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| Titel |
Simulating the budget and distribution of δ¹⁷O in CO₂ with a global atmosphere-biosphere model |
| VerfasserIn |
Wouter Peters, Linda Schneider, Magdalena E. G. Hofmann, Ivar van der Velde, Thomas Röckmann |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250113301
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| Publikation (Nr.) |
 EGU/EGU2015-13497.pdf |
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| Zusammenfassung |
| The isotope ratios of 16O, 17O and 18O in CO2 are referred to as the triple-oxygen isotope
composition of CO2, and have long held promise to better understand terrestrial carbon
cycling. However, measurement precision as well as an incomplete understanding of
fractionation during equilibrium exchange and diffusion of CO2 have been a challenge,
especially for the estimation of gross primary production (GPP) and respiration from
measured δ17O and δ18O isotope ratios in CO2. The excess-17O in CO2 (δ17O), defined as
the deviation of the δ17O and δ18O ratios from an expected mass-dependent fractionation
line, is in principle easier to interpret as many processes that simultaneously affect δ17O and
δ18O are not reflected in δ17O. Two global box model simulations suggest that
atmospheric δ17O is therefore mostly determined by transport of relatively δ17O
enriched CO2 from the stratosphere, and its equilibration in leaf-water back to an
excess of close to zero, following diffusion as part of photosynthetic CO2 uptake
by vegetation. This makes δ17O an interesting tracer for photosynthesis at the
global scale, and the first decadal time series have recently been published that
indeed suggest strong GPP-driven variations in atmospheric δ17O. In this study, we
expand the modeling of δ17O beyond the current two global box model results
published by explicitly simulating the global atmospheric δ17O distribution over a five
year period. We specifically are interested whether regional gradients in δ17O
in areas with large GPP such as Amazonia leave an imprint on δ17O that can be
measured with the rapidly improving measurement precision (10-40 permeg currently).
Therefore, we used the SIBCASA biosphere model at 1x1 degrees globally to simulate
hourly fluxes of δ17O into and out of C3 and C4 vegetation as well as soils. These
fluxes were then fed into the TM5 atmospheric transport model at 6x4 degrees
horizontal resolution to simulate the hourly spatial gradients in δ17O all over the globe.
Our results suggest that there are indeed strong regional signatures of biospheric
uptake in atmospheric δ17O that could be measured at the current precision. These
signals are formed by the seasonal GPP of the biosphere as well as by the seasonal
transport of stratospheric δ17O, in addition to spatial gradients in areas with high
GPP. We will explain our modeling capacity, demonstrate these signatures, and
make a first attempt to compare our model to observed δ17O in this presentation. |
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