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      A Large Northern Hemisphere Terrestrial CO 2 Sink Indicated by the 13 C/ 12 C Ratio of Atmospheric CO 2

      1 , 2 , 3 , 4 , 5
      Science
      American Association for the Advancement of Science (AAAS)

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          Abstract

          Measurements of the concentrations and carbon-13/carbon-12 isotope ratios of atmospheric carbon dioxide can be used to quantify the net removal of carbon dioxide from the atmosphere by the oceans and terrestrial plants. A study of weekly samples from a global network of 43 sites defined the latitudinal and temporal patterns of the two carbon sinks. A strong terrestrial biospheric sink was found in the temperate latitudes of the Northern Hemisphere in 1992 and 1993, the magnitude of which is roughly half that of the global fossil fuel burning emissions for those years. The challenge now is to identify those processes that would cause the terrestrial biosphere to absorb carbon dioxide in such large quantities.

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          Most cited references18

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          Biomass burning in the tropics: impact on atmospheric chemistry and biogeochemical cycles.

          Biomass burning is widespread, especially in the tropics. It serves to clear land for shifting cultivation, to convert forests to agricultural and pastoral lands, and to remove dry vegetation in order to promote agricultural productivity and the growth of higher yield grasses. Furthermore, much agricultural waste and fuel wood is being combusted, particularly in developing countries. Biomass containing 2 to 5 petagrams of carbon is burned annually (1 petagram = 10(15) grams), producing large amounts of trace gases and aerosol particles that play important roles in atmospheric chemistry and climate. Emissions of carbon monoxide and methane by biomass burning affect the oxidation efficiency of the atmosphere by reacting with hydroxyl radicals, and emissions of nitric oxide and hydrocarbons lead to high ozone concentrations in the tropics during the dry season. Large quantities of smoke particles are produced as well, and these can serve as cloud condensation nuclei. These particles may thus substantially influence cloud microphysical and optical properties, an effect that could have repercussions for the radiation budget and the hydrological cycle in the tropics. Widespread burning may also disturb biogeochemical cycles, especially that of nitrogen. About 50 percent of the nitrogen in the biomass fuel can be released as molecular nitrogen. This pyrdenitrification process causes a sizable loss of fixed nitrogen in tropical ecosystems, in the range of 10 to 20 teragrams per year (1 teragram = 10(12) grams).
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            Observational contrains on the global atmospheric co2 budget.

            Observed atmospheric concentrations of CO(2) and data on the partial pressures of CO(2) in surface ocean waters are combined to identify globally significant sources and sinks of CO(2). The atmospheric data are compared with boundary layer concentrations calculated with the transport fields generated by a general circulation model (GCM) for specified source-sink distributions. In the model the observed north-south atmospheric concentration gradient can be maintained only if sinks for CO(2) are greater in the Northern than in the Southern Hemisphere. The observed differences between the partial pressure of CO(2) in the surface waters of the Northern Hemisphere and the atmosphere are too small for the oceans to be the major sink of fossil fuel CO(2). Therefore, a large amount of the CO(2) is apparently absorbed on the continents by terrestrial ecosystems.
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              Carbon pools and flux of global forest ecosystems.

              Forest systems cover more than 4.1 x 10(9) hectares of the Earth's land area. Globally, forest vegetation and soils contain about 1146 petagrams of carbon, with approximately 37 percent of this carbon in low-latitude forests, 14 percent in mid-latitudes, and 49 percent at high latitudes. Over two-thirds of the carbon in forest ecosystems is contained in soils and associated peat deposits. In 1990, deforestation in the low latitudes emitted 1.6 +/- 0.4 petagrams of carbon per year, whereas forest area expansion and growth in mid- and high-latitude forest sequestered 0.7 +/- 0.2 petagrams of carbon per year, for a net flux to the atmosphere of 0.9 +/- 0.4 petagrams of carbon per year. Slowing deforestation, combined with an increase in forestation and other management measures to improve forest ecosystem productivity, could conserve or sequester significant quantities of carbon. Future forest carbon cycling trends attributable to losses and regrowth associated with global climate and land-use change are uncertain. Model projections and some results suggest that forests could be carbon sinks or sources in the future.
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                Author and article information

                Journal
                Science
                Science
                American Association for the Advancement of Science (AAAS)
                0036-8075
                1095-9203
                August 25 1995
                August 25 1995
                : 269
                : 5227
                : 1098-1102
                Affiliations
                [1 ]National Oceanic and Atmospheric Administration's Climate Monitoring and Diagnostics Laboratory (NOAA/CMDL), R/E/CG1, 325 Broadway, Boulder, CO 80303, USA, and LMCE-DSM Commissariat a I'Energie Atomique, L'Orme des Meurisiers, 91191, Gif sur Yvette Cedex, France
                [2 ]NOAA/CMDL, R/E/CG1, 325 Broadway, Boulder, CO 80303, USA.
                [3 ]NOAA/CMDL, R/E/CG1, 325 Broadway, Boulder, CO 80303, USA, and Institute of Arctic and Alpine Research (INSTAAR), University of Colorado, Boulder, CO 80309, USA.
                [4 ]INSTAAR, and Department of Geological Sciences, University of Colorado, Boulder, CO 80309, USA.
                [5 ]Commonwealth Scientific and Industrial Research Organisation, Division of Atmospheric Research, Mordialloc, Victoria 3195, Australia
                Article
                10.1126/science.269.5227.1098
                17755534
                5d2de186-3ce7-4be3-b469-515bb1c917a8
                © 1995

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