Amazonia as a carbon source linked to deforestation and climate change

Amazonia hosts the Earth's largest tropical forests and has been shown to be an important carbon sink over recent decades1-3. This carbon sink seems to be in decline, however, as a result of factors such as deforestation and climate change1-3. Here we investigate Amazonia's carbon budget and the main drivers responsible for its change into a carbon source. We performed 590 aircraft vertical profiling measurements of lower-tropospheric concentrations of carbon dioxide and carbon monoxide at four sites in Amazonia from 2010 to 20184. We find that total carbon emissions are greater in eastern Amazonia than in the western part, mostly as a result of spatial differences in carbon-monoxide-derived fire emissions. Southeastern Amazonia, in particular, acts as a net carbon source (total carbon flux minus fire emissions) to the atmosphere. Over the past 40 years, eastern Amazonia has been subjected to more deforestation, warming and moisture stress than the western part, especially during the dry season, with the southeast experiencing the strongest trends5-9. We explore the effect of climate change and deforestation trends on carbon emissions at our study sites, and find that the intensification of the dry season and an increase in deforestation seem to promote ecosystem stress, increase in fire occurrence, and higher carbon emissions in the eastern Amazon. This is in line with recent studies that indicate an increase in tree mortality and a reduction in photosynthesis as a result of climatic changes across Amazonia1,10.</p

Amazonia as a carbon source linked to deforestation and climate change

Amazonia hosts the Earth’s largest tropical forests and has been shown to be an important carbon sink over recent decades1,2,3. This carbon sink seems to be in decline, however, as a result of factors such as deforestation and climate change1,2,3. Here we investigate Amazonia’s carbon budget and the main drivers responsible for its change into a carbon source. We performed 590 aircraft vertical profiling measurements of lower-tropospheric concentrations of carbon dioxide and carbon monoxide at four sites in Amazonia from 2010 to 20184. We find that total carbon emissions are greater in eastern Amazonia than in the western part, mostly as a result of spatial differences in carbon-monoxide-derived fire emissions. Southeastern Amazonia, in particular, acts as a net carbon source (total carbon flux minus fire emissions) to the atmosphere. Over the past 40 years, eastern Amazonia has been subjected to more deforestation, warming and moisture stress than the western part, especially during the dry season, with the southeast experiencing the strongest trends5,6,7,8,9. We explore the effect of climate change and deforestation trends on carbon emissions at our study sites, and find that the intensification of the dry season and an increase in deforestation seem to promote ecosystem stress, increase in fire occurrence, and higher carbon emissions in the eastern Amazon. This is in line with recent studies that indicate an increase in tree mortality and a reduction in photosynthesis as a result of climatic changes across Amazonia1,10

CO2 emissions in the Amazon: are bottom-up estimates from land use and cover datasets consistent with top-down estimates based on atmospheric measurements?

Amazon forests are the largest forests in the tropics and play a fundamental role for regional and global ecosystem service provision. However, they are under threat primarily from deforestation. Amazonia's carbon balance trend reflects the condition of its forests. There are different approaches to estimate large-scale carbon balances, including top-down (e.g., CO2 atmospheric measurements combined with atmospheric transport information) and bottom-up (e.g., land use and cover change (LUCC) data based on remote sensing methods). It is important to understand their similarities and differences. Here we provide bottom-up LUCC estimates and determine to what extent they are consistent with recent top-down flux estimates during 2010 to 2018 for the Brazilian Amazon. We combine LUCC datasets resulting in annual LUCC maps from 2010 to 2018 with emissions and removals for each LUCC, and compare the resulting CO2 estimates with top-down estimates based on atmospheric measurements. We take into account forest carbon stock maps for estimating loss processes, and carbon uptake of regenerating and mature forests. In the bottom-up approach total CO2 emissions (2010 to 2018), deforestation and degradation are the largest contributing processes accounting for 58% (4.3 PgCO2) and 37% (2.7 PgCO2) respectively. Looking at the total carbon uptake, primary forests play a dominant role accounting for 79% (−5.9 PgCO2) and secondary forest growth for 17% (−1.2 PgCO2). Overall, according to our bottom-up estimates the Brazilian Amazon is a carbon sink until 2014 and a source from 2015 to 2018. In contrast according to the top-down approach the Brazilian Amazon is a source during the entire period. Both approaches estimate largest emissions in 2016. During the period where flux signs are the same (2015–2018) top-down estimates are approximately 3 times larger in 2015–2016 than bottom-up estimates while in 2017–2018 there is closer agreement. There is some agreement between the approaches–notably that the Brazilian Amazon has been a source during 2015–2018 however there are also disagreements. Generally, emissions estimated by the bottom-up approach tend to be lower. Understanding the differences will help improve both approaches and our understanding of the Amazon carbon cycle under human pressure and climate change

CO2 Vertical Profiles on Four Sites over Amazon from 2019 to 2020

To improve diagnosis of Amazonia's carbon cycle, we present a 2 year data (2019 to 2020), complementary to our previosly 9 years (2010 to 2018) observations of lower troposphere CO2 concentrations performed regularly at four aircraft vertical profiling sites spread over the Brazilian Amazonia (Gatti et al., 2021). The four sites from the CARBAM project at Amazonia: SAN (2.86S 54.95W); ALF (8.80S 56.75W); RBA (9.38S 67.62W) and TEF (3.39S 65.6W), started in 2013. The sampling period was typically twice per month (Gatti et al., 2021; Gatti et al., 2014; Basso et al., 2016; Miller et al., 2007; d'Amelio et al., 2009; Domingues et al., 2020). From 2019 to 2020, a total of 141 vertical profiles from 4420 m to 300 m asl. was performed at the 4 sites. The vertical profiles were usually taken between 12:00 and 13:00 local time. Air is sampled by semi-automatic filling of 0.7 L boro-silicate flasks inside purpose-built suitcases (PFP -Programmable Flask Package) (Tans et al., 1996); there are two versions, one with 17 flasks at SAN, and another with 12 flasks at TEF, ALF and RBA. This suitcase is connected to a compressor package (PCP –Portable Compressor Package), containing batteries and 2 compressors, which is connected to an air inlet on the outside of the aircraft at wing or window, depending on the aircraft model. Once a PFP (i.e. one vertical profile) has been filled with air the PFP is transported to the INPE/ LaGEE(Instituto Nacional de Pesquisas Espaciais/Greenhouse Gases Laboratory), in Sao Jose dos Campos, Sao Paulo state, Brazil. This laboratory is a replica of the NOAA/ESRL/GMD trace gas analysis system at Boulder, Colorado, USA, and was constructed in 2003 and sent to IPEN where started the analysis in 2004.Air samples were analysed with a non-dispersive infrared (NDIR) analyser for CO2. To ensure the accuracy, we construct a calibration curve every 2 samples. The calibration curve constructed with 3-standards concentrations, produced by NOAA/ESRL/GMD. The “High” (10 ppm higher than medium), “medium” (similar to mean CO2 concentration founded in Amazonia), and “Low” (10 ppm lower than medium). We have an intercomparison program with NOAA at Natal site (5S, 35W, located at Brazilian northeast coast) where the comparison IPEN/INPE-NOAA was -0.05 ± 0.38ppm. The precision is analysed based on CO2mole fraction from “target tanks” (calibrated CO2in air in high pressure cylinders treated as unknowns by NOAA) and demonstrated long-term repeatability of 0.03ppm and a difference between measured and calibrated values of 0.03 ppm. Additional information can be shared from the LaGEE/INPE group as temperature, precipitation, and others parameters used by the group for the Nature paper entitled “Decrease in Amazonia carbon uptake linked to trends in deforestation and climate” (Gatti et al, 2021)

CH4 Aircraft Vertical Profiles Measurements at Four Amazonian Sites Between 2010 and 2018

To improve diagnosis of Amazonia's carbon cycle, starting in 2010, we initiated regular observation of lower troposphere CH4 concentrations at four aircraft vertical profiling sites spread over the Brazilian Amazonia. The four sites from the CARBAM project at Amazonia: SAN (2.86S 54.95W); ALF (8.80S 56.75W); RBA (9.38S 67.62W); TAB (5.96S 70.06W) was from 2010 to 2012 and TEF (3.39S 65.6W), started in 2013. The sampling period was typically twice per month (Gatti et al., 2014; Basso et al., 2016; Miller et al., 2007; d'Amelio et al., 2009; Domingues et al., 2020). Over nine-years, 590 vertical profiles were performed in a descending spiral profile from 4420 m to 300 m a.s.l. A mean of 75 vertical profiles was performed per year from 2010 to 2018 at the 4 sites, except for 2015 and 2016. In 2015 the flight collection was stopped in April at all sites, returning only in November at RBA. In 2016 only RBA and ALF were measured. The vertical profiles were usually taken between 12:0 and 13:00 local time. Air is sampled by semi-automatic filling of 0.7 L boro-silicate flasks inside purpose-built suitcases (PFP -Programmable Flask Package) (Tans et al., 1996); there are two versions, one with 17 flasks at SAN, and another with 12 flasks at TAB_TEF, ALF and RBA. This suitcase is connected to a compressor package (PCP –Portable Compressor Package), containing batteries and 2 compressors, which is connected to an air inlet on the outside of the aircraft at wing or window, depending on the aircraft model. Once a PFP (i.e. one vertical profile) has been filled with air the PFP is transported (from 2010 to 2014) to the IPEN (Instituto de Pesquisas Energéticas e Nucleares) Atmospheric Chemistry Laboratory in Sao Paulo, Brazil and since 2015 to the INPE/ LaGEE(Instituto Nacional de Pesquisas Espaciais/Greenhouse Gases Laboratory), in Sao Jose dos Campos, Sao Paulo state, Brazil. This laboratory is a replica of the NOAA/ESRL/GMD trace gas analysis system at Boulder, Colorado, USA, and was constructed in 2003 and sent to IPEN where started the analysis in 2004. The CH 4 analysis system is an FID (Flame Ionization Detector) chromatography (HP6890 Plus+ model) with pre-column of 198 cm of length and 3/16” o.d. (Silica Gel 80/100 mesh), a column of 106 cm of length and 3/16” o.d. (Molecular Sieve 5A 80/100 mesh), and a 12 mL volume sample loop (see Basso et al. 2016 for a detailed description). In order to assess the accuracy and long-term repeatability of the CH4 measurements, a previously calibrated sample is measured as an unknown in the system regularly. These results indicate long-term repeatability (one sigma) of 1.0 ppb. An inter-comparison between INPE and NOAA of weekly measurements at NAT (Brazilian northeast coast site) had a mean difference of 0.24±2.67 ppb (r = 0.98)

CO2 Vertical Profiles on Four Sites over Amazon from 2010 to 2018

To improve diagnosis of Amazonia's carbon cycle, starting in 2010, we initiated regular observation of lower troposphere CO2 concentrations at four aircraft vertical profiling sites spread over the Brazilian Amazonia. The four sites from the CARBAM project at Amazonia: SAN (2.86S 54.95W); ALF (8.80S 56.75W); RBA (9.38S 67.62W); TAB (5.96S 70.06W) was from 2010 to 2012 and TEF (3.39S 65.6W), started in 2013. The sampling period was typically twice per month (Gatti et al., 2014; Basso et al., 2016; Miller et al., 2007; d'Amelio et al., 2009; Domingues et al., 2020). Over nine-years, 590 vertical profiles were performed in a descending spiral profile from 4420 m to 300 m a.s.l. A mean of 75 vertical profiles was performed per year from 2010 to 2018 at the 4 sites, except for 2015 and 2016. In 2015 the flight collection was stopped in April at all sites, returning only in November at RBA. In 2016 only RBA and ALF were measured. The vertical profiles were usually taken between 12:0 and 13:00 local time. Air is sampled by semi-automatic filling of 0.7 L boro-silicate flasks inside purpose-built suitcases (PFP -Programmable Flask Package) (Tans et al., 1996); there are two versions, one with 17flasks at SAN, and another with 12 flasks at TAB_TEF, ALF and RBA. This suitcase is connected to a compressor package (PCP –Portable Compressor Package), containing batteries and 2 compressors, which is connected to an air inlet on the outside of the aircraft at wing or window, depending on the aircraft model. Once a PFP (i.e. one vertical profile) has been filled with air the PFP is transported (from 2010 to 2014) to the IPEN (Instituto de Pesquisas Energéticas e Nucleares) Atmospheric Chemistry Laboratory in Sao Paulo, Brazil and since 2015 to the INPE/ LaGEE(Instituto Nacional de Pesquisas Espaciais/Greenhouse Gases Laboratory), in Sao Jose dos Campos, Sao Paulo state, Brazil. This laboratory is a replica of the NOAA/ESRL/GMD trace gas analysis system at Boulder, Colorado, USA, and was constructed in 2003 and sent to IPEN where started the analysis in 2004.Air samples were analysed with a non-dispersive infrared (NDIR) analyser for CO2. To ensure the accuracy, we construct a calibration curve every 2 samples. The calibration curve constructed with 3-standards concentrations, produced by NOAA/ESRL/GMD. The “High” (10 ppm higher than medium), “medium” (similar to mean CO2 concentration founded in Amazonia), and “Low” (10 ppm lower than medium). We have an intercomparison program with NOAA at Natal site (5S, 35W, located at Brazilian northeast coast) where the comparison IPEN/INPE-NOAA was -0.05 ± 0.38ppm. The precision is analysed based on CO2mole fraction from “target tanks” (calibrated CO2in air in high pressure cylinders treated as unknowns by NOAA) and demonstrated long-term repeatability of 0.03ppm and a difference between measured and calibrated values of 0.03 ppm. Additional information can be shared from the LaGEE/INPE group as temperature, precipitation, and others parameters used by the group for the Nature paper entitled “Decrease in Amazonia carbon uptake linked to trends in deforestation and climate” (Gatti et al, 2021)