Eroding the carbon cycle

Recent attention on the anthropogenic CO2 budget has strongly focused on the apparent imbalance between CO2 atmospheric increase, emission from fossil fuels and changes in land use, and oceanic uptake. The residual terrestrial carbon sink is traditionally estimated from the closure of the anthropogenic CO2 budget. Several processes contribute to this net uptake on land which still has large uncertainties. In particular, traditional analysis omit that carbon originally xed by land plants is continuously displaced laterally along the Earth’s surface, from upland soils to streams and rivers and further down to the ocean.

Using evidence from both experimental and modeling studies, we show that this perturbation of the C cycle is large and has profound implications for the estimation of the amount of carbon stored on land. Finally, we discuss the consequences for the pre-industrial as well as for the present and future atmospheric CO2 budget.