Extrapolations of In Situ Observations

In addition to the top-down and bottom-up modeling, several key datasets of regional and global extent have been painstakingly compiled. These also permit an assessment of location, magnitude, and variability of surface sources and sinks. Air-sea CO2 partial pressure difference measurements allow the estimation of local air-sea fluxes (e.g., Takahashi et al. 2002). Carbon inventory changes, observed from repeated oceanic surveys or inferred by back-calculations of in situ inorganic carbon concentration measurements, allow basinwide estimates of ocean carbon uptake rates (e.g., Gruber 1998; Sabine et al. 1999, 2002; Gloor et al. 2003). On land, repeated forest inventories from national forestry statistics allow an estimation of changing carbon stocks in living biomass. Direct flux measurements above the vegetation by the eddy correlation technique provide in situ net carbon exchanges, and remote sensed information on land cover and land properties (e.g., Normalized Divided Vegetation Index) may be related to carbon fluxes. All these direct observations of carbon fluxes or carbon stock changes may, in principle, be used to estimate regional-scale carbon fluxes by means of scaling and extrapolation techniques (e.g., Pacala et al. 2001; Janssens et al. 2003; Papale and Valentini 2003).

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