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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 108, NO. D16, 4492, doi:10.1029/2003JD003562, 2003

Implications of ice core smoothing for inferring CO₂ flux variability

C. M. Trudinger

CSIRO Atmospheric Research, Aspendale, Victoria, Australia

P. J. Rayner

CSIRO Atmospheric Research, Aspendale, Victoria, Australia

I. G. Enting

CSIRO Atmospheric Research, Aspendale, Victoria, Australia

M. Heimann

Max Planck Institut für Meteorologie, Hamburg, Germany

M. Scholze

Max Planck Institut für Meteorologie, Hamburg, Germany

Abstract

Ice core records are commonly used to infer information about past variability of CO₂ fluxes. Because of processes involved in enclosing this air in ice, ice core records are a smoothed representation of the actual past atmospheric variations. As such, there is a limit to how much information ice core measurements can contain about flux variability on short timescales. With a numerical model of the firn processes we quantify this smoothing and describe how it can be reproduced with pulse response functions. We generate and make available pulse response functions for CO₂ at the DE08 site on Law Dome, Antarctica. We discuss implications of the smoothing for inferring CO₂ flux variability from the Law Dome ice core record. In particular we look at results from an intercomparison of terrestrial biosphere models over the twentieth century and show how much of the CO₂ variability would be reflected in the Law Dome ice core record. We also smooth atmospheric δ¹³CO₂ from a study that compared fixed and varying isotopic discrimination. We find that the impact of changing discrimination, shown previously to be large on interannual timescales, is small on the decadal scales accessible from ice core records.

Received 5 March 2003; accepted 21 May 2003; published 19 August 2003.

Index Terms: 0315 Atmospheric Composition and Structure: Biosphere/atmosphere interactions; 1610 Global Change: Atmosphere (0315, 0325); 1615 Global Change: Biogeochemical processes (4805).

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Citation: Trudinger, C. M., P. J. Rayner, I. G. Enting, M. Heimann, and M. Scholze (2003), Implications of ice core smoothing for inferring CO₂ flux variability, J. Geophys. Res., 108(D16), 4492, doi:10.1029/2003JD003562.

Copyright 2003 by the American Geophysical Union.