High‐quality eddy‐covariance CO₂ budgets under cold climate conditions

Abstract

This study aimed at quantifying potential negative effects of instrument heating to improve eddy‐covariance flux data quality in cold environments. Our overarching objective was to minimize heating‐related bias in annual CO2 budgets from an Arctic permafrost system. We used continuous eddy‐covariance measurements covering three full years within an Arctic permafrost ecosystem with parallel sonic anemometers operation with activated heating and without heating as well as parallel operation of open‐ and closed‐path gas analyzers, the latter serving as a reference. Our results demonstrate that the sonic anemometer heating has a direct effect on temperature measurements while the turbulent wind field is not affected. As a consequence, fluxes of sensible heat are increased by an average 5 W m−2 with activated heating, while no direct effect on other scalar fluxes was observed. However, the biased measurements in sensible heat fluxes can have an indirect effect on the CO2 fluxes in case they are used as input for a density‐flux WPL correction of an open‐path gas analyzer. Evaluating the self‐heating effect of the open‐path gas analyzer by comparing CO2 flux measurements between open‐ and closed‐path gas analyzers, we found systematically higher CO2 uptake recorded with the open‐path sensor, leading to a cumulative annual offset of 96 gC m−2, which was not only the result of the cold winter season but also due to substantial self‐heating effects during summer. With an inclined sensor mounting, only a fraction of the self‐heating correction for vertically mounted instruments is required.

Accurate measurements of atmospheric carbon dioxide and methane mole fractions at the Siberian coastal site Ambarchik

“…We interpret the stronger CO 2 and CH 4 signals at Ambarchik as stronger local and regional fluxes compared with those captured at Barrow. Strong CH 4 enhancements were recorded at Ambarchik well into the winter, which is evidence for the relevance of cold season emissions (Kittler et al, 2017b;Mastepanov et al, 2008;Zona et al, 2016). While the average growth rate of CO 2 at Ambarchik matched that at Barrow, the growth rate of CH 4 at Ambarchik was smaller.…”

The Net Landscape Carbon Balance—Integrating terrestrial and aquatic carbon fluxes in a managed boreal forest landscape in Sweden

“…At high latitudes, the EC measurement uncertainty may be relatively larger during the winter, for example, due to frozen sonic and/or more frequently malfunctioning gas analyzer, which may potentially result in a larger proportion of data gaps and the associated greater gap-filling uncertainty (Kittler et al, 2017).…”

Shifted energy fluxes, increased Bowen ratios, and reduced thaw depths linked with drainage-induced changes in permafrost ecosystem structure

“…For more details regarding instrumentation setup, data processing and data quality assessment, please refer to Appendix A and Kittler et al (2016Kittler et al ( , 2017, which also summarizes our approach to constrain eddy-covariance data uncertainty. Since we used exactly the same instrumentation at both drainage and control sites, and also the same data processing and quality assessment approaches, our experimental setup rules out systematic differences in the observational data sets between the treatments that can be linked to methodological issues.…”