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© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  08 Jan 2020

08 Jan 2020

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A revised version of this preprint is currently under review for the journal BG.

Lagged effects dominate the inter-annual variability of the 2010–2015 tropical carbon balance

A. Anthony Bloom1, Kevin W. Bowman1, Junjie Liu1, Alexandra G. Konings2, John R. Worden1, Nicholas C. Parazoo1, Victoria Meyer1, John T. Reager1, Helen M. Worden5, Zhe Jiang6, Gregory R. Quetin2, T. Luke Smallman3,4, Jean-François Exbrayat3,4, Yi Yin1, Sassan S. Saatchi1, Mathew Williams3,4, and David S. Schimel1 A. Anthony Bloom et al.
  • 1Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91101, USA
  • 2Department of Earth System Science, Stanford University, Stanford, CA 94305, USA
  • 3School of Geosciences, University of Edinburgh, Edinburgh, EH9 3FF, UK
  • 4National Centre for Earth Observation, Edinburgh EH9 3FF, UK
  • 5National Center for Atmospheric Research, Boulder, 80301 CO, USA
  • 6School of Earth and Space Sciences, University of Science and Technology of China, Hefei, 230026, China

Abstract. Inter-annual variations in the tropical land carbon (C) balance are a dominant component of the global atmospheric CO2 growth rate. Currently, the lack of quantitative knowledge on processes controlling net tropical ecosystems C balance on inter-annual timescales inhibits accurate understanding and projections of land-atmosphere C exchanges. In particular, uncertainty on the relative contribution of ecosystem C fluxes attributable to concurrent meteorological forcing anomalies (concurrent effects) and those attributable to the continuing influence of past phenomena (lagged effects) stifles efforts to explicitly understand the integrated sensitivity of tropical ecosystem to climatic variability. Here we present a conceptual framework – applicable in principle to any meteorology-forced land biosphere model – to explicitly quantify net biospheric exchange (NBE) as the sum of anomaly-induced concurrent changes and climatology-induced lagged changes to terrestrial ecosystem C states (NBE = NBECON + NBELAG). We apply this framework to an observation-constrained analysis of the 2010–2015 tropical C balance: we use a data-model integration approach (CARDAMOM) to merge satellite-retrieved land-surface C observations (leaf area, biomass, solar-induced fluorescence), soil C inventory data and satellite-based atmospheric inversion estimates of CO2 and CO fluxes to produce a data-constrained analysis of the 2010–2015 tropical C cycle. We find that the inter-annual variability of lagged effects explain the majority of NBE inter-annual variability (IAV) throughout 2010–2015 across the tropics (NBELAG IAV = 112 % of NBE IAV, r = 0.87) relative to concurrent effects (NBECON IAV = 54 % of total NBE IAV, r = 0.03) and the dominance of NBELAG IAV persists across both wet and dry tropical ecosystems. The magnitude of lagged effect variations on NBE across the tropics is largely attributable to lagged effects on net primary productivity (NPP; NPPLAG IAV 88 % of NBELAG IAV, r = −0.99, p-value < 0.05), which emerge due to the dependence of NPP on inter-annual variations in canopy C mass and plant-available water states. We conclude that concurrent and lagged effects need to be explicitly and jointly resolved to retrieve an accurate understanding the processes regulating the present-day and future trajectory of the terrestrial land C sink.

A. Anthony Bloom et al.

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Status: final response (author comments only)
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A. Anthony Bloom et al.

A. Anthony Bloom et al.


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Publications Copernicus
Short summary
We use a model of the 2010–2015 tropical land carbon cycle, with satellite measurements of land and atmospheric carbon, to disentangle lagged and concurrent effects (due to past and concurrent meteorological events, respectively) on annual land-atmosphere carbon exchanges. The variability of lagged effects explains most annual 2010–2015 carbon flux variations. We conclude that concurrent and lagged effects need to be accurately resolved to better predict the world's land carbon sink.
We use a model of the 2010–2015 tropical land carbon cycle, with satellite measurements of land...