labs_title

Regional atmospheric CO2 inversion reveals seasonal and geographic differences in Amazon net biome exchange

C.B. Alden, J.B. Miller, L.V. Gatti, M.M. Gloor, K. Guan, A.M. Michalak, I.T. van der Laan-Luijkx, D. Touma, A. Andrews, L.S. Basso, C.S.C. Correia, L.G. Domingues, J. Joiner, M.C. Krol, A.I. Lyapustin, W. Peters, Y.P. Shiga, K. Thoning, I.R. van der Velde, T.T. van Leeuwen, V. Yadav and N.S. Diffenbaugh

The tropics are considered to be a potential “tipping element” in the climate system, because changes in net carbon balance could lead to substantial climate feedbacks. This work aims to understanding the role of climate variability in controlling net carbon update in the Amazon. Using atmospheric observations over the amazon coupled with an atmospheric transport model, the analysis revealed that more carbon was emitted to the atmosphere during a period of heat and drought in 2010 relative to other years, indicating a strong sensitivity to both temperature and precipitation.


Figure: Monthly and annual basin-wide and regional Net Biome Exchange (NBE). A positive NBE indicates a source to the atmosphere.

Abstract

Understanding tropical rainforest carbon exchange and its response to heat and drought is critical for quantifying the effects of climate change on tropical ecosystems, including global climate–carbon feedbacks. Of particular importance for the global carbon budget is net biome exchange of CO2 with the atmosphere (NBE), which represents nonfire carbon fluxes into and out of biomass and soils. Subannual and sub-Basin Amazon NBE estimates have relied heavily on process-based biosphere models, despite lack of model agreement with plot-scale observations. We present a new analysis of airborne measurements that reveals monthly, regional-scale (~1–8 × 106 km2) NBE variations. We develop a regional atmospheric CO2 inversion that provides the first analysis of geographic and temporal variability in Amazon biosphere–atmosphere carbon exchange and that is minimally influenced by biosphere model-based first guesses of seasonal and annual mean fluxes. We find little evidence for a clear seasonal cycle in Amazon NBE but do find NBE sensitivity to aberrations from long-term mean climate. In particular, we observe increased NBE (more carbon emitted to the atmosphere) associated with heat and drought in 2010, and correlations between wet season NBE and precipitation (negative correlation) and temperature (positive correlation). In the eastern Amazon, pulses of increased NBE persisted through 2011, suggesting legacy effects of 2010 heat and drought. We also identify regional differences in postdrought NBE that appear related to long-term water availability. We examine satellite proxies and find evidence for higher gross primary productivity (GPP) during a pulse of increased carbon uptake in 2011, and lower GPP during a period of increased NBE in the 2010 dry season drought, but links between GPP and NBE changes are not conclusive. These results provide novel evidence of NBE sensitivity to short-term temperature and moisture extremes in the Amazon, where monthly and sub-Basin estimates have not been previously available.

Alden, C.B., J.B. Miller, L.V. Gatti, M.M. Gloor, K. Guan, A.M. Michalak, I.T. van der Laan-Luijkx, D. Touma, A. Andrews, L.S. Basso, C.S.C. Correia, L.G. Domingues, J. Joiner, M.C. Krol, A.I. Lyapustin, W. Peters, Y.P. Shiga, K. Thoning, I.R. van der Velde, T.T. van Leeuwen, V. Yadav, N.S. Diffenbaugh (2016), "Regional atmospheric CO2 inversion reveals seasonal and geographic differences in Amazon net biome exchange", Global Change Biology, 22 (10), 3427-3443, doi:10.1111/gcb.13305.