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Abstract
Recent time-series measurements of atmospheric O2 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 δ13CO2 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 δ13C and the O2 data show significant interannual variability in carbon storage over the period of record. The general agreement of the independent estimates from O2and δ13C is a robust signal of variable carbon uptake by both the land biosphere and the oceans.
↵* Present address: Department of Physics and Astronomy, Bowdoin College, 8800 College Station, Brunswick, ME 04011, USA.
