HR: 17:45h
AN: B34A-08    [Abstracts]
TI: Response of the Terrestrial Carbon Cycle to the El Nino-Southern Oscillation
AU: Qian, H
EM: haifee@atmos.umd.edu
AF: Univ Maryland, AOSC and ESSIC, College Park, MD 20742, United States
AU: * Zeng, N
EM: zeng@atmos.umd.edu
AF: Univ Maryland, AOSC and ESSIC, College Park, MD 20742, United States
AU: Joseph, R
EM: rjoseph@atmos.umd.edu
AF: Univ Maryland, AOSC and ESSIC, College Park, MD 20742, United States
AB: Interannual variability of atmospheric CO2 growth rate is strongly associated with the El Niño Southern Oscillation (ENSO). Recent studies have emphasized land as the dominant contributor to the interannual variability of global carbon fluxes. In this study, we used a dynamic terrestrial carbon cycle model, VEGAS (VEgetation-Global-Atmosphere-Soil), to identify and isolate the responses of terrestrial carbon cycle to the physical climate variations associated with ENSO. The veracity of the simulated terrestrial carbon flux (Fta) of VEGAS is verified by evaluating it against observations on interannual time scales. The simulated global total land-atmosphere flux agrees well with the observationsbased on inversion modeling studies on ENSO timescales and both of them are consistent with the atmospheric CO2 growth rate variation at the Mauna Loa station. Correlation of the model based Leaf Area Index (LAI) with satellite derived NDVIproduces values values significant at the 99% level. Regional and Global comparison indicates the tropics as the dominant contributor to the global carbon flux. Composite analysis of the variations of terrestrial responses and climate factors during El Niño and La Niña has identified that tropical carbon flux anomaly lags ENSO 5-6 months, similar to the atmospheric CO2 growth rate. This Fta anomaly in the tropics during ENSO period is suggested to be related to physical climate fields (e. g. temperature, precipitation) in regulating the variation of vegetation activity and soil decomposition. Carefully designed sensitivity simulations of VEGAS were conducted to isolate and quantify the effects of the individual climate fields. It was estimated that precipitation variation during ENSO contributes 56% of this Fta anomaly mainly through photosynthesis. Temperature variation accounts for the remaining 44%, which includes 25% from its direct effect on the temperature-dependent soil decomposition, 7% from its direct effect on the photosynthesis, and 12% from its indirect effect on the photosynthesis through soil wetness. Such a decomposition of the direct and indirect effects of climaticfactors also emphasizes the importance of the poorly studied factor of the global terrestrial carbon flux: soil moisture
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0428 Carbon cycling (4806)
DE: 0429 Climate dynamics (1620)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting