HR: 11:05h
AN: B22B-04    [Abstracts]
TI: Observations and Modelling of Oxygen Isotopic Signatures of the CO2 Efflux From a Forest Soil
AU: * Seibt, U
EM: useibt@stanford.edu
AF: Dept of Global Ecology, Carnegie Institution of Washington, 260 Panama Street, Stanford, CA 94305 United States
AU: Wingate, L
EM: lwingate@ed.ac.uk
AF: School of GeoSciences, University of Edinburgh, West Mains Road, Edinburgh, EH9 3JN United Kingdom
AU: Hemming, D
EM: debbie.hemming@metoffice.com
AF: Hadley Centre for Climate Prediction and Research, FitzRoy Road, Exeter, EX1 3PB United Kingdom
AU: Lloyd, J
EM: j.lloyd@leeds.ac.uk
AF: School of Geography, University of Leeds, Woodhouse Lane, Leeds, LS2 9JT United Kingdom
AU: Berry, J
EM: joeberry@globalecology.stanford.edu
AF: Dept of Global Ecology, Carnegie Institution of Washington, 260 Panama Street, Stanford, CA 94305 United States
AB: We determined the rates and δ¹⁸O signatures of the soil CO₂ efflux from soil chamber measurements over the diurnal cycle in July and September 2000, and May and July 2001 in a Sitka spruce plantation, Scotland. Concurrent estimates of the δ¹⁸O composition of soil water were obtained from soil samples collected in the vicinity of the chambers. The observed δ¹⁸O signatures of the soil CO₂ efflux were diurnally variable and strongly depleted compared to those expected from a simple evasion of CO₂ at isotopic equilibrium with soil water. We then simulated the δ¹⁸O signatures of the soil CO₂ efflux using a model of soil gas exchange that includes the concurrent flux of atmospheric invasion of CO₂ entering and leaving the soil with concomitant isotopic equilibration with soil water. The modelled δ¹⁸O signatures of the soil CO₂ efflux agreed well with the measurements when acceleration of isotopic exchange between CO₂ and soil water by carbonic anhydrase activity was included. We hypothesize that carbonic anhydrase is present in the litter or surface soil layers. This introduces a feedback between the apparent flux signature and the δ¹⁸O of canopy CO₂, where diurnal variations of background δ¹⁸O can result in diurnally variable apparent δ¹⁸O signatures of soil CO₂ fluxes. In the context of global models, this means that the explicit description of a canopy air space with variable δ¹⁸O signatures of CO₂ is required to simulate the δ¹⁸O signature of the soil CO₂ efflux.
DE: 0315 Biosphere/atmosphere interactions (0426, 1610)
DE: 1615 Biogeochemical cycles, processes, and modeling (0412, 0414, 0793, 4805, 4912)
DE: 1655 Water cycles (1836)
DE: 1851 Plant ecology (0476)
DE: 3322 Land/atmosphere interactions (1218, 1631, 1843)
SC: Biogeosciences [B]
MN: Fall Meeting 2005