Soil respiration-driven CO₂ pulses dominate Australia's flux variability

The Australian continent contributes substantially to the year-to-year variability of the global terrestrial carbon dioxide (CO₂) sink. However, the scarcity of in situ observations in remote areas prevents the deciphering of processes that force the CO₂ flux variability. In this study, by examining atmospheric CO₂ measurements from satellites in the period 2009-2018, we find recurrent end-of-dry-season CO₂ pulses over the Australian continent. These pulses largely control the year-to-year variability of Australia's CO₂ balance. They cause two to three times larger seasonal variations compared with previous top-down inversions and bottom-up estimates. The pulses occur shortly after the onset of rainfall and are driven by enhanced soil respiration preceding photosynthetic uptake in Australia's semiarid regions. The suggested continental-scale relevance of soil-rewetting processes has substantial implications for our understanding and modeling of global climate-carbon cycle feedbacks.