Koren, Gerbrand: Resolving the diurnal cycle of Δ¹⁷O in CO₂ at the ecosystem level: Simulations and observations at the mid-latitude pine forest Loobos
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Similaire à Koren, Gerbrand: Resolving the diurnal cycle of Δ¹⁷O in CO₂ at the ecosystem level: Simulations and observations at the mid-latitude pine forest Loobos
Similaire à Koren, Gerbrand: Resolving the diurnal cycle of Δ¹⁷O in CO₂ at the ecosystem level: Simulations and observations at the mid-latitude pine forest Loobos (20)
Koren, Gerbrand: Resolving the diurnal cycle of Δ¹⁷O in CO₂ at the ecosystem level: Simulations and observations at the mid-latitude pine forest Loobos
1. Resolving the diurnal cycle of Δ17O in CO2 at the ecosystem level:
Simulations and observations at the mid-latitude pine forest Loobos
Tea Talk, 20 Feb 2020
Gerbrand Koren, Getachew A. Adnew, Jordi Vilà-Guerau de Arellano,
Michiel van der Molen, Bart Kruijt, Thomas Röckmann, Wouter Peters
5. Δ17O in CO2 as tracer of GPP
• Stratospheric CO2 is enriched in Δ17O
Δ17Oleaf
Δ17Ostrat ≈ 0.66 ‰
Δ17Otrop
Gerbrand Koren Wageningen University 4
6. Δ17O in CO2 as tracer of GPP
• Stratospheric CO2 is enriched in Δ17O
• CO2 can exchange oxygen isotopes after
dissolving into water
• Most exchange of isotopes between CO2 and
water occurs in vegetation (carbonic anhydrase)
Δ17Oleaf ≈ -0.07 ‰
Δ17Ostrat ≈ 0.66 ‰
Δ17Otrop
Gerbrand Koren Wageningen University 5
7. Δ17O in CO2 as tracer of GPP
• Stratospheric CO2 is enriched in Δ17O
• CO2 can exchange oxygen isotopes after
dissolving into water
• Most exchange of isotopes between CO2 and
water occurs in vegetation (carbonic anhydrase)
• Δ17O in tropospheric CO2 represents a dynamic
balance between stratosphere and biosphere
exchange Δ17Oleaf ≈ -0.07 ‰
Δ17Ostrat ≈ 0.66 ‰
Δ17Otrop = ??
Gerbrand Koren Wageningen University 6
8. • Δ17O in CO2 was first proposed as tracer for GPP by Hoag et al. (2005)
• Less sensitive to hydrological cycle than δ18O in CO2
Δ17O as tracer of GPP
Gerbrand Koren Wageningen University 7
9. Global budget of Δ17O in CO2
stratosphere
troposphere
FAS = −64
Δ17Ostrat = 0.66
FAL = −514
FSA = 64
FLA = 400
Fresp = 111
Δ17Oleaf = −0.07
Δ17O isotope signatures in ‰
CO2 fluxes in PgC/yr
Gerbrand Koren Wageningen University 8
10. Global budget of Δ17O in CO2
Δ17Oocean = −0.01
stratosphere
troposphere
FAS = −64
Δ17Ostrat = 0.66
FAL = −514
FOA = 87
FAO = −90
FSA = 64
FLA = 400
Fresp = 111
Δ17Osoil = −0.01
Δ17Oleaf = −0.07
FSIA = 30
FASI = −30
Δ17O isotope signatures in ‰
CO2 fluxes in PgC/yr
Gerbrand Koren Wageningen University 9
11. Global budget of Δ17O in CO2
Δ17Oocean = −0.01
stratosphere
troposphere
FAS = −64
Δ17Ostrat = 0.66
FAL = −514
Fff = 9
FOA = 87
FAO = −90
FSA = 64
FCO+OH = 1
Δ17Off = −0.39
FLA = 400
Fresp = 111
Fbb = 2
Δ17Obb = −0.23
Δ17Osoil = −0.01
Δ17Oleaf = −0.07
Δ17OCO = 5.0
FSIA = 30
FASI = −30
Δ17O isotope signatures in ‰
CO2 fluxes in PgC/yr
Gerbrand Koren Wageningen University 10
12. Global budget of Δ17O in CO2
Δ17Oocean = −0.01
stratosphere
troposphere
FAS = −64
Δ17Ostrat = 0.66
FAL = −514
Fff = 9
FOA = 87
FAO = −90
FSA = 64
FCO+OH = 1
Δ17Off = −0.39
FLA = 400
Fresp = 111
Fbb = 2
Δ17Obb = −0.23
Δ17Osoil = −0.01
Δ17Oleaf = −0.07
Δ17OCO = 5.0
FSIA = 30
FASI = −30
Δ17O isotope signatures in ‰
CO2 fluxes in PgC/yr
Gerbrand Koren Wageningen University 11
• Many processes, but main source: stratosphere, and main sink: biosphere
13. Research objective
• Previous studies for Δ17O in CO2 were done on the leaf-scale
(Adnew et al., 2020) and the global scale (Koren et al., 2019)
• This is the first study of the diurnal cycle for Δ17O in CO2 in a forest
1. Is there a measurable variation during the day?
2. If so, how does Δ17O in CO2 vary during the day?
3. Which are the main processes at the ecosystem level?
Gerbrand Koren Wageningen University 12
14. TM5 model MXL model
Loobos obs.
Methods overview
Gerbrand Koren Wageningen University 13
15. Measurement strategy
• Loobos flux tower (NL-Loo), pine forest on sandy soil
• 24 hours campaign in summer 2019, 30 flasks
• Frequent measurements during morning transition
• Air collected in flasks from 2 levels (~0.5m, ~25m)
• Isotopic composition measured at Utrecht University
• Dry sampling is crucial!
Gerbrand Koren Wageningen University 14
16. Cloudy conditions
• Cloudy on 15-16 August 2019, but no rain!
Gerbrand Koren Wageningen University 15
MODIS
17. Boundary layer height
Gerbrand Koren Wageningen University 16
• Good agreement of ABL height between observations, MXL model and TM5 meteo
18. Tower and surface obs. for CO2 and δ13C
• Increase of CO2 and decrease of δ13C during night, largest signal close to surface
Gerbrand Koren Wageningen University 17
19. Gerbrand Koren Wageningen University 18
• Tower Δ17O signal exceeds measurementuncertainty, but interpretation is difficult
Tower and surface obs. for δ18O and Δ17O
20. Gerbrand Koren Wageningen University 19
• Systematicvariation of meteorological variables (humidity in free troposphere,
cloud cover) and isotope parameters (degree of equilibration)
MXL model allows to explore sensitivities
(a, b)
t = 9:00
(c, d)
t = 15:00
21. Gerbrand Koren Wageningen University 20
Tracer tagging in TM5 model
CO2CO2 CO2CO2
• For CO2 in the 1°×1° grid box over Loobos, the main processes are the
biospheric exchange and fossil fuel combustion
22. Gerbrand Koren Wageningen University 21
• For Δ17O in CO2 the amplitude of the combined signal is smaller than the signal
of some individual processes (since these are in anti-phase)
Tracer tagging in TM5 model
23. Diurnal amplitude of Δ17O across the globe
• Largest Δ17O amplitude
in the tropics (~20 per
meg)
• Seasonality in diurnal
Δ17O amplitude for NH
• Good that we collected
samples in the summer!
• Model underestimates
measured variability
Gerbrand Koren Wageningen University 22
24. Conclusions
Observations:
• First measurementsof Δ17O in a forest: signal exceeds measurement uncertainty
MXL model:
• Reasonable agreement with observations
• Ideal tool to explore sensitivity of Δ17O in CO2
TM5 model:
• Timing of different processes leads to reduced amplitude in Δ17O in CO2
• Largest diurnal cycle expected in tropics, with highest biospheric contribution
Gerbrand Koren Wageningen University 23