HR: 1340h
AN: B23D-1591    [Abstracts]
TI: Soil Biogeochemistry in the Ent DGVM
AU: * Kharecha, P A
EM: pushker@giss.nasa.gov
AF: NASA GISS/Columbia University Earth Institute, 2880 Broadway, New York, NY 10025, United States
AU: Kiang, N Y
AF: NASA GISS/Columbia University Earth Institute, 2880 Broadway, New York, NY 10025, United States
AU: Aleinov, I
AF: NASA GISS/Columbia University Earth Institute, 2880 Broadway, New York, NY 10025, United States
AU: Moorcroft, P
AF: Harvard University, Dept. of Organismic and Evolutionary Biology, 22 Divinity Ave, Cambridge, MA 02138, United States
AU: Koster, R
AF: NASA GSFC, GMAO, Code 610.1, Greenbelt, MD 20771, United States
AB: As the global climate continues to warm in the 21st century, it will be vital to assess the degree of carbon cycle feedbacks from the terrestrial biosphere, particularly the soil. Global soil carbon stocks, which amount to approximately double the carbon stored in vegetation, could provide either positive or negative climate feedbacks, depending on a given ecosystem's response to warming. To predict changes in net terrestrial CO₂ fluxes and belowground organic carbon storage, we have developed and evaluated a soil biogeochemistry submodel for the Ent dynamic global vegetation model currently being tested within the GISS GCM. It is a modified version of the soil submodel in the CASA biosphere model (Potter et al., Glob. Biogeoch. Cyc. 7, 1993). We have enhanced it to allow for explicit depth structure (2 soil layers, 0-30 cm and 30-100 cm), first-order inter-layer (vertical) soil organic carbon transport, and a variable-Q10 temperature dependence for soil microbial respiration. We have tested the soil model in numerous offline runs. To spin up the simulated carbon pools offline, we conducted multi-century runs using meteorological and ecological data from various FLUXNET field sites that represent 7 of the 8 GISS GCM plant functional types: tundra, grassland, shrubland, savanna, deciduous forest, evergreen needleleaf forest, and tropical rainforest (the eighth, cropland, will be dealt with in a separate study). We then compare the magnitudes of the simulated spun-up soil pools to soil carbon stock data from these field sites as well as the biome-aggregated data from Post et al. (Nature 317, 1985). Net ecosystem CO₂ fluxes and soil respiration are also compared to site-specific measurements where available. Preliminary results suggest that simulated fluxes are reasonably close to measured values, but simulated carbon storage tends to be lower than the measurements. In addition to site-specific comparisons, we discuss the broader implications of our results, e.g., the effects of including explicit depth structure and inter-layer soil carbon transport on simulated soil respiration, carbon storage, and estimation of the global carbon budget.
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0428 Carbon cycling (4806)
DE: 1631 Land/atmosphere interactions (1218, 1843, 3322)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting