ASICA

Finding the Balance: Climate Change, Carbon Cycling and the Amazon The Amazon region holds great interest to climate scientists, because large amounts of CO2 enter and exit the atmosphere here, with strong impacts on the climate system.

Now researchers in the ASICA project aim to gain a more precise understanding of the extent of CO2 uptake by the Amazon rainforest, as Professor Wouter Peters explains The Amazonian region

has been affected by a number of serious droughts since the turn of the century, which affected the amount of CO2 that the rainforest removed from the atmosphere. Normally, the Amazon region acts as a net sink of carbon, as Professor Wouter Peters explains. “In normal years the Amazon rainforest takes up a lot of CO2 through photosynthesis, as it’s an extremely large, green area with a lot of plants, yet it also releases a lot of CO2 mainly through wildfires.

Overall, it removes a little bit of CO2 from the atmosphere,” he outlines. However, the region experienced serious droughts in both 2005 and 2010, and 2015 as well, which proved highly disruptive in these terms. “In 2010 we saw that the influence of the drought on vegetation was really turning the Amazon from what is normally a sink of CO2 to being a source of CO2,” says Professor Peters.

This holds significant implications in terms of our understanding of the climate and how it is likely to evolve in future. While it is thought the Amazon region has been acting as a carbon sink for a fairly long period, the records in this area only extend back around 10- 15 years; now researchers in the ASICA project are gathering more atmospheric data. “We’re collecting air samples from light aircraft flying over the area,” explains Professor Peters, ASICA’s Principal Investigator. These samples are quite wellmixed. “Motion in the atmosphere has brought signals from the surface into a very deep layer of the atmosphere,” says Professor Peters. “So we’re not just measuring at the leaf, or over the head of the individual tree – we’re really sampling a very large area. We call this the integrating capacity of aircraft measurements.”

measurements, to measure different processes going on inside trees and leaves,” he says. The challenge is to build a deeper understanding of what’s happening on those scales and connect it with the wider picture in the Amazon as a whole.

“The idea is that the behaviour of this one large area, of a million square kilometres, is in the end what drives CO2 in terms of climate. This is the climate signal that we need to understand and to simulate,” continues Professor Peters.

This is a complex challenge, even in areas

challenging work. “There’s not a lot of CO2 in this air to begin with. In this programme we specifically try to measure the stable isotopes of CO2 – 13C, 17O and 18O – which are much, much less abundant,” says Professor Peters.

These isotopes are also very tricky to handle. They’re a little heavier than normal CO2, which means that they tend to stick to things, so Professor Peters says a lot of care is required when collecting the samples. “You have to be really careful when collecting this

In normal years the Amazon rainforest takes up a lot of CO2 through photosynthesis, as it’s an extremely large, green area with a lot of plants, yet it also releases a lot of CO2.

Overall, it removes a little bit of CO2 from the atmosphere where there are well-established atmospheric monitoring networks. ASICA is playing a pioneering role in this respect, with light aircraft used in the project to gather samples at different altitudes, up to around 6,000 metres. “There is a micro-computer on the aircraft, which we have programmed in the lab to fill twelve flasks at different levels in the atmosphere,” outlines Professor Peters.

The pilot follows a pre-programmed schedule, gathering samples from different altitudes, which are then sent to a laboratory in Brazil for measurement and analysis; this is technically

air to make sure that you don’t come into contact with certain surfaces like liquid water, and that you don’t have pressure gradients,” he explains. It is also important to consider the overall composition of the air samples when looking to measure stable isotopes.

“One of the biggest challenges we’ve been able to solve in this programme is getting rid of water vapour, which is very abundant in the tropical atmosphere. It completely destroys the signature of the oxygen isotopes that we’re interested in, the 17O and 18O isotopes in the CO2 molecule,” continues Professor Peters.

The exchange of CO₂ and its stable isotopes during uptake by leafs. When passing through small openings called ‘stomata’ the ratio of 13C, 18O, and 17O in CO₂ change by a measurable amount. ASICA aims to measure and use this signal to estimate photosynthesis over the rain forest.

Data gathering The data itself is being gathered from four sites across the Amazon region. This data is complemented by ground-based measurements, from which Professor Peters and his colleagues in the project can then look to build a more complete picture. “People on the ground are looking at specific eco-systems, or plots of trees. They’ve been monitoring them over long periods and doing very intricate

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EU Research

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

Project Objectives

View of the Madeira river shortly after take off for a CO₂ sampling flight over the Amazon rain forest.

Flasks with dry air collected during this flight are analyzed for stable isotopes in the ASICA program.

CO2 uptake The approach to measuring 13C in CO2 is by contrast much more established, and researchers have been able to gather a lot of data over the course of the project. This provides the foundations for Professor Peters and his colleagues to investigate wider questions. “Some of our staff in the project are dedicated to modelling, numerical modelling analysis, and trying to understand what our measurements mean for CO2 uptake over the Amazon rainforest,” he says. Researchers are looking at two main questions in particular.

“The first is, how large is the carbon uptake by the Amazon rainforest? This means the oneway uptake – the gross primary production (GPP), all the CO2 that is removed through photosynthesis,” outlines Professor Peters.

The second question is – how does that number change during serious droughts?”

The problem in addressing these questions is that the one-way flux of CO2, effectively how much goes into the forest through photosynthesis, is almost completely balanced by how much comes out again. However, once this exchange has happened there is a change in the amount of 13C in CO2 in the atmosphere, from which new insights can be drawn. “The plants that take up CO2 have a preference for the lighter isotope – 12C – over 13C. So that means that after you’ve had a lot of exchange there’s a bit more of the heavier molecule – 13 C – in the atmosphere. That’s a signal we are trying to measure,” says Professor Peters.

A more detailed understanding of these processes and the overall CO2 uptake over the Amazon could help to inform the ongoing development of climate models, underlining the wider relevance of the project’s work. Alongside providing rigorous figures for the uptake of CO2 over the Amazon region, Professor Peters also hopes to gain new insights into the underlying processes behind these figures. “Those will

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be the main results of the ASICA programme, acting as atmospheric constraints on the exchange of CO2 from the Amazon,” he says.

“With the project infrastructure in place and the data-gathering practices now fairly wellestablished, we’re starting to focus more on numerical analysis and interpretation,” he says.

Further data will still be gathered over the remainder of the project however, and looking further forward Professor Peters believes that it’s important to continue taking these measurements beyond the end of the ASICA Funding Term. It is predicted that the Amazon region will change dramatically in future due to the impact of climate change, so Professor Peters says it’s essential to carry on gathering data.

“We only have one chance to measure things – you can always model and analyse them again afterwards,” he points out. “Future modellers are going to be looking for historical data about this area, to see how it’s changed over time. That’s what we’re gathering now.”

Staff at the LaGee lab in Brazil receive training on isotope measurements using laser spectroscopy. With this technique, ASICA researchers have made the first ever measurements of C17OO/C18OO ratios over the tropical rain forest.

Severe droughts in Amazonia in 2005 and 2010 caused widespread loss of carbon from the terrestrial biosphere. This loss, almost twice the annual fossil fuel CO2 emissions in the EU, suggests a large sensitivity of the Amazonian carbon balance to a predicted more intense drought regime in the next decades. This is a dangerous inference though, as there is no scientific consensus on the most basic metrics of Amazonian carbon exchange: the gross primary production (GPP) and its response to moisture deficits in the soil and atmosphere.

Measuring them on scales that span the whole Amazon forest was thus far impossible, but in this project we aim to deliver the first observation-based estimate of pan-Amazonian GPP and its drought induced variations.

Project Funding

EU contribution: EUR 2,275,993

Project Partners

• WAGENINGEN UNIVERSITY, Netherlands • UNIVERSITEIT UTRECHT, Netherlands • RIJKSUNIVERSITEIT GRONINGEN, Netherlands • UNIVERSITY OF LEEDS, United Kingdom • INSTITUTO NACIONAL DE PESQUISAS ESPACIAIS, Brazil

Contact Details

Professor Wouter Peters Department of Meteorology and Air Quality Environmental Sciences Group Wageningen University, The Netherlands & Centre for Isotope Research Energy and Sustainability Research Institute Wageningen Wageningen University, Droevendaalsesteeg 4 6708 PB Wageningen The Netherlands T: +31 (0)317 486654 E: Wouter.Peters@wur.nl W: http://www.asica.eu

Professor Wouter Peters

Professor Wouter Peters investigates the rising levels of carbon dioxide in our atmosphere. His research combines measurements of greenhouse gases and their isotopic composition with powerful computer models of weather, and climate. His current research focuses on the rapidly changing carbon cycle of the Amazon rain forest.

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