eScholarship (California Digital Library) · 2001 · 245 citations · 0 references
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Natural SciencesEarth SciencesEnvironmental SciencesAtmospheric ChemistryAtmospheric ScienceBiogeochemistryCarbon CycleCarbon Cycle VariabilityCarbon CyclingClimate ChangeAtmospheric Carbon DioxideBiosphere ExchangeCarbon DioxideCarbon Dioxide FluxesDeconvolutionIsotopic Ratio AnalysisIsotopic RatiosTerrestrial Carbon Exchange
Atmospheric CO₂ rose from 335 ppm in 1978 to 368 ppm in 1999, as measured at ten global stations. The study aims to deduce regional CO₂ exchanges by applying latitudinal gradients derived from the same atmospheric data. A double‑deconvolution method, allowing a ~1 ‰ change in terrestrial plant discrimination, was used to separate terrestrial and oceanic fluxes and to compute regional exchanges. CO₂ concentration rose irregularly, peaking in 1980, 1983, 1987, 1990, 1994, and 1998—years linked to El Niño—while isotopic ratios varied similarly, indicating dominant terrestrial exchange and a phase‑opposite, variable oceanic exchange that may be over‑estimated because of an assumed constant plant discrimination.
Author(s): Keeling, Charles D; Piper, Stephen C; Bacastow, Robert B; Wahlen, Martin; Whorf, Timothy P; Heimann, Martin; Meijer, Harro A | Abstract: From 1978 through 1999 the global average concentration of atmospheric carbon dioxide increased from 335 ppm to 368 ppm according to measurements of air samples collected at an array of ten stations extending from the Arctic to the South Pole. The global average rate of increase varied widely, however, with highest rates occurring in 1980, 1983, 1987, 1990, 1994, and 1998, all but the first of these calendar years near times of El Nin˜o events. The 13C/12C isotopic ratio of carbon dioxide, measured on the same air samples, varied in a similarly irregular manner, suggesting that exchange of atmospheric CO2 with terrestrial plants and soil is the dominant cause of both signals. Quantitative analysis of the data by a procedure called a double deconvolution supports this hypothesis but also suggests a variable exchange with the oceans, opposite in phase to the terrestrial exchange. This result may be in error, however, because it depends on an assumption that the global average isotopic discrimination of terrestrial plants has been constant. Allowing for a variation in discrimination of only about 1°/°° would eliminate the opposing fluctuations in oceanic flux, if its phasing has been opposite to that of the observed fluctuations in rate of change of CO2 concentration. In three companion articles that follow, we further deduce regional exchanges of CO2, making use of latitudinal gradients computed from the same atmospheric carbon dioxide data used in this global study.