Spatial variability of CO<sub>2</sub> uptake in polygonal tundra: assessing low-frequency disturbances in eddy covariance flux estimates
The large spatial variability in Arctic tundra complicates the representative assessment of CO<sub>2</sub> budgets. Accurate measurements of these heterogeneous landscapes are, however, essential to understanding their vulnerability to climate change. We surveyed a polygonal tundra lo...
| Main Authors: | , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2017-06-01
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| Series: | Biogeosciences |
| Online Access: | https://www.biogeosciences.net/14/3157/2017/bg-14-3157-2017.pdf |
| Summary: | The large spatial variability in Arctic tundra complicates the
representative assessment of CO<sub>2</sub> budgets. Accurate measurements of these
heterogeneous landscapes are, however, essential to understanding their
vulnerability to climate change. We surveyed a polygonal tundra lowland on
Svalbard with an unmanned aerial vehicle (UAV) that mapped ice-wedge morphology to complement eddy
covariance (EC) flux measurements of CO<sub>2</sub>. The analysis of spectral
distributions showed that conventional EC methods do not accurately capture
the turbulent CO<sub>2</sub> exchange with a spatially heterogeneous surface that
typically features small flux magnitudes. Nonlocal (low-frequency) flux
contributions were especially pronounced during snowmelt and introduced a
large bias of −46 gC m<sup>−2</sup> to the annual CO<sub>2</sub> budget in conventional
methods (the minus sign indicates a higher uptake by the ecosystem). Our improved
flux calculations with the ogive optimization method indicated that the site
was a strong sink for CO<sub>2</sub> in 2015 (−82 gC m<sup>−2</sup>). Due to
differences in light-use efficiency, wetter areas with low-centered polygons
sequestered 47 % more CO<sub>2</sub> than drier areas with flat-centered polygons.
While Svalbard has experienced a strong increase in mean annual air
temperature of more than 2 K in the last few decades, historical aerial
photographs from the site indicated stable ice-wedge morphology over the last
7 decades. Apparently, warming has thus far not been sufficient to
initiate strong ice-wedge degradation, possibly due to the absence of extreme
heat episodes in the maritime climate on Svalbard. However, in Arctic regions
where ice-wedge degradation has already initiated the associated drying of
landscapes, our results suggest a weakening of the CO<sub>2</sub> sink in polygonal
tundra. |
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| ISSN: | 1726-4170 1726-4189 |