Kalman filter analysis of ice core data 2. Double deconvolution of CO2 and δ13C measurements

A new method for deconvolving ice core CO 2 and δ 13 CO 2 measurements to estimate net CO 2 uptake by the terrestrial biosphere and the oceans has been developed. The method, which uses the Kalman filter, incorporates statistical analysis into the calculation. This allows a more rigorous analysis of CO 2 variability than the usual deconvolution method. The Kalman filter method estimates uncertainties on the deduced fluxes as part of the calculation. The deconvolution method is applied to the Law Dome CO 2 and δ 13 C ice core record. The calculation suggests that natural variability in CO 2 fluxes may be as large as 1 GtC yr −1 (GtC is gigatonnes carbon, 1 Gt = 10 15 g) on the timescale of just less than a decade. The Law Dome CO 2 measurements show a slight decrease in CO 2 around the 1940s. Analysis with the carbon cycle model and a numerical model of firn processes suggests that about 3 GtC yr −1 uptake (mostly oceanic) is required in the 1940s to match the ice core measurements. The estimates of variation in the terrestrial biospheric flux between 1950 and 1980 from the double deconvolution calculation are in very good agreement with an independent estimate of the global terrestrial flux from a climate‐driven ecosystem model.