  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 deciphering the
processes that force the CO2 flux variability. Here, 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, due to
2-3 times higher seasonal variations compared to previous top-down inversions
and bottom-up estimates. The CO2 pulses occur shortly after the onset of
rainfall and are driven by enhanced soil respiration preceding photosynthetic
uptake in Australia's semi-arid regions. The suggested continental-scale
relevance of soil rewetting processes has large implications for our
understanding and modelling of global climate-carbon cycle feedbacks.
