HR: 09:45h
AN: B11E-08 INVITED    [Abstracts]
TI: Process Model for Studying Regional ¹³C Stable Isotope Exchange between Vegetation and Atmosphere
AU: * Chen, J M
EM: chenj@geog.utoronto.ca
AF: University of Toronto, 100 St. George Street, Toronto, ON L4Z 3Y7, Canada
AU: Chen, B
EM: baozhang.chen@ubc.ca
AF: University of Toronto, 100 St. George Street, Toronto, ON L4Z 3Y7, Canada
AU: Huang, L
EM: lin.huang@ec.gc.ca
AF: Environment Canada, 4905 Dufferin Street, Toronto, ON M3H 5T4, Canada
AU: Tans, P
EM: pieter.tans@noaa.gov
AF: Global Monitoring Division, NOAA, 325 Broadway, Boulder, CO 80305-3337, United States
AU: Worthy, D
EM: doug.worthy@ec.gc.ca
AF: Environment Canada, 4905 Dufferin Street, Toronto, ON M3H 5T4, Canada
AU: Ishizawa, M
EM: misa.ishizawa@ec.gc.ca
AF: University of Toronto, 100 St. George Street, Toronto, ON L4Z 3Y7, Canada
AU: Chan, D
EM: douglas.chan@ec.gc.ca
AF: Environment Canada, 4905 Dufferin Street, Toronto, ON M3H 5T4, Canada
AB: The variation of the stable isotope ¹³CO₂ in the air in exchange with land ecosystems results from fractionation processes in both plants and soil during photosynthesis and respiration. Its diurnal and seasonal variations therefore contain information on the carbon cycle. We developed a model (BEPS-iso) to simulate its exchange between vegetation and the atmosphere. To be useful for regional carbon cycle studies, the model has the following characteristics: (i) it considers the turbulent mixing in the vertical profile from the soil surface to the top of the planetary boundary layer (PBL); (ii) it scales individual leaf photosynthetic discrimination to the whole canopy through the separation of sunlit and shaded leaf groups; (iii) through simulating leaf-level photosynthetic processes, it has the capacity to mechanistically examine isotope discrimination resulting from meteorological forcings, such as radiation, precipitation and humidity; and (iv) through complete modeling of radiation, energy and water fluxes, it also simulates soil moisture and temperature needed for estimating ecosystem respiration and the ¹³C signal from the soil. After validation using flask data acquired at 20 m level on a tower near Fraserdale, Ontario, Canada, during intensive campaigns (1998–2000), the model has been used for several purposes: (i) to investigate the diurnal and seasonal variations in the disequilibrium in ¹³C fractionation between ecosystem respiration and photosynthesis, which is an important step in using 13C measurements to separate these carbon cycle components; (ii) to quantify the ¹³C rectification in the PBL, which differs significantly from CO₂ rectification because of the diurnal and seasonal disequilibriums; and (iii) to model the ¹³C spatial and temporal variations over the global land surface for the purpose of CO₂ inversion using ¹³C as an additional constraint.
DE: 0315 Biosphere/atmosphere interactions (0426, 1610)
DE: 0322 Constituent sources and sinks
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0426 Biosphere/atmosphere interactions (0315)
DE: 0428 Carbon cycling (4806)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting