Ninth International Conference on Permafrost ... - IARC Research

Ni n t h In t e r n at i o n a l Co n f e r e n c e o n Pe r m a f r o s tsmaller magnitude and a more non-linear fashion. Most ofthe time, increased precipitations result in increased latentheat fluxes and reduced sensible heat fluxes, and vice versa.These results imply that the heat fluxes at the Barrow site aremore controlled by temperatures than precipitations; it is anenergy-limited moist site.Carbon fluxes and poolsFigure 3 shows clear seasonal cycles and large interannualvariability of Net Ecosystem Exchange (NEE) and woodpool modeled by SiBCASA. During summer months, whentemperatures increase, the photosynthesis uptake exceedsthe respiratory carbon release, resulting in increased net CO 2uptake. This might be a result of very long daylight hoursin Arctic summer. The model shows minimal sensitivityof NEE in winter months, largely because the negligibleR during very cold winter and the complete shutdown ofphotosynthetic uptake. In general, increase temperatures andprecipitations lead to increased wood pools, and vice versa.Presently, more detailed statistical analyses are beingperformed to the results from the SiBCASA sensitivityexperiments.AcknowledgmentsThis study is supported by the U.S. National Aeronauticsand Space Administration (NASA) grant NNX06AE65G tothe University of Colorado at Boulder.Figure 2. SiBCASA-simulated latent and sensible heat fluxes from1982 through 2004 at the Barrow site. Also shown are changes inheat fluxes to perturbations of temperatures and precipitations. Inthese plots, monthly mean values are aggregated from 15-minutetime-step model outputs.Figure 3. SiBCASA-simulated net ecosystem exchange and woodpools from 1982 through 2004 at Barrow site. Also shown arechanges in NEE and wood pool to perturbations of temperatures andprecipitations. In these plots, monthly mean values are aggregatedfrom 15-minute time-step model outputs.ReferencesLawrence, D.M. & Slater, A.G. 2005. A projection ofsevere near-surface permafrost degradation duringthe 21st century. Geophys. Res. Lett. 32(24):doi:10.1029/2005GL025080.Potter, C.S., Randerson, J.T., Field, C.B., Matson, P.A.,Vitousek, P.M., Mooney, H.A., & Klooster, S.A.1993. Terrestrial ecosystem production: A processorientedmodel based on global satellite and surfacedata. Global Biogeochem. Cycles 7: 811-842.Randerson, J.T., Thompson, M.V., Conway, T.J., Field,C.B. & Fung, I.Y. 1996. Substrate limitations forheterotrophs: Implications for models that estimatethe seasonal cycle of atmospheric CO 2. GlobalBiogeochem. Cycles 10(4): 585-602.Schaefer, K, Collatz, G.J., Tans, P, Denning, A.S., Baker, I.,Berry, J., Prihodko, L., Suits, N. & Philpott, A. 2008a.The combined Simple Biosphere/Carnegie-Ames-Stanford Approach (SiBCASA) terrestrial carboncycle model. J. Geophys. Res. (in press).Schaefer, K., Zhang, T.J., Lu, L. & Baker, I. 2008b. Applyingsnow classification system and organic soil propertiesto the SiBCASA model. JGR-Atmosphere (to besubmitted).Seller, P.J., Randall, D.A., Collatz, G.J., Berry, J.A.,Field, C.B., Dazlich, D.A., Zhang, C., Collelo,G.D. & Bounoua, L. 1996a. A revised land surfaceparameterization of GCMs, Part I: Model Formulation.J. Clim. 9(4): 676-705.Sellers, P.J., Los, S.O., Tucker, C.J., Justice, C.O., Dazlich,D.A., Collatz, G.J. & Randall, D.A. 1996b: A revisedland surface parameterization of GCMs, Part II: Thegeneration of global fields of terrestrial biosphysicalparameters from satellite data. J. Clim. 9(4): 706-737.Sturm, M., Holgren, J. & Liston, G.E. 1995. A seasonalsnow cover classification system for local to globalapplications, J. Clim. 8(5): 1261-1283.194