Abstract
Large changes in the Arctic carbon balance are expected as warming linked to climate change threatens to destabilize ancient permafrost carbon stocks. The eddy covariance (EC) method is an established technique to quantify net losses and gains of carbon between the biosphere and atmosphere at high spatio-temporal resolution. Over the past decades, a growing network of terrestrial EC tower sites has been established across the Arctic, but a comprehensive assessment of the network’s representativeness within the heterogeneous Arctic region is still lacking. This creates additional uncertainties when integrating flux data across sites, for example when upscaling fluxes to constrain pan-Arctic carbon budgets, and changes therein. This study provides an inventory of Arctic (here >= 60° N) EC sites, which has also been made available online (https://cosima.nceas.ucsb.edu/carbon-flux-sites/). Our database currently comprises 120 EC sites, but only 83 are listed as active, and just 25 of these active sites remain operational throughout the winter. To map the representativeness of this EC network, based on 18 bioclimatic and edaphic variables, we evaluated the similarity between environmental conditions observed at the tower locations and those within the larger Arctic study domain. With the majority of sites located in Fennoscandia and Alaska, these regions were assigned the highest level of network representativeness, while large parts of Siberia and patches of Canada were classified as under-represented. This division between regions is further emphasized for wintertime and methane flux data coverage. Across the Arctic, particularly mountainous regions were poorly represented by the current EC observation network. We tested three different strategies to identify new site locations, or upgrades of existing sites, that optimally enhance the representativeness of the current EC network. While 15 new sites can improve the representativeness of the pan-Arctic network by 20 percent, upgrading as few as 10 existing sites to capture methane fluxes, or remain active during wintertime, can improve their respective network coverage by 28 to 33 percent. This targeted network improvement could be shown to be clearly superior to an unguided selection of new sites, therefore leading to substantial improvements in network coverage based on relatively small investments.
Highlights
We tested three different strategies to identify new site locations, or upgrades of existing sites, that optimally enhance the representativeness of the current eddy covariance (EC) network
We use the results from the representativeness analyses to identify the most suitable locations for new observation sites, and upgrades to existing infrastructure, that would optimally enhance the performance of the Arctic EC network as a whole
Even though the methane network has been growing steadily over the past years owing to the availability of a new generation of gas analyzers, the number of sites at which CH4 fluxes are monitored is lagging far behind the CO2 data coverage: 2019, only 32 active sites were identified, 14 (30 %) were inactive. This is similar to the wintertime data coverage: even though methane flux data coverage has been improving over recent years, there are still large gaps in the network, and data coverage is at about the level the CO2 summertime data featured in the early 2000s
Summary
Inaccessibility and extreme climate of the Arctic zone, research in this region is a complex endeavour. Despite the difficulties listed above, many EC sites that measure greenhouse gases fluxes have been established in the Arctic (Kutzbach et al, 2007; Dolman et al, 2012; Ueyama et al, 2013; Zona et al, 2014; Emmerton et al, 2016; Zona et al, 2016; Parmentier et al, 2017), which for this study we consider as the region north of 60 degrees latitude. Our analysis aims at evaluating how representative different versions of the EC network are to capture the spatio-temporal variability of surfaceatmosphere exchange fluxes across the pan-Arctic ecosystem distribution. We use the results from the representativeness analyses to identify the most suitable locations for new observation sites, and upgrades to existing infrastructure, that would optimally enhance the performance of the Arctic EC network as a whole This manuscript and its corresponding online tool aim at providing an accessible source of information on Arctic flux monitoring 85 infrastructure and literature for scientists working on the carbon cycle
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