11 Feb 2022
11 Feb 2022
Status: a revised version of this preprint is currently under review for the journal ACP.

Interannual variability in the Australian carbon cycle over 2015–2019, based on assimilation of OCO-2 satellite data

Yohanna Villalobos1,2,5, Peter J. Rayner1,2,3, Jeremy D. Silver1,4, Steven Thomas1, Vanessa Haverd5,, Jürgen Knauer9,5, Zoë M. Loh6, Nicholas M. Deutscher7, David W. T. Griffith7, and David F. Pollard8 Yohanna Villalobos et al.
  • 1School of Geography, Earth and Atmospheric Sciences, University of Melbourne, Australia
  • 2ARC Centre of Excellence for Climate Extremes, Sydney, Australia
  • 3Climate & Energy College, University of Melbourne, Melbourne, Australia
  • 4School of Mathematics and Statistics, University of Melbourne, Melbourne, Australia
  • 5CSIRO Oceans and Atmosphere, Canberra, 2601, Australia
  • 6CSIRO Oceans and Atmosphere, Aspendale, Victoria 3195, Australia
  • 7Centre for Atmospheric Chemistry, School of Chemistry, University of Wollongong, Wollongong, NSW, 2522, Australia
  • 8National Institute of Water and Atmospheric Research Ltd (NIWA), Lauder, New Zealand
  • 9Hawkesbury Institute for the Environment, Western Sydney University, Penrith, NSW 2751, Australia
  • deceased, 19 January 2021

Abstract. In this study, we employ a regional inverse modelling approach to estimate monthly carbon fluxes over the Australian continent for 2015–2019 using the assimilation of the total column-averaged mole fractions of carbon dioxide from the Orbiting Carbon Observatory-2 (OCO-2, version 9). Subsequently, we study the carbon cycle variations and relate their fluctuations to anomalies in vegetation productivity and climate drivers. Our five-year regional carbon flux inversion suggests that Australia was a carbon sink averaging −0.46 ± 0.08 PgC yr−1 (excluding fossil fuel emissions), largely influenced by a strong carbon uptake (−1.04 PgC yr−1) recorded in 2016. Australia semi-arid ecosystems, such as sparsely vegetated regions (in central Australia) and savanna (in northern Australia), were the main contributors to the carbon uptake in 2016. These regions showed relatively high vegetation productivity, high rainfall and low temperature in 2016. In contrast to the large carbon sink found in 2016, the large carbon outgassing recorded in 2019 coincides with an unprecedented deficit of rainfall and higher than average temperature across Australia. Comparison of the posterior column average CO2 concentration against the Total Carbon Column Observing Networks (TCCON) and in situ measurements offers limited insight into the fluxes assimilated with OCO-2. However, the lack of these monitoring stations across Australia, mainly over ecosystems such as the savanna and areas with sparse vegetation, impedes us from providing strong conclusions. Comparison of our flux inversion to the ensemble mean carbon flux of the OCO-2 Multi-model Intercomparison Project (MIP) (2015–2018) agrees with our findings, and their results also suggest that Australia was a strong carbon sink in 2016 (−0.73 ± 0.41 PgC yr−1). The analysis of the variability of the nine models that participate in the OCO-2 MIP also aligns with our findings, and it gives us the confidence to say that changes in rainfall and temperature drive most of the carbon flux variability across Australia.

Yohanna Villalobos et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2022-15', Anonymous Referee #1, 14 Mar 2022
  • RC2: 'Comment on acp-2022-15', Anonymous Referee #2, 28 Mar 2022
  • AC1: 'Comment on acp-2022-15', Yohanna Villalobos Cortes, 10 May 2022

Yohanna Villalobos et al.

Yohanna Villalobos et al.


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Short summary
We study the interannual variability of Australian carbon fluxes for 2015–2019 derived from OCO-2 satellite data. Our results suggest that Australia's semi-arid ecosystems are highly responsive to variations in climate drivers such as rainfall and temperature. We found that high rainfall and low temperatures recorded in 2016 led to an anomalous carbon sink over the savanna and sparsely vegetated regions, while unprecedented dry and hot weather in 2019 led to anomalous carbon release.