Respiration driven CO2 pulses dominate Australia's flux variability

TL;DR

This study reveals that respiration-driven CO2 pulses during Australia's dry season significantly influence the country's annual CO2 flux variability, highlighting the importance of soil rewetting processes in climate-carbon cycle interactions.

Contribution

It identifies the dominant role of dry-season CO2 pulses in Australia's flux variability and links these pulses to soil rewetting and respiration processes, using satellite data.

Findings

End-of-dry-season CO2 pulses are recurrent over Australia.

These pulses control the interannual variability of Australia's CO2 balance.

Soil rewetting after rainfall drives the CO2 pulses.

Abstract

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.