New constraints on the Amazonian carbon balance from airborne observations of the stable isotopes of CO2

Project Information

ASICA

Grant agreement ID: 649087

DOI

10.3030/649087

Project closed

EC signature date 13 July 2015

Start date 1 September 2015

End date 28 February 2021

Funded under

• EXCELLENT SCIENCE - European Research Council (ERC)

Total cost

€ 2 269 688,76

EU contribution

€ 2 269 688,76

Coordinated by

WAGENINGEN UNIVERSITY
Netherlands

Periodic Reporting for period 4 - ASICA (New constraints on the Amazonian carbon balance from airborne observations of the stable isotopes of CO2)

Reporting period: 2020-03-01 to 2021-02-28

Summary of the context and overall objectives of the project

The ASICA project aimed to better understand the carbon cycle of the Amazon rain forest. Thereto, air samples were gathered from light aircraft flying over the rain forest. These air samples were subsequently transported to a laboratory in Sao Jose de Campos, run by co-PI Luciana Gatti and her team. In this lab we measured the concentrations of CO2, CH₄, N2O, CO, and H2 in the air that was collected. Through ASICA, we also measured the stable isotopes of CO2 on these samples: δ¹³C, δ18O, and Δ17O. To make these very difficult measurements possible was one of the main challenges for ASICA. But the program also built a long-term record of these compounds from a network of sites, and analyzed them together to make major discoveries:

(1) We found that the Amazon rain forest has decreased capacity to sequester CO2 from the atmosphere, especially in the regions that are subject to deforestation and rapid warming
(2) We found that the Amazon rain forest responded strongly to the El Nino drought of 2015/2016 with reduced photosynthesis for multiple months, and followed by a secondary lapse in carbon uptake 9 months later
(3) We used a completely new method in the laboratory to understand how plants respond to drought, and what the role is of various stages between the plant opening (stoma) and the enzymes that convert CO2 to sugars

These results are relevant beyond scientific interest, because this large forest provides very important services to society not just in terms of products (wood, food, medicine, etc) but also as a source of water to the area (though evaporation, precipitation, and rivers) and as a sink of carbon dioxide. The continued existence of this carbon dioxide sink is now questioned, and our data can help constrain current climate models that disagree whether ongoing warming will turn the area into a source of CO2 or not.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

ASICA results have led to a number of major research outputs including two completed PhD theses, four published papers, three submitted manuscripts, and one article in production for Nature. These papers document many of the goals of the Action that have been reached successfully:

An accepted paper in Nature, led by INPE PI Luciana Gatti (ASICA) on the analysis of long-term CO2 records from our flasks: Gatti et al., Amazonia as a carbon source linked to deforestation and climate change, Nature, 2021, in press

- To complete this paper we had to continue the measurements from four air strips for another five years, adding the period 2016-2021 to the existing 2010-2015 record. Analysis was done jointly with the full team

A published paper in Nature Geosciences: Peters, W. et al. Increased water-use efficiency and reduced CO2 uptake by plants during droughts at a continental scale. Nature Geoscience 19, 1 (2018).

- This paper resulted from our investments in δ¹³C inverse modeling, supported by ASICA.

The paper on mechanisms of drought-stress during the ENSO of 2015/2016: Schaik, E. van et al. Changes in surface hydrology, soil moisture and gross primary production in the Amazon during the 2015/2016 El Niño. Philosophical Transactions Of The Royal Society Of London Series B-Biological Sciences 373, 20180084 (2018).

- This paper resulted from our work on biosphere modeling as well as hydrological modeling for the basin, done to better understand isotopic exchange and the carbon balance of the region.

The paper from Dipayan Paul (ASICA) describing the ASICA dryer that we developed under this Action: Paul, D. et al. Evaluation of a field-deployable NafionTM-based air-drying system for collecting whole air samples and its application to stable isotope measurements of CO2. Atmospheric Measurement Techniques 13, 4051–4064 (2020).

- This paper was a major achievement and a milestone in the project, as we indicated already before the action that the capacity to dry very wet tropical air would be key to our success

A publication by Erik van Schaik (ASICA) describing a new retrieval method for sun-induced fluorescence suitable for tropical environments like the Amazon: Schaik, E. van et al. Improved SIFTER v2 algorithm for long-term GOME-2A satellite retrievals of fluorescence with a correction for instrument degradation. Atmospheric Measurement Techniques 13, 4295–4315 (2020).

- The spin-off to look into SIF retrievals came by when we realized this dataset might hold new clues to the photosynthesis response of vegetation during the ENSO drought of 2015/2016. A specific tropical retrieval (accounting for high water vapor) was needed though. The resulting dataset is freely downloadable for everyone.

A paper by Getachew Adnew (ASICA) on plant experiments with the UU-built Δ17O instrument: Adnew, G. A., Pons, T. L., Koren, G., Peters, W. & Röckmann, T. Leaf-scale quantification of the effect of photosynthetic gas exchange on Δ17O of atmospheric CO2. Biogeosciences 17, 3903–3922 (2020).

- This paper could not have been possible without the investments in high-precision measurement techniques that we did in ASICA.

A paper by Koren et al (2018): Widespread reduction in sun-induced fluorescence from the Amazon during the 2015/2016 El Niño. Philosophical Transactions Of The Royal Society Of London Series B-Biological Sciences 373, 20170408 (2018).

- This paper uniquely describes the ENSO impact on Amazon rain forest photosynthesis as documented through SIF and hydrological modeling

A submitted paper by Getachew Adnew (ASICA) on the determination of leaf conductance from Δ17O: Adnew et al., Exploring the use of 17O-excess of CO2 for estimating mesophyll conductance of C3 and C4 plants, submitted to Plant Physiology, (2021)

- This paper tried a breakthrough method to use 17O (instead of 18O or 13C) to measure leaf-conductance in plants. The plan to do this was suggested in our Action, and the covid-19 extension allowed us to complete the manuscript and submit it.

A paper in preparation by Gerbrand Koren (ASICA) on the legacy drought of 2016 detected from ASICA measurements: Koren et al., “Persistent impact of the 2015/16 El Nino drought on the 2016 dry season in the Amazon”, (2021)

- This paper identifies a so-far undetected secondary drought that followed the ENSO of 2015/2016, and in fact constitutes a carry-over from that drought through soil moisture deficits that persist. It resulted from our previous investments in modeling of this region, and in the unique record of CO2 that we now also publsihed in Nature.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

The project strongly advanced the state-of-the-art in the following ways:

(1) Our CO2 record (and isotopes) has doubled the number of years in the Amazon that can be studied, and allowed the first decadal assessment of its net carbon uptake. This has allowed a first assessment of its decline due to warming and droughts, and shows a decline that certainly is a breakthrough in our view of this system.
(2) Our records recorded an El-Nino induced drought, and a never-seen-before "legacy" drought and described the mechanisms by which they affected vegetation carbon exchange. These are breakthrough because they create the first (and only) target for climate models to reproduce.
(3) We set new standards for measuring 17O in CO2, partly through building an innovative dryer system for (tropical) wet air. We expect future projects to follow our examples in building this capacity. The establishment of isotope analysis capacity in Brazil/South America is also a breakthrough in my opinion.

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