ICOS Science Conference 2022: Day 3, Session 22

1. 1
Isotopologue Flux Measurements
in the Amazon Rainforest
Constraining the land-Atmosphere exchange of H2O and CO2
using flux measurements of stable isotopologues

2. Land Atmosphere exchange
Radiative and turbulent
1. Driven by solar radiation
2. Gradients in atmospheric surface layer
3. Turbulent exchange due to buoyancy
4. Governed by many processes at surface
Seems to be well understood;
What is the issue?

3. Problems:
Complexity
3
• Non – linear processes
• Interdependent (error accumulation)
• Feedbacks (clouds)
• Superpositions  need partitioning
CloudRoots Philosophy:
Describe processes and turbulent
exchange at small spatial and
temporal resolutions with advanced
in situ measurements and modelling.

4. Amazon Rainforrest
The facts;
4
CO2
• Biosphere is main sink & source of atmospheric CO2
• Amazon Rainforest is key contributor
H2O
• Precipitation up to 3600 mm year-1 locally
• Forrest recycles rain water
General
• ~400 billion trees
• 50 % of all earths rainforest

5. Stable isotopologues
What can we learn?
5
• Natural tracers in
exchange processes
• Fractionation (Change in Ratio)
• Evaporation fractionation:
• 18O equilibrates in stomata between
CO2 and H2O
18

6. 6
Received
intensity
Laser wavenumber [k]
1. Air
2. Laser
3. Detector
13CO2
12CO2 C18OO
C17OO
Laser spectrometer
Workings
CO2
Aerodyne TILDAS-CS
H2O:
Picarro L2130-i (flight)

7. Measurement setup
On ATTO tower
7
• Micromet & high-frequency laser spectrometry
• Heated, turbulent & short inlet
 no exchange & independent samples
• Isotopic composition & fluxes
 Smaller footprint
 Source composition
 Allows for partitioning to gross fluxes
• CloudRoots:
Integrated measurements at soil and leaf level,
radiation, boundary layer etc.

8. Operation
of laser spectrometers
• Lab instruments
• Harsh climate for
any device
 Enclosure for
instruments and
calibration systems
Enclosures provide:
Weatherproofing
Active drying
CO2 free air (for CO2 instrument)
Temperature stabilization

9. 9
• 𝜹 - values: 𝜹𝑫 = [
𝑫
𝑯 𝒔𝒂𝒎𝒑𝒍𝒆
𝑫
𝑯 𝒔𝒕𝒂𝒏𝒅𝒂𝒓𝒅
− 𝟏]
• Standard iso-fluxes: 𝐰′𝛿𝐃′ = 𝐹𝛿𝐃[
‰𝐦
𝐬
]
• Composition of flux:
𝐰′𝒒−𝑫𝑯𝑶′
𝐰′𝐪−𝐇𝟐𝐎′
∗
𝑴𝑯𝟐𝑶
𝑴𝑫𝑯𝑶
=
𝑫
𝑯 𝒔𝒐𝒖𝒓𝒄𝒆
Other definition: 𝛿𝐹 =
𝐼∗𝐶𝑎
𝐹
+ 𝛿𝑎
Isotope and isoflux equations
Atmosphere
𝜹 – Value
Biosphere
𝜹 – Value
Exchange
“Flux”

10. Calibration
Laser spectrometers
Mole fraction Calibration
Aerodyne CO2 isotope monitor
Span Calibration
Picarro H2O isotope monitor

11. Timeseries
H2O isotopologues
• Daytime turbulence
• Boundary layer
effects  dry / wet

12. Flux overview
Isotope analysers
• Exchange fluxes
match EC
• Still; net fluxes

13. Cospectra
Usefull tool
• Spectral shapes overlap well
• No high frequency signal loss

14. Fluxes
And related gradients
• Large fluxes during
daytime
• CO2 uptake, enriching
ambient air in 𝜹13C

15. Source composition
Of H2O flux
• Sources enriched due to
evaporation
fractionation
• Value similar to root water
• Gradient in e.g. 𝜹18O

16. Further analysis
16
1. Lab analysis of the isotopic composition of leaf, soil & air samples
 Allows for partitioning when combined with isotope fluxes.
2. Minute scale isotope fluxes using scintillometer (path integrated flux)
3. Integration of isotope effects and fluxes in column and LES models

17. The end
17
Thanks for your attention,
And the regards of the Amazonian locals!
Thanks to:
• INPA, Max Planck Jena &
Max Planck Mains for
allowing us to make use of
their facilities.
• Max planck Jena team for
scientific support
• ATTO tower employees for
extensive practical support
and keeping us alive.