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April 2006 Abstracts

Geomorphic control of landscape carbon accumulation

Abstract: Figure. We use the CREEP process-response model to simulate soil organic carbon accumulation in an undisturbed prairie site in Iowa. Our primary objectives are to identify spatial patterns of carbon accumulation, and explore the effect of erosion on basin scale C accumulation. Our results point to two general findings. First, redistribution of soil carbon by erosion results in a net increase in basin-wide carbon storage relative to a non-eroding environment. Landscape-average mean residence times are increased in an eroding landscape due to the burial/preservation of otherwise labile C. Second, field observations taken along a slope transect may overlook significant intra-slope variations in carbon accumulation. Spatial patterns of modeled deep C accumulation are complex. While surface carbon with its relatively short equilibration time is predictable from surface properties, deep carbon is strongly influenced by the landscape’s geomorphic and climatic history, resulting in wide spatial variability. Convergence and divergence associated with upland swales and interfluves result in bimodal carbon distributions in upper and mid-slopes; variability in carbon storage within modeled mid-slopes was as high as simulated differences between erosional shoulders and depositional valley bottoms. The bi-modality of mid-slope C variability in the model suggests that a three-dimensional sampling strategy is preferable over the traditional 2-dimensional analog or ‘catena’ approach.

Authored by Nan A Rosenbloom¹, Jennifer W Harden², Jason C Neff³, David S. Schimel¹

¹National Center for Atmospheric Research, 1850 Table Mesa Drive, Boulder CO 80305
² US Geological Survey, 345 Middlefield Road, Menlo Park, Ca 94025
³ Benson Earth Sciences Building, Campus Box 399, 2200 Colorado Ave, University of Colorado at Boulder, Boulder CO 80309

Journal of Geophysical Research, Vol. 111, G01004, doi:10/1029/2005JG000077, 2006

keywords: landscape carbon accumulation; catena; loess; dust; 10Be isotopes; carbon sequestration; carbon burial; landscape evolution

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Estimates of the global water budget and its annual cycle using observational and model data

Figure. A brief review is given of research in the Climate Analysis Section at NCAR on the water cycle. A new estimate is provided of the global hydrological cycle for long-term annual means that includes estimates of the main reservoirs of water as well as the flows of water among them. For precipitation P over land a comparison among three datasets enables uncertainties to be estimated. In addition, results are presented for the mean annual cycle of the atmospheric hydrological cycle based on 1979 to 2000 data. These include monthly estimates of P, evapotranspiration E, atmospheric moisture convergence over land, and changes in atmospheric storage, for the major continental land masses, zonal means over land, hemispheric land means and global land means. The evapotranspiration is computed from the Community Land Model run with realistic atmospheric forcings, including precipitation that is constrained by observations for monthly means but with high frequency information taken from atmospheric reanalyses. Results for P-E are contrasted with those from atmospheric moisture budgets based on ERA-40 reanalyses. The latter show physically unrealistic results, because evaporation often exceeds precipitation over land especially in the tropics and subtropics.

Authored by Kevin E. Trenberth, Lesley Smith, Taotao Qian, Aiguo Dai and John Fasullo
National Center for Atmospheric Research, 1850 Table Mesa Drive, Boulder CO 80305
Phone: (303) 497 1318, Fax: (303) 497 1333, email: trenbert@ucar.edu

J. Hydrometeor. (GEWEX issue), 6 April 2006, Revised 7 July 2006, In press, November 2006