Soil respiration–driven CO ₂ pulses dominate Australia’s flux variability

Abstract

The Australian continent contributes substantially to the year-to-year variability of the global terrestrial carbon dioxide (CO 2 ) sink. However, the scarcity of in situ observations in remote areas prevents the deciphering of processes that force the CO 2 flux variability. In this study, by examining atmospheric CO 2 measurements from satellites in the period 2009–2018, we find recurrent end-of-dry-season CO 2 pulses over the Australian continent. These pulses largely control the year-to-year variability of Australia’s CO 2 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.

A Comprehensive Assessment of Anthropogenic and Natural Sources and Sinks of Australasia's Carbon Budget

“…We calculated two GOSAT flux estimates derived from the TM5‐4DVAR inversion (Metz et al., 2023). One flux was derived from two independent GOSAT retrievals (ACOS and RemoTeC), and another derived from GOSAT (ACOS and RemoTeC) but combined with in situ measurements.…”

“…For this assessment, we selected global and regional inversion-based flux estimates. Global from the Global Carbon Project (GCP) (Friedlingstein et al, 2020), MIROC4-ACTM (Chandra et al, 2022), OCO-2 MIP (Byrne et al, 2023), and GOSAT TM5-4DVAR (Metz et al, 2023). Regional from two independent inversion systems, one developed in Australia (Villalobos et al, 2022) and the other in New Zealand (Bukosa et al, 2023;Steinkamp et al, 2017).…”

Twenty Years of Progress, Challenges, and Opportunities in Measuring and Understanding Soil Respiration

“…Manipulative drought experiments consistently report strong negative effects on Rs (Morris et al, 2022;. Substantial CO 2 pulses can occur upon soil rewetting (D.-G. Kim et al, 2012;Thomey et al, 2011), and in some ecosystems annual fluxes are dominated by "hot moments" of rainfall-driven Rs pulses (Delgado-Balbuena et al, 2023;Metz et al, 2023;Vargas et al, 2018). Rainfall/drought experiments are crucial because of the confounding effect between soil temperature and moisture (Davidson et al, 1998;Lellei-Kovács et al, 2011), and interactive effects between drought and CO 2 enrichment have also been reported (Reinthaler et al, 2021).…”

“…At ecosystem scales, Rs dominates ecosystem respiration (Law et al, 2002). Rs variability can drive the carbon balance of ecosystems (Desai et al, 2022) to entire continents (Ballantyne et al, 2017;Metz et al, 2023). Rs is the second largest carbon flux in the earth system after photosynthesis (Friedlingstein et al, 2022), and almost an order of magnitude larger than anthropogenic carbon emissions (Bond-Lamberty and Thomson, 2010b), and can thus affect the terrestrial carbon cycle (Ballantyne et al, 2017).…”