Kevin
M
Schaefer, National Snow and Ice Data Center, kevin.schaefer@nsidc.org
(Presenting)
Tingjun
Zhang, National Snow and Ice Data Center, tzhang@nsidc.org
Lixin
Lu, Cooperative Institute for Research in Environmental Sciences, University of Colorado, lixin@atmos.colostate.edu
Ian
Baker, Department of Atmospheric Science, Colorado State University, baker@atmos.colostate.edu
We analyzed output from the Simple Biosphere Carnegie-Ames-Stanford Approach (SiBCASA) model to evaluate how snow cover, soil temperature, and soil freeze-thaw processes influence terrestrial net carbon flux. We ran SiBCASA globally with the NCEP reanalysis at 2x2 degrees and locally at eddy covariance flux towers with the NARR reanalysis. Net Ecosystem Exchange (NEE) is R - GPP, where R is respiration and GPP is Gross Primary Productivity or photosynthesis. GPP for plant growth removes CO2 from the atmosphere while R due to the decay of dead plants returns CO2 to the atmosphere.
Variations in winter snow depth are preserved as variations in soil temperature, producing time-delayed effects on R and GPP and modulating NEE for the entire year. Deeper snow in winter insulates the soil, resulting in warmer soil temperatures the following spring and summer, increasing R and GPP, but at different magnitudes throughout the year. In spring and fall, warmer soils increase R, but GPP is low, resulting in increased NEE. The magnitude of the effect of winter snow depth on summer NEE depends on what limits GPP. In permafrost, active layer depth limits GPP, so warmer winter soil temperatures increase active layer depth in summer, increasing GPP and decreasing NEE. In boreal forests, summer GPP is limited by water availability, so winter snow depth influences spring and fall NEE by modulating R, but exerts a weaker influence on summer NEE.
NASA Carbon Cycle & Ecosystems Active Awards Represented by this Poster: