Drought rapidly diminishes the large net CO2 uptake in 2011 over semi-arid Australia

Authors: MA, X. - University Of Technology Sydney; HUETE, A. - University Of Technology Sydney; CLEVERLY, J. - University Of Technology Sydney; EAMUS, D. - University Of Technology Sydney; CHEVALLIER, F. - Centre National De La Recherche Scientifique; JOINER, J. - National Aeronautics And Space Administration (NASA); POULTER, B. - Montana State University; ZHANG, Y. - Nanjing Tech University; GUANTER, L. - Helmholtz Centre; MEYER, W. - University Of Adelaide; XIE, Z. - University Of Technology Sydney; Ponce Campos, Guillermo

Submitted to: Scientific Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/1/2016
Publication Date: 11/25/2016
Citation: Ma, X., Huete, A., Cleverly, J., Eamus, D., Chevallier, F., Joiner, J., Poulter, B., Zhang, Y., Guanter, L., Meyer, W., Xie, Z., Ponce Campos, G.E. 2016. Drought rapidly diminishes the large net CO2 uptake in 2011 over semi-arid Australia. Scientific Reports. 6:37747. https://doi.org/10.1038/srep37747.
DOI: https://doi.org/10.1038/srep37747

Interpretive Summary: Historical data on carbon sinks show that increasing absorption by land and oceans has ensured atmospheric CO2 concentrations have not risen more than has been observed. In 2011 an exceptionally large global land carbon sink anomaly was recorded of which more than half was attributed to Australia’s semi-arid ecosystems, a phenomenon that remains largely unknown. By using satellite information, we obtained CO2 and photosynthetic activity along with in-situ carbon exchange flux measurements. Results show that this large carbon sink triggered by wet 2011 La Niña was rapidly dissipated by the following dry years with a 40% reduction in 2012 and by 67% in 2013. Here we show that this fast depletion of the carbon sink mirrored the significant increase in global average CO2 growth rates and a high correlation between Australia’s terrestrial primary productivity and global CO2. These events were compared to early 21st century La Niña events showing very similar patterns on the resilient nature of Australia ecosystems as a major carbon sink. We suggest that carbon sink episodes will have a significant impact on global carbon cycle-climate patterns in the following years, representing a critical piece of information for carbon and climate models.

Technical Abstract: An exceptionally large global land carbon sink anomaly was recorded in 2011, of which more than half was attributed to Australia’s semi-arid ecosystem. However, the fate, persistence and spatially explicit attribution of this carbon sink remain largely unknown. To address these issues, we conducted an observation-based analysis of the land carbon sink using satellite retrievals of atmospheric CO2 and photosynthetic activity (vegetation index and chlorophyll fluorescence), and in-situ flux tower measures of net ecosystem carbon exchange. Here we show the large carbon sink resulting from the wet 2011 La Niña was transient and rapidly dissipated by subsequent drought, and largely ascribed to tropical savannas and grasslands. The size of 2011 carbon sink was reduced by 40% in 2012 and by 67% in 2013. This rapid depletion of the carbon sink mirrored the sharp increase in global average atmospheric CO2 growth rates and an overall strong correlation between Australia’s terrestrial primary productivity and global atmospheric CO2 growth rate was identified (R = 0.55, p < 0.05). We further report evidence of episodic Australian carbon sink events of similar strength, coupled to early 21st -century La Niña-induced wet pulses in 2000-01 and 2010-11. Given a significant increasing trend (p < 0.001) in extreme wet year precipitation amounts and a repetitive, yet resilient nature of Australia’s carbon sink and source dynamics under intensified hydroclimatic variations, we hereby suggest that these carbon sink episodes will exert greater future impacts on global carbon cycle-climate feedbacks in the coming decades.