Global Carbon Sinks and Their Variability Inferred from Atmospheric O 2 and δ 13 C

Abstract

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 δ 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 δ 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 δ 13 C is a robust signal of variable carbon uptake by both the land biosphere and the oceans.