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Published December 1997 | Published
Journal Article Open

The contribution of terrestrial sources and sinks to trends in the seasonal cycle of atmospheric carbon dioxide


We characterized decadal changes in the amplitude and shape of the seasonal cycle of atmospheric CO_2 with three kinds of analysis. First, we calculated the trends in the seasonal cycle of measured atmospheric CO_2 at observation stations in the National Oceanic and Atmospheric Administration Climate Monitoring and Diagnostic Laboratory network. Second, we assessed the impact of terrestrial ecosystems in various localities on the mean seasonal cycle of CO_2 at observation stations using the Carnegie‐Ames‐Stanford Approach terrestrial biosphere model and the Goddard Institute for Space Studies (GISS) atmospheric tracer transport model. Third, we used the GISS tracer model to quantify the contribution of terrestrial sources and sinks to trends in the seasonal cycle of atmospheric CO_2 for the period 1961–1990, specifically examining the effects of biomass burning, emissions from fossil fuel combustion, and regional increases in net primary production (NPP). Our analysis supports results from previous studies that indicate a significant positive increase in the amplitude of the seasonal cycle of CO_2 at Arctic and subarctic observation stations. For stations north of 55°N the amplitude increased at a mean rate of 0.66% yr^(−1) from 1981 to 1995. From the analysis of ecosystem impacts on the mean seasonal cycle we find that tundra, boreal forest, and other northern ecosystems are responsible for most of the seasonal variation in CO_2 at stations north of 55°N. The effects of tropical biomass burning on trends in the seasonal cycle are minimal at these stations, probably because of strong vertical convection in equatorial regions. From 1981 to 1990, fossil fuel emissions contributed a trend of 0.20% yr^(−1) to the seasonal cycle amplitude at Mauna Loa and less than 0.10% yr^(−1) at stations north of 55°N. To match the observed amplitude increases at Arctic and subarctic stations with NPP increases, we find that north of 30°N a 1.7 Pg C yr^(−1) terrestrial sink would be required. In contrast, over regions south of 30°N, even large NPP increases and accompanying terrestrial sinks would be insufficient to account for the increase in high‐latitude amplitudes.

Additional Information

© 1997 American Geophysical Union. (Received October 22, 1996; revised July 20, 1997; accepted July 30, 1997.) Paper number 97GB02268. We wish to thank R. Andres for providing the fossil fuel maps, W. M. Hao for providing the biomass burning data, and J. John for assistance with the GISS tracer model. J. A. Berry, C. M. Maimstrom, J. F. Polsenberg, C. J. Still, P.M. Vitousek, and three anonymous reviewers provided very helpful suggestions. This work was supported in part by a NASA EOS/IDS grant to P. J. Sellers and H. A. Mooney and a grant to C.B.F. and J. A. Berry from the Western Regional Center of the DOE National Institute for Global Environmental Change. J.T.R. was supported by a NASA Earth System Science Graduate Fellowship. The Pathfinder NDVI data were acquired from the Distributed Active Archive Center (code 902.2) at the Goddard Space Flight Center, Greenbelt, Maryland. The maps of NEP fluxes and the CASA computer code used in this study are available via anonymous ftp at arbutus.stanford.edu in the directory pub/amp. This is CIW-DPB publication 1324.

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August 19, 2023
October 19, 2023