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The large spatial variability in Arctic tundra complicates therepresentative assessment of CO2 budgets. Accurate measurements of theseheterogeneous landscapes are, however, essential to understanding theirvulnerability to climate change. We surveyed a polygonal tundra lowland onSvalbard with an unmanned aerial vehicle (UAV) that mapped ice-wedge morphology to complement eddycovariance (EC) flux measurements of CO2. The analysis of spectraldistributions showed that conventional EC methods do not accurately capturethe turbulent CO2 exchange with a spatially heterogeneous surface thattypically features small flux magnitudes. Nonlocal (low-frequency) fluxcontributions were especially pronounced during snowmelt and introduced alarge bias of −46 gC m−2 to the annual CO2 budget in conventionalmethods (the minus sign indicates a higher uptake by the ecosystem). Our improvedflux calculations with the ogive optimization method indicated that the sitewas a strong sink for CO2 in 2015 (−82 gC m−2). Due todifferences in light-use efficiency, wetter areas with low-centered polygonssequestered 47 % more CO2 than drier areas with flat-centered polygons.While Svalbard has experienced a strong increase in mean annual airtemperature of more than 2 K in the last few decades, historical aerialphotographs from the site indicated stable ice-wedge morphology over the last7 decades. Apparently, warming has thus far not been sufficient toinitiate strong ice-wedge degradation, possibly due to the absence of extremeheat episodes in the maritime climate on Svalbard. However, in Arctic regionswhere ice-wedge degradation has already initiated the associated drying oflandscapes, our results suggest a weakening of the CO2 sink in polygonaltundra

biogeosciences

Spatial variability of CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; uptake in polygonal tundra: assessing low-frequency disturbances in eddy covariance flux estimates