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- Title
Lagged effects dominate the inter-annual variability of the 2010-2015 tropical carbon balance.
- Authors
Bloom, A. Anthony; Bowman, Kevin W.; Junjie Liu; Konings, Alexandra G.; Worden, John R.; Parazoo, Nicholas C.; Meyer, Victoria; Reager, John T.; Worden, Helen M.; Zhe Jiang; Quetin, Gregory R.; Smallman, T. Luke; Exbrayat, Jean-François; Yi Yin; Saatchi, Sassan S.; Williams, Mathew; Schimel, David S.
- Abstract
nter-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.
- Subjects
ATMOSPHERIC carbon dioxide; WATER masses; LEAF area; BIOMASS; CARBON; BIOSPHERE
- Publication
Biogeosciences Discussions, 2020, p1
- ISSN
1810-6277
- Publication type
Article
- DOI
10.5194/bg-2019-459