Lagged effects regulate the inter-annual variability of the tropical carbon balance
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 ecosystem C balance on inter-annual timescales inhibits accurate understanding and p...
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Veröffentlicht in: | Biogeosciences 2020-12, Vol.17 (24), p.6393-6422 |
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Zusammenfassung: | 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 ecosystem 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 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 a tropical ecosystem to climatic variability. Here we present a conceptual
framework – applicable in principle to any 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 2001–2015 tropical C balance: we use
a data–model integration approach (CARbon DAta-MOdel fraMework – 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 2001–2015 tropical C cycle. We find that the inter-annual
variability of both concurrent and lagged effects substantially contributes to the 2001–2015 NBE inter-annual variability throughout 2001–2015 across
the tropics (NBECON IAV = 80 % of total NBE IAV, r = 0.76;
NBELAG IAV = 64 % of NBE IAV, r = 0.61), and the prominence 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
113 % of NBELAG IAV, r = −0.93, p value |
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ISSN: | 1726-4189 1726-4170 1726-4189 |
DOI: | 10.5194/bg-17-6393-2020 |