moisture Active Passive (SMAP) Mission ...details

Poster Location ID: 261