Abstract
The tropical carbon balance dominates year-to-year variations in the CO2 exchange with the atmosphere through photosynthesis, respiration and fires. Because of its high correlation with gross primary productivity (GPP), observations of sun-induced fluorescence (SIF) are of great interest. We developed a new remotely sensed SIF product with improved signal-to-noise in the tropics, and use it here to quantify the impact of the 2015/2016 El Niño Amazon drought. We find that SIF was strongly suppressed over areas with anomalously high temperatures and decreased levels of water in the soil. SIF went below its climatological range starting from the end of the 2015 dry season (October) and returned to normal levels by February 2016 when atmospheric conditions returned to normal, but well before the end of anomalously low precipitation that persisted through June 2016. Impacts were not uniform across the Amazon basin, with the eastern part experiencing much larger (10–15%) SIF reductions than the western part of the basin (2–5%). We estimate the integrated loss of GPP relative to eight previous years to be 0.34–0.48 PgC in the three-month period October–November–December 2015.This article is part of a discussion meeting issue ‘The impact of the 2015/2016 El Niño on the terrestrial tropical carbon cycle: patterns, mechanisms and implications’.
Highlights
Variations in the annual atmospheric increase of CO2 in the atmosphere are dominated by carbon exchange in the tropical regions [1,2,3,4,5]
Our results demonstrate the substantial impact of the 2015/ 2016 El Nino on gross primary productivity (GPP) of the Amazon basin, but we caution against a direct extrapolation of the impact on the net carbon balance
This would mean that a sun-induced fluorescence (SIF)-based GPP anomaly would not directly translate to a carbon balance anomaly in vegetation, and that expected relations between environmental drivers (T, VPD, soil moisture, fPAR) and GPP would change during droughts
Summary
Variations in the annual atmospheric increase of CO2 in the atmosphere (the so-called growth rate of CO2) are dominated by carbon exchange in the tropical regions [1,2,3,4,5]. The CO2 growth rate variations, in turn, correlate strongly with tropical temperature and precipitation anomalies [7]. Years with higher than average temperatures and lower than average precipitation over tropical land areas have led to the highest annual increases of atmospheric CO2 on record. This was used by Cox et al [8] to calculate a climate sensitivity for tropical net ecosystem exchange (NEE), which can tentatively inform us on climate impacts over longer time scales, if the controlling mechanisms turn out to be the same.
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