Lagged effects regulate the inter-annual variability of the tropical carbon balance
<p>Inter-annual variations in the tropical land carbon (C) balance are a dominant component of the global atmospheric CO<span class="inline-formula"><sub>2</sub></span> growth rate. Currently, the lack of quantitative knowledge on processes controlling net tro...
| Main Authors: | , , , , , , , , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2020-12-01
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| Series: | Biogeosciences |
| Online Access: | https://bg.copernicus.org/articles/17/6393/2020/bg-17-6393-2020.pdf |
| Summary: | <p>Inter-annual variations in the tropical land carbon (C) balance are a
dominant component of the global atmospheric CO<span class="inline-formula"><sub>2</sub></span> 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 <span class="inline-formula">=</span> NBE<span class="inline-formula"><sup>CON</sup>+NBE<sup>LAG</sup></span>). 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 CO<span class="inline-formula"><sub>2</sub></span> 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 (NBE<span class="inline-formula"><sup>CON</sup></span> IAV <span class="inline-formula">=</span> 80 % of total NBE IAV, <span class="inline-formula"><i>r</i></span> <span class="inline-formula">=</span> 0.76;
NBE<span class="inline-formula"><sup>LAG</sup></span> IAV <span class="inline-formula">=</span> 64 % of NBE IAV, <span class="inline-formula"><i>r</i></span> <span class="inline-formula">=</span> 0.61), and the prominence of NBE<span class="inline-formula"><sup>LAG</sup></span> 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; NPP<span class="inline-formula"><sup>LAG</sup></span> IAV
113 % of NBE<span class="inline-formula"><sup>LAG</sup></span> IAV, <span class="inline-formula"><i>r</i></span> <span class="inline-formula">=</span> <span class="inline-formula">−</span>0.93, <span class="inline-formula"><i>p</i></span> value < 0.05), which emerge due to the dependence of NPP on inter-annual variations in foliar C and
plant-available H<span class="inline-formula"><sub>2</sub></span>O states. We conclude that concurrent and lagged
effects need to be explicitly and jointly resolved to retrieve an accurate
understanding of the processes regulating the present-day and future trajectory of the terrestrial land C sink.</p> |
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| ISSN: | 1726-4170 1726-4189 |