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Semi-arid ecosystems emerging role in global carbon cycle dynamics

Poulter, B, D Frank, P Ciais, RB Myneni, N Andela, J Bi, G Broquet, JG Canadell, F Chevallier, YY Liu, SW Running, S Sitch and GR van der Werf. 2014. Contribution of semi-arid ecosystems to interannual variability of the global carbon cycle.

Nature, published online: 21 May 2014

Paper Abstract

The land and ocean act as a sink for fossil-fuel emissions, thereby slowing the rise of atmospheric carbon dioxide concentrations. Although the uptake of carbon by oceanic and terrestrial processes has kept
pace with accelerating carbon dioxide emissions until now, atmospheric carbon dioxide concentrations exhibit a large variability on interannual timescales, considered to be driven primarily by terrestrial
ecosystem processes dominated by tropical rainforests. We use a terrestrial biogeochemicalmodel, atmospheric inversion and global carbon budget accounting methods to investigate the evolution
of the terrestrial carbon sink over the past 30 years, with a focus on the underlying mechanisms responsible for the exceptionally large land carbon sink reported in 2011. Here we show that our three
terrestrial carbon sink estimates are in good agreement and support the finding of a 2011 record land carbon sink. Surprisingly, we find that the global carbon sink anomaly was driven by growth of semiarid
vegetation in the Southern Hemisphere, with almost 60 per cent of carbon uptake attributed to Australian ecosystems, where prevalent La Nina conditions caused up to six consecutive seasons of increased
precipitation. In addition, since 1981, a six per cent expansion of vegetation cover over Australia was associated with a fourfold increase in the sensitivity of continental net carbon uptake to precipitation.
Our findings suggest that the higher turnover rates of carbon pools in semi-arid biomes are an increasingly important driver of global carbon cycle inter-annual variability and that tropical rainforests may become less relevant drivers in the future. More research is needed to identify to what extent the carbon stocks accumulated during wet years are vulnerable to rapid decomposition or loss through fire in subsequent years.



Illustrative Photos (available free if credited as specified).

Semi-arid ecosystem  
Credit: Eva van Gorsel, CSIRO
(2000x1318, jpg 1.3 mb)