Table 2. Cross-Tropopause Fluxes of C16O16O, C16O17O, and C16O18Oa

	F	F(delta17O)	F(delta18O)	F(Delta17O)
Model A	56.4	78.2	50.5	52.2
Model B	51.2	82.6	53.5	55.0
Model C	81.4	75.1	46.8	51.0
Model D	56.9	53.3	31.3	37.2
Model E	51.1	80.5	51.9	53.7
Averaged	59.4	73.9	46.8	49.8

aDownward fluxes (F) of CO2 across the tropopause. Values of normal and isotopically substituted CO2 are in PgC/a and permil PgC/a, respectively. F(Delta17O) is defined as F(delta17O) - 0.515 x F(delta18O).