Seasonal Cycles and Mean Annual Spatial Gradients

4 Seasonal Cycles and Mean Annual Spatial Gradients 

The seasonal signal in atmospheric CO2 in the northern hemisphere is mostly generated by the terrestrial biosphere (Heimann et al, 1986 1989 1998 Fung et al, 1987 Knorr and Heimann, 1995), oceanic seasonal fluxes being largely buffered by the ocean chemistry and the slow sea-air gas exchange of CO2. This is not true for O2 which in the Northern Hemisphere, at least in oceanic 

Here 50, denotes the observed deviation of the atmospheric O, concentration from a standard. The atmospheric tracer APO is dominated primarily by oceanic gas exchanges in addition to a relatively small contribution from fossil fuel not accounted for by the terrestrial stoichiometric factor (i.e., the fossil fuel component scaled by the factor Observations of the seasonal variation of APO in conjuction with surface-water oxy gen measurements have been used to constrain the large-scale magnitude of the air-sea gas exchange coefficient (Keeling et al, 1998) and of marine productivity (Six and Maier-Reimer, 1996 Balkan.ski et al, 1999). Mean annual gradients of APO have also been shown to provide powerful constraints on biogeochemical air-sea fluxes computed by ocean-circulation models with an embedded ocean carbon cycle (Stephens et al, 1998). 

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