HR: 0800h
AN: B11A-0990    [Abstracts]
TI: What are the instrumentation requirements for measuring isotopic composition of net ecosystem exchange of CO2 via eddy covariance methods?
AU: Shorter, J
EM: shorter@aerodyne.com
AF: Aerodyne Research, Inc., 45 Manning Road, Billerica, MA 01821 United States
AU: * Saleska, S
EM: saleska@email.arizona.edu
AF: Ecology & Evolutionary Biology, University of Arizona, Tucson, AZ 85721 United States
AU: Herndon, S
EM: herndon@aerodyne.com
AF: Aerodyne Research, Inc., 45 Manning Road, Billerica, MA 01821 United States
AU: Jimenez-Pizarro, R
EM: jimenez@fas.harvard.edu
AF: Dept. of Earth and Planetary Sciences and Division of Engineering and Applied Sciences, Harvard University 20 Oxford Street, Cambridge, MA 02139 United States
AU: McManus, J B
EM: mcmanus@aerodyne.com
AF: Aerodyne Research, Inc., 45 Manning Road, Billerica, MA 01821 United States
AU: Munger, J W
EM: jwm@io.harvard.edu
AF: Dept. of Earth and Planetary Sciences and Division of Engineering and Applied Sciences, Harvard University 20 Oxford Street, Cambridge, MA 02139 United States
AU: Nelson, D D
EM: ddn@aerodyne.com
AF: Aerodyne Research, Inc., 45 Manning Road, Billerica, MA 01821 United States
AU: Zahniser, M
EM: mz@aerodyne.com
AF: Aerodyne Research, Inc., 45 Manning Road, Billerica, MA 01821 United States
AB: Better quantification of isotope ratios of atmosphere-ecosystem exchange of CO2 could substantially improve our ability to probe underlying physiological and ecological mechanisms controlling ecosystem carbon exchange, but the ability to make long-term continuous measurements of isotope ratios of exchange fluxes has been limited by measurement difficulties. In particular, direct eddy covariance methods have not yet been used for measuring the isotopic composition of ecosystem fluxes. Here we explore the feasibility of such measurements by: (a) proposing a general criterion for judging whether a sensor's performance is sufficient for making such measurements (the criterion is met when the contribution of sensor error to the flux measurement error is comparable to or less than the contribution of meteorological noise inherently associated with turbulence flux measurements); (b) using data-based numerical simulations to quantify the level of sensor precision and stability required to meet this criterion for making direct eddy covariance measurements of the 13C/12C ratio of CO2 fluxes above a specific ecosystem (a mid-latitude temperate forest in central Massachusetts, USA); and (c) testing whether the performance of a new sensor -- a prototype pulsed quantum cascade laser-based isotope-ratio absorption spectrometer (and plausible improvements thereon) -- is sufficient for meeting the criterion in this ecosystem. We found that the error contribution from a prototype sensor (0.2 per mil, 1 SD of 10-sec integrations) to total isoflux measurement error was comparable to (1.5 to 2X) the irreducible meteorological noise inherently associated with turbulent flux measurements above this ecosystem (daytime measurement error SD of 60 percent of flux versus meteorological noise of 30-40 percent for instantaneous half-hour fluxes). Our analysis also shows that plausible instrument improvements (increase of sensor precision to 0.1 per mil, 1 SD of 10-sec integrations, and increased sensor stability during the half-hour needed to integrate eddy covariance measurements) should decrease the contribution of sensor error to the point where it is less than the contribution from meteorological noise. This suggests that new sensors using quantum cascade laser-based isotope ratio absorption spectroscopy should make continuous long-term observations of the isotopic composition of CO2 fluxes via eddy covariance methods feasible.
DE: 0426 Biosphere/atmosphere interactions (0315)
DE: 0428 Carbon cycling (4806)
DE: 0454 Isotopic composition and chemistry (1041, 4870)
SC: Biogeosciences [B]
MN: Fall Meeting 2005