Figure 3.4: Partitioning
of fossil fuel CO2 uptake using O2 measurements (Keeling
and Shertz, 1992; Keeling et al., 1993; Battle et al., 1996, 2000; Bender et al.,
1996; Keeling et al., 1996b; Manning, 2001). The graph shows the relationship
between changes in CO2 (horizontal axis) and O2 (vertical
axis). Observations of annual mean concentrations of O2, centred on
January 1, are shown from the average of the Alert and La Jolla monitoring stations
(Keeling et al., 1996b; Manning, 2001; solid circles) and from the average of
the Cape Grim and Point Barrow monitoring stations (Battle et al., 2000; solid
triangles). The records from the two laboratories, which use different reference
standards, have been shifted to optimally match during the mutually overlapping
period. The CO2 observations represent global averages compiled from
the stations of the NOAA network (Conway et al., 1994) with the methods of Tans
et al. (1989). The arrow labelled “fossil fuel burning” denotes the
effect of the combustion of fossil fuels (Marland et al., 2000; British Petroleum,
2000) based on the relatively well known O2:CO2 stoichiometric
relation of the different fuel types (Keeling, 1988). Uptake by land and ocean
is constrained by the known O2:CO2 stoichiometric ratio
of these processes, defining the slopes of the respective arrows. A small correction
is made for differential outgassing of O2 and N2 with the
increased temperature of the ocean as estimated by Levitus et al. (2000).
