Global carbon sinks and their variability inferred from atmospheric O2 and δ13C

Recent time-series measurements of atmospheric O-2 show that the land biosphere and world oceans annually sequestered 1.4 +/- 0.8 and 2.0 +/- 0.6 gigatons of carbon, respectively between mid-1991 and mid-1997. The rapid storage of carbon by the Land biosphere from 1991 to 1997 contrasts with the 1980s, when the land biosphere was approximately neutral. Comparison with measurements of delta(13)CO(2) implies an isotopic flux of 89 +/- 21 gigatons of carbon per mil per year, in agreement with model- and inventory-based estimates of this flux. Both the delta(13)C and the O-2 data show significant interannual variability in carbon storage over the period of record. The general agreement of the independent estimates from O-2 and delta(13)C is a robust signal of variable carbon uptake by both the Land biosphere and the oceans.