Global carbon sinks and their variability inferred from atmospheric O-2 and delta C-13

Recent time-series measurements of atmospheric O-2 show that the land biosp here and world oceans annually sequestered 1.4 +/- 0.8 and 2.0 +/- 0.6 giga tons of carbon, respectively between mid-1991 and mid-1997. The rapid stora ge of carbon by the Land biosphere from 1991 to 1997 contrasts with the 198 0s, when the land biosphere was approximately neutral. Comparison with meas urements of delta(13)CO(2) implies an isotopic flux of 89 +/- 21 gigatons o f carbon per mil per year, in agreement with model- and inventory-based est imates 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 ge neral agreement of the independent estimates from O-2 and delta(13)C is a r obust signal of variable carbon uptake by both the Land biosphere and the o ceans.